Las bases teóricas de la propagación de ondas electromagnéticas fueron descritas por primera vez
por James Clerk Maxwell. Heinrich Rudolf Hertz, entre 1886 y 1888, fue el primero en validar
experimentalmente la teoría de Maxwell. Estos científicos pusieron las bases teóricas y técnicas
para que la radio saliera adelante, ya que la propagación de las ondas electromagnéticas
fue esencial para desarrollar lo que posteriormente se ha convertido en uno de los grandes medios
de comunicación de masas.
El primer sistema práctico de comunicación mediante ondas de radio fue el diseñado por
Guillermo Marconi, quien en el año 1901 realizó la primera emisión trasatlántica radioeléctrica.
Actualmente, la radio toma muchas otras formas, incluyendo redes inalámbricas, comunicaciones
móviles de todo tipo, así como la radiodifusión.
Usos de la Radiofrecuencia en comunicaciones:
Radionavegación
Artículo principal: Radionavegación
Uno de sus primeros usos fue en el ámbito naval, para el envío de mensajes en código Morse entre
los buques y tierra o entre buques. Actualmente también se usa en aeronavegación.
Radiodifusión AM y FM
Las primeras transmisiones regulares, comenzaron en 1920. Antes de la llegada de la televisión,
la radiodifusión comercial incluía no solo noticias y música, sino dramas, comedias, shows de
variedades, concursos y muchas otras formas de entretenimiento, siendo la radio el único medio
de representación dramática que solamente utilizaba el sonido. Actualmente la radio es el medio
en el que algunos géneros del periodismo clásico alcanzan su máxima expresión.
Televisión
La televisión hasta tiempos recientes, principios del siglo XXI, fue analógica totalmente y su
modo de llegar a los televidentes era mediante el aire con ondas de radio en las bandas de
VHF y UHF. Pronto salieron las redes de cable que distribuían canales por las ciudades. Esta
distribución también se realizaba con señal analógica; las redes de cable debían tener una banda
asignada, más que nada para poder realizar la sintonía de los canales que llegan por el aire
junto con los que llegan por cable. En los años 1990 aparecen los sistemas de alta definición,
primero en forma analógica y luego, en forma digital.
Radioaficionados
La radio afición es tanto una afición como un servicio en el que los participantes utilizan varios
tipos de equipos de radiocomunicaciones para comunicarse con otros radioaficionados para el servicio
público, la recreación y la autoformación. Los operadores de radio afición gozan
(y, a menudo en todo el mundo) de comunicaciones inalámbricas personales entre sí y son capaces de
apoyar a sus comunidades con comunicaciones de emergencia y de desastres si es necesario.
Radioastronomia:
La radioastronomía es la rama de la astronomía que estudia los objetos celestes y los fenómenos
astrofísicos midiendo su emisión de radiación electromagnética en la región de radio del espectro.
Las ondas de radio tienen una longitud de onda mayor que la de la luz visible. En la radioastronomía,
para poder recibir buenas señales, se deben utilizar grandes antenas, o grupos de antenas más pequeñas
trabajando en paralelo. La mayoría de los radiotelescopios utilizan una antena parabólica para
amplificar las ondas, y así obtener una buena lectura de estas. Esto permite a los astrónomos observar
el espectro de radio de una región del cielo. La radioastronomía es un área relativamente nueva de la
investigación astronómica, que todavía tiene mucho por descubrir.
En la actualidad, existen gigantescos radiotelescopios, permitiendo observaciones de una resolución
imposible en otras longitudes de onda. Entre los problemas que la radioastronomía ayuda a estudiar, se
encuentran la formación estelar, las galaxias activas, la cosmología, etc.
El Radar:
El radar (término derivado del acrónimo inglés Radio Detection And Ranging, "detección y medición de
distancias por radio") es un sistema que usa ondas electromagnéticas para medir distancias, altitudes,
direcciones y velocidades de objetos estáticos o móviles como aeronaves, barcos, vehículos motorizados,
formaciones meteorológicas y el propio terreno. Su funcionamiento se basa en emitir un impulso de radio,
que se refleja en el objetivo y se recibe típicamente en la misma posición del emisor. A partir de este
"eco" se puede extraer gran cantidad de información. El uso de ondas electromagnéticas permite detectar
objetos más allá del rango de otro tipo de emisiones (luz visible, sonido, etc.)
Entre sus ámbitos de aplicación se incluyen la meteorología, el control del tráfico aéreo y terrestre y
gran variedad de usos militares.
Amplitud Modulada
Amplitud modulada (AM) o modulación de amplitud es un tipo de modulación lineal que consiste en hacer
variar la amplitud de la onda portadora de forma que esta cambie de acuerdo con las variaciones de nivel
de la señal moduladora, que es la información que se va a transmitir.
AM es el acrónimo de Amplitude Modulation (en español: Modulación de Amplitud) la cual consiste en modificar
la amplitud de una señal de alta frecuencia, denominada portadora, en función de una señal de baja frecuencia,
denominada moduladora, la cual es al señal que contiene la información que se desea transmitir. Entre
los tipos de modulación AM se encuentra la modulación de doble banda lateral con portadora (DSBFC).
Aplicaciones tecnológicas de la AM.
Una gran ventaja de AM es que su demodulación es muy simple y, por consiguiente, los receptores son sencillos
y economicos, todo esto gracias a Robert Herzenbert que en 1932 patento el termino AM; un ejemplo de esto es
más eficientes en ancho de banda o potencia pero en contrapartida los receptores y transmisores son más caros
y difíciles de construir, ya que además deberán reinsertar la portadora para conformar la AM nuevamente y poder
demodular la señal trasmitida.
La AM es usada en la radiofonía, en las ondas medias, ondas cortas, e incluso en la VHF: es utilizada en las
comunicaciones radiales entre los aviones y las torres de control de los aeropuertos. La llamada "Onda Media"
(capaz de ser captada por la mayoría de los receptores de uso doméstico) abarca un rango de frecuencia que va
desde 550 a 1600 kHz.
Frecuencia modulada:
Una señal moduladora (la primera) puede transmitirse modulada en AM (la segunda) o FM (la tercera), entre otras.
En telecomunicaciones, la frecuencia modulada (FM) o modulación de frecuencia es una modulación angular que
transmite información a través de una onda portadora variando su frecuencia (contrastando esta con la amplitud
modulada o modulación de amplitud (AM), en donde la amplitud de la onda es variada mientras que su frecuencia
se mantiene constante). En aplicaciones analógicas, la frecuencia instantánea de la señal modulada es
proporcional al valor instantáneo de la señal moduladora. Datos digitales pueden ser enviados por el
desplazamiento de la onda de frecuencia entre un conjunto de valores discretos, una modulación conocida como FSK.
La frecuencia modulada es usada comúnmente en las radiofrecuencias de muy alta frecuencia por la alta fidelidad
de la radiodifusión de la música y el habla (véase Radio FM). El sonido de la televisión analógica también es
difundido por medio de FM. Un formulario de banda estrecha se utiliza para comunicaciones de voz en la radio
comercial y en las configuraciones de aficionados. El tipo usado en la radiodifusión FM es generalmente llamado
amplia-FM o W-FM (de la siglas en inglés "Wide-FM"). En la radio de dos vías, la banda estrecha o N-FM
(de la siglas en inglés "Narrow-FM") es utilizada para ahorrar banda estrecha. Además, se utiliza para enviar
señales al espacio.
Aplicaciones en radio
Dentro de las aplicaciones de F.M. se encuentra la radio, en donde los receptores
emplean un detector de FM y exhiben un fenómeno llamado efecto de captura, en donde el sintonizador es capaz de
recibir la señal más fuerte de las que transmiten en la misma frecuencia. Sin embargo, la falta de selectividad
por las desviaciones de frecuencia causa que una señal sea repentinamente tomada por otra de un canal adyacente.
Otra de las características que presenta F.M., es la de poder transmitir señales estereofónicas, y entre otras
de sus aplicaciones se encuentran la televisión, como sub-portadora de sonido; en micrófonos inalámbricos; y como
ayuda en navegación aérea.
La frecuencia modulada también se utiliza en las frecuencias intermedias de la mayoría de los sistemas de vídeo
analógico, incluyendo VHS, para registrar la luminancia (blanco y negro) de la señal de video. La frecuencia
modulada es el único método factible para la grabación de video y para recuperar de la cinta magnética sin la de
istorsión extrema, como las señales de vídeo con una gran variedad de componentes de frecuencia - de unos pocos
hercios a varios megahercios, siendo también demasiado amplia para trabajar con equalisers con la deuda al ruido
electrónico debajo de -60 dB. La FM también mantiene la cinta en el nivel de saturación, y, por tanto, actúa como
una forma de reducción de ruido del audio, y un simple corrector puede enmascarar variaciones en la salida de la
reproducción, y que la captura del efecto de FM elimina a través de impresión y pre-eco. Un piloto de tono continuo,
si se añade a la señal - que se hizo en V2000 o video 2000 y muchos formatos de alta banda - puede mantener el
temblor mecánico bajo control y ayudar al tiempo de corrección.
Dentro de los avances más importantes que se presentan en las comunicaciones, el mejoramiento de un sistema de
transmisión y recepción en características como la relación señal – ruido, sin duda es uno de los más importantes,
pues permite una mayor seguridad en las mismas. Es así como el paso de Modulación en Amplitud (A.M.), a la
Modulación en Frecuencia (FM.), establece un importante avance no solo en el mejoramiento que presenta la relación
señal ruido, sino también en la mayor resistencia al efecto del desvanecimiento y a la interferencia, tan comunes
en A.M.
La frecuencia modulada también se utiliza en las frecuencias de audio para sintetizar sonido. Está técnica,
conocida como síntesis FM, fue popularizada a principios de los sintetizadores digitales y se convirtió en una
característica estándar para varias generaciones de tarjetas de sonido de computadoras personales.
Espectro Electromagnético
Diagrama del espectro electromagnético, mostrando el tipo, longitud de onda con ejemplos, frecuencia y temperatura
de emisión de cuerpo negro.
