Grid Dip Meter

A weekend project to build a grid dip meter

I found my self in need of a grid dip meter. I tried to use my Antenna Analyzer as a grid dip meter, but it did not work as I had expected. I did a google search and came up with this wonderful page that has lots of info on the GDO. I also remembered an article in one of my older ARRL handbooks for a dip meter. Interestingly enough the dip meter in the hand book and the dip meter from iz7ath where very similar in design. I took the two designs, and added a few changes of my own. One of the things I did not want to do is to have to calibrate all the dials for each coil. I decided to add a frequency counter output to my GDO. This requited a buffer be added to keep the counter from loading down the oscilator. Here are the results!

I did not have a metal case so used circuit board material to create shielding around the capacitor and the circuit board. The meter is constructed manhattan style, and placed in a Radio Shack project box. The meter is a 200ua that I had on hand. The capacitor is from a Heathkit color bar generator and has reduction drive and a range of about 50 pf or so. None of the values are supper critical, so you can substitute what you have on hand.

The dip meter currently covers 2.5Mhz to 60 Mhz with the coils that I have built. Most of the coils where wound on 1/2 inch pvc pipe and where wound by trial and error. I tied to get each one to cover the major ham bands and have some overlap. The connector is a 5 pin din plug which I had on hand. The plug fits nicely on the end of the PVC. I also built an adapter that takes the 5 pin DIN and has an RCA connector on the other end. My 60 Mhz coil is built with an RCA connector. This lets me easily wind a custom coil for any other project.

Looking at the capacitor specifications in the hand book article I put the two capacitors Cx and Cx in the grid dip meter, and by shorting pins x,x and x,x on the DIN connector the internal capacitors can be selected. The 80 meter coil needed different capacitor values so those are installed in the coil form, and Pins X,X and X,X are not shorted.

I also built a few test circuits to use to test the GDO. I measured some coil values from the junk box and determined the needed capacitor to get them to resonate at a know frequency. The measured value was very close to the calculated values. These will be saved for future reference.

I have used this meter for a few projects and it has worked as expected. When the weather gets a little better I need to take down my Cushcraft R7 and trouble shoot some of the traps on it.

If you do not own a GDO this makes a great weekend project, and is a valuable piece of equipment to have on hand.

Here are some additional links on Grid dip meters found on the net

IZ7ATH wonderful GDO web page

Here is a modern Grid Dip Meter kit offered by QRP Project in Germany