list of satellite systems

Assignment 9

SATELLITE SYSTEMS

INTRODUCTION.
Satellite communication is a process where a radio signal is transmitted to a satellite above your horizon. That satellite rebroadcasts that signal, on a different frequency, either to a ground station, or to another satellite to be relayed further. It allows communications without any local infrastructure, such as wires, towers, or other equipment. All that is needed is a receiver/transmitter which operates in the correct frequency bands, and which has sufficient power and sensitivity to communicate with a satellite, and the satellites.
Satellite communication allowed the boats in the Volvo Round the World Ocean sailboat race to communicate with the race headquarters, irregardless of where in the world the boats were.

diagram of satellite operation.

TYPES AND FUNCTION
Satellites" are satellites that are armed, designed to take out enemy warheads, satellites, other space assets. They may have particle weapons, energy weapons, kinetic weapons, nuclear and/or conventional missiles and/or a combination of these weapons.
Astronomical satellites are satellites used for observation of distant planets, galaxies, and other outer space objects.
Biosatellites are satellites designed to carry living organisms, generally for scientific experimentation.
Communications satellites are satellites stationed in space for the purpose of telecommunications. Modern communications satellites typically use geosynchronous orbits, Molniya orbits or Low Earth orbits.
Miniaturized satellites are satellites of unusually low weights and small sizes. New classifications are used to categorize these satellites: minisatellite (500–200 kg), micro satellite (below 200 kg), Nan satellite (below 10 kg).
Navigational satellites are satellites which use radio time signals transmitted to enable mobile receivers on the ground to determine their exact location. The relatively clear line of sight between the satellites and receivers on the ground, combined with ever-improving electronics, allows satellite navigation systems to measure location to accuracies on the order of a few meters in real time.
Reconnaissance satellites are Earth observation satellite or communications satellite deployed for military or intelligence applications. Little is known about the full power of these satellites, as governments who operate them usually keep information pertaining to their reconnaissance satellites classified.
Earth observation satellites are satellites intended for non-military uses such as environmental monitoring, meteorology, map making etc. (See especially Earth Observing System.)
Space stations are man-made structures that are designed for human beings to live on in outer space. A space station is distinguished from other manned spacecraft by its lack of major propulsion or landing facilities — instead, other vehicles are used as transport to and from the station. Space stations are designed for medium-term living in orbit, for periods of weeks, months, or even years.
Tether satellites are satellites which are connected to another satellite by a thin cable called a tether.
Weather satellites are primarily used to monitor Earth's weather and climate.


Satellite in Africa.

EXAMPLES.
1, Eutelsat W6 Satellite Beamfound in Europe, Middle East, North Africa
- 24 Transponders
- Downlink EIRP 47 dBW at center
- Uplink G/T +3 dB/K at center
Frequencies
Uplink13.00 - 13.25 GHz13.75 - 14.50 GHz
Downlink10.95 - 11.70 GHz12.50 - 12.75 GHz
Algeria, Egypt, Libya, Morocco/Western Sahara,
2. Express AM1 Satellite BeamEurope, Middle East, North Africa
- 28 Transponders
- Downlink EIRP 47 dBW at center
- Uplink G/T +3 dB/K at center

Frequencies
Uplink13.75 - 14.50 GHz
Downlink10.95 - 11.70 GHz
EXAMPLE

KTN,KBCTV TS: 2.05 Mbp,NTV ,TS: 2.07 Mbp all are Eutelsat

The frequency the satellite uses to beam the transmission down to Earth. This is known as the "downlink" frequency - as opposed to the frequency used to send the transmission to the satellite in the first place, which is known as the "uplink" frequency.

There are two main frequency bands in use;

-the C-Band with downlink frequencies in the 3 and 4 GHz range,

-the Ku-Band with frequencies in the 10, 11 and 12 GHz range.1 GHz = 1000 MHz = 1000000 kHz = 1000000000 Hz. (Hz = Hertz).Example: 3.456 GHz = 3456 MHz

REFERENCE

http://www.satcodx.com/

. Transmission Line circuit representation diagram and describe the role of RF circuit in radio Television transmitter.

ASSIGNMENT 1.


Transmission Line circuit representation .



Classification of transmission lines

Transmission lines are classified as :
1.Short,
2.Medium
3.Long.
Short transmission lines
When the length of the line is less than about 80Km the effect of shunt capacitance and conductance is neglected and the line is designated as a short transmission line. For these lines the operating voltage is less than 20KV.


