A plot showing the paths of the recently-tracked and currently-tracked satellites. The receiver`s location is the `bull`s eye` in the center while the top of the plot represents the North pole. The red line shows the `EFC` value - the setting of the electronic tuning adjustment which is an indication of how far the Z3801`s internal oscillator departs from GPS time and the tuning
KA7OEI GPS - schematic

required to correct it. This page is intended to document only how I put my system together and a few other miscellaneous items. It should go without saying that there are probably better ways to do these things, that your mileage may vary, blah blah blah. Back in 2003 I bought a used HP Z3801A GPS receiver (often called a "Z-Box") with the intent of using it as a time/frequency reference. As with most projects, this one was ongoing, with incremental progress dependent on available time and current whim. Nevertheless, it didn`t take too long to get it up and running, following the "make it work, then make it look good. " mantra. A known-good frequency reference is handy for making sure that everything else is on frequency. At this location (Utah) reception of WWV on 10 MHz (the most convenient frequency for calibrating against) is very sporadic and it is often difficult to get a good zero beat owing to the constantly changing path and the usual presence of WWVH. Over the years the Z3801 has been invaluable for use as a frequency reference. With it, I have been able to assess the stability of OCXOs (Oven-Control Crystal Oscillators) and Rubidium references for use with microwave ( 10 and 24 GHz transverters ) as well as use its 10 MHz output as an external reference for a frequency synthesizer to generate reference markers for use in the ARRL Frequency Measurement Tests (FMT`s) - among many other things - and with accuracy...

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