The personal website of Scott W Harden

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...

Markdown source code last modified on January 18th, 2021
---
title: Minimal Radio Project Continues...
date: 2011-02-09 00:18:26
tags: circuit, amateur radio, old
---

# 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!

![](https://www.youtube.com/embed/KTQZzNkMuC8)

<div class="text-center img-border">

[![](IMG_5278_thumb.jpg)](IMG_5278.jpg)

</div>

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). 

<div class="text-center img-border">

[![](IMG_5275_thumb.jpg)](IMG_5275.jpg)

</div>

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">

<div class="text-center img-border">

[![](IMG_5261_thumb.jpg)](IMG_5261.jpg)

</div>

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. 

<div class="text-center img-border">

[![](IMG_5263_thumb.jpg)](IMG_5263.jpg)

</div>

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

<div class="text-center img-border">

[![](IMG_5284_thumb.jpg)](IMG_5284.jpg)

</div>

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...

<div class="text-center img-border">

[![](IMG_5282_thumb.jpg)](IMG_5282.jpg)

</div>