[time-nuts] More recent information on BG7TBL GPSDO?

Bob Camp kb8tq at n1k.org
Tue Apr 28 17:47:54 EDT 2015


Hi

The accuracy required by NTP can be met with a <$20 GPS board. It’s much
easier to simply do a stand alone device than to try to tie everything together. 
Fewer ground loops / fewer things to go wrong / easier to keep running. 

The frequency offset in the device appears to be a design choice made by the
people running the project. There is no way to find out if they have changed their
design other than buying more devices. That *assumes* that the later devices
have later firmware versions ….

Bob

> On Apr 28, 2015, at 2:57 PM, John Laur <johnlaur at gmail.com> wrote:
> 
> Hello all. Long time listener; first time caller.
> 
> I picked up one of the BG7TBL GPSDO units from Ebay, and I am still waiting
> for it to arrive. I understand it has its flaws, but my needs are fairly
> simple, and I think it will serve.
> 
> My intent is to use it as a reference which is better than the 0.1ppm TCXO
> in my HF radio, an ANAN-100D (HPSDR architecture); I would like a PPS
> reference so that I can experiment with timestamped IQ samples; and I would
> like to build an NTP server using a BeagleBone Black. I think this will
> serve to do these things even if it is not the ideal equipment.
> 
> I have read I believe all of the previous discussion on this list over the
> past few months including the excellent study by John KE5FX, and I had a
> few questions to see if there had been any new developments. I understand
> some may have communicated with the designer as well.
> 
> Does anyone else have further information on the serial interface? Is the
> NMEA data directly to/from the U-Blox module or does the internal firmware
> filter/augment it to allow monitoring or tuning of other internal
> parameters - for instance can one set cable delay? What is its suitability
> for running as a GPS/PPS reference for an NTP server? Any other software
> suggestions for keeping an eye on it?
> 
> Second, has the small frequency error identified by John been corrected, or
> is it a problem endemic to the design (I think maybe this was identified as
> a resolution limit of the DAC providing OCXO control voltage; could it be
> dithered?)
> 
> As this is my first moderately accurate device in the shack, is my best
> approach just to put it on the shelf, leave it on for a long time, and
> trust it? I can see how its easy to begin the slide when there is only one
> clock to stare at skeptically.
> 
> Thanks,
> John Laur
> K5IT
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