Fellow time-nuts, This (long) post is a review of the HP/Symmetricom Z3810A (or Z3810AS) GPSDO system built for Lucent circa 2000. I wrote it because I looked for more information before I bought one, and couldn't find much. It's relevant because (as of this writing), you can buy a full system on the usual auction site for about $150 plus shipping. For those of you lamenting the dearth of cheap Thunderbolts, this looks like one of the best deals going. The description of these objects does not include "GPSDO", so time-nuts may have missed it. Search for one of the part numbers in the subject line and you should find it.
So what is it? It's a dual GPSDO built by HP as a reference (Redundant Frequency and Time Generator, or RFTG) for a Lucent cell-phone base station, built to Lucent's spec KS-24361. Internally, it's a close cousin of a later-model Z3805A. Externally, it looks to be almost a drop-in replacement for the earlier RFTG system built to Lucent's spec KS-24019. That was a redundant system containing one rubidium (LPRO, in the one I have) and one OCXO in two almost-identical boxes. That spec went through several revisions with slightly different nameplates and presumably slightly different internals. You can generally find one or two examples on the auction site (search for RFTG or KS-24019). This system is similar, but the two boxes each contain a Milliren (MTI) 260-0624-C 5.000MHz DOCXO, and neither contains a rubidium. The Milliren DOXCO is the same one used in the later models of the HP Z3805A / 58503A. It's a very high-performance DOCXO, in the same class as the legendary HP 10811, and better than the one in most surplus Thunderbolts. The 5 MHz output is multiplied up to 10 MHz in at least one unit, and 15 MHz in both units. I don't have the ability to measure phase noise on these outputs, but I'd be interested to see the results if someone could. Nomenclature: The Z3810AS (there always seems to be an "S" at the end) is a system consisting of the Z3811A (the unit containing a GPS receiver), the Z3812A (the unit with no GPS receiver), and the Z3809A (a stupid little interconnect cable). The GPS receiver inside the Z3811A is a Motorola device, presumably some version of an OnCore. Where the Z3811A has a TNC GPS antenna input, the Z3812A has an SMA connector labeled "10MHz TP". That is indeed a 10 MHz output. It comes active as soon as power is applied to the unit, and its frequency follows the warmup curve of the OCXO. The two units have identical PCBs (stuffed slightly differently), and I have no doubt that someone can figure out how to add a 10 MHz output to the Z3811A as well. Operation: From the outside, these units are broadly similar to earlier units in the Lucent RFTG series. The (extremely valuable) website run by Didier, KO4BB, has a lot of information on those earlier units, much of which still applies here. The purpose of these units was to provide a reliable source of frequency and timing information to the cell-site electronics. The 15 MHz outputs from both units were connected to a power combiner/splitter and directed to various parts of the transmitter. The units negotiate with each other so that only one 15 MHz output is active at a time. The outputs labeled "RS422/1PPS" contained a 4800 baud (?) serial time code as well as the PPS signal, which were sent to the control computer. Power is applied to the connector labeled "+24VDC" and "P1", in exactly the same way as the earlier RFTG units. Apply +24V to pin 1 and the other side of the power supply (GND or RTN) to pin 2. In these units, that power supply goes directly to an isolated Lucent DC/DC converter brick labeled "IN: DC 18-36, 1.9A". Presumably you can run both units with a 4-amp supply. Once you have applied power, connect the Z3809A cable between the jacks labeled "INTERFACE J5" on each unit. The earlier RFTG units used a special cable between two DE-9 connectors, and it mattered which end of the cable connected to which unit. The interconnect for these units is a high-density DE-15 connector (like a VGA plug). The Z3809A cable is so short that the two units need to be stacked one above the other, or the cable won't reach. It doesn't seem to matter which end of the cable goes to which unit. I don't know whether it's a straight-through cable, or whether you could use a VGA cable as a substitute. When you apply power, all the LEDs on the front panel will flash. The "NO GPS" light will continue flashing until you connect a GPS antenna. Once it sees a satellite, the light will stop flashing and remain on. The unit will conduct a self-survey for several hours. Eventually, if all is well, the Z3812A ("REF 0" on its front panel) will show one green "ON" light and the Z3811A ("REF 1") will show one yellow "STBY" light. This means that the Z3812A is actually transmitting its 15MHz output, and the other one is silently waiting to take over if it fails. Most time-nuts want to see more than a pretty green light. The old RFTG series allowed you to hook up a PC to the "RS422/PPS" port and peek under the hood with a diagnostic program. The program is available on the