Short Transmission LineThe equivalent circuit and vector diagram of a short transmission line are shown in the figure given below. In the equivalent circuit short transmission line is represented by the lumped parameters R and L. R is the resistance (per phase) L is the inductance (per phase) of the entire transmission line. As said earlier the effect of shunt capacitance and conductance is not considered in the equivalent circuit. The line is shown to have two ends: sending end (designated by the subscript S) at the generator, and the receiving end (designated R) at the load.





Medium transmission lines.

For medium transmission lines the length of the line is in between 80km - 240km and the operating line voltage wil be in between 21KV-100KV.In this case the shunt capacitance can be assumed to be lumped at the middle of the line or half of the shunt capacitance may be considered to be lumped each end of the line. The two representations of medium length lines are termed as nominal-T and nominal- π respectively.

long transmission lines.

Lines more than 240Km long and line voltage above 100KV require calculations in terms of distributed parameters. Such lines are known as long transmission lines. This classification on the basis of length is more or less arbitrary and the real criterion is the degree of accuracy required.

REFERENCE

http://www.maxim-ic.com/appnotes.cfm/an_pk/742/

. What is the importance of The Smith Chart in RF System.

ASSIGNMENT 2
Why use smith charts.
Use of the Smith Chart utility has grown steadily over the years and it is still widely used today, not only as a problem solving aid, but as a graphical demonstrator of how many RF parameters behave at one or more frequencies, an alternative to using tabular information. The Smith Chart can be used to represent many parameters including impedances, admittances, reflection coefficients; a Smith chart is the RF engineer's best friend! It's easy to master, and it adds an air of "analog coolness" to presentations, which will impress your friends, if not your dates! A master in the art of Smith-charting can look at a thoroughly messed up VSWR of a component or network, and synthesize two or three simple networks that will impedance-match the circuit in his head
ROLE OF SMITH CHART IN RF.
1. Wider bandwidths it is usually necessary to apply Smith Chart techniques at more than one frequency across the operating frequency band.
2. Since impedances and admittances change with frequency, the problems is solved using the Smith Chart can only manually using one frequency at a time, the result being represented by a point?
3Normalised scaling allows the Smith Chart to be used for problems involving any characteristic impedance or system impedance, although by far the most commonly used is 50 ohms.
4Use of the Smith Chart and the interpretation of the results obtained using it requires a good understanding of AC circuit theory and transmission line theory, both of which are pre-requisites for RF engineers
5. With relatively simple graphical construction it is straightforward to convert between normalized impedance (or normalized admittance) and the corresponding complex voltage reflection coefficient.
6. On line calculations ensure monitoring of proper operation and display the information to the user in an efficient way.

7. In addition, an advanced load impedance monitoring diagnostic has been implemented, being displayed as a Smith Chart, for example one which is based on the system used at the SRS in Daresbury, England.

8. Smith chart has made it possible to compare the following parameter of universal interest:
- Pure resistance line.
- Resistance circle set.
- Two wavelengths .
- Reflection coefficient angle.
- Reflection coefficient magnitude.
- dB of loss .
example

circuit.

smith chart representation.

REFERENCE

http://www3.interscience.wiley.com

Submit a block diagram of a microwave system circuit indicating the RF section

ASSIGNMENT 3
MICROWAVE BLOCK DIAGRAMWITH RF SECTION

REFERENCE

http://www.arrl.org/tis/info/antproj.html

Cellular phone block diagram and circuit if possible indicate the RF section and describe its main function.

ASSIGNMENT 6
Cellular phone block diagram

panasonic

panasonic

universal


REFERENCE
www.chipidea.com
www.panasonic .com

Amplifier Classes of Operation and Biasing Networks.

ASSINGMENT 7

Amplifier Classes of Operation and Biasing Networks
INTRODUCTION .
The main characteristics of an amplifier are Linearity, efficiency, output power, and
Signal gain. In general, there is a trade off between these characteristics. For example,
Improving amplifier’s linearity will degrade its efficiency. Therefore knowing the importance
degree of each one of these characteristics is an essential step in designing an Amplifier. This
Can be jugged based on the application. As an example high output power Amplifier is used
in the transmitter side of a transceiver, whereas high linear amplifier used in the receiver side.

