[time-nuts] BG7TBL GPS Disciplined Source

Lars Walenius lars.walenius at hotmail.com
Mon Mar 14 15:40:44 EDT 2016


Hi

If you are lucky the MV89 might be a very good OCXO and U-Blox makes very good GPS modules. The NEO-6M is not the best as it isn´t a timing module. But in your GPSDO the GPS module with an external antenna is not the limiting factor but more the controller and it´s limited resolution on the time measurement that is larger than the ripple from the GPS module. Also the software with FLL seems to limit the performance a lot. But with the long time constant the frequency accuracy, even with the offset due to the FLL, will be quite good.

U-blox own software uCenter have worked well for me.

Lars

Från: Gedas<mailto:w8bya at mchsi.com>
Skickat: den 14 mars 2016 20:00
Till: Discussion of precise time and frequency measurement<mailto:time-nuts at febo.com>
Ämne: Re: [time-nuts] BG7TBL GPS Disciplined Source

Hi Hal, and TU for the reply. Tu also to everyone else with the very
helpful hints and info.  Following the advice of Joe I checked out the
EEV Blog site.....very good information about the different variants of
this maker.  Turns out, because I have a model (date code) of 2014-12-09
that it corresponds to this revision and information:

custom board with surplus russianmorion mv89
<http://www.morion-us.com/catalog_pdf/MV89.pdf>OCXO. gps isu-blox
NEO-6M-0-001 <https://www.u-blox.com/en/product/neo-6-series>.

Who would have guessed a Russian OCXO.  And, I guess the U-Blox is not
one of the better GPS units based on what Paul mentioned.  But I think
there is software out there that will let me at least monitor what my
unit is doing and how many birds it is receiving data from. I also have
the 8-port signal splitter which is nice as I can now run my reference
to all my various TE.

Oh well, it is what it is as I do not have the money to purchase a
different one. To answer your question I am using the supplied "hockey
puck" style antenna placed outside my basement window well, sitting on a
small wooden shelf, but close to ground level.  The antenna should have
a clear view from 90-280 degrees, from an elevation angle of 0-90
degrees.  Anything from West to North to East (~280-90 degrees) is
blocked by the house.  I guess my next step, as Bob suggested will be to
install some monitoring software to see how many birds I am able to see
on average.

Gedas, W8BYA

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On 3/14/2016 12:55 AM, Hal Murray wrote:
> w8bya at mchsi.com said:
>> This is where I really embarrass myself.....sometime ago I purchased an
>> inexpensive 10 MHz GPS based reference source (BG7TBL GPS Disciplined
>> Source) for my various counters, transceivers, spectrum analyzers, etc  and
>> was wondering if it was a good purchase and if anyone else used a  similar
>> unit.  I guess in the end I am curious to know what the short &  long term
>> accuracy and stability of my unit may be?  I no longer have  access to any
>> accurate (known) frequency sources like I did while  employed and I do not
>> think I have the equipment here at home to measure  my unit myself.
> Long term accuracy will be very good - you are tracking GPS.
>
> You didn't say anything about your antenna.  That's probably the major
> contributor to your short term accuracy.
>
> Google found:
>    http://www.eevblog.com/forum/testgear/bg7tbl-gpsdo-master-reference/
> Looks like there are various versions.
>
>

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