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 straightforward. 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:-) Regards Nigel GM8PZR In a message dated 22/10/2014 07:38:07 GMT Daylight Time, [email protected] writes:
> Message: 7 > Date: Tue, 21 Oct 2014 06:59:04 -0400 > From: [email protected] > To: [email protected] > Subject: Re: [time-nuts] Lucent KS-24361, HP/Symmetricom Z3809A, > Z3810A, Z3811A, Z3812... > Message-ID: <[email protected]> > 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 > cost. > > 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. > > Regards > > Nigel > GM8PZR 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. Cheers! -Stu _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