An amplifier is said to be linear if it preserves the details of the signal waveform, that
is to say,

where,
Vi and Vo are the input and output signals respectively.
and A is a constant gain representing the amplifier gain. But if the relationship between Vi and Vo contains the higher power of Vi, then the amplifier produces nonlinear distortion.
The amplifier’s efficiency is a measure of its ability to convert the dc power of the
Supply into the signal power delivered to the load. The definition of the efficiency can be
represented in an equation form as

For an ideal amplifier, the efficiency is one. Thus, the power delivered to the load is equal to
the power taken from the DC supply. In this case, no power would be consumed in the
amplifier. In reality, this is not possible, especially in high frequency realm of RF circuits. In
many high frequency systems, the output stage and driver stage of an amplifier consumed
Power in the amplification process.
The gain of the amplifier (G) is equal to the magnitude of the output signal (Xo) over
the magnitude of the input signal (Xi) as shown in the equation.
Amplifier Classification
Amplifiers are classified according to their circuit configurations and methods of
operation into different classes such as A, B, C, and F. These classes range from entirely
linear with low efficiency to entirely non-linear with high efficiency. The analysis presented
in this chapter assumes piecewise-linear operation of the active device.

The active device used in this research is the field effect transistor. The reason for
choosing this type of transistor is its superior performance in the microwave range
The characteristics of the FET can be described by:

Class A Amplifiers

Class A amplifiers operate over a relatively small portion of a tube’s plate-current or a transistor’s collector-current range and have continuous plate- or collector-current flow throughout each RF cycle. Their efficiency in converting DC-source-power to RF-output-power is poor. DC source power that is not converted to radio frequency output power is dissipated as heat. However, in compensation, Class A amplifiers have greater input-to-output waveform linearity (lower output-signal distortion) than any other amplifier class. They are most commonly used in small-signal applications where linearity is more important than power efficiency, but also are sometimes used in large-signal applications where the need for extraordinarily high linearity outweighs cost and heat disadvantages associated with poor power efficiency.

Class B Amplifiers

Class B amplifiers have their tube control-grids or transistor bases biased near plate- or collector-current cutoff, causing plate- or collector-current to flow only during approximately 180 degrees of each RF cycle. That causes the DC-source-power to RF-output-power efficiency to be much higher than with Class A amplifiers, but at the cost of severe output cycle waveform distortion. That waveform distortion is greatly reduced in practical designs by using relatively high-Q resonant output “tank” circuits to reconstruct full RF cycles.
The effect is the same in principle as pushing a child in a swing through half-swing-cycles and letting the natural oscillatory characteristics of the swing move the child through the other half-cycles. However, low sine-wave distortion results in either case only if the Q of the oscillatory circuit (the tank circuit or the swing) is sufficiently high. Unless the Q is infinite, which it never can be, the amplitude of one-half cycle will be larger than the other, which is another way of saying there always will be some amount of harmonic energy. (Coupling an antenna system too tightly to the resonant output tank circuit of an amplifier will lower its Q, increasing the percentage of harmonic content in the output.)
Another effective method commonly used to greatly reduce Class B RF amplifier output waveform distortion (harmonic content) is to employ two amplifiers operating in “push-pull” such that one conducts on half-cycles where the other is in plate- or collector-current cutoff. Oscillatory tank circuits are still used in the outputs of Class B push-pull amplifiers to smooth switching transitions from the conduction of one amplifier to the other, and to correct other nonlinearities, but lower-Q tank circuits can be used for given percentages of harmonic content in the output. (Tank circuits can be loaded more-heavily for given percentages of harmonic output where two amplifiers operate in push-pull.)

Class AB Amplifiers

As the designation suggests, Class AB amplifiers are compromises between Class A and Class B operation. They are biased so plate- or collector-current flows less than 360 degrees, but more than 180 degrees, of each RF cycle. Any bias-point between those limits can be used, which provides a continuous selection-range extending from low-distortion, low-efficiency on one end to higher-distortion, higher-efficiency on the other.
Class AB amplifiers are widely used in SSB linear amplifier applications where low-distortion and high power-efficiency tend to both be very important. Push-pull Class AB amplifiers are especially attractive in SSB linear amplifier applications, because the greater linearity resulting from having one amplifier or the other always conducting makes it possible to bias push-pull Class AB amplifiers closer to the Class B end of the AB scale where the power-efficiency is higher. Alternatively, push-pull Class AB amplifiers can be biased far enough toward the highly-linear Class A end of the scale to make broadband operation without resonant tank circuits possible in applications where broadband operation or freedom from tuning is more important than power-efficiency.
Class C Amplifiers

Class C amplifiers are biased well beyond cutoff, so that plate- or collector-current flows less than 180 degrees of each RF cycle. That provides even higher power-efficiency than Class B operation, but with the penalty of even higher input-to-output nonlinearity, making use of relatively high-Q resonant output tank circuits to restore complete RF sine-wave cycles essential. High amplifying-nonlinearity makes them unsuitable to amplify AM, DSB, or SSB signals.
However, most Class C amplifiers can be amplitude-modulated with acceptably low distortion by varying plate- or collector-voltage, because they generally are operated in the region of plate- or collector-saturation so that the RF output voltage is very closely dependent upon instantaneous DC plate- or collector-voltage. They also are commonly used in CW and frequency-shift-keyed radiotelegraph applications and in phase- and frequency-modulated transmitter applications where signal amplitudes remain constant.

