[time-nuts] Trak 8821B ---- was Z3815A Internal SMA 10Mhz Output
GandalfG8 at aol.com
GandalfG8 at aol.com
Wed Aug 22 18:21:03 UTC 2012
Hi Bjorn
Mine did come from a UK Ebay seller in Scotland, just under four years ago,
and he told me at that time he had two more and we'd originally discussed
swapping those two for a radio, until the first one arrived and my
enthusiasm tailed off a bit:-)
It's been a while since I've had it running but I don't recall any GPS
problems, I'll run it up again later and see how it behaves now.
I do remember it needs a negative 48 Volt supply and am pretty sure also
that it feeds 12 Volts to the antenna.
Although the choice of oscillator shouldn't affect the IRIG B output it did
occur to me after posting earlier that it might have affected the
programming for the Low-Rate output, and if the 1MPPS had been generated from 10MHz
by a simple hardware divider, for example, then switching the oscillator
to 16.384MHz might have been less than ideal for that function:-)
With regards to the Oncore VP carrier phase measurement option, I'm not
too sure that the 8821B does actually make use of that.
My 8821B, manufactured in 1999, does contain the 8 channel Oncore VP
B8121Z116 as I mentioned previously, and the 8821 data sheet from 2004 does
refer to all 8821 models as using an 8 channel receiver, but the 8821A manual
from 1997 refers to that as using a 6 channel receiver.
Given that the only obvious difference between the 8821A and 8821B seems to
be the oscillator module I'm assuming the change to the 8 channel receiver
would have occured simultaneously for both versions, and am wondering if
that might not just have been based on availability rather than to take
advantage of any technical enhancements.
Regards
Nigel
GM8PZR
---------------------
In a message dated 22/08/2012 14:55:03 GMT Daylight Time, bg at lysator.liu.se
writes:
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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