[time-nuts] Some observations of the BG7T BL GPSDO

Bob Stewart bob at evoria.net
Sun Mar 22 22:02:57 EDT 2015

Hi John,
Doesn't that have a NEO-6M in it rather than a timing receiver?


      From: John Miles <john at miles.io>
 To: 'Discussion of precise time and frequency measurement' <time-nuts at febo.com> 
 Sent: Sunday, March 22, 2015 5:49 PM
 Subject: Re: [time-nuts] Some observations of the BG7T BL GPSDO
> Curious, but I'm wondering whether there are any artefacts that might have
> been caused by the weak GPS signal? I would feel more comfortable if the unit
> had its planned strong GPS signal throughout the test. I know it's meant to cope
> with that, but it might have thrown up an obscure software bug. Exactly how
> that might have nudged the frequency off I can't figure.

I will say that when the Thunderbolt went into holdover, the BG7TBL unit barely twitched (see http://www.ke5fx.com/gpscomp/holdover.png ).  In fact, this was the only time its frequency error went positive for a significant period.

It's likely that many/most newer GPSDOs have better receivers than the Thunderbolt.  If the BG7TBL unit had been less consistently off-frequency, I'd be more inclined to agree that test wasn't fair due to the weak signal. 

Another area of concern is that I don't know how the unit manages its self-survey process.  If it still thinks it's in China, then it obviously isn't going to perform at its best.  Ideally it would recognize that it's been moved since the last powerup, but I can't be sure about that, not having any software or documentation for its serial port...

-- john, KE5FX
Miles Design LLC

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