Class-A Benefits
Since Class-A amps are inefficient, generate lots of heat, and require a far more complex power supply than conventional Class-AB amplifiers, there have to be some compelling reasons to use this arrangement. The first is circuit simplicity. In the light of the above discussion, the circuit is not simple, but for the audio signal it can be far less complex than for a conventional power amp.
The benefit of this is that the signal is subjected to comparatively little amplification, resulting in an open loop (i.e. without feedback) gain which is generally fairly low - probably less than 250 (48dB), and possibly as low as 50 or so (34dB). This means that very little overall feedback is used, so stability and phase should be excellent over the audio frequencies. A well designed Class-A amplifier should not require any frequency compensation (or very little), so the open loop gain will remain reasonably constant over the audio range. This results in superior transient response, and dramatically reduced "Transient Intermediation Distortion" (or TID, aka Dynamic Intermodulation Distortion), which is thought by many designers to be caused by phase and time delays between the input and feedback signals. It may be possible that this is the cause, although the existence of TID is virtually zero in any competently designed amp.
The simple fact is that the more amplifying devices that are introduced into the chain, the more phase shift must be introduced. No amplifying device is capable of responding instantaneously to a change of input - all have some inherent delay (which usually includes different turn-on and turn-off times). With fewer devices in the audio circuit, there must be less delay between a change in the input causing a change in the output. The simplified topology used for most Class-A amps can also be used with Class-AB - often with very good results indeed.


conclusion
Class-A Output device(s) conduct through 360 degrees of input cycle (never switch off) - A single output device is possible. The device conducts for the entire waveform in Figure 1
Class-B Output devices conduct for 180 degrees (1/2 of input cycle) - for audio, two output devices in "push-pull" must be used (see Class-AB)
Class-AB Halfway (or partway) between the above two examples (181 to 200 degrees typical) - also requires push-pull operation for audio. The conduction for each output device is shown in Figure 1.
Class-C Output device(s) conduct for less than 180 degrees (100 to 150 degrees typical) - Radio Frequencies only - cannot be used for audio! This is the sound heard when one of the output devices goes open circuit in an audio amp! See Figure 1, showing the time the output device conducts (single-ended operation is assumed, and yes this does work for RF).When I first wrote this article, I had completely forgotten about the Quad "Current-Dumping" amp, which uses a low power "good" amplifier, with a push-pull Class-C type amp to supply the high currents needed for high power. Although these enjoyed a brief popularity, they seem to have faded away. I was reminded of their existence by an article by Douglas Self ("Class Distinction", in the March 1999 issue of Electronics World ), in which he quite rightly points out that the current-dumper is (at least in part) Class-C.
Class-D Quasi-digital amplification. Uses pulse-width-modulation of a high frequency (square wave) carrier to reproduce the audio signal - although my original comments were valid when this was written, there have been some very significant advances since then. There are some very good sounding Class-D amplifiers being made now, and they are worthy of an article of their own.

Reference
http://sound.westhost.com/class-a.htm

Different kinds of antenna their function, matching and application.

Assignment 8



ANTENNAS
INTRODUCTION.
Antennas generally fall into the following categories: Omnidirectional and Directional. Although there are many different
antennas, most are just variations of these two basic types.

Omnidirectional antennas
Omnidirectional antennas (omnis) radiate a pattern in all directions, IE: 360 degrees. Omnis are good for large open areas where there is little in the way of obstructions. Warehouses with low racking and high ceilings, and manufacturing areas are
examples.

