Updating my G3RUH GPSDO

Inspired by the design of the Rapco 1804P9 GPSDO, I decided to look at ways of enhancing my home-brew GPSDO wich is based on a design by James Miller, G3RUH. Since I now own a professional GPSDO, I figured it wouldn’t hurt to strip down my old one then re-build it as a viable back-up. See here for the original article by G3RUH.

As previously mentioned, following the failure of the Isotemp 134-10 OCXO (twice!), my  GPSDO has since been running a much smaller OCXO by Isotemp, a 143-141. Unlike the larger 134-10 which ran from 13V and delivered a 2V p-p sine-wave into 50-ohms, the 143-141 runs from a 5V supply and the 10MHz output is TTL … Not ideal for some applications.    

August 2016:

The photograph above shows the GPS receiver on the right with the home-brew PLL board on the left. The 8-pin IC is for amplifying the control voltage to a level compatible with the 134-10 OCXO. This is not required when the OCXO is a type 143-141. In fact the output of the amplifier is too high for the latter. I could have changed the value of one of the resistors so that the gain was unity but it was simpler just to take the control voltage from the input to the op-amp; tacking the wire onto the junction of R1 and C1. The two 4K7 resistors on the output of the OCXO have been isolated since the output of the 143-141 is TTL. James Millar has improved the design of this board since I built it, so there are some differences.

My plan was to re-build the GPSDO such that it had multiple 10MHz outputs, each delivering at least 2V p-p into 50 ohms … And I would base my design on the output stages in the Rapco 1804 … And I might as well include a suitable PSU to power the GPSDO at the same time. The PSU would need to provide +/-12V for the line drivers, +5V for the OCXO and nominally +12V for the GPS receiver and the PLL board.