[time-nuts] Chinese GPSDOs

[ew]

All three seam to be Chinese customer specific devices with focus on time. I bought three of the Trimble units we call them Tbolt 2 because of design similarities. On LH you will notice one thing like the original Tbolt it shows frequency jumps of 1 E -10 but also once every hour it does a major correction plus or minus. It is once an hour depending on when powered up. Frequency measurements confirm the excursions. The result is a maximum 1 pps excursion of  plus minus 4 nsec. This is comparable to the Furuno GT87 and four times better than Tbolt 1. All tests are 24 hours against a very good HP 5065A, backed up with Cs.
Bert Kehren
In a message dated 4/17/2020 11:52:31 AM Eastern Standard Time, time-nuts at welwarsky.de writes:

On Freitag, 17. April 2020 16:04:15 CEST Steve - Home wrote:
> There are some Chinese GPSDOs currently on eBay, containing a Symmetricom
> 10MHz oscillator and a Furuno GT-8031 GPS receiver. Has anyone had any
> experience with them? It’s hard to tell from the pictures what the power
> requirements are. I know the GT-8031 is an older 8-channel receiver. I was
> considering one for a portable 10MHz reference. Anyone checked these out
> yet?

I own three of them. One of them is the Symmetricom/Furuno combination you mentioned. 
Another one has a Samsung OXCO and a Ublox LEA-6T receiver. A third one is supposedly a 
Trimble OXCO, but I have no idea which GPS receiver it is using. It's the only one in an 
enclosure and I didn't bother yet to open it.

They're all basically identical in form and structure. Same form factor, same inputs and 
outputs. I even bothered to make an adapter PCB with a switching regulator so that I can 
operate them more easily. They operate on 5.5V, taking in a little over 2A while the OCXO 
heats up.

I have no equipment yet to assess their performance. Anyway they're all scrap telecom 
equipment, many of them are unchecked and damaged, with components missing (ripped 
off of the PCBs), cables cut. The OCXOs are genuine as far as I can tell but they all have 
undocumented service life and you don't know what they have been exposed to 
mechanically.

If you plan to order one, I suggest to get one with an Ublox receiver. The Furuno is likely 
the oldest and weakest, it's also GPS-only. Afaict, the LEA-6T can at least receive GPS and 
GLONASS. From all three, I like the Samsung best, going by the performance I see when 
connecting it to "Lady Heather". The Symmetricom is the worst. Probably the OCXO has 
taken a hit.
The Trimble is so-so.

Of course there's a thread on the EEVblog forum dealing with all their variants:

https://www.eevblog.com/forum/projects/a-look-at-my-symmetricom-gpsdo-(ocxo-furuno-receiver)/[1] 

HTH.

BR,
Matthias
> 
> Steve
> WB0DBS
> 
> 
> 
> 
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--------
[1] https://www.eevblog.com/forum/projects/a-look-at-my-symmetricom-gpsdo-(ocxo-furuno-receiver)/
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