[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

Hi Stewart
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 
sure anyway.
I suspect "repurposing" of the 15MHz outputs to 10MHz might not  be too 
straightforward either.
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
> cost.
> 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.
> Regards
> Nigel

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
the list.

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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