KC9KEP - A work in progress

  Homebrew Radio Projects - Grid Dip Oscillator

Hello, and welcome to my official Grid Dip Oscillator page!

The GDO is a device that I'd seen mentioned over & over in early radio pubs, but never had any first hand experience with.  (I didn't even know what a GDO did!)
That's the great part of building something yourself.  It's a great way to learn and this project was no exception for me :-)

It's an indispensable tool for designing and building your own radio tank circuits.

After you calculate the inductance that you want for your coil, winding it, and connect your variable capacitor to the coil, the GDO will show you what frequency your circuit is resonating at.  You do this by holding the GDO's coil close to your coil under investigation, turning the GDO's tuning knob, a watching for a "dip" displayed on the GDO's meter.

This is all done with the radio's power off.  It works very nicely for crystal radios too! 

And, it can be used as an RF signal source too.

This is, of course, one of the projects covered in the Impoverished Radio Experimenter by Lindsay pubs.  It is very thoroughly covered in the publication.

I made my own aluminum box & tuning disk.  I used 0.090" aluminum for the box, but a lighter gauge may have been easier to work with.
The round dial disk was made by drawing a circle onto light gauge aluminum, snipping off the corners, and progressively sanding with a bench disk sanding wheel.
The dial indicator in was made in Canvas.  After many trials of collecting data on temporary paper dials, I transferred the data into an Excel worksheet.  (I used a radio to "listen" to what the GDO frequency was and logged it on a temp dial face.)

I was then able to actually place a line onto the dial face by entering the number of degrees right from the Excel worksheet.  It actually was quite accurate :-)