This website contains information and files relevant to gps-related projects that I have been working on. Use the index below to find out more.
GPS-based Frequency Standard
Frequency standards come at a wide range of prices and qualities. Interestingly, some of the very best (and surely the most expensive) are in the sky above our heads. At any given moment six or more of these standards are in view from any place on earth. I refer of course to the atomic clocks aboard the GPS satellites kindly provided by the US Department of Defense.
My project uses the signals broadcast by these GPS satellites to control (discipline) the frequency of a local quartz or rubidium oscillator and to thereby obtain superb accuracy at a very modest cost. Better yet, most of the hard work has already been done by the manufacturers of the little hand-held GPS receivers.
The high accuracy low-cost frequency standard project was described in the amateur radio journal QST, July 1998, pp. 37-43. It has now been nearly 3 years since the article was published and interest in the project continues. Many of the inquiries I get are from outside the US where QST is not readily available. For this reason I have put an Acrobat PDF-format file of the article here QST_GPS.pdf (796 Kbytes)
I don't know how many of these GPS-controlled standards are in use but I personally have programmed more than 300 PIC microprocessors and sent them to requestors. I have also had correspondence with many people who have programmed their own PICs using the binary file available from this webpage and the QST archives.
In addition to conventional uses of the GPS-disciplined frequency standard, a number of more exotic applications have been made or proposed. These include determining the height of a "homemade" rocket that will attempt to set the world's amateur altitude record (200 km!), tracking the movement of elephants in dense jungle in Africa, and measuring the arrival time of neutrino bursts at an massive underground detector array in Japan.
Surveying is another area where GPS is having a big impact. Surveying has traditionally been done by measuring angles with a transit and distances with a steel tape (or a chain in the old days). GPS has changed all that for professional surveyors. However, professional surveying quality GPS receivers are very expensive and so is the post-processing software needed to analyze their data. High cost has severely restricted the application of this new technology
The project aims to develop methods and software that will provide professional-level results at low cost. This is still mostly a work-in-progress, however it wouldn't hurt to have a look...
If you find these results interesting and have comments or questions you can contact the author, Brooks Shera, W5OJM, at firstname.lastname@example.org . I would be happy to hear from you.
Last updated November 21, 2006