Rapco 1804P9
GPS Disciplined Precision Frequency Source
Page 3

Now with my newly acquired Rapco GPSDO I decided to attempt to mount the puck clear of the roof. In the process I removed the dish and the failed GPS PCB antenna from the mast.


Using a U-bolt salvaged from the dish, I clamped an L-shaped piece of steel plate to the top of the pole that supports my 2.3GHz beacon yagi, and placed the magnetic puck on top; see the photograph on the left. It isn’t an ideal position since there will be some obstruction from the rotator body but the receiver never sees less than 8 satellites at any time. I should probably also provide some UV protective cover for the antenna.


The RS-232 port on the rear of  the 1804P9 provides an ASCI stream derived from the RAW NMEA data from the Trimble RX.

David GM8ARV has written a little program for displaying this on a Windows-based PC. Originally written for the 1804M there were one or two elements of data that were either

August 2016:

Back in 2007 when I built my own GPSDO I used a ‘surplus’ PCB-based active antenna which I mounted in a little plastic box. This was mounted outside on a pole attached to the mast supporting my UHF and uWave antennas. A few years ago this failed and since low-cost GPS puck antennas had become available I bought one and simply placed it on the LNB arm of our redundant Freeview Satellite dish … and there it sat happily doing its job until last weekend.

missing or incorrect. However after providing David with a sample of the ASCII output from the 1804P9, he kindly made a few tweaks to his program so that the PDOP and Mode fields are now correct.


The 1804P9 does not output an ‘Average Position’ periodically, so that field remains blank. On the other hand, the P9 outputs a parameter labelled ‘DAC output’ every 512s once a fix has been obtained and Control asserted. I believe this to be the Oscillator Steering Voltage in millivolts.