The personal website of Scott W Harden
⚠️ Warning: This article is obsolete.
Articles typically receive this designation when the technology they describe is no longer relevant, code provided is later deemed to be of poor quality, or the topics discussed are better presented in future articles. Articles like this are retained for the sake of preservation, but their content should be critically assessed.
Minimal Radio Project Continues...
February 9th, 2011

Minimal Radio Project Continues...

I got a big bag of fresh, new, copper clad PC board and I now wish I purchased a big pack months ago! Don't laugh at me, but I was buying 4''x6'' sheets of it at Radio Shack for about $5 a pop - ouch! I probably purchased 3 boards in my lifetime, but at that price you can imagine how careful I was not to use them. I soldered minimally to them, and only used them for the most important, established projects. Wake up Scott! If your experimental platform actually inhibits experimentation, there's something fundamentally wrong. Anyway, I got a stack of the stuff and I no longer hesitate to grab a fresh board and start working. I made some progress today simplifying my ultra-minimalist functional radio project. Here's what I came up with!

As you can see, it's running on 9V batteries! The frequency counter has its own 9V battery and a spiffy new hand-me-down case (originally used for a power supply I think, before which it was a watch case!). The IC is a SA602, SA612, or NE602 (all about the same) direct conversion receiver (Gilbert cell mixer).

I now have a small battery powered handheld frequency counter. SWEET! I need to contrive a spectacular case for it. I can't wait! It's probably the most impressive thing I've ever made with respect to the "cool factor". Does it look like a bomb? That probably makes it cooler! It just needs a big red on/off switch labeled "MISSILE LAUNCH", then it'll be the coolest thing on the planet! ... moving on ... <a <a="" href="http://www.SWHarden.com/blog/images/IMG_5261.JPG">

This is the receiver component. It's about as simple as it gets. No antenna or headphone connector is attached, but doing this is trivial! A resonant front-end filter might make it more sensitive, and add some complexity, so comparisons are needed to get a feel for how much better it really is with one attached.

For this board, I added a buffer chip (74HC240) to take the pretty sine wave and turn it into a higher-power square wave...

The quality of the oscillator is reflected in the smoothness of the sine wave (purity?) and its amplitude (indicating high Q?), though more investigation/research is required to fully understand what makes a good oscillator circuit for this chip. My strategy has been to throw components in the air, let them fall randomly, and eventually something happens and the thing starts oscillating...

Newer: First Injections
Older: Frequency Counter Working!
All Blog Posts