Se denomina espectro electromagnético a la distribución energética del conjunto de las ondas electromagnéticas.
Referido a un objeto se denomina espectro electromagnético o simplemente espectro a la radiación electromagnética
que emite (espectro de emisión) o absorbe (espectro de absorción) una sustancia. Dicha radiación sirve para identificar
la sustancia de manera análoga a una huella dactilar. Los espectros se pueden observar mediante espectroscopios que,
además de permitir observar el espectro, permiten realizar medidas sobre éste, como la longitud de onda, la frecuencia
y la intensidad de la radiación.
El espectro electromagnético se extiende desde la radiación de menor longitud de onda, como los rayos gamma y
los rayos X, pasando por la luz ultravioleta, la luz visible y los rayos infrarrojos, hasta las ondas electromagnéticas
de mayor longitud de onda, como son las ondas de radio. Se cree que el límite para la longitud de onda más pequeña
posible es la longitud de Planck mientras que el límite máximo sería el tamaño del Universo (véase Cosmología física)
aunque formalmente el espectro electromagnético es infinito y continuo.
Antenas
Una antena es un dispositivo diseñado con el objetivo de emitir o recibir ondas electromagnéticas hacia el espacio libre.
Una antena transmisora transforma voltajes en ondas electromagnéticas, y una receptora realiza la función inversa.
Existe una gran diversidad de tipos de antenas, dependiendo del uso a que van a ser destinadas. En unos casos deben
expandir en lo posible la potencia radiada, es decir, no deben ser directivas (ejemplo: una emisora de radio comercial
o una estación base de teléfonos móviles), otras veces deben serlo para canalizar la potencia en una dirección y no
interferir a otros servicios (antenas entre estaciones de radioenlaces). También es una antena la que está integrada
en la computadora portátil para conectarse a las redes Wi-Fi.
Las características de las antenas dependen de la relación entre sus dimensiones y la longitud de onda de la señal de
radiofrecuencia transmitida o recibida. Si las dimensiones de la antena son mucho más pequeñas que la longitud de onda
las antenas se denominan elementales, si tienen dimensiones del orden de media longitud de onda se llaman resonantes,
y si su tamaño es mucho mayor que la longitud de onda son directivas.
Ancho de banda:
Es el margen de frecuencias en el cual los parámetros de la antena cumplen unas determinadas características.
Se puede definir un ancho de banda de impedancia, de polarización, de ganancia o de otros parámetros.
informacion suministrada por www.wikipedia.com
hecho por Wiston J Marquez Medina
CAF.
domingo, 21 de marzo de 2010
Radiofrecuencia
Radiofrecuencia
QUE ES LA RADIOFRECUENCIA (RF)Una red de área local por radio frecuencia o wlan (wirless lan) puede definirse como una red local que utiliza tecnología de radio frecuencia para enlazar los equipos conectados a la red en lugar de los medios utilizados en las LAN convencionales cableadas.
No son algo realmente novedoso ni revolucionario dentro del mundo de la informática ya que sus inicios son de los años ochenta.
Surgieron por la necesidad de tener interconectividad dentro de espacios abiertos en los que no se podía llegar con cables tan fácilmente.
BENEFICIOS
Movilidad: Proveen a los usuarios de una LAN acceso a la información en tiempo real en cualquier lugar dentro de la organización. Simplicidad: Es rápida y fácil de instalar y además elimina o minimiza la necesidad de tirar cables.
Flexibilidad en la instalación: Permite a la red ir donde la alámbrica no puede ir.
Inversión rentable: Tiene un costo de inversion inicial alto, pero los beneficios y costos a largo plazo son superiores en ambientes dinámicos que requieren acciones y movimientos frecuentes.
Escalabilidad: Pueden ser configurados en una amplia variedad de topologías. Las configuraciones son fáciles de cambiar y además es sencilla la incorporación de nuevos usuarios a la red.
EVOLUCION TECNOLOGICA
Existen varias tecnologías utilizadas en redes inalámbricas. El empleo de cada una de ellas depende mucho de la aplicación. Cada tecnología tiene sus ventajas y desventajas. A continuación se listan las más importantes en este genero:Infrarrojo (Infrared)
Banda Angosta (Narrowband)
Banda Ancha (Spread Spectrum)
Secuencia Directa (Direct Secuence)
Secuencia de Saltos (frecuency Hopping)
Infrarrojo
Utilizan muy altas frecuencias, justo abajo del espectro de la luz visible para transportar datos. No puede penetrar objetos opacos, ya sea directamente o indirectamente (reflectiva). Su se reduce a conectar dos redes fijas. La tecnología reflectiva no requiere línea de vista pero se limita a cuartos individuales en zonas cercanas.
BANDAS DE TRANSMISION
Banda AngostaTransmite y recibe en una radio frecuencia especifica.
Mantiene la frecuencia de la señal de radio tan angostamente posible para pasar la información.
Debe evitar el cruzamiento de canales coordinando diferentes usuarios en diferentes canales de frecuencia.
La privacidad y la no-interferencia se incrementa por el uso de frecuencias separadas de radio.
El radio receptor filtra todas aquellas frecuencias que no son de su competencia.
Usa una amplia gama de frecuencias, uno para cada usuario, lo cual es impráctico si se tienen muchos.
Necestita de permiso de la SUBTEL
Transmite aproximadamente 5 a 19 Kbps.
Banda Ancha
Espectro extendido (Spread Spectum)
Fue desarrollada por los militares estadounidenses, provee comunicaciones seguras, confiables y de misión critica.
Intercambia eficiencia en ancho de banda por confiabilidad, integridad y seguridad.
Reduce la interferencia entre la señal procesada y otras señales ajenas al sistema.
Existen equipos que utilizan estas frecuencias u otras y que producen una energía de radiofrecuencia, pero que no transmiten información. Ejemplos de estos equipos son: limpiadores domésticos de joyería, humidificadores ultrasónicos, calefacción industrial, hornos de microondas, etc.
2 Mbps FHSS (Frecuency Hopping Spread Spectrum)
Minimiza la interferencia entre múltiples usuarios.
Evita la interferencia de señales externas.
Evita la intervención de las transmisiones.
Aprovecha la velocidad de transmisión de datos 2Mbps.
Trabaja en redes de área local (sin permisos).
Transmite con saltos de frecuencia cada 100 msg. coordinando saltos en 79 frecuencias diferentes, con 66 patrones diferentes.
Posee estándar internacional norma IEEE 802.11
Concepto de roaming preventivo.
Balanceo de carga.
11 Mbps DSSS (Direct Sequence Spread Spectrum)
Divide el ancho de banda once canales, si recibe 6 de los 11 envíos correctos, asume datos correctos.
Al compartir ancho de banda, independiente del canal, logran una velocidad casi seis veces mayor a FSSS (11Mbps).
Ideal para aplicaciones donde trafican paquetes de información de mayor tamaño, (powerpoint, video, etc.).
Trabaja en el estándar internacional IEEE 802.11b cuyo objetivo es la interoperabilidad entre equipos de distintas marcas.
Para lograr una cobertura total en toda la superficie a 11Mbps con RF, hay que colocar un número mayor de Antenas que con 2Mbps.
¿CUANDO UTILIZAR 2 MBPS O BIEN 11 MBPS?
OTRAS TECNOLOGIAS SURGENTES
Bluetooth Es una tecnología que permite interconectar teléfonos móviles, agendas electrónicas, ordenadores, etc., ya sea en el hogar, en la oficina o en el automóvil, con una conexión inalámbrica de corto alcance.
Estos dspositivos tienen un chip que transmite y recibe a una velocidad de 1 Mbps a 2,4 GHz.
Homerf
Está basada en el protocolo de acceso compartido (Shared Wireless Access Protocol, SWAP), encamina sus pasos hacia la conectividad sin cables dentro del hogar.
Este novedoso estándar se encuentra en una fase de evolución demasiado prematura, en comparación con las otras tecnologías.
ANTENAS (Access Point)
Es el responsable de extender la red alambrada existente, a una red inalámbrica de Radio Frecuencia que interactuará con el resto de los elementos RF.
Está diseñado para dar un acceso transparente desde redes inalámbricas compatibles a redes Ethernet.
Posee la capacidad de ser un Repeater y Bridge inalámbrico, permitiendo la ser utilizado como "enlaces" entre unos y otros para extender la red a otras zonas de trabajo sin necesidad de cableados físicos.
TERMINALES PORTATILES
Son quienes se encargan de recibir y enviar datos, por medio de la antena hacia el servidor, permitiendonos interactuar directamente con la base de datos del cliente.Estos poseen algún tipo de emulador, ya sea para Windows 95, 98, 2000, NT, AS400, UNIX, etc., que se cargan en su EPROM, sean estos portátiles, personales, de grúa, etc., que los hacen parte de la red corporativa, exactamente igual que el PC de escritorio.
Estudio de Campo (Site Survey)
Permite determinar la cantidad de antenas necesarias para una aceptable propagación de la RF, en las áreas en que se desea trabajar con equipos móviles conectados en forma inalámbrica a una red de datos.
El proceso de medición consiste en situar un equipo estacionario receptor de RF en diferentes puntos del área en la cual se desea tener cobertura y desplazarse con unidades móviles.
html.rincondelvago.com/radiofrecuencia.html
Maria Gabriela Medina Maldonado
C.I. 16779553
CAF
Wireless Antenas TypesThere are three main categories of antennas
Wireless Antenas TypesThere are three main categories of antennas:
Omni-directional - Omni-directional antennas radiate RF in a fashion similar to the way a table or floor lamp radiates light. They are designed to provide general coverage in all directions.
Semi-directional - Semi-directional antennas radiate RF in a fashion similar to the way a wall sconce is designed to radiate light away from the wall or the way a street lamp is designed to shine light down on a street or a parking lot, providing a directional light across a large area.
Highly-directional - Highly-directional antennas radiate RF in a fashion similar to the way a spotlight is designed to focus light on a flag or a sign. Each type of antenna is designed with a different objective in mind.
