[time-nuts] Lucent KS-24361, HP/Symmetricom Z3809A, Z3810A, Z3811A, Z3812...
stewart.cobb at gmail.com
Wed Oct 22 06:37:31 UTC 2014
> Message: 7
> Date: Tue, 21 Oct 2014 06:59:04 -0400
> From: GandalfG8 at aol.com
> To: time-nuts at febo.com
> Subject: Re: [time-nuts] Lucent KS-24361, HP/Symmetricom Z3809A,
> Z3810A, Z3811A, Z3812...
> Message-ID: <eac2.4de53503.41779678 at aol.com>
> Content-Type: text/plain; charset="US-ASCII"
> It seems from the auction revision table that this seller has been offering
> these for some time, so perhaps another "hidden" gem:-), but it's perhaps
> also worth noting that if this system functions on similar principles to
> earlier RFTG kit then the GPS conditioning is only applied to the unit
> actually containing the GPS module, with the other unit intended as a standby
> should the first one fail.
> In other words, unless the system redundancy is really required most users
> would probably only need the GPS based unit, or would at least be better
> off buying two of those for the same money that the "matched" pair would
> The only advantage, as far as I'm aware anyway, of the non-GPS unit is that
> it contains a 10MHz output.
> However, Skip Withrow published modification details in January 2013
> showing how straightforward it was to add the the 10MHz output, to the
> RFTGm-II-XO module, the PCB location for the socket was already available, so I
> would suspect it wouldn't be too difficult on these either.
I'm sorry, but most of this is inaccurate. The earlier RFTG units
(built by Datum and its successors, I think) had one rubidium and one
OCXO. Both were disciplined by the GPS receiver. In the set that I
have (RFTGm-II Rb and XO), the diagnostic software can actually
display a list of the last ten or so frequency and time corrections to
both the Rb and the OCXO (two separate lists). The OCXO is indeed a
backup in these units, but it is disciplined by the GPS receiver so
that it is constantly ready to take over if needed.
The current HP units appear to function the same way. Both units
contain the equivalent of a Z3805A, and both steer their OCXOs to lock
to GPS time and frequency. Both can be interrogated independently to
observe their steering corrections and statistics. I assume that the
PPS and timetag data is fed across the interconnect cable from the
unit with a GPS receiver to the one without.
Finally, the current HP units are completely different internally from
the older RFTG units. The 10 MHz modification mentioned above does
not apply to the HP units. I believe there is an equivalent
modification, involving several surface-mount resistors, one
surface-mount capacitor, and an output cable, that can add a 10 MHz
output to the unit which lacks it. However, I have not yet completed
or tested this mod. If I get it to work reliably, I will post it to
A better solution for time-nuts would be to repurpose the 15 MHz
outputs on both units and set them up to output 10 MHz instead.
However, that mod would require much more detailed tracing of the
circuitry than I have done.
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