Custom Built Ham Radio Gear

Lately I've gotten very interested in the challenge and fun of amateur radio. I haven't been licensed yet (next exam in 2 weeks!) but the practice tests were pretty easy. Early on I made the decision to custom build all of my equipment to facilitate my understanding of the various modulation modes, as well as communications and electromagnetism in general. Ultimately I hope to communicate around the world and with satellites, 'working the birds' as they call it in ham radio.

I decided to start simple, but still with practical applications. I've built a VHF (very high frequency) receiver. VHF is the electromagnetic spectrum from 30MHz to 300MHz. This particular device can receive and demodulate FM (frequency modulated) signals in any 5MHz portion of the 136 to 176 MHz (2 meter) band. This band is commonly used by weather, police, and fire department communication so it should be fun to listen to.

Before I start designing devices from scratch, I decided to build one from a kit. I chose the Ramsey FR146 for its price and simplicity. A block diagram is below:

This is a dead simple example of a superheterodyne receiver, or 'superhet'. The signal is received by the antenna, band-pass filtered, pre-amplified and mixed with a local oscillator to produce an IF (intermediate frequency) that is easier to work with. The core of the device is the Motorola MC3359 FM IC (datasheet), which performs demodulation and produces an audio signal, which is amplified by the famous LM386 audio amplifier (datasheet).

The kit provides frequency selection, volume, and squelch controls.

It works well enough but I'm getting a lot of interference, probably because I live in the middle of such a large city. The next step will be to construct a suitable antenna rather than using a cheap one from Radio Shack. I'm finishing up a design for a simple dipole and will post the CAD and simulation files as soon as I can.