[time-nuts] Lucent KS-24361, HP/Symmetricom Z3809A, Z3810A, Z3811A, Z3812A GPSDO system

Bruce Lane kyrrin at bluefeathertech.com
Tue Oct 21 00:25:16 EDT 2014

	I just bought one myself, as a backup for my existing Z3801 (yes, that

	Thanks for digging into this, Stewart. I look forward to further

On 19-Oct-14 21:53, Stewart Cobb wrote:
>  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
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Bruce Lane, ARS KC7GR
kyrrin (at) bluefeathertech dot com
"Quando Omni Flunkus Moritati" (Red Green)

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