While responding to another post, I realized that this sounds like something some folks here might eb interested in checking out.

A couple of months ago i was lucky enough to stumble across some interesting new GPS tools and I was just blown away by them. Basically, a friend of mine is an RF engineer based in Italy. He designs various kinds of receivers, and he and I share a common interest in GPS. My interest right now is mostly antennas, and he knows a lot more than I do about the functioning of the GPS signal processing chain.

For many years, a subset of GPS modules have supported various kinds of raw data tools that allow a user to do their own processing of GPS satellite data, in their own computer, instead of letting the computer inside the GPS chipset do it. The receivers are of various qualities, but some of them are quite good. And the price has been falling. The chips wholesale can cost as little as $30-ish. But they need some additional components in order to give you a usable receiver.

They are also VERY small. So small you can build the entire receiver into a box the size of a USb flash drive, which is what my friend has done. That is actually really good because it means you can stick your receiver inside of the antenna. Also, it lends itself to portable applications.

Paired with a decent antenna and a computer (or simply a data logger) it would be possible to log data and hen correct it, either in real time (you'd need a data link between your two receivers, your base station and your "rover") or later.

Anyway, I think this stuff is really cool. Its not going to cost a lot of money at all, and its going to let people do some very neat stuff.

For example, calculate things like speed and location with a lot more accuracy than people now expect from GPS.

Many, but not all of the chips that can do this are listed at RTKlib.com. (We've been using the RTKlib library, which is really pretty slick. And its free.)

Ive been making a lot of different antennas trying to find a sweet spot. My best performing antenna so far has been whats called a log spiral. It looks kind of like a spiral galaxy, or the op art posters from the 60s. Since there are a number of GPS systems now, occupying a range from 1 tp 2 GHz, we felt that a broadband antenna would be good if we could make one. We also have been experienting with helical (quadrifilar) and now patch antennas. Quadrifilar antennas seem to be pretty accurate in the N-S and E-W axis but less accurate in the vertical dimension than patch antennas.

Patch antenna I am expecting to be better at up-down. Anyway, to most people this stuff is kind of boring but I think its quite interesting.

If anyone is interested, let me know, I'd be glad to show you how to do it. Some of you may even have GPS's that support it but not know it.