> As a > newbie to the field of timekeeping, I'm a bit uncertain what would make a > good first system. The price tag of the high end masers unfortunately puts > them outside my range, based on what I could see on eBay. I'll be happy to > pay for good equipment, but once it gets to 4 digits it starts > putting some > serious dents in my bank account. I'm hoping to build my own > circuit around > the device, which might cut down the costs somewhat. Some rubidium sources > on eBay go for less than $100, but I'm not sure what quality to > expect. Any > advice or suggestions are appreciated!
It's interesting to consider how well a GPS clock can perform relative to a local cesium. I took a plot (attached) of a Thunderbolt with a 10811-60109 (t=850s) and one of the sub-$100 LPRO-101 rubidiums, then drew some lines on it to indicate the spec limits of one of the better cesium standards (the HP 5071A). I also tried to copy the traces from Tom's Z3801a at http://www.leapsecond.com/pages/gpsdo/ onto the plot. It seems that the *unlocked* OCXO in Tom's Z3801A is turning in a performance better than the specs of a 5071A with the high-performance tube option, all the way out to tau ~= 400 seconds. It's better than a standard 5071A until about 2000 seconds. If the Z3801A had a much longer lock bandwidth -- say if there were a rubidium standard between the GPS receiver and OCXO that could be locked at tc >> 2000s -- then the GPS receiver might be pretty competitive with the standard 5071A model, at 1/20 the price. -- john, KE5FX
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