Microwave communication system [ECE] --- by V.K. Mourya
# Basic Microwave Communication Link :-
Microwave signal are used for communication over long distance continental or intercontinental. Microwave is the communication link which make the communication possible. The basic block diagram of microwave communication system is shown in figure.
Construction:
Antenna:- Mostly a parabolic refractor types of antenna are used which is used to transmit and receive the signal.
Circulator: A circulator is used to isolate transmitter with the receiver input and to couple transmitter to antenna and antenna to receiver input.
Protection Circuitry: It provides safety to the mixer from overloads.
Mixer (Receiver): It has two outputs. One is the incoming signal and other is the signal from lower band pass filter (BPF).The mixer gives an IF signal of 70Mhz.
Band pass filter (BPF): It provides the necessary selectivity to the receiver and it prevents the interference.
IF amplifier and AGC:- It amplifies the signal up to a intermediate frequency of 70Mhz. and its gain is controlled through AGC (automatic gain control)
Amplitude limiter: As the signal is frequency modulated one so as amplitude limiter is used to avoid unwanted amplitude variations.
Mixer (Transmitter): It is used to convert IF frequency to transmitting microwave frequency band to pass through it and hence prevent interference.
POWER AMPLIFIER:-This amplifier amplifies the transmitted power from a repeater section in the range of 0.2W to 10W.
MICROWAVE SOURCE:- Klystron & Gunn Oscillators were used as microwave source. Now, V H F transistor crystal oscillators are used for microwave source.
POWER SPLITTER:- It divides the output power from a microwave source and feeds a large portion to the transmitter mixer, which converts it into transmitting microwave frequency.
SHIFT OSCILATOR:- It provides one of the inputs to the balanced mixer so that it produces 70MHz IF at the output of receiver mixer.
This microwave link communicates with 600 to 2700 channels per carrier. Thus the number of carriers in each direction can be four to twelve.
