My First Homebrew Radio: DC Receiver

Whenever I get into a new hobby, I tend to jump in with both feet. The first radio that I built, back in 2009, was a simple Direct Conversion (DC) receiver. I used the circuit design provided in the first chapter (page 1.8) of Experimental Methods in RF Design, with a few minor component changes due to what I had on hand. An NE612 is used for the mixer and local oscillator and an LM386 is used to amplify the baseband audio. For board construction, I used the “Manhattan” technique, i.e. PCB islands glued to a PCB substrate. The remaining circuitry was wired using the “point-to-point” method. The radio can be powered with either a 9-volt battery (preferred) of a 9 to 12-volt wall wart (not recommended).

The frequency range was determined to be about 5.9 MHz to 7.2 MHz, which covers the 41 meter shortwave listening (SWL) band and the 40 meter amateur band. The radio's local oscillator frequency is subject to temperature drift due to the use of an LC Colpitts oscillator. The radio is also subject to “microphonics” (signal noise caused by mechanical vibration of components) due to the use of a Whitman Sampler candy tin for the enclosure. For my first homebrew radio, I was pretty happy with the results. It was exciting to listen to radio stations that were hundreds, if not thousands, of miles away with a simple radio I built myself and a 25-foot longwire antenna inside a garage.

Below is a photo of the interior of the DC radio. Apologies for the lousy focus. It was hard to get any good depth of field.

In true homebrewing spirit, I used a Whitman Sampler candy tin for the DC radio. I did bother with a paint job - just a hand-drawn dial map for different SWL radio stations and bands that I found. as well as an indication of the proper adjustment direction for the fine tuning knob.