In addition to antennas acting as radiators and focusing signals that are being transmitted, it is often overlooked that they also focus signals that are received. If you were to walk outside and look up at a star, it would appear fairly dim.
Not only do they amplify signal that is being transmitted, they also amplify signal that is being received. High gain microphones work in the same way, allowing us to not only watch the action of our favorite sport on television, but to also hear the action.
Omni-directional
Antennas Omni-directional antennas radiate RF signal in all directions. The small rubber dipole antenna , often referred to as a “rubber duck” antenna, is the classic example of an omni-directional antenna and is the default antenna of most access points. A perfect omni-directional antenna would radiate RF signal.
If you were to slice the bagel in half horizontally, as if you were planning to spread butter on it, the cut surface of the bagel would represent the azimuth chart, or H-plane, of the omni-directional antenna.
If you took another bagel and sliced it vertically instead, essentially cutting the hole that you are looking through in half, the cut surface of the bagel would now represent the elevation, or E-plane, of the omni-directional antenna.
In previous article we learned that antennas can focus or direct the signal that they are transmitting. It is important to know that the higher the dBi or dBd value of an antenna, the more focused the signal.
When discussing omni-directional antennas, it is not uncommon to initially question how it is possible to focus a signal that is radiated in all directions. With higher-gain omni-directional antennas, the vertical signal is decreased and the horizontal power is increased.
Figure 1 shows the elevation view of three theoretical antennas. Notice that the signal of the higher-gain antennas is elongated, or more focused horizontally.
The horizontal beamwidth of omni-directional antennas is always 360 degrees, and the vertical beamwidth ranges from 7 to 80 degrees, depending upon the particular antenna. Because of the narrower vertical coverage of the higher-gain omni-directional antennas, it is important to carefully plan how they are used.
Placing one of these higher-gain antennas on the first floor of a building may provide good coverage to the first floor, but because of the narrow vertical coverage, the second and third floors may receive minimal signal.
In some installations you may want this; in others you may not. Indoor installations typically use low-gain omni-directional antennas with gain of about 2.14 dBi. Antennas are most effective when the length of the element is an even fraction (such as 1/4 or 1/2 ) or a multiple of the wavelength ( λ ).
A 2.4 GHz half-wave dipole antenna (see Figure 2) consists of two elements, each 1/4λ in length (about 1 inch), running in the opposite direction from each other.
Omni-directional antennas are typically used in point-to-multipoint environments. The omni-directional antenna is connected to a device (such as an access point) that is placed at the center of a group of client devices, providing central communications capabilities to the surrounding clients.
High-gain omni-directional antennas can also be used outdoors to connect multiple buildings together in a point-to-multipoint configuration. A central building would have an omni-directional antenna on its roof, and the surrounding buildings would have directional antennas aimed at the central building.
In this configuration, it is important to make sure that the gain of the omni-directional antenna is high enough to provide the coverage necessary but not so high that the vertical beamwidth is too narrow to provide an adequate signal to the surrounding buildings.
Figure 3 shows an installation where the gain is too high.
Semi-directional Antennas
Unlike omni-directional antennas that radiate RF signals in all directions, semi-directional antennas are designed to direct a signal in a specific direction. Semi-directional antennas are used for short- to medium-distance communications, with long-distance communications being served by highly-directional antennas.
There are three types of antennas that fit into the semi-directional category:
Patch
Panel
Yagi (pronounced “YAH-gee”)
Unfortunately, it has become common practice to use the terms patch and panel interchangeably. If you are unsure of the antenna’s specific design, it is better to refer to it as a planar antenna. Patch refers to a particular way of designing the radiating elements inside the antenna.
Highly-directional Antennas
Highly-directional antennas are strictly used for point-to-point communications, typically to provide network bridging between two buildings. They provide the most focused, narrow beamwidth of any of the antenna types.
The grid antenna resembles the rectangular grill of a barbecue, with the edges slightly curved inward. The spacing of the wires on a grid antenna is determined by the wavelength of the frequencies that the antenna is designed for.
Because of the high gain of highly-directional antennas, they are ideal for long-distance communications as far as 35 miles (58 km). Due to the long distances and narrow beamwidth, highly-directional antennas are affected more by antenna wind loading, which is antenna movement or shifting caused by wind.
Even slight movement of a highly-directional antenna can cause the RF beam to be aimed away from the receiving antenna, interrupting the communications. In high-wind environments, grid antennas, due to the spacing between the wires, are less susceptible to wind load and may be a better choice.
Another option in high-wind environments is to choose an antenna with a wider beamwidth. In this situation, if the antenna were to shift slightly, due to its wider coverage area, the signal would still be received. No matter which type of antenna is installed, the quality of the mount and antenna will have a huge effect in reducing wind load.
These antennas can be used for outdoor point-to-point communications up to about a mile but are more commonly used as a central device for indoor point-to-multipoint communications.
It is common for patch or panel antennas to be connected to access points to provide directional coverage within a building. Planar antennas can be used effectively in libraries, warehouses, and retail stores with long aisles of shelves.
Due to the tall, long shelves, omni-directional antennas often have difficulty providing RF coverage effectively. In contrast, planar antennas can be placed high on the side walls of the building, aiming through the rows of shelves.
The antennas can be alternated between rows with every other antenna being placed on the opposite wall. Since planar antennas have a horizontal beamwidth of 180 degrees or less, a minimal amount of signal will radiate outside of the building.
With the antenna placement alternated and aimed from opposite sides of the building, the RF signal is more likely to radiate down the rows, providing the necessary coverage. Planar antennas are also often used to provide coverage for long hallways with offices on each side or hospital corridors with patient rooms on each side.
A planar antenna can be placed at the end of the hall and aimed down the corridor. A single planar antenna can provide RF signal to some or all of the corridor and the rooms on each side and some coverage to the floors above and below.
How much coverage will depend upon the power of the transmitter, the gain and beamwidth (both horizontal and vertical) of the antenna, and the attenuation properties of the building.
Maria Gabriela Medina Maldonado
C.I. 16779553
CRF
RF Transmission Lines and Antennas
RF Transmission Lines and Antennas
Overview:
For the next few weeks we are going to be taking a look at Radio Frequency transmission lines and antennas. Obviously, a transmission line is designed to transfer RF energy from your rig to your antenna when transmitting and from your antenna to rig when receiving. And, following that an antenna is the device that is on the opposite end of your transmission line from your rig. Its purpose is to radiate RF energy or to receive RF energy that has been radiated. The efficient transfer of energy, with it's superimposed intelligence, from your rig to a distant rig and the reverse for someone you are attempting to communicate with makes amateur radio possible.
As has been frequently said any antenna is better than no antenna. It is better to get an antenna and transmission line up and working than to try and spend days, weeks and maybe months trying to find and install the perfect system. Every system has compromises, some can be mitigated with little effort and some are impossible to overcome. Most fall somewhere in between. This somewhere in between makes antenna systems fun and challenging to deal with.
One fundamental fact about transmission lines and antennas that seems to be forgotten from time to time is that a complete circuit back to it's source is required for radiation of RF energy. If that return path is not provided as you learned in electronic fundamentals the result is that your antenna system will not function as intended. RF as opposed to direct current most likely will make it's own path if one is not provided. When that happens some grotesque things can and do happen to your signal and perhaps to your equipment or to you. We will discuss this in more detail later.
Transmission lines:
I. Types of transmissions: Over the years, transmission lines and antennas have taken many different shapes and sizes. Today transmission lines are composed of three different types.
1. Coax cables. These are the most common today and are the round cable that most of us are familiar with that goes from our rig to our antenna. These have one conductor in the middle surrounded by an insulator which is surrounded by an outer braid which is surrounded by outside insulation. Coax cables are considered to be unbalanced as the outer conductor is intended to be held at ground potential and the inner conductor carries the RF energy. Of course, the inner conductor is at a potential other than ground.
2. Parallel wire lines. These are usually flat cables with two wires running parallel to each other from your rig to your antenna. These are less common than coax cables but due to their efficiency they are popular with some users. Parallel wire lines are balanced because both conductors have the same voltage and current relationships with respect to ground.
3. Waveguides. These are hollow and flat metal transmission devices that RF energy simply radiates through from one end to the other. These are used primarily for the upper end of the UHF band and for super high frequencies such as microwaves. These are used by hams when operating on frequencies near one Giga hertz and higher. For our series of discussions here we will not address waveguides as those using them are normally well versed in their use and theory.
II. Characteristics of transmission lines:
1. Regardless of their lengths, all transmission lines have resistance, inductance and capacitance. These can be combined and are called impedance. Resistance is simply the DC resistance of wire. Inductance is resistance to an AC voltage. Capacitance is resistance to AC current. These definitions are not all inclusive but will suffice for our discussion. Impedance may also be known as attenuation. Impedance increases as RF frequency increases. Thus as frequency is increased a point is reached for a given transmission line that the attenuation causes unacceptable loses in both transmitted and received RF energy.
2. When we speak of a 50 ohm (a measure of resistance) coax cable we are speaking of 50 ohms of impedance; that is resistance, inductance and capacitance combined is 50 ohms. Impedance is always measured in ohms.
3. When we speak of a 300 ohm parallel wire line we are again speaking of 300 ohms of impedance which again is a combination of resistance, inductance and capacitance.
4. The characteristic impedance of transmission lines is determined by several factors that influences resistance, inductance and capacitance. These include diameter of wires, and insulation inside the coax, distance between wires to include inner and outer conductor in coax lines and types of insulation. Coaxes tend to be in the 50-75 ohm impedance range and parallel wire lines tend to be 300-450 ohm impedance range. Parallel wire has higher resistance because the parallel wires are farther apart than coax inner conductor and outer shield.
5. Transmission lines also have a characteristic know as "velocity factor." This simply means it takes more time for RF energy to travel the same distance through a transmission than it does through the atmosphere or space. Why is that? Their characteristic impedance as we mentioned is composed of resistance, inductance and capacitance. It takes more time for RF energy to travel through these than it does through space. This is due to the fact that their impedance opposes RF energy more than the impedance of space.