Omnis need to be mounted out in the clear. Many times an omni is found mounted on a ceiling extending downfrom the support beams.Omnidirectional antennas can vary in shape. Depending on the gain, most are just black or white sticks in varying lengthsOthers look somewhat like smoke detectors or simplified small, flattened hockey pucks.Some omnidirectional antennas have customizable patterns. The radiation pattern can be modified during installation toprovide more coverage in some areas and a less in others. Even the "uptilt" and "downtilt" of the signal can be adjusted. Thisallows the pattern to be customized to the installation. This insures that signal is not wasted in directions where it is notneeded and/or wanted. These kinds of antennas are used outdoors to cover large open areas such as theme parks oroutdoor malls.The gain of the antenna affects the coverage pattern. A low gain omni will have a relatively small coverage area, but it will bevery broad vertically. This is why low gain omnis are used for high bay warehouses where the antenna is mounted in high generally 35 feet or higher. This broad coverage also wraps around racking better. These kinds of antennas work well when the antennas need to be mounted high and the user population is at ground level.
High gain omnis radiate a signal further in a more narrow form. These antennas are deployed for outdoor use where users are not near, but more of a distance away. A good example of this is point to multipoint bridging. The center pointwould use a higher gain omni with the outer areas using directional antennas pointing towards the center point. (Directionalantennas are discussed below.) It would not be wise to use a high gain omnidirectional antenna in a high bay warehouse. Thesignal would be radiating outwards, without enough downward signal to the users at ground level.

Directional antennas

There are varieties of directional antennas. Although these are all directional antennas, a large difference exists among each.The difference is the coverage patterns.
Yagi antennas are the most well known. The Yagi looks a lot like an older television antenna. long boom with horizontalsticks (elements) along its length. The higher the frequency, the smaller the elements. A Yagi for 2.4Ghz has elements less
than 3 inches long. In fact, the most common Yagi antenna for 2.4Ghz looks like a long cylinder. The cylinder is just aweatherproof cover. Yagi antennas work by focusing more signal in one direction like a mirror behind a light bulb. Thehigher the gain of the antenna, the narrower the radiated signal will be. One use for Yagi Antennas is within large
warehouses with high racking and long aisles. An Omni may not fit between the top of the racks and the ceiling, therefore, aseries of Yagis become the antenna of choice. They are used to fire asignal down the aisles. Yagi’s can also be used outdoors as bridge links between two locations over a long distance. In many cases a Yagi may cover up to 3 or more miles.
Sector Antennas are somewhat similar to Yagis, however, they present a much wider coverage. Yagi’s tend to be less than 35 degrees in coverage where as a Sectored Antenna typically is between 60 and 120 degrees in coverage. Sectored Antennas are used mainly outdoors where the antenna may be at the edge or corner of the coverage area.
Patch or Panel Antennas are flat, square, or round and used where a low profile is needed. Many times this is due to esthetics or reducing the risk of an antenna being damaged. Patch and Panel Antennas are much like Sectored Antennas. One type of Patch is a hemispherical. This antenna type has a 180 degree coverage. It’s well recognized for coverage in retail
stores, parking lots, and convention halls. Another style of Patch is the bi-directional. It’s a small antenna that fires a signal in two directions, 180 degrees from each other. These are know for coverage in long hallways such as hospital corridors. The Parabolic is the "big gun" of the directional antennas. The Parabolic is used exclusively for outdoor, long distance point
to point bridging. Typically demanding coverage of 10 to 35 miles.

other types.


Multipolarized Antennas
Antenna development for Wi-Fi (and other wireless technologies) is a hot area right now, with many new developments. For example, a company named WiFi-Plus, Inc., has developed multipolarized antennas. According to the company's chief technology officer, Jack Nilsson, these antennas have the ability to propagate and receive signals that are both horizontal and vertical. These models are better than conventional models for going around obstructions. WiFi-Plus's multipolarized antennas can also be used in situations where Wi-Fi is being broadcast using a directional antenna to a deep valley. A conventional directional antenna might broadcast signals that would overshoot the valley, but a multipolarized antenna is capable of broadcasting signals that travel horizontally following the direction of the RF beam, but also can be received down in the valley.

ANTENNA GAIN.
One item that needs to be discussed in more detail is Gain. Gain is defined as the compressing of the vertical component of the antenna pattern, in effect causing the radiation pattern of the antenna to reach out further toward a base station or cell site Antenna Gain is an antenna’s ability to gather in signal and radiate signal.
Usually the higher the Gain, the larger the antenna will be. For an omnidirectional, that means height. For Yagi Antennas, length. Gain is expressed in dBi-a unit of antenna gain. The dBi measure is referenced to a theoretical, dimensionless point source with a completely spherical radiation pattern (http://www.antenna.com/faqs_theory.html). This is the only way to
compare relative performance when looking at similar antennas. Most manufacturers rate their antennas in dBi. A few still use dB. When comparing gain, the units must be the same for both.


