Hi Attila,

You might check the OCXO.  I recently repaired a Symmetricom UCCM that
the oscillator had died.  There are replacements available on-line and
there are footprints on the PCB to accommodate various versions.  The
only gotcha on the Symmetricom version was that it uses an oscillator
with 12V supply and 5V oscillators did not work. Had to replace with
same.  The others, Trimble and Samsung, use more generic 5V oscillators.

David N1HAC

On 4/14/24 8:24 AM, Attila Kinali via time-nuts wrote:

Hi

Cost wise, the surplus UCCM Trimble’s (or the Symmetricom version) still seem be the one to go with. At the same price, I’d go for the Trimble version. Both appear to work pretty well.

If cost is no object, there are lots of crazy choices.  Each of them has it's own unique advantages and (usually) unique issues. The SRS FS740 is one example. It does indeed have its quirks. Not exactly cheap, and still far from the most expensive option.

https://www.thinksrs.com/products/fs740.html

At least two list members have one of them.

In this era of multi-band GNSS as well as anti-spoofing / anti-jam there are a lot of ways to run up the price :).

How crazy do you want to get?

Bob

hi Atilla,

Assuming you can find one: the Samsung UCCM is form/fit compatible but sports a much more sensitive GPS module. Fast satellite lock with signal levels that made Trimble and Symm. UCCM modules very slow to acquire lock.

I happen to own 2 of these Samsungs. Previously also had both a Trimble and a Symm UCCM. The Samsungs were to stay.

hth,
Wilko

I have been doing an analysis of GPSDO's from the usual auction site. These are usually coupled with a crystal I have done the $99.99 TM4313 one and the BG7TBL (2019 version) $150.00. I have started to keep a spread sheet of the Allen variance as well as the Pk-Pk deviation. The analysis has been 100 Samples averaged with gate times of 0.01, .1, 1, 10, and 100 seconds. I have found them to wobble around 20uHz range and up in to the low mHz (>9mHz) If there is a place I can post the Excel document I am happy to do so.

Testing was done on a HP 53230A with an SRS FS725 as its time base. This is backed up by a GPSDO 1pps -> FS725.
Warm up and settling times are as follows

FS725 - more than a month
HP 53230A - More than 1 Hour (Internal clock not used)
GPSDO under test - 24 Hours or more for stability

I will have videos about this testing on YouTube in a few weeks.

Eric

-----Original Message-----
From: Wilko Bulte via time-nuts time-nuts@lists.febo.com
Sent: Sunday, April 14, 2024 4:06 PM
To: Discussion of precise time and frequency measurement time-nuts@lists.febo.com
Cc: Attila Kinali attila@kinali.ch; Wilko Bulte wkb@xs4all.nl
Subject: [time-nuts] Re: GPSDO replacement recommendation

hi Atilla,

Assuming you can find one: the Samsung UCCM is form/fit compatible but sports a much more sensitive GPS module. Fast satellite lock with signal levels that made Trimble and Symm. UCCM modules very slow to acquire lock.

I happen to own 2 of these Samsungs. Previously also had both a Trimble and a Symm UCCM. The Samsungs were to stay.

hth,
Wilko

time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-leave@lists.febo.com

The only caution for the Samsung version is it has a bit different
serial protocol, but Lady Heather version 6.14 knows how to talk to it. 
There is also a patch that helps - grounding pin 39 of the 50-pin
connector to sync to the internal GPS PPS (this is true of all
versions).  The Samsung is also very critical for supply voltage, 5V
min, 5.5V max, to keep the power fail light off.  I have several of all
versions.

David N1HAC

On 4/15/24 8:43 AM, Wilko Bulte via time-nuts wrote:

Does the BG7TBL unit still