6. The velocity factor of each type of transmission line is well documented and should be used when determining the electrical length of a section of transmission line. Velocity factor is expressed as a percentage. That is a direct comparison of the velocity of RF in a transmission line when compared to the velocity of RF in space. For example the velocity of RF in free space is 300,000 meters per second. That same RF in a coax might have a velocity of only 210,000 meters per second. Thus the velocity factor would be 70 percent. Other words the distance traveled in space would be 300,000 meters in a second and in our coax it would travel only 210,000 meters per second.
7. The velocity factor of coax is usually near 70 percent and in parallel lines it is usually near 90 percent. A document such as the ARRL Antenna Handbook should always be consulted for the correct velocity factor for the specific transmission line being used.
8. The type of insulation and the spacing between the inner and outer conductors of coax and between the two wires of parallel lines determines the maximum amount of power that can be applied to a transmission line. The frequency of RF energy also plays a major role in power handling capability. The higher the frequency the less power a transmission line can handle. An abnormally high standing wave ratio can also adversely affect the amount of power that can be handled. We will discuss SWR in more detail later.
2. When we speak of a 50 ohm (a measure of resistance) coax cable we are speaking of 50 ohms of impedance; that is resistance, inductance and capacitance combined is 50 ohms. Impedance is always measured in ohms.
3. When we speak of a 300 ohm parallel wire line we are again speaking of 300 ohms of impedance which again is a combination of resistance, inductance and capacitance.
4. The characteristic impedance of transmission lines is determined by several factors that influences resistance, inductance and capacitance. These include diameter of wires, and insulation inside the coax, distance between wires to include inner and outer conductor in coax lines and types of insulation. Coaxes tend to be in the 50-75 ohm impedance range and parallel wire lines tend to be 300-450 ohm impedance range. Parallel wire has higher resistance because the parallel wires are farther apart than coax inner conductor and outer shield.
5. Transmission lines also have a characteristic know as "velocity factor." This simply means it takes more time for RF energy to travel the same distance through a transmission than it does through the atmosphere or space. Why is that? Their characteristic impedance as we mentioned is composed of resistance, inductance and capacitance. It takes more time for RF energy to travel through these than it does through space. This is due to the fact that their impedance opposes RF energy more than the impedance of space.
6. The velocity factor of each type of transmission line is well documented and should be used when determining the electrical length of a section of transmission line. Velocity factor is expressed as a percentage. That is a direct comparison of the velocity of RF in a transmission line when compared to the velocity of RF in space. For example the velocity of RF in free space is 300,000 meters per second. That same RF in a coax might have a velocity of only 210,000 meters per second. Thus the velocity factor would be 70 percent. Other words the distance traveled in space would be 300,000 meters in a second and in our coax it would travel only 210,000 meters per second.
7. The velocity factor of coax is usually near 70 percent and in parallel lines it is usually near 90 percent. A document such as the ARRL Antenna Handbook should always be consulted for the correct velocity factor for the specific transmission line being used.
8. The type of insulation and the spacing between the inner and outer conductors of coax and between the two wires of parallel lines determines the maximum amount of power that can be applied to a transmission line. The frequency of RF energy also plays a major role in power handling capability. The higher the frequency the less power a transmission line can handle. An abnormally high standing wave ratio can also adversely affect the amount of power that can be handled. We will discuss SWR in more detail later.
Next week we will turn our attention to antenna basics. Once we learn some of the basic properties of transmission lines and antennas we will combine that knowledge and talk about SWR, radiation patterns and other factors affecting signal levels and quality.
Maria Gabriela Medina Maldonado
C.I. 16779553
CRF
TDWR Antenna Pedestal Operating Requirements For the Market Survey to Replace the TDWR Antenna Pedestal Drive System
TDWR Antenna Pedestal Operating Requirements For the Market Survey to Replace the TDWR Antenna Pedestal Drive System
1.0 Mission Statement
1.1 Intent. The intent of this document is to define what the TDWR antenna pedestal motor and drive requirements are and what the minimum expectations are of a replacement antenna pedestal motor and drive system. This document is also intended to provide enough information for a prospective company/vendor to decide whether or not they may be capable of providing a replacement antenna pedestal motor and drive system within the confines of the present environment.
1.2 Expectations. The replacement pedestal motor and drive system will be expected to meet or exceed the specifications and capabilities of the present pedestal drive system. The replacement pedestal motor and drive system will be designed around a brushless drive motor/tachometer system to minimize maintenance and to increase the reliability of the TDWR antenna pedestal.
1.3 Facilities. The numbers of TDWR facilities that are requiring this antenna pedestal motor and drive system retrofit are 47. Spare parts will be required for each facility and spared parts will also need to be located at the central depot located in Oklahoma City.
The TDWR antenna tower heights vary in 5-meter increments and range from 5 meters to 30 meters in height.
1.4 Mission of TDWR
1.4.1 Primary Mission of TDWR. The primary mission of the TDWR is to enhance the safety of air travel through the timely detection and reporting of hazardous wind shear in and near the terminal approach and departure zones of an airport. Specific sources of the hazardous wind shear that are to be detected are microbursts and gust fonts.
1.4.2 Secondary Mission. The secondary mission of the TDWR is to improve the management of air traffic in the terminal area through the forecast of gust front induced wind shifts at the airport, detection of precipitation and reporting of storm motion.
1.4.3 Operational Environment. The TDWR is deployed at an unmanned location, visited only for preventive and corrective maintenance. As such, the TDWR is expected to meet full functional requirements in all operational modes as an unattended system. TDWR operates 24 hours a day, 7 days a week, except when shut down for corrective or preventive maintenance. Operator interaction is from the FAA Remote Maintenance Monitoring Subsystem (RMMS). Routine measurements and adjustments are accomplished remotely through the Remote Monitoring System (RMS). Local control is through the Maintenance Data Terminal (MDT), also via the RMS. In the event of a failure, Built-In-Test Equipment and Built-In-Tests (BITE/BIT) will be used to identify the probable location of the fault and report the probable location of the fault to the RMS MDT so that a maintenance specialist can bring the appropriate Line Replaceable Units (LRUs) to the site. The same BITE/BIT used to identify a fault will also be used to verify the system repair. Defective LRUs will be sent to a central Government depot for repair. Additionally, the RMS controls the execution of certification tests to validate that a system is ready to be returned to operational status.
2.0 Requirements
2.1 Contents. This document contains specifications of the current TDWR antenna pedestal drive system. Titles to reference documentation to these specifications can be found in the Applicable Documents section at the end of this document. Contained within the current requirements stated here are also modifications to the existing system that are necessary to obtain a better performing system.
2.2 Performance Requirements
2.2.1 Antenna Pedestal Positioning Resolution. The resolutions of the antenna pedestal position measurements are 0.012 degrees or better.
2.2.2 Antenna Pedestal Position Repeatability. The antenna pedestal positioning response to an angle input command is repeatable to within +/- 0.024 degrees of any previous identical angle input command.
2.2.3 Antenna Pedestal Elevation Drive. The pedestal elevation drive has a controllable velocity of 0 to 15 degrees per second in steps no greater than 1 degree per second with an accuracy +/- 0.5 degrees per second. The elevation drive positions and holds the antenna with +/- 0.05 degrees of the selected elevation angle when commanded.
2.2.4 Antenna Pedestal Azimuth Drive. The pedestal azimuth drive shall have a controllable velocity of 0 to 30 degrees per second in steps no greater than 1 degree per second with an accuracy of +/- 0.5 degrees per second. The azimuth drive positions and holds the antenna within +/- 0.05 degrees of the selected azimuth angle when commanded. In normal operation, antenna rotation is in the clockwise direction.
2.2.5 Acceleration/Deceleration. Both the elevation and azimuth drives are capable of accelerating and decelerating the specified antenna load from 0 degrees per second squared to 15 degrees per second squared maximum about their respective axis. Acceleration of the elevation and azimuth drives is controllable to the thousandth of a degree per second squared.
2.3 Physical Requirements
2.3.1 Antenna Pedestal Drive Limits. The pedestal shall operate using all the TDWR scanning strategies. These strategies include 360-degree azimuth scans in either direction, sector scans, and Range Height Indicator (RHI) scans from -1 to +60 degrees in elevation.
2.3.2 Duty Cycle. The pedestal shall have a 100 percent duty cycle 24 hours per day for 20 years. The pedestal shall operate continuously with any or all of the scan strategies in the scan strategy algorithm.
2.3.4 Power Fail. In the event of the unexpected loss of prime electrical power or in the event of servo drive failure, the moving pedestal shall be brought to a safe stop within 6 degrees for the elevation axis without the moving structures (including motors, etc.) or the pedestal drive electronics sustaining any damage.
2.3.5 Antenna Braking System. There is no requirement for motor braking. Motor brakes shall not be included in the servo motor design. Electrical limits, mechanical stops, and hydraulic buffers are currently provided to prevent damage to the antenna and its support structure.
3.0 Maintenance Requirements
3.1 Periodic Maintenance. The antenna pedestal motors will be maintained in accordance with manufacturers' recommendations. It is expected that drive motor periodic maintenance will consist of listening for worn or deteriorating bearings only. Based upon the bearing life determined by the manufacturer, motors will be periodically changed at scheduled intervals to prevent unscheduled outages of the TDWR system. There will be no other periodic maintenance.
faaco.faa.gov/.../TDWR_Antenna_Requirements.doc - Estados Unidos
faaco.faa.gov/.../TDWR_Antenna_Requirements.doc - Estados Unidos
Maria Gabriela Medina Maldonado
C.I. 16779553
CRF
Workshop: RF Circuits, Systems, and Wireless Comunications Standards
Workshop: RF Circuits, Systems, and Wireless Comunications Standards
This workshop will cover overall RF system design issues including antennas, radio propagation, transceivers, and data modulations. It also links RFIC design specifications and wireless standards system requirements. Many RFIC designers design the IC's without knowing where the specifications came from. The objective of this tutorial is to let attendees learn the overall picture of RF systems, how to derive RFIC specifications from wireless standards, and the tradeoffs between different transceiver architectures.