FACTORS TO CONSIDER.
install their own WLAN’s in a small office or home, the antenna is not a major factor since most cards and access pointshave built in antennas. However, for large installations such as warehouses, manufacturing plants, hospitals, airports andsimilar areas, the antenna becomes a critical part of the entire system. The correct selection and usage of antennas maymean the difference between a cost effective installation with robust reliable performance, and a network with areas ofweak coverage, unreliable communications and poor performance. The correct selection and usage of antennas may alsomean the avoidance of potential expenses due to too many access points and regular visits by technicians searching to fix a
network problem.
EXAMPLES.

TV Antennas (DT-950)
Specifications:

1) Frequency (MHz): 45 ~ 860

2) Gain (dB):

a) VHF (L): 26

b) VHF (...

outdoor TV antenna NAME: OUT DOOR USE CAR ANTENNA PACKING:20 SETS/ CTN CTN SIZE(CM):56*34*21 N.W.:10KG G.W.:9KG PACKAGE: BLESTER AND PAPER CARD INSTALL: STICK BY TAPE INSTALLATION:STICK ON THE CAR ROOF ITEM NO.:HL-90(OUT-SIDE.....

ABS plastic dish, easy assembled, high quality, Outdoor Rotating TV Antenna/ Aerial 1) Gain: 25-30dB 2) Output Frequency: 47-900MHz 3) Output Impedance: 75OhM 4) Standing Wave Ratio: 6m

SPECIFICATION: VHF OUTDOOR ANTENNA ELEMENTS:

5 CHANNELS: 1-12

FREQUENCY: 46-230dB GAIN: 3.5-7dB

IMPEDANCE: 75/ 300 OHMS PACKING: EACH IN PRINTED BOX

outdoor TV antenna NAME: OUT DOOR USE CAR ANTENNA PACKING:20 SETS/ CTN CTN SIZE(CM):56*34*21 N.W.:10KG G.W.:9KG PACKAGE: BLESTER AND PAPER CARD INSTALL: STICK BY TAPE INSTALLATION:STICK ON THE CAR ROOF ITEM NO.:HL-90(OUT-SIDE.....

TV intenna(indoor and outdoor) , Should any of our products are in your favour, please tell us without any hesitation. We assure you both of our high quality products and best services at all times. For your.....

SPECIFICATION: VHF OUTDOOR ANTENNA ELEMENTS: 5 CHANNELS: 1-12 FREQUENCY: 46-230dB GAIN: 3.5-7dB IMPEDANCE: 75/ 300 OHMS PACKING: EACH IN PRINTED BOX

outdoor TV antenna NAME: OUT DOOR USE CAR ANTENNA PACKING:20 SETS/ CTN CTN SIZE(CM):56*34*21 N.W.:10KG G.W.:9KG PACKAGE: BLESTER AND PAPER CARD INSTALL: STICK BY TAPE INSTALLATION:STICK ON THE CAR ROOF ITEM NO.:HL-90(OUT-SIDE.....

Impedance matching.
As an electro-magnetic wave travels through the different parts of the antenna system (radio, feed line, antenna, free space) it may encounter differences in impedance (E/H, V/I, etc). At each interface, depending on the impedance match, some fraction of the wave's energy will reflect back to the source[, forming a standing wave in the feed line.

The ratio of maximum power to minimum power in the wave can be measured and is called the standing wave ratio (SWR). A SWR of 1:1 is ideal. A SWR of 1.5:1 is considered to be marginally acceptable in low power applications where power loss is more critical, although an SWR as high as 6:1 may still be usable with the right equipment. Minimizing impedance differences at each interface (impedance matching) will reduce SWR and maximize power transfer through each part of the antenna system.

Complex impedance of an antenna is related to the electrical length of the antenna at the wavelength in use. The impedance of an antenna can be matched to the feed line and radio by adjusting the impedance of the feed line, using the feed line as an impedance transformer. More commonly, the impedance is adjusted at the load (see below) with an antenna tuner, a balun, a matching transformer, matching networks composed of inductors and capacitors, or matching sections such as the gamma match.

Impedance matching is the electronics design practice of setting the output impedance (ZS) of a signal source equal to the input impedance (ZL) of the load to which it is ultimately connected, usually in order to maximize the power transfer and minimize reflections from the load. This only applies when both are linear devices.The concept of impedance matching was originally developed for electrical power, but can be applied to any other field where a form of energy (not just electrical) is transferred between a source and a load.
Matching is obtained when ZL = ZS.

