[time-nuts] worth salvaging ?

Mark J. Blair nf6x at nf6x.net
Sat Jan 29 18:14:21 UTC 2011

On Jan 29, 2011, at 6:43 AM, paul swed wrote:
> It seems to interpret the almanacs wrong because amazingly enough its
> actually does know the correct GPS week which was a shock to me. Unless
> thats a simple calculation from the date I might guess.

It's the other way around: The GPS week is directly decoded from the GPS signal. If I'm not mistaken, the GPS week roll-over causes a problem of being able to correctly calculate the calendar date from the GPS week. I could be mistaken, but I think that a receiver that doesn't handle the rollover properly but is otherwise in good shape should be able to track satellites and provide a correct position, but the calendar/clock time calculation would be wrong.

In a receiver that doesn't have a recent almanac, and particularly in an older receiver that takes a very simple approach to downloading ephemeris and almanac information, initial acquisition could take a long time. It'll need to do a slow full-sky search for its first satellite, and older receivers couldn't do that nearly as quickly as newer ones can. Once it gets that first bird, it may sit there downloading ephemeris and almanac data for at least 12.5 minutes before it does anything else. With an old receiver from that era, give it at least a half hour of good open-sky conditions before you begin to suspect that it's dead.

Back to the original topic now: That OCXO may seem mundane by time-nutty standards, but I'd certainly consider it to be worth salvaging. It could have all sorts of applications for radio stuff, portable test equipment, and even time-nutty stuff in an application that wants to be smaller and more portable than a Rb standard or full GPSDO.

I also agree that there's likely to be a lot more salvageable stuff on those boards. I see lots of socketed parts. UV-erasable EPROMs are worth saving. Are those Altera parts reprogrammable? If so, then they're worth keeping. Keep any microcontrollers or CPUs that are reprogrammable, or rely on external program memory, or can still be used in spite of fixed internal programming (e.g., an old mask-programmed 8051 can be used as an 8031 by strapping a pin to tell it to ignore its mask ROM and use external program memory).

I'd say that any units which track satellites at all after a half hour should be considered for repair, and the rest of the units are goldmines of parts.

Mark J. Blair, NF6X <nf6x at nf6x.net>
Web page: http://www.nf6x.net/
GnuPG public key available from my web page.

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