The tutorial will begin with an interesting demo of FM radio interference. The explanation which involves the antenna, the receiver architecture, and the non-ideal components will be given at the end of the tutorial, with the experimental proof by using spectrum analyzer.
In addition, I plan to give the following two seminars:
Seminar: Remote Detection of Human Vital Signs Using Microwave Radar.
In this talk, the method of detecting human heartbeat and respiration remotely without any sensor attached to body will be described. The theory and experimental results will be presented and the analysis to increase detection accuracy and detection range will be discussed.
Seminar: IEEE Microwave Theory and Techniques Society (MTT-S) Administrative Committee, Its Major Conferences Sponsored, and Their Operations.
In this talk, I will give an introduction of the MTT AdCom organization including its standing committees and ad-hoc committees. Based on my experience with International Microwave Symposium (IMS), Radio Frequency Integrated Symposium (RFIC), and Radio and Wireless Symposium (RWS) committees, I will also describe their operations and the interactions with MTT AdCom. The purpose of this talk is to encourage the volunteer participation of MTT members in Taiwan, promote membership growth in Taiwan, and answer any questions from members and non-members.
Maria Gabriela Medna Maldonado
C.I. 16779553
CRF
Z-Band, Inc. High Definition Video Distribution System Preliminary Specifications for Design Applications
Z-Band, Inc. High Definition Video Distribution System Preliminary Specifications for Design Applications
1.0 Introduction
1.0 Introduction
Describe the Owner's site-specific requirements. Provide details concerning the intended use and implementation of the video or other elements to be distributed over the Z-Band RF High Definition Video Distribution System. The description must comprehensively describe the expected use of the System and may be expanded to include information on the actual channels to be employed on the System. Information on a head-end for the System to incorporate CATV, satellite earth station receiver, off-air and local origination channels may also be included. If the head-end is to be a part of this project, then appropriate sections for the commissioning and testing of the complete System should be incorporated in the document.
This document may be accompanied with floor plans and details of the desired System. At a minimum, the owner must identify the existing conditions including the facilities and the existing cable system. If no cable system exists, then a separate or combined cable system specification should be generated.
The Owner requires a RF High Definition Video Distribution System capable of delivering up to 134 RF video channels (6 MHz NTSC Channels containing NTSC, ATSC and QAM modulated programs) and IP Video over an installed Category 5e/6/7 shielded or unshielded twisted pair cable system. The System shall utilize a cable plant comprised of a TIA/EIA 568 compliant horizontal distribution cable system and a coaxial and/or single mode fiber backbone system. The System shall employ Active Automatic Gain Control Electronics to adjust the video signal levels to each TV and shall be capable of supporting up to 14,000 connected devices. The System shall support bi-directional RF transmission for backbone interconnections. Note: see paragraph 2.01.G for Category 5e frequency limitations.
Optional – A combination of outside plant coaxial and optical fiber backbone system will be deployed to connect between several remote buildings on the campus or office complex.
The High Definition System shall provide video distribution to rooms in the main building and to the rooms in each of the remote buildings. The System components shall be installed in racks in the main equipment room and throughout telecommunications closets in the building/campus. The System components shall be co-located with the existing Category 5e/6/7 termination hardware to facilitate proper patching from the patch panels and the Video Distribution System equipment. The Installer shall configure the System and place the System components throughout the facility as required. After installation, the Installer shall conduct a series of tests to ensure that the System is fully operational to vendor specifications in all areas of the building.
Optional – The Contractor shall be required to commission the System and live test the System in its entirety. The commissioning shall include the power up of all equipment, the tuning of the head-end, the placement of all ancillary equipment and the final adjustment of the televisions and video input devices.
2.0 Products
The RF High Definition Video Distribution System shall consist of user-configurable and auto-configuring components, which facilitate simple modifications and additions to the System. The System shall allow cascading of units up to four levels deep. All passive and active electronic components of the System shall be FCC certified to operate on a Category 5e/6/7 cable plant, shall be compliant with "FCC Regulations, Part 15," and shall be UL/CSA listed. Additionally, the components shall be designed with passive circuitry to simultaneously allow transmission of IP Voice, IP Video, data or other low voltage signal types on the pairs of the Category 5e/6/7 cable which are unused by the System.
2.01 RF BROADBAND HIGH DEFINITION VIDEO DISTRIBUTION HUB ("HD GigaBUD"):
24 Port - P/N HZ 6001-1, 12 Port - P/N HZ 6001-2, 24 Port w/Return Video - HZ 6001-1R & 12 Port w/Return Video - HZ 6001-2R.
A. Provides a method of distributing up to 134 RF modulated NTSC, ATSC or QAM channels and seven sub-channels (T7-T13) over Category 5e/6/7 in a TIA/EIA 568 horizontal cabling infrastructure. The "HD GigaBUD" requires a 23dBmV CATV flat NTSC signal input for maximum performance. The optimum ATSC/QAM input signal level is 17dBmv for (Digital) and 20dBmV (Digital) for cable box applications.
B. The "HD GigaBUD" shall be self-configuring and plug-and-play so as to easily accommodate adds, moves and changes, and maintains proper signal level and slope to all drops.
C. The "HD GigaBUD" shall combine, split, amplify and equalize the signals so as to achieve a high picture quality and to be in compliance with "FCC Regulation, Part 15".
D. The "R" series "HD GigaBUD" shall have Return Video channels T7 - T13 & channels 2 - 6 available; the Standard unit provides Return Video channels on T7 - T13 only.
E. The "HD GigaBUD" shall cascade up to four levels deep and accommodate up to 14,000 outlets.
F. The maximum distances between the cascaded "HD GigaBUDs" are: 400' with RG-6 coaxial cable, 600' with RG-11, and 1050' with .500 semi-flex coax. These shall reflect an attenuation budget of 12.5 dB at 240 MHz. Single mode fiber up to 25km may be used to cascade "HD GigaBUDs".
G. Category 6/7 cable and hardware shall have the ability to transport NTSC, ASTC and or QAM signals up to 860 MHz and a distance of 100 meters.
H. Category 5e cable and hardware shall have the ability to transport NTSC, ATSC or QAM signals up to 750 MHz and a distance of 100 meters, or 860 MHz of NTSC, ATSC or QAM signals up to a distance of 70 meters.
2.02 INTELLIGENT/REMOTELY POWERED HIGH DEFINITION RF VIDEO BALUN ("HD GigaBOB"- Free-Hanging without diplexer - P/N HZ 5002-1, Free Hanging with diplexer - HZ 5002-2, Wall Mount without diplexer - HZ 5004-3, Wall Mount with diplexer - HZ 5004-4):
B. The "HD GigaBOB" shall provide an F-Connector for output to a device with a NTSC/ATSC/QAM RF tuner (TV, Cable Box, PC with Tuner Card) labeled "TO TV".
C. The "HD GigaBOB" shall provide a Modular Jack to connect to the RJ-45 outlet in the workspace labeled "TO WALL".
D. The "HD GigaBOB" shall provide a second Modular Jack for auxiliary services such as 10/100 Ethernet labeled "TO AUX".
E. The "HD GigaBOB" shall provide LED distance indicators. (Red-short, Yellow-medium, Orange-long, Orange Green-Extra Long)
2.03 BI-DIRECTIONAL FIBER OPTIC TRANSCEIVERS "FIL" (P/N BF-1162679):
A. The "FIL" shall be used to extend the backbone distance over single mode fiber, beyond the limitations of coaxial cable. The operational distance over single mode fiber shall be at least 25 km
B. The "FIL" shall be comprised of two transceiver units connected by single mode fiber with a 1550/1310nm optical window. Connection and splice points shall use SCAP (Angle polished) connectors or fusion-splicing techniques so as to assure a minimum back reflection of 50 dB.
C. Each "FIL" shall have a RF input port and a RF output port for connection to a "HD GigaBUD". Optical input and output ports shall connect to the single mode fiber
D. All fiber terminations shall use an Angle Polished (AP) SC Connector and Fusion Splicing.
B. The "FIL" shall be comprised of two transceiver units connected by single mode fiber with a 1550/1310nm optical window. Connection and splice points shall use SCAP (Angle polished) connectors or fusion-splicing techniques so as to assure a minimum back reflection of 50 dB.
C. Each "FIL" shall have a RF input port and a RF output port for connection to a "HD GigaBUD". Optical input and output ports shall connect to the single mode fiber
D. All fiber terminations shall use an Angle Polished (AP) SC Connector and Fusion Splicing.
2.04 AGILE ANALOG (AMAC) & DIGITAL (DMAC) MODULATOR & ADAPTOR BALUN FOR REMOTE VIDEO ORIGINATION
A. HZ 3000-2 (AMAC for NTSC Analog Modulation), HZ 3000-3 (DMAC for QAM Digital Modulation)
B. Channel selection available on both the AMAC and DMAC is T7-T13 and Channels 2 - 6.
B. Channel selection available on both the AMAC and DMAC is T7-T13 and Channels 2 - 6.
3.0 SYSTEM RF CHARACTERISTICS
3.01 INPUT LEVEL to RF BROADBAND HIGH DEFINITION VIDEO DISTRIBUTION HUB:
A. +23 dBmV flat NTSC
B. +17 dBmV flat ATSC or QAM
C. +20 dBmV flat QAM for cable box only applications
3.02 OUTPUT LEVEL at RJ-45 OUTLET 10-100 METERS IN DISTANCE:
A. For Analog: 0 to +15 dBmV
B. Digital: -10 to +10 dBmV
C. Max Slope: 12 dB positive or negative
3.03 COMPOSITE TRIPLE BEAT (CTB): 50 dB (134 CHANNEL LOADING)
3.04 COMPOSITE SECOND ORDER (CSO): 51dB (134 CHANNEL LOADING)
3.05 MODULATION ERROR RATE (MER): GREATER THAN 32 dB
3.06 CARRIER-TO-NOISE (C/N): GREATER THAN 43 dB
4.0 SYSTEM POWER REQUIREMENTS
4.01 "HD GIGABUD": 90TO 264 VAC AT 47 TO 63 HZ AT 2 AMPS (AUTO SENSING)
4.02 AGILE MODULATOR ADAPTOR: (8 VDC ½ WATT) REMOTELY SELF-POWERED
4.03 "HD GIGABOB": (8 VDC, ½ WATT) REMOTELY SELF-POWERED
5.0 ENVIRONMENTAL
5.01 OPERATING TEMPERATURE: 0 TO 55C
5.02 BTU/HR: APPROX. 200
6.0 QUALITY ASSURANCE
6.01 ALL EQUIPMENT SHALL BE "FCC REGULATIONS, PART, 15 COMPLIANT"
6.02 ALL EQUIPMENT SHALL BE UL/CSA LISTED
www.z-band.com/Portals/0/docs/ZBIDSPEC.doc6.02 ALL EQUIPMENT SHALL BE UL/CSA LISTED
Maria Gagriela Medina
C.I.16008525
CAF
DESIGN AUTOMATION
DESIGN AUTOMATION
Education
Graduate Courses: Management of Research and Development, 1961; Solid-State Physics, 1954; and Theory of Solid State, 1955; Boston University, Boston, Massachusetts.
