Am/Fm Vhf Receiver

AM/FM VHF RECEIVER This compact, sensitive, communications receiver has a tuning range of 80 to 135 MHz, covering part of the VHF-low band, the entire VHF broadcast band, and the VHF air band. The upper frequency limit of the receiver can be changed fairly easily to include the 2-metre amateur band. by J. Bareford The block diagram given in Fig. 1 shows that the present receiver is a single- conversion type with an intermediate fre- quency of 10.7 MHz. The RF section, comprising the RF input amplifier, the mixer and the local oscillator, is of con- ventional structure, and requires no further detailing here. An integrated cir- cuit, to be discussed later, provides the necessary IF amplification, and at the same time comprises the AM and FM demodulators. A squelch (noise suppres- sion) circuit, built from discrete compo- nents, works in AM as well as FM mode. RF circuit With reference to the circuit diagram of the RF section of the VHF receiver, given in Fig. 2, the aerial signal i...