titi - PLJ-8LED-C.pdf looks very useful, and dR-mR, thank you for http://www.radioradar.net/en/measurements_technics/2_5_ghz_12_digit_frequency_counter_with_add_on_gps_accuracy.html
- it looks really useful.
Thank you to everyone who has replied.
The forum links in PLJ-8LED-C.pdf look really interesting, but I don't know Chinese. I have a friend who does, and he's back from Chinese New year holiday on Monday, so I may get some progress there. Specifically I'd like source code that I can modify.
I'm sorry there has been such a long delay in replying but a friend was diagnosed with terminal Cancer, so spare time has been spent supporting him. He died and I'm trying to sort out his estate. Life has been pretty much on hold for a year and still isn't back to normal. Profound apologies.