[time-nuts] Lucent KS-24361, HP/Symmetricom Z3809A, Z3810A, Z3811A, Z3812...

GandalfG8 at aol.com GandalfG8 at aol.com
Tue Oct 21 06:59:04 EDT 2014


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
 
 
In a message dated 20/10/2014 05:53:29 GMT Daylight Time,  
stewart.cobb at gmail.com writes:

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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