After building the first tracker, I knew that I needed something a bit more elegant. And smaller.

Making things smaller starts with the GPS receiver and antenna. There are a number of very small GPS engines available at atractive prices. As a starting point, I picked up a TF30. This unit has a full shield on it to protect from RFI. This will be usefull since there will be a transmitter nearby. When I ordered the GPS unit, I also picked up a few passive antennas.

In this picture the antenna is at bottom right, GPS engine (with coax cable) at the top, and a piece of 38mm coupler on the left. The grid you see is 1".

The GPS engine with the coax is a tight fit in the coupler. I think that when I build the 38mm version I will use another engine that is a bit smaller. The antenna also fits into the coupler but this is decieving.

The antenna is a "patch" design. This is designed to be installed on a ground plane which effects its center frequency and radiation pattern. This particular patch needs a 40mm by 40mm ground plane which will not fit into a 38mm coupler.

But I can use these antennas for the 54mm version. These COTS antennas are very nice for a couple of resaons. First is that the dimensions of the patch a very critical so it is nice that some else must worry about it. The second is that they are $8 apiece.

One problem with patch antennas is that their radiation (or reception) pattern is hemispherical. Any thing below the ground plane just isn't going to be received. In order to compensate for that I will use two patch antennas. One on each side of the ground plane.

This brings things to the point where it really starts to get interesting. In order to use these antennas, I need to: a) combine the signals, b) bandpass filter the signal, c> amplify the signal, and finally d) deliver it to the GPS unit. This requires design and fabrication techniques that I have never used. But that is good because I will learn a few things along the way.