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Design and Development of C band RF Transceiver basics

This section of tutorial describes C band RF Transceiver design and development. It covers RF Tranceiver specifications, RF Transceiver Block schematic, RF Up converter, RF down converter, 10MHz OCXO, RF synthesizer, Local oscillator, RF power divider, IF power divider, M & C card, power supply etc. It also mention useful links to manufacturers and basics of rf transceiver.

In this article we will go through step by step design of C band RF Transceiver or RFT which is used in VSAT or Earth station for providing satellite based connectivity to cater voice/data call facility to remote users. The same design steps can be followed for designing other band based RF transceivers such as L band, Ku band, K band and Ka bands.

RF Transceiver Specifications

We will consider following basic specifications in order to demonstrate design and development of C band RF Transceiver.

Transmitter part specifications:

Input frequency- 52 to 88 MHz
Output frequency- 5925 to 6425 MHz
RF frequency selection- In the steps of about 1 MHz
Conversion Gain- 20 dB minimum
Gain flatness- +/- 1 dB over entire band
Gain Variation- +/-1 dB over temperature of 0 deg. C to 50 deg. C
Gain adjustment- 10 dB
Input power level- from -5 to -25dBm
Spurious and harmonics level- better than -40 dBc
1 dB compression point- better than +3dBm

Receiver part specifications:

Input frequency- 3.7 to 4.2 GHz
Output frequency- 52 to 88 MHz
RF frequency selection- In the steps of about 1 MHz
Conversion Gain- 40 dB minimum
Input level- -40dBm to -85dBm
Gain flatness- +/- 1 dB over entire band of 36MHz
Gain Variation- +/-1 dB over temperature of 0 deg. C to 50 deg. C
Gain adjustment- 10 dB
Noise Figure- better than 14dB
Image rejection- better than -50dBc
Spurious and harmonics level- better than -40 dBc

Other than above frequency stability both short term and long term is also considered which is very vital for VSAT system stability for long time as well as providing quality RF link

RF Transceiver Block Schematic

The function of RF Transceiver is convert modulated IF into RF and vice versa. It interfaces one side with modem (base band part) and other side with PA/LNA. It is also called Outdoor Unit due to location in the VSAT system.

It consists of two main parts Up converter and down converter. As shown in following figure UP converter converts modulated IF IN (70+/-18 MHz) into modulated RF OUT (5925-6425MHz). DOWN converter converts modulated RF IN (3700-4200) MHz to IF OUT (70+/-18 MHz).

C band RF Transceiver design and development

As shown in the block diagram figure 1 , RF Transceiver consists of modules which include Up converter, down converter, OCXO, Synthesizer, Local oscillator, RF divider, IF divider, M & C card and power supply.


RF Up converter and RF down converter

RF transceiver basics can be well understood by understanding design of RF up converter and downconverter. They are designed using micro-strip PCB fabrication technology. Refer our page on design of RF up converter in Articles section to understand step by step approach to develop RF frequency converter of your own using RF components available from market.

As shown in the figure 2 and explained above RF Up converter converts modulated IF data in the frequency band of 52-88 MHz to C band. This is done by using mixers and filters. Here Dual conversion approach is followed. In the first conversion 70MHz beats with 1112.5MHz LO and will produce sum and difference frequencies. Out of these sum frequencies are picked up and passed through filter of 1182.5+/- 18 MHz. This 1182.5 band of frequencies beat with 4680-5375 MHz RF synthesizer and will produce C band of about 5925-6425 MHz.

For the case of RF down converter, LNA signal frequencies of about 3.7GHz band is converted to IF frequencies of about 70MHz. This is possible again with the use of appropriate mixers/filters. In the first step of conversion 3.7GHz band is converted to 1042.5MHz band after beating with synthesizer. The same 1042.5MHz band is converted to 70MHz IF signal after beating with fixed IF Local oscillator of 1112.5MHz frequency.

rf upconverter downconverter

10MHz OCXO

This RF oscillator is used as reference for both IFLO and synthesizer in the RF Transceiver. Small power divider circuit is designed which splits sinusoidal power output of oscillator to two places. Out of these one is fed as input to IF Local oscillator and the other is fed as input to RF synthesizer. This module is designed by purchasing RF components required along with 10 MHz crystal oscillator of OCXO type and developing micro strip based board.

Radio Frequency synthesizer

Synthesizer is used to change RF frequency of operation in RF Transceiver used for VSAT. RF synthesizer here is of frequency 4680 to 5375 MHz and frequency can be set in the step of 1 MHz. There are many manufactures of RF synthesizer modules which one can buy for the development or can be designed and developed. Refer our page in terminology section to design RF synthesizer using modules/ICs such as VCO, PLL, Loop filters etc.

Local oscillator

RF Local oscillator will generate fixed frequency and cannot be changed unlike RF synthesizer. RF local oscillator value of 1112.5MHz is used here in our design.

RF power divider

RF divider module is designed using micro strip concept. Various methods are available used to develop RF divider; popular among them is Wilkinson power divider. RF divider divides RF output of synthesizer into two paths, one is used as input to mixer for RF up conversion and the other is used as input to mixer for RF down conversion.

IF power divider

IF divider module is designed using micro strip concept. Various methods are available to design and develop this module. IF divider divides IF output of Local oscillator into two paths, one is used as input to mixer for IF up conversion and the other is used as input to mixer for IF down conversion.

M & C card

Monitoring and control card is used here in order to monitor and control various parameters such as power level(Gain), RF carrier frequency, oscillator reference adjustment, synthesizer frequency control and more. M & C card is composed of microcontroller, RAM, EPROM, RS232 interface, DAC/ADC and more. RS232 interface is used to remotely control various parameters using RS232 interface from PC. Sometimes RS485 is used due to its multi-drop and long distance advantages.

Power supply

Very stable power is used in order to achieve better phase noise required for interworking with satellite network. Power supply here converts -48V DC to other DC voltages such as +/-12, +/-15, +/-5 which are fed to other modules in the RF Transceiver. Power supply should have minimum ripple to obtain good performance.

RF Transceiver RELATED LINKS

RF Trasceiver Manufacturers
RF Transceiver Test Procedure, how to test transceiver
5G RF Trasceiver Manufacturers
LoRa RF Trasceivers
Application of RF Trasceiver in VSAT

RF and Wireless Terminologies


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