Lecture Series sponsored by local IEEE chapter: "Microwave Devices & Applications," 1975; "Applications of Coding and Modulation Techniques to Digital Communication," 1973; "Computer-Aided Electronic Engineering," 1968.
Professional Experience
Mr. Sokal founded DESIGN AUTOMATION, INC. in 1965 and has been President of the company since then. He supervised and contributed to many of the projects and products described in the company brochures. His work involved product design, design review, product evaluation, and problem-fixing for electronic equipment and systems for industrial, military, space, and consumer applications, both analog and digital, from dc to UHF, from microwatts to megawatts. Examples are given below.
Analog signal processing and high-precision instrumentation: a digitally-controlled analog radar signal cross-correlator; a speech signal processor comprising six precisely-adjustable low-noise feedback-type active filters; a microelectronic random-digit generator of high randomness and low autocorrelation, based on electrical random noise; high-speed wide-dynamic-range precision nonlinear function generators with high-current outputs, for linearizing the nonlinear control characteristics of PIN-diode RF attenuators; a radar video quantizer and digital signal storage and signal processor for a marine collision-avoidance system
Switching-mode power conversion and motor-speed control: design of high-efficiency switching-mode power amplifiers (up to 2.5 GHz), dc/dc converters (switching frequency up to 14 MHz), dc/ac inverters, and motor-speed controllers; development of new lossless-snubber technology for improving efficiency and reducing transistor stress in switching-mode power
converters and amplifiers; analysis of system instabilities caused by negative input impedance of switching-mode regulating or amplifying systems, and possible remedies
High-speed, high-current pulse drivers: development of high-speed high-current drivers to drive PIN-diode RF switches and computer clock buses
Digital signal integrity: modification and new design of printed circuit wiring, ground distribution, and line terminations to reduce ringing, overshoot, and undershoot in transmission of high-speed digital signals (particularly, heavily loaded clock busses) in computers and
digital-communication equipments
Analog monolithic and hybrid IC development: architecture design of a current-mode-control IC and a resonant-converter control IC, for use in switching-mode power supplies; circuit design of monolithic IC for use in electronic push-button switch; analyses of possible timing and logic traps for a LSI monolithic integrated circuit for control of the drive motor in an automatic camera; design of hybrid ICs for RF, IF, audio, and control circuits of radio-paging receiver
High-efficiency RF power generation: invention and development of Class E switching-mode high-efficiency RF power amplifier; same for high-efficiency high-linearity RF power amplifier (e.g., for use in Single-Side-Band transmitter)
RF technology: PIN-diode RF power switches; conventional-sized and microelectronic RF filters, power amplifiers, and receivers; system design and analysis for a time-division-multiplexed i-f amplifier system for a monopulse radar, considering high-speed switches, spectral analyses of sampled signals, switching noise and channel-to-channel crosstalk as functions of signal bandwidth, sampling rate, and non-idealities of the switches, amplifiers, and filters
EMI/RFI: equipment redesign to eliminate malfunctions caused by susceptibility to, and generation of, radiated and conducted electromagnetic interference
Video display equipment: development of high-speed video and deflection amplifiers for magnetic-deflection CRT displays and computer-output-to-microfilm equipment
Digital data-communication equipment: computer interfaces and digital data modems for data communication via RS-232, RS-422, RS-423, and coaxial-cable channels
Prediction of nuclear-radiation effects: computer simulation of numerous analog and digital circuits for prediction of response to transient radiation and of long-term performance degradation from total dose
Computer-aided design: development and application of techniques for efficient use of computer programs for analysis of electronic circuits and systems; development of semiconductor-device modeling methods for use in circuit simulation; computer simulation and analysis of many analog and digital circuits for pre-fabrication design, analysis, optimization, and evaluation of production-tolerance effects; development of Design Automation's HEPA, HB, and RESOCAD programs for very fast simulation of the steady-state periodic response and of the transient response to a change of any combination of circuit parameters, of a circuit driven by periodically operated switches, and circuit design, analysis, and optimization; consulting to clients' software-development projects on simulation-program specifications and evaluation of their program design
Technical assistance to attorneys: preparing drafts for patent applications, and dialogs with U. S. Patent Office examiners about patentability; analyses of clients' patents and opponents' equipment, clients' equipment and opponents' patents, and client's opponent's similar unpatented designs, to determine technical bases for allegations or defenses regarding patent infringement or copying of trade dress, including expert-witness testimony in court; assisting client in preparation of a claim against the U. S. Government for a contract change of scope based on allegations of inconsistencies among the contract requirements, deficiencies in the Government-furnished design, misrepresentations by the Government as to the adequacy of the design, and technical direction (and lack thereof) furnished by the Government during the contract effort; expert witness in lawsuits alleging defective design of automatic doors which closed and struck pedestrians who were passing through doorways
Teaching: seminars in computer-aided circuit analysis, device modeling for computer simulation, high-frequency power-converter design, switching-mode power-supply design, RF power amplifiers, and maintaining signal quality in high-speed digital systems
Automatic test equipment: devising and programming test methods for production-testing of Polaris and Poseidon analog and digital electronic assemblies on programmable general-purpose automatic test equipment
From 1964 to 1965, Mr. Sokal was Manager of Research and Development at Di/An Controls, Inc., Boston, MA, directing development projects on low-power miniature aerospace magnetic-core memories, high-speed general-purpose core memories, magnetic-core/transistor logic elements and stable oscillators, and a system design study for a satellite-borne digital data processor to insert latitude/longitude grids and auxiliary annotations onto weather pictures to be transmitted from the Automatic Picture Transmission system on NIMBUS weather satellites.
From 1959 to 1964, Mr. Sokal was with Sylvania Electronic Systems Division, Needham, MA. His first assignment was as a Section Head responsible for the design of several series of digital logic circuits for use in commercial digital flight simulators and in military computers and
digital communications systems, and a semiautomatic tester for performing functional, dynamic, and dc production tests on one of the series of digital modules, which were constructed in high-density cordwood potted modules. Three of the military developments went into large-scale production and demonstrated excellent performance in the field. In 1962, Mr. Sokal was
promoted to Department Manager in charge of advanced development of digital electronic techniques. He was responsible for planning and directing development projects in all-magnetic logic, magnetic thin-film memory, 400-MHz tunnel-diode logic, data electronics and servos for a high-performance militarized magnetic tape transport, and automated design of electronic
circuits. He also served as a consultant to Sylvania Semiconductor Division on logic functions and circuit design for integrated digital logic circuits. Sylvania's introduction of TTL integrated circuits to the market evolved from his recommendations at that time.
From 1956 to 1959, he was a Senior Engineer with Di/An Controls, Inc., and its predecessor, Mack Electronics Division. He was responsible for the development of an interferometer counter and readout system with formatted Flexowriter punched tape and typed output for rocket flight data reduction, and two different digital cross-correlated sonar signal detection systems using binary pseudo-random transmitted code streams. Each system cross-correlated the contents of two recirculating shift registers. One system used two 500-stage 2-MHz transistor-circuit shift registers; the other used 2048-bit coincident-current core memories operated in sequential-address mode. He designed major portions of other core memories and special-purpose magnetic computing and data-processing equipment. During his last year at Di/An Controls he was also Technical Sales Manager, responsible for customer technical contacts, application engineering, and preparation of product specifications and data sheets.
From 1951 to 1956, he was at the M.I.T. Lincoln Laboratory, Lexington, MA; as a Staff Member from 1951 to 1954, and as an Air Force Lieutenant from 1954 to 1956. He designed an electronic facsimile system using a CRT flying-spot scanner, and the data modems to transmit and receive the facsimile signals via long-distance carrier telephone circuits. He designed the equipment and the tests for experimental evaluation of a new synchronization method for transmission of digital data over carrier-telephone circuits; the new method was shown to have greatly superior resistance to frequency shifts in a suppressed-carrier system, and to line noise. He performed a theoretical prediction and experimental confirmation of dynamic performance and error in a sampled-data azimuth position servo for a radar PPI indicator. He designed the following subsystems for a digital radar data processor later manufactured as the AN/FST-2: a video quantizer, a video-mapper attachment for a radar indicator, and clock and range-mark generators. He designed the memory test equipment and conducted experiments on an air-supported magnetic drum for high-density storage of digital data. He calculated the expected propagation loss for a VHF radio link, taking account of the antennae heights and the terrain contour along the propagation path.
From 1950 to 1951, Mr. Sokal was an Electronic Engineer with Holmes and Narver, Inc., Los Angeles, California, engaged in instrumentation, data recording, and data reduction for the 1951 series of atomic-weapons tests at Eniwetok Atoll, Marshall Islands.
During his junior, senior, and graduate years at M.I.T., Mr. Sokal was a Cooperative Student Engineer at Philco Corporation, Philadelphia, PA. During four semesters at Philco he worked in the Research, Engineering, and Test Engineering Departments. He designed a low-noise 30-MHz IF amplifier for use in studies of low-noise microwave detectors, a Geiger counter, the control unit for the AN/APS-35 radar, and test equipment for power thyratrons, and he made acoustic and electrical tests of loudspeakers and cabinets, and of design changes to them.
