I was sat in a 737 the other day, my N810 got a cold lock (I had previously used gps-ui near that location, but no list of satellites was shown - does that mean cold?).

Anyway, I got a lock in ~5min with the N810 by the window, then it dropped out, and I couldn't get a lock again (even though the satellites were all still shown). Is this a signal strength problem - my SNRs (I presume that's what's displayed above each satellite) were ~26 and lower.

Does anyone have some info on required SNRs? This is presumably down to the antenna quality, but the internal processing will also have an effect with a fixed (low) SNR to work from.

Anyway, it was just painful to sit there with lots of satellites in view (between 9 and 11) but still not be able to get a lock.

Same was true when we were flying, but then it is doubtless going to be more difficult to get a lock when you're not stationary (but ~ 35k' and ~500mph) (still less than the ITAR limits of 1000 knots & 60k' though, so it ought to work eventually - I tried for 45min)