[time-nuts] yet another GPSDO

Bob Camp kb8tq at n1k.org
Fri Aug 7 19:49:37 EDT 2015


That sounds like a close cousin of the Z3805


> On Aug 7, 2015, at 2:53 PM, Arthur Dent <golgarfrincham at gmail.com> wrote:
> I picked up yet another version of a GPSDO on Ebay the other
> day. I thought that I'd mention this because sometimes when
> one unit shows up there are a lot more that will be listed
> for sale later, like with the many Lucent RFTG units that
> are currently being sold on Ebay.
> This one is a Symmetricom CGBA with absolutely no info other
> than the photos in the listing. The board is about 9"x13" and
> has date codes from 2003. It has a Symmetricom 5Mhz OCXO that
> feeds a doubler with L/C filtering and a 10Mhz crystal to
> further filter the 10Mhz and give a nice clean sine wave
> feeding a 27 ohm termination resistor. Then the signal goes
> to 3 EL2257 dual gated opamps That seem to make the signal
> look much worse so there may have been more than one design
> engineer on this project. ;-)
> I traced out 2 lines for power, each one goes thru its own
> fuse to a diode bridge so it doesn't care about polarity.
> From the bridge the power goes to several discreet onboard
> switchers that give +12, +12 OCXO, -12, +5, and +3.3VDC. I
> found that the minimum voltage to make the board operate was
> 22-28VDC so I'm running it on 36VDC. The current draw is 0.5A
> cold to 0.25A with the OXCO warmed up.
> The GPS is made by Furumo and has what looks like an HP part
> number 0960-1060(HP31) and has +5VDC for an active antenna on
> the antenna connector. There are unused pads on the main board
> for SMA size connectors that are marked 10M, PP2S, 4.096M, 100Hz,
> 30.72M, 40.96S, and 8K. Not all of these are active and the
> 3 dual opamps are not 'on' either so some of the pins in the
> connectors on the back of the assembly may do some controlling
> of signals or these may be options not implemented on this board.
> When powered up it goes through a light flashing sequence then
> the GPS LED goes flashing green when it sees the satellites, then
> solid green when it locks, and the ACT LED turns from flashing red
> to flashing green. Using my modified Tbolt to test the unit shows
> it stays within +/-200PPT for about the first 2 hours then settles
> down.
> There is an RJ-45 connector on the front plus there is a 15 pin
> 'D' connector behind the panel that may have been for some
> testing purpose because it can't be accessed from the front.
> At this time I'm just happy to see how well it works and later
> I'll see if I can communicate with it somehow.
> -Arthur
> http://i906.photobucket.com/albums/ac262/rjb1998/CGBA_zpsd4rricto.jpg
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