[mole42uk]

I am really quite pleased tonight. Thanks to many people on this forum and a smattering of experience of my own, I have a working GPSDO for my workshop.

Having gone down a dead-end route, I then found the ublox GPS receivers that are perfect for this applicaton. The antenna, receiver and RS232 driver are in a masthead enclosure outside my workshop, and the 100kHz synchronised feed is brought into the Disciplined Oscillator on a plain multi-core cable. The whole works well, please view the circuit I have posted below.

The bit that I found most difficult was to derive a 1MHz sine wave with low enough impedance to drive any load I could imagine, from the square wave that exists inside the control loop. However, with perseverance, help from this forum and LTspice the circuit developed and now I have a very nice 4v p-p sine output which doesn't seem to care if I load it quite severely.