[time-nuts] Trak 8821B ---- was Z3815A Internal SMA 10Mhz Output

[bg at lysator.liu.se]

Hi Nigel,

Yes, I have the same version. We might have got it from the same UK epay
source. The GPS did not work reliably, and I did start testing that module
outside the Trak unit, and also tried VP(8chan) receivers that I had. Did
not really conclude why the GPS did not behave properly. I was, like you,
disappointed by the lack of IRIG and other features that are in the
standard units. I also drew the conclusion this was a "high volume"
special model, where it was cost effective to eliminate all - for the
specific application - unuseful outputs.

However it is a very decent size OCXO inside.

The phase measurement Oncore model is interesting, since I have seen very
few GPSDOs that use phase information. It gives the possibility to reduce
the short term GPS noise to cm/s level. However this is probably lost in
the PPS generation hardware, since the Oncore does not lock its internal
crystal to the external OCXO.

--

    Björn

> Hi Bjorn
>
> Is yours also the cut down 2.084MHz version, or do you have a "proper"
> 8821B with a more useful GPSDO frequency and all the outputs fitted?
> I think this one was originally used in a trunked radio  system.
>
> I've just checked and the fitted VP Oncore is  the B8121Z116, so perhaps
> the same module, but I'd forgotten until I  looked again that the unit is
> without the IRIG-B output as well  as the Low-Rate output that normally
> allows a
> variety of pre-set pulse rates,  hence my "cut down" comment.
>
> The Low-Rate ouput speciification suggests some interesting  possibilities
> for experiments in conditioning other oscillators, as  amongst some very
> slow pulse rates it also offered an option of 1  MPPS.
> Unfortunately, not only are the connectors not fitted but quite a lot of
> presumably associated PCB components in that area are also missing.
>
> Do you have a manual for the 8821B?
> I've only ever found a manual for the 8821A, although I suspect the  only
> significant difference may be the fitting of the larger B7A OCXO  to the
> 8821B, which necessitated the height increase to 2U, but it would be nice
> to be
> able to compare them.
>
> regards
>
> Nigel
> GM8PZR
>
> In a message dated 21/08/2012 21:05:02 GMT Daylight Time,
> bg at lysator.liu.se
>  writes:
>
> Hi  Nigel,
>
> Have one of those Trak 8821B too. It is a bit interesting since  the
> Motorola Oncore VP inside mine has the Z option (phase  measurement).
>
> --
>
> Björn
>
>
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