KO4BB website. It is written for an old version of Windows, and I had no luck getting it to run under Windows 7. It does run under WINE (the Windows emulator for Linux) on Ubuntu 12.04 LTS. To use it, you need to make an adapter cable to connect the oddball RS-422 pinout to a conventional PC RS-232 pinout. The adapter cable looks like this: RFTG PC DE-9P DE-9S 7 <----------> 5 8 <----------> 3 9 <----------> 2 (According to the official specs, this is cheating, because you're connecting the negative side of the differential RS-422 signals to the RS-232, and ignoring the positive side of the differential signals. However, it's a standard hack, and it's worked every time I've tried it.) With that adapter, you can see the periodic timetag reports from the unit. The RFTG program will interpret these timetags when it starts up in "normal mode". However, when I try to use any of the diagnostic features built into the program, it crashes WINE. The timetag output was required for compatibility, but I suspect that HP didn't bother to implement the Lucent diagnostics. Instead, they added a connector which is not on the previous RFTG series. That connector is labeled, logically enough, "J8-DIAGNOSTIC". It too is wired with RS-422, so you need to use the same adapter cable as before. Once you do, you'll find that this connector speaks the usual HP SCPI command set (Hooray!). I used the official SATSTAT program (again under WINE on 12.04 LTS), but I'm sure that other programs written for this command set will work as well. The default SATSTAT serial port settings of 9600-8-N-1 worked for me. After about 24 hours, with a poorly-sited indoor GPS antenna, my system has converged to TFOM=3, FFOM=0 (the best possible numbers), and a "predicted 24-hour holdover uncertainty" of 5.2 microseconds, which is not too shabby. It found the correct day and year without any assistance, so if it has a "GPS week number rollover" problem, it's still in the future. I don't currently have the ability to compare the 10 MHz output to anything else. Again, if someone else can, I'd be interested to see the results. Additional Notes: The parts on the boards all have date codes of 1998 or 1999. The Motorola GPS receiver has a firmware label that reads "02/04/00". The SCPI error logs inside the HP units were virgin when I first got them. They had 84 and 94 power cycles, respectively. Before the GPS receiver acquired time, the error log timestamps read "2000-05-09 00:00:00", which I interpret as a firmware release date. The PCB has an interesting feature. Next to each soldered-in pin of the Milliren OCXO is a single-pin socket soldered into the board. I'm guessing this was used in manufacturing, to temporarily install a Milliren and confirm that the system worked before permanently soldering it in. (At production prices, the Milliren would have cost far more than the rest of the PCB.) You might be able to use this in reverse, if you have a set of Millirens to test from another source. The Z3809A interconnect cable has three of the 15 pins on each end clipped a bit shorter than the rest. Not so short that they won't eventually make contact, but short enough to make contact later than the rest. Don't know why, but it's clearly deliberate. A lot of hot-plug connectors are built that way, including USB connectors. I have no idea what the pinout of the interconnect is. The redundant system slaves both DOCXOs to the same GPS reference. Inside the GPS loop bandwidth, the two oscillators will have almost the same frequency and will differ only by phase noise and short-term stability. This is almost a perfect setup for experimenting with certain kinds of time-nut measurements, assuming someone can figure out how to get 10MHz out of the Z3811A unit. If you then command both units into holdover, you could measure longer-term stability as well. The units are described as "new in factory sealed box". After an archeological investigation of the various strata of labels and tape on the boxes, I would say that's probably accurate. My set seems to have been shipped from the Agilent factory in Korea to Symmetricom in Sunnyvale, CA sometime in August, 2000, shortly after it was built, and remained untouched until I opened it. I'm guessing it was built and saved as part of a spares program for Lucent, and kept until Lucent decided they didn't need spares any more. I have no connection with the current seller of these units (or any other sellers, for that matter) except as a satisfied customer. I think I'll order another set as a spare, before the feeding frenzy hits. Request for help: Both the SatStat and RFTG programs run under WINE on stock Ubuntu 12.04 LTS (32-bit) without any tricks or special configuration. Neither seems to run under WINE on Ubuntu 14.04 LTS (64-bit). I am a WINE novice. Any hints from WINE experts would be appreciated. Also, I've been able to run TimeLab under WINE, but I can't connect it to my USB-to-488 interface, so I can't take data. If anyone can tell me how to set that up, I'd be extremely grateful. Cheers! --Stu _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.