Professional Organizations
Elected a Fellow, Institute of Electrical and Electronics Engineers, for his contributions to the technology of high-efficiency power conversion and RF-power amplification; he is a member of the IEEE professional groups on Power Electronics, Industrial Electronics, Industry Applications, and Microwave Theory and Techniques.
Member, The Electromagnetics Academy, Eta Kappa Nu, and Sigma Xi honorary professional societies.
Participating Member, Design Automation Technical Committee and Simulation Technical Committee of IEEE Computer Society, and IEEE Technical Committee on Computers in Power Electronics
Technical Advisor on RF power amplifiers, radio transmitters, and dc power supplies since 1979 and Member since 1968, American Radio Relay League
Research Management Association; Board of Governors 1975 to 1980 (Chairman 1978-1980)
Reviewer of technical papers for publications and conferences: IEEE publications: J. Solid-State Circuits, Trans. Circuits and Systems, Trans. Electron Devices, Trans. Microwave Theory and Techniques, Microwave and Guided-Wave Letters, Microwave and Wireless Components Letters, Trans. Aerospace and Electronic Systems, Trans. Power Electronics, Trans. Industrial Electronics, Trans. Industry Applications, and Proceedings; IEEE conferences: Power Electronics Specialists Conference (Program Committee since 1987), International Symposium on Circuits and Systems (Program Committee, 1975), Applied Power Electronics Conference (Program Committee since 1986), and Design Automation Conference (Program Committee since 1985); Trans. South African Institute of Electrical Engineers, EPE [European Power Electronics] Journal and EPE Conference, International Power Electronics Conference [IEE of Japan], and IEE [Institution of Electrical Engineers, U.K.]: Proc. Circuits, Devices, & Systems.
External Reviewer for University of Hong Kong: Ph.D. theses and research-grant applications
Specialist Referee for Hong Kong Research Grants Council, evaluating proposals for research grants to be awarded by the Government of Hong Kong
Reviewer of proposals for research grants: National Science Foundation, and Rehabilitative Engineering Research and Development Service, Dept. of Medicine and Surgery, U.S. Veterans' Administration
www.boston-consult.org/member/resume/108_2.doc
Maria Gabriela Medina
C.I.16779553
CAF
sábado, 20 de marzo de 2010
RADIO-FREQUENCY CHANNEL ARRANGEMENTS FOR MEDIUM AND HIGH CAPACITY ANALOGUE OR DIGITAL RADIO-RELAY SYSTEMS OPERATING IN THE UPPER 6 GHZ BAND
RADIO-FREQUENCY CHANNEL ARRANGEMENTS FOR MEDIUM AND
HIGH CAPACITY ANALOGUE OR DIGITAL RADIO-RELAY SYSTEMS
OPERATING IN THE UPPER 6 GHz BAND
HIGH CAPACITY ANALOGUE OR DIGITAL RADIO-RELAY SYSTEMS
OPERATING IN THE UPPER 6 GHz BAND
Introduction
Developments in fixed wireless equipment technology has emnabled the use of higher order modulation schemes that reduce the radio channel bandwidth requirements. Specific to the upper 6 GHz band, the use of higher order modulation techniques has enable the deployment of SDH STM-1 systems in 30MHz channles instead of currently specified 40 MHz channels. The UK therefore proposes the addition of an RF arrangement permitting the use of 30 MHz channels in the upper 6 GHz band.
Developments in fixed wireless equipment technology has emnabled the use of higher order modulation schemes that reduce the radio channel bandwidth requirements. Specific to the upper 6 GHz band, the use of higher order modulation techniques has enable the deployment of SDH STM-1 systems in 30MHz channles instead of currently specified 40 MHz channels. The UK therefore proposes the addition of an RF arrangement permitting the use of 30 MHz channels in the upper 6 GHz band.
The ITU Radiocommunication Assembly,
considering
a) that radio-relay systems with a capacity of 2 700 telephone channels should prove to be feasible in the 6 GHz band, if due care is exercised in the planning of radio paths to reduce multipath effects;
b) that it is sometimes desirable to be able to interconnect, at radio frequencies, radio-relay systems on international circuits in the 6 GHz band;
c) that it may be desirable to interconnect up to eight go and eight return channels in a frequency band 680 MHz wide;
d) that economy may be achieved if at least four go and four return channels can be interconnected between systems, each of which uses common transmit-receive antennas;
e) that a common radio-frequency (RF) channel arrangement for both up to 1 260 and 2 700 telephone channel radio relay systems offers considerable advantages;
f) that the use of certain types of digital modulation (see Recommendation ITU-R F.1101) permits the use of the RF channel arrangement defined for 2 700 telephone channel systems for the transmission of digital channels with a bit rate of the order of 140 Mbit/s or synchronous digital hierarchy bit rates;
g) that for these digital 140 Mbit/s radio systems, further economies are possible by accommodating up to eight go and return channels on a single antenna with suitable performance characteristics;
h) that many interfering effects can be reduced substantially by a carefully planned arrangement of the radio frequencies in radio-relay systems employing several RF channels;
j) that RF channels should be so arranged that for analogue radio-relay systems an intermediate frequency of 70 MHz may be used for up to 1 260 telephone channels;
k) that RF channels should be so arranged that for analogue radio-relay systems an intermediate frequency of 140 MHz may be employed for 2 700 telephone channels;
l) that single- and multi-carrier digital radio-relay systems are both useful concepts to achieve the best technical and economic trade-off in system design,
m) that digital radio-relay systems can deliver SDH STM-1 capacities using high order modulation techniques that reduce the necessary bandwidth
recommends
1 that the preferred radio-frequency channel arrangement for up to eight go and eight return channels, each accommodating 2 700 telephone channels, or a bit rate of the order of 140 Mbit/s, or synchronous digital hierarchy bit rates (Note 3), and operating at frequencies in the upper 6 GHz band, should be derived as follows:
Let f0 be the frequency of the centre of the band of frequencies occupied (MHz),
fn be the centre frequency of one RF channel in the lower half of the band (MHz),
f ¢n be the centre frequency of one RF channel in the upper half of the band (MHz),
then the frequencies of individual channels are expressed by the following relationships:
lower half of the band: fn = f0–350+40 n MHz
upper half of the band: f ¢n = f0–10+40 n MHz
where:
n = 1, 2, 3, 4, 5, 6, 7 or 8;
2 that, in the section over which the international connection is arranged, all the go channels should be in one half of the band, and all the return channels should be in the other half of the band;
3 that different polarizations should be used alternately for adjacent radio-frequency channels in the same half of the band;
4 that, when common transmit-receive antennas are used, and not more than four channels are accommodated on a single antenna, it is preferred that the channel frequencies be selected by making either:
n = 1, 3, 5 and 7 in both halves of the band
or
n = 2, 4, 6 and 8 in both halves of the band (Note 4);
5 that the preferred arrangement of RF polarization
considering
a) that radio-relay systems with a capacity of 2 700 telephone channels should prove to be feasible in the 6 GHz band, if due care is exercised in the planning of radio paths to reduce multipath effects;
b) that it is sometimes desirable to be able to interconnect, at radio frequencies, radio-relay systems on international circuits in the 6 GHz band;
c) that it may be desirable to interconnect up to eight go and eight return channels in a frequency band 680 MHz wide;
d) that economy may be achieved if at least four go and four return channels can be interconnected between systems, each of which uses common transmit-receive antennas;
e) that a common radio-frequency (RF) channel arrangement for both up to 1 260 and 2 700 telephone channel radio relay systems offers considerable advantages;
f) that the use of certain types of digital modulation (see Recommendation ITU-R F.1101) permits the use of the RF channel arrangement defined for 2 700 telephone channel systems for the transmission of digital channels with a bit rate of the order of 140 Mbit/s or synchronous digital hierarchy bit rates;
g) that for these digital 140 Mbit/s radio systems, further economies are possible by accommodating up to eight go and return channels on a single antenna with suitable performance characteristics;
h) that many interfering effects can be reduced substantially by a carefully planned arrangement of the radio frequencies in radio-relay systems employing several RF channels;
j) that RF channels should be so arranged that for analogue radio-relay systems an intermediate frequency of 70 MHz may be used for up to 1 260 telephone channels;
k) that RF channels should be so arranged that for analogue radio-relay systems an intermediate frequency of 140 MHz may be employed for 2 700 telephone channels;
l) that single- and multi-carrier digital radio-relay systems are both useful concepts to achieve the best technical and economic trade-off in system design,
m) that digital radio-relay systems can deliver SDH STM-1 capacities using high order modulation techniques that reduce the necessary bandwidth
recommends
1 that the preferred radio-frequency channel arrangement for up to eight go and eight return channels, each accommodating 2 700 telephone channels, or a bit rate of the order of 140 Mbit/s, or synchronous digital hierarchy bit rates (Note 3), and operating at frequencies in the upper 6 GHz band, should be derived as follows:
Let f0 be the frequency of the centre of the band of frequencies occupied (MHz),
fn be the centre frequency of one RF channel in the lower half of the band (MHz),
f ¢n be the centre frequency of one RF channel in the upper half of the band (MHz),
then the frequencies of individual channels are expressed by the following relationships:
lower half of the band: fn = f0–350+40 n MHz
upper half of the band: f ¢n = f0–10+40 n MHz
where:
n = 1, 2, 3, 4, 5, 6, 7 or 8;
2 that, in the section over which the international connection is arranged, all the go channels should be in one half of the band, and all the return channels should be in the other half of the band;
3 that different polarizations should be used alternately for adjacent radio-frequency channels in the same half of the band;
4 that, when common transmit-receive antennas are used, and not more than four channels are accommodated on a single antenna, it is preferred that the channel frequencies be selected by making either:
n = 1, 3, 5 and 7 in both halves of the band
or
n = 2, 4, 6 and 8 in both halves of the band (Note 4);
5 that the preferred arrangement of RF polarization
6 that a co-channel arrangement may also be used for digital radio-relay systems which can be derived from the arrangements
www.ofcom.org.uk/static/achive/ra/topics/...r/.../cp-03-05.doc
Maria Gabriela Medina
C.I.16779553
CAF
Maria Gabriela Medina
C.I.16779553
CAF
MUTUAL FLUCTUATIONS BETWEEN CARRIERS IN A BROADBAND
MUTUAL FLUCTUATIONS BETWEEN CARRIERS IN A BROADBAND
Abstract – Mutual fluctuations between two carriers in a broadband millimeter-wave communication system may be observed from the heterodyne signal spectrum of the carriers. Laboratory measurements made on equipment developed for local multipoint distribution system (LMDS) applications indicated the degradation in the heterodyne spectrum was mainly in the form of increased background noise with L(f) close to the beat-tone carrier essentially unaffected. Synchronization and orthogonal relationship between the carriers are therefore well preserved by the millimeter-wave link. This property is a key requirement for supporting modulation schemes with high spectral efficiency.
