T7B: Transmitter and receiver block diagrams; purpose and operation of low-pass, high-pass and band-pass filters


If block 1 in Figure T7-1 is a variable-frequency oscillator, the circuit pictured is a VFO-controlled transmitter.


If block 1 in Figure T7-1 is a crystal oscillator, the circuit pictured is a crystal-controlled transmitter.


If block 1 of Figure T7-2 is a product detector the circuit represents a simple CW and SSB receiver.

If Figure T7-2 is a diagram of a simple single-sideband receiver, the circuit shown in block 1 is a product detector.

A circuit function found in all types of receivers is the detector.


If block 1 is a frequency discriminator, the circuit pictured in Figure T7-3 is an FM receiver.

The circuit for an FM receiver uses a limiter and a frequency discriminator to produce an audio signal.


Modern HF transmitters have a built-in low-pass filter in their RF output circuits to reduce harmonic radiation.

A circuit that blocks RF energy above and below certain limits is called a band-pass filter.

A filter used in the IF section of receivers to block energy outside a certain frequency range is called a band-pass filter.

You would use a duplexer to connect a dual-band antenna to a mobile transceiver which has separate VHF and UHF outputs.