Trawl-in those unusual contacts on the 88MHz to 125MHz band.

As a variation on Amateur Radio, the idea for this project came about after operating a commercial v.h.f. (very high frequency) receiver, which unfortunately was “deaf” to narrowband transceiver signals beyond 100MHz.

Adding a long aerial, an impedance matcher and a wideband aerial amplifier offered a marginal improvement, but it soon became clear an improved detector stage and better low-pass filtering was required. Although built from scratch, the result is a circuit based on the Philips IDA7000 f.m. processor i.c., incorporating phase-locked loop detection, mixer and necessary oscillator stages.

Strictly speaking, the project is really a v.h.f. receiver providing a nominal coverage from 88MHz to 125MHz but in use it covers a variety of signals. (The range can also be extended to a top limit of approximately 146MHz.) This includes wideband f.m. broadcasts, aeronautical communications, fixed and private mobile radio, amateur bands activity on the lower frequency channels and the occasional shortwave transmission via satellite.

With a little care and a few precautions, this project can be easily built and set up using a long aerial as opposed to a co-axial cable and feeder system. The cost of a slow-motion drive (these can be difficult to obtain) is also avoided since accurate tuning can be achieved using ordinary tuning capacitors.