>Bob said - " A GPSDO with a poor sky view will not do well" Thanks for the feedback. I am exactly 100 miles South of Hadrian's wall and a smidgeon West of The Prime Meridian. My house is in pretty clear surroundings except for a large willow tree in the front garden, which faces South. I can easily mount a pole-mounted GPS antenna on the roof above any obstruction on the roof. So, with luck, I should have a reasonably clear view, and I can always pollard the Willow ... Lady Heather was on my 'to buy' list so it sounds as though I should get her now and a cheap GPS brick to see what the viewing is like. I have a couple of old M12 eval modules from back in the day that were never switched on and a couple of uBlox LEA-M8T-0-10 modules chopped out of Huawei PCBs by the Chinese, but it will probably be quicker and easier to get a cheap module as you suggest. My electronics Lab faces South so I can sit one of the small patch antennas that came with the Motorola kit on the window ledge for initial trials before climbing on the roof. >Tom said - "look into Leo Bodnar GPSDO" seconded by Wes. Thank you both, they look interesting - and low postal charges! >Hal said "older GPS receivers" Thanks, that's one of the reasons that I have decided to buy a low-cost device rather than try to revive the M12 kits, they are over a decade old. >Mete - thanks for recounting your experiences, I can see this is a long journey. :-) >Erik compared rooftop antenna with east window ... sounds like I need to get on the roof, eventually. Thanks for that Erik (sounds like Belgium or the Netherlands?). John