An out-of-the-rut domestic receiver

Following the recent Practical Radio Circuits series (June ’03 to Jan ’04), a number of readers have requested a design for a simple VHF FM receiver.

Three types of circuit meet the requirement for simplicity. The first two, superregenerators and synchronous oscillators, were rejected because they can be difficult to set up and operate, and the lack of automatic frequency control causes problems in use.

The third utilizes the superhet principle, but adopts a simple resistance/capacitance coupled intermediate frequency amplifier instead of the conventional tuned circuit arrangement. The aerial input is broadly tuned to the FM band, and only the oscillator has a variably tuned circuit. This greatly simplifies the construction and setting up of the chosen Simple FM Radio design described here.

Readers will, no doubt, have their own ideas about audio amplifiers, speakers and cabinet size, so the FM Tuner section is assembled on a separate printed circuit board (p.c.b.). It can be combined with simple amplifiers – such as those described in the Simple Audio Circuits (May ’02 to Aug ’02) series or the radio series mentioned at the start – to form a small portable, or it can be teamed with more ambitious audio stages to produce an out-of-the-rut domestic receiver.

The latter approach has been adopted here, and details of a wide range tone control unit, a “robust” audio amplifier, and a mains power supply are included.