[time-nuts] Lucent KS-24361, HP/Symmetricom Z3809A, Z3810A, Z3811A, Z3812...
GandalfG8 at aol.com
GandalfG8 at aol.com
Wed Oct 22 04:35:40 EDT 2014
Yup, I was certainly wrong re the conditioning, sorry about that and
thanks for the correction.
I was under the impression from way back that in the original RFTG setup it
was only the OCXO that was GPS conditioned but see now the manual, that
I've also had from way back, confirms exactly what you say.
RTFM obviously holds as good today as it ever did:-)
However, aside from the incorrect justification, I still believe for
anyone not actually needing the redundancy, and even for those who might fancy
the idea but don't actually require it in the same physical frame, that two
of the GPS inclusive units, especially at the same price as the "matched"
pair, are a much better deal and potentially a lot more useful.
That of course would not apply if one unit contained a rubidium module
such as with your RFTGm, regardless of whether or not that was GPS
conditioned, but for two units virtually identical except for one lacking the GPS
module then, for me at least, the conclusion seemed obvious.
I'm well aware that these units are not physically the same as earlier
versions but was just using the previous modification by way of example to
suggest that modifying these for 10MHz might also be reasonably
This was based in part at least on an assumption that, as in previous
versions, both units are likely to share the same circuit board but whether
such modification is really necessary, other than "just because", I'm not too
I suspect "repurposing" of the 15MHz outputs to 10MHz might not be too
A few years ago Efratom rubidium modules were being sold from China with
Lucent 15MHz interface boards still attached but less the outer cases,
perhaps part of the original FRTG?, and these contained a very nice purpose
built 15MHz synthesiser, complete with hardware band pass filtering etc.
I still have the schematic somewhere, prepared at the time by another list
member, and it soon became fairly obvious that in the "real" world the
best use for that board was to provide an interface connector to the rubidium
module and to ditch the frequency conversion altogether.
Similarly, with this RFTG-u kit I'd be more inclined to look for ways of
routing the native 5MHz from the GPS conditioned Milliren 260 series
oscillator to the outside world, and to just treat any other use found for the
processed 15MHz as a bonus:-)
In a message dated 22/10/2014 07:38:07 GMT Daylight Time,
stewart.cobb at gmail.com writes:
> 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
> these for some time, so perhaps another "hidden" gem:-), but it's
> 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
> should the first one fail.
> In other words, unless the system redundancy is really required most
> would probably only need the GPS based unit, or would at least be
> 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
> 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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