I. Introduction
To meet with the need for higher information throughput and to provide better flexibility in geographical coverage, multipoint distribution systems employing millimeter-wave carriers have been introduced in recent years [1, 2]. Such systems offer unprecedented instantaneous bandwidth and versatility in spectrum usage that have not been previously offered by a commercial wireless connectivity. Because of the flexibility in system configuration and baseband formats, there are often several ways to accomplish the same set of goals using rather diverse design approaches. Nevertheless, it is not unusual to find a local multipoint distribution system (LMDS) built upon a broadcast or point-to-multipoint type of architecture, with a headend communicating with a multitude of subscribers within a region, often referred to as a cell. While there may be similarities to a cellular phone system or a satellite communication system, LMDS finds itself rather unique in a variety of aspects. Many of these are due to the frequency of operation being in the millimeter-wave bands and the magnitude of the bandwidth, leading to special device requirements and composite signal propagation characteristics.
As complex modulation methods are introduced to achieve higher spectral efficiency, the ability of the radio frequency (RF) channel in maintaining the synchronization or orthogonality of two carriers is of fundamental interest to the system designer, for this aspect has direct influence on the quality of transmission as well as on receiver design. In this paper, an experiment to directly observe the mutual fluctuations between two carriers after being transmitted through a millimeter-wave communication system is described. Various components in the system may exhibit nonlinear effects [3] and may contribute to the noise in the received broadband signal. Through the spectrum of the heterodyne signal of the two carriers, one is able to observe the mutual fluctuations between them.
II. System Description
Since the measurements involved the high-frequency portion of the millimeter-wave system, the description will only concentrate on this part of the equipment. The system accepts an intermediate fre-quency (IF) input at the transmitter side at 3.5 – 4.5 GHz and block-converts it to 27.5 – 28.5 GHz. The upconverted signal is amplified by a traveling wave tube and a portion of the output is radiated by a horn antenna. A signal path attenuation representing 3 km free-space loss was introduced in the laboratory.
The transmitted signal is received by a horn antenna and downconverted to IF for observation. In a typical measurement, two synchronized carriers at 3.96 GHz and 4.00 GHz are inserted to a multi-carrier IF and fed to the transmitter. These two tones are retrieved by bandpass filters at the receiver and mixed to generate a beat signal at 40 MHz nominally. The spectrum of this beat signal is monitored by a spectrum analyzer as shown in figure 1.
As in phase-noise measurements, fluctuations be-tween two oscillators can be revealed by mixing their outputs and displaying the beat signal on a spectrum analyzer. The spectrum of the transmitter input IF around the two carriers are shown in figure 2, while their heterodyne signal spectrum (lower sideband) centered at 40 MHz, their difference frequency, is shown in figure 3.
After being upconverted to Ka-band, transmitted, re-ceived, and downconverted to IF at the receiver, the signal exhibits some degradation, as shown in figure 4. Notable from the spectrum are the appearance of intermodulation products and the increase in noise level. To observe the mutual fluctuations between these received carriers, they are each extracted by 20 MHz bandpass filtering and the heterodyne signal spectrum is shown in figure 5. The 20 MHz bandwidth was chosen to ensure that the filters do not have influence on the near carrier spectral contents of each of the carriers. A comparison of the spectra in figure 3 and figure 5 shows that the millimeter-wave communication system has minimal effect on the mutual fluctuations between the two carriers.
III. Discussions
Millimeter-wave frequency bands offer several dis-tinct advantages as the vehicle for providing the capacity and flexibility in system deployment needed by emerging broadband communication system initia-tives. Channel characteristics in this frequency range call for special attention being given to system design. With the employment of modulation techniques that rely on the synchronization or orthogonal relation between carriers and subcarriers, RF channel induced mutual fluctuations between the carriers are of fundamental importance. Laboratory measurements made on a broadband millimeter-wave communication system indicated that fluctuations caused by the equipment is only significant in raising the background noise of the heterodyne signal for a pair of carrier 40MHz apart from each other at 28 GHz, for which a carrier-to-noise ratio of over 30 dB can be sustained. This indicates that the current millimeter-wave technology is effective in providing support for broadband information access with significant throughput and spectral efficiency.
www.crimico.org/doc/Example_E.doc
MARIA GABRIELA MEDINA
C.I.16779553
CAF
Abstract – Mutual fluctuations between two carriers in a broadband millimeter-wave communication system may be observed from the heterodyne signal spectrum of the carriers. Laboratory measurements made on equipment developed for local multipoint distribution system (LMDS) applications indicated the degradation in the heterodyne spectrum was mainly in the form of increased background noise with L(f) close to the beat-tone carrier essentially unaffected. Synchronization and orthogonal relationship between the carriers are therefore well preserved by the millimeter-wave link. This property is a key requirement for supporting modulation schemes with high spectral efficiency.
I. Introduction
To meet with the need for higher information throughput and to provide better flexibility in geographical coverage, multipoint distribution systems employing millimeter-wave carriers have been introduced in recent years [1, 2]. Such systems offer unprecedented instantaneous bandwidth and versatility in spectrum usage that have not been previously offered by a commercial wireless connectivity. Because of the flexibility in system configuration and baseband formats, there are often several ways to accomplish the same set of goals using rather diverse design approaches. Nevertheless, it is not unusual to find a local multipoint distribution system (LMDS) built upon a broadcast or point-to-multipoint type of architecture, with a headend communicating with a multitude of subscribers within a region, often referred to as a cell. While there may be similarities to a cellular phone system or a satellite communication system, LMDS finds itself rather unique in a variety of aspects. Many of these are due to the frequency of operation being in the millimeter-wave bands and the magnitude of the bandwidth, leading to special device requirements and composite signal propagation characteristics.
As complex modulation methods are introduced to achieve higher spectral efficiency, the ability of the radio frequency (RF) channel in maintaining the synchronization or orthogonality of two carriers is of fundamental interest to the system designer, for this aspect has direct influence on the quality of transmission as well as on receiver design. In this paper, an experiment to directly observe the mutual fluctuations between two carriers after being transmitted through a millimeter-wave communication system is described. Various components in the system may exhibit nonlinear effects [3] and may contribute to the noise in the received broadband signal. Through the spectrum of the heterodyne signal of the two carriers, one is able to observe the mutual fluctuations between them.
II. System Description
Since the measurements involved the high-frequency portion of the millimeter-wave system, the description will only concentrate on this part of the equipment. The system accepts an intermediate fre-quency (IF) input at the transmitter side at 3.5 – 4.5 GHz and block-converts it to 27.5 – 28.5 GHz. The upconverted signal is amplified by a traveling wave tube and a portion of the output is radiated by a horn antenna. A signal path attenuation representing 3 km free-space loss was introduced in the laboratory.
The transmitted signal is received by a horn antenna and downconverted to IF for observation. In a typical measurement, two synchronized carriers at 3.96 GHz and 4.00 GHz are inserted to a multi-carrier IF and fed to the transmitter. These two tones are retrieved by bandpass filters at the receiver and mixed to generate a beat signal at 40 MHz nominally. The spectrum of this beat signal is monitored by a spectrum analyzer as shown in figure 1.
As in phase-noise measurements, fluctuations be-tween two oscillators can be revealed by mixing their outputs and displaying the beat signal on a spectrum analyzer. The spectrum of the transmitter input IF around the two carriers are shown in figure 2, while their heterodyne signal spectrum (lower sideband) centered at 40 MHz, their difference frequency, is shown in figure 3.
After being upconverted to Ka-band, transmitted, re-ceived, and downconverted to IF at the receiver, the signal exhibits some degradation, as shown in figure 4. Notable from the spectrum are the appearance of intermodulation products and the increase in noise level. To observe the mutual fluctuations between these received carriers, they are each extracted by 20 MHz bandpass filtering and the heterodyne signal spectrum is shown in figure 5. The 20 MHz bandwidth was chosen to ensure that the filters do not have influence on the near carrier spectral contents of each of the carriers. A comparison of the spectra in figure 3 and figure 5 shows that the millimeter-wave communication system has minimal effect on the mutual fluctuations between the two carriers.
III. Discussions
Millimeter-wave frequency bands offer several dis-tinct advantages as the vehicle for providing the capacity and flexibility in system deployment needed by emerging broadband communication system initia-tives. Channel characteristics in this frequency range call for special attention being given to system design. With the employment of modulation techniques that rely on the synchronization or orthogonal relation between carriers and subcarriers, RF channel induced mutual fluctuations between the carriers are of fundamental importance. Laboratory measurements made on a broadband millimeter-wave communication system indicated that fluctuations caused by the equipment is only significant in raising the background noise of the heterodyne signal for a pair of carrier 40MHz apart from each other at 28 GHz, for which a carrier-to-noise ratio of over 30 dB can be sustained. This indicates that the current millimeter-wave technology is effective in providing support for broadband information access with significant throughput and spectral efficiency.
www.crimico.org/doc/Example_E.doc
MARIA GABRIELA MEDINA
C.I.16779553
CAF
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