With modern audio electronics, impedance matching degrades audio performance[1] [2], so impedance bridging is used insteadComplex conjugate matchingThis is used in cases in which the source and load are reactive. This form of impedance matching can only maximize the power transfer between a reactive source and a reactive load at a single frequency. In this case,
Zload = Zsource*
(where * indicates the complex conjugate).
If the signals are kept within the narrow frequency range for which the matching network was designed, reflections (in this narrow frequency band only) are also minimized. For the case of purely resistive source and load impedances, all reactance terms are zero and the formula above reduces to
Zload = Zsource
as would be expected.

REFERENCE .
www.szamic .com
http://www.paranoma.com/

special components (semiconductor device) use in RF systems.

ASSIGNMENT 5

special components (semiconductor device) use in RF systems

Introduction.

The radio-frequency system, or RF system, supplies power to the ALS in the form of microwaves. Microwaves are radio waves with a wavelength between about one meter and one millimeter, which are the wavelengths used for radio and television broadcasts as well as radar and microwave ovens. Most parts of the RF system supply microwave radiation with a wavelength of about 0.6 meter (see Electromagnetic Radiation for an explanation of wavelengths). Microwave power is used to energize electrons, keeping them whirling around the ALS storage ring at almost the speed of light. Eventually, the electrons release this energy as x rays and ultraviolet light. Scientists use this light, which is called synchrotron radiation, to carry out experiments at the ALS. How important is the RF system? All the energy released as synchrotron radiation originates as RF power.



basic component of an rf system

The basic components of the RF system include:
Klystrons
Waveguides
RF Cavities


OTHER COMPONENTS INCLUDES

RF DIODES

schottky diodes

PIN diode

varactor diode

IMPATT diode

Tunnel diode

TRAPATT(TRApped Avallanche and Transit Time)s diode

BARRITT(BARRier Injection Transit Time)diode

Gunn diode

RF TRANSIATORS

MISFET(Metal Insulated semiconductor

JFET

MESFET (Metal semicomductor)
Hetero fet
RF semiconductors devices are 7 major categories: Bandpass Filters; Lowpass Filters; Highpass Filters; Notch Filters; Diplexers/Duplexers; Cavities/Combiners; and Ceramics/Helicals.



PICTURE OF RF CABINNET FULLY PACKED WITH COMPONENTS

EXAMPLES OF RF FILTERS.

REFERENCE
www.eparonoma.com

different kinds of filter designs and specific function

ASSINGMENT 4

Different kinds of filter designs


INTRODUCTION.


There are several varieties of active filter. Some of them, also available in passive form, are:
High-pass filters – attenuation of frequencies below their cut-off points.
Low-pass filters – attenuation of frequencies above their cut-off points.
Band-pass filters – attenuation of frequencies both above and below those they allow to pass.
Notch filters – attenuation of certain frequencies while allowing all others to pass.
To design filters, different types are available to set the component value based on mathematical properties (which define "shape" of the frequency bands)this include
Chebyshev filter
Butterworth filter
Bessel filter
Elliptic filter

Chebyshev filters.
Chebyshev filters are analog or digital filters having a steeper roll-off and more passband ripple (type I) or stopband ripple (type II) than Butterworth filters. Chebyshev filters have the property that they minimize the error between the idealized filter characteristic and the actual over the range of the filter, but with ripples in the passband. This type of filter is named in honor of Pafnuty Chebyshev because their mathematical characteristics are derived from Chebyshev polynomials.
Because of the passband ripple inherent in Chebyshev filters, filters which have a smoother response in the passband but a more irregular response in the stopband are preferred for some applications.
You must select four parameters to design a Chebyshev filter:
(1) a high-pass or low-pass response,
(2) the cutoff frequency,
(3) the percent ripple in the passband,
(4) the number of poles. Just what is a pole? Here are two answers.

Elliptic filter
An elliptic filter (also known as a Cauer filter, named after Wilhelm Cauer) is an electronic filter with equalized ripple (equiripple) behavior in both the passband and the stopband. The amount of ripple in each band is independently adjustable, and no other filter of equal order can have a faster transition in gain between the passband and the stopband, for the given values of ripple (whether the ripple is equalized or not). Alternatively, one may give up the ability to independently adjust the passband and stopband ripple, and instead design a filter which is maximally insensitive to component variations.
As the ripple in the stopband approaches zero, the filter becomes a type I Chebyshev filter. As the ripple in the passband approaches zero, the filter becomes a type II Chebyshev filter and finally, as both ripple values approach zero, the filter becomes a Butterworth filter.
The gain of a lowpass elliptic filter as a function of angular frequency ω is given by:
where Rn is the nth-order elliptic rational function (sometimes known as a Chebyshev rational function) and
ω0 is the cutoff frequency :ε is the ripple factor :ξ is the selectivity factor
The value of the ripple factor specifies the passband ripple, while the combination of the ripple factor and the selectivity factor specify the stopband ripple.

Butterworth filter
Operation
The Butterworth filter is composed of a series of "branches" which are alternately connected in series or shunt with the source-to-load path. In low-pass and high-pass filters, each branch is either a capacitor or an inductor. In band-pass and band-stop filters, each branch is either a series or parallel resonant circuit composed of a capacitor and an inductor. (see figures 1 and 2). The first branch of any filter may be selected as either a series or a shunt branch.
Upon running the program, the user must first specify if a low-pass/high-pass or a band-pass/band-stop filter is desired. If the low-pass high-pass design is chosen, the user must then specify two frequencies in Hz, each followed by the respective attenuation desired (this may be a very small value but never exactly zero). The source resistance must then be specified. The program will then calculate and display the minimum number of branches required for the specifications, and request if the first branch is to be series or shunt. The program will then calculate all required component values rounded to 3 significant digits and displayed in the most common units. The rounding feature may be eliminated by changing statement 830 to "LET X1=X". The program will then provide a table of attenuation vs. frequency for any specified range and increment of frequency.
If the band-pass/band-stop design is selected, the process is similar except that first the center frequency of the filter must be specified, and then two frequency bandwidths with their respective attenuations. These filters are geometrically symmetrical, i.e. the center frequency is not exactly the arithmetic average of the limit frequencies of any bandwidth. The relationship is really fc=SQRT(f1xf2).
The given examples demonstrate the use of this program. The first filter designed is a band-stop filter for 11 meters, providing 20 dB attenuation over 26.965 to 27.405 MHz (bandwidth of 440 kHz) and only 1 dB attenuation over 26.37 to 28.0 MHz (bandwidth of 1.63 MHz). This type of filter may be designed for the input of a linear amplifier to prevent operation on the 11 meter band while permitting operation on the 10 meter band. This filter requires only 3 branches (total of 6 components), and its response over 26 to 28 MHz is shown in the printout.
The second example shows design of a low-pass filter, such as used for TVI suppression.. An attenuation of 30 dB is specified at 54 MHz, while a loss of 1 dB is specified at 28 MHz. This filter would require 7 elements, and its response over 5 to 55 MHz is shown in the table.
This program offers the radio amateur the ability to synthesize modern Butterworth filter circuits with all calculations performed by a computer. All previously published articles in amateur magazines on this subject present tables of normalized filter values or only a few "typical" values for certain common frequencies. This program offers the full flexibility possible by using the original formulas for synthesis of Butterworth filters. It is possible to write such programs for Chebyshev and other modern filters, and these will require slightly more complicated formula derivations. This is one of the author's future projects for programing on the Timex Sinclair 1000.

DESIGN.

BANDSTOP FILTER DESIGN

CENTER FREQUENCY 27.185 MHZ

BANDWIDTHFREQUENCY

ATTENUATION (DB) 440000 201630000

1RESISTANCE (OHMS): 50

NO BRANCHES=3

1ST EL. (SERIES=1, SHUNT=-1) -1

BANDSTOP FILTER COMPONENTS
BRANCH 1 SHUNT L 1 = 6.12 UH IN SERIES WITH C 1 = 5.6 PF
BRANCH 2 SERIES C 2 = .00122 UF IN PARALLEL WITH L 2 = .028 UH BRANCH 3 SHUNT L 3 = 6.12 UH IN SERIES WITH C 3 = 5.6 PF

LOWPASS FILTER DESIGn

FREQMHZ

ATTENUATION (DB)28 154 30

RESISTANCE = 50 OHMS

NO. BRANCHES=71ST EL. (SERIES=1, SHUNT=-1) -1

LOWPASS FILTER COMPONENTS
BRANCH 1 SHUNT C 1 = 45.9 PF
BRANCH 2 SERIES L 2 = 0.322 UH
BRANCH 3 SHUNT C 3 = 186 PF
BRANCH 4 SERIES L 4 = 0.516 UH
BRANCH 5 SHUNT C 5 = 186 PF
BRANCH 6 SERIES L 6 = 0.322 UH
BRANCH 7 SHUNT C 7 = 45.9 PF

Comparison with other linear filters
Here is an image showing the elliptic filter next to other common kind of filters obtained with the same number of coefficients:



Reference
http://www.qsl.net/kp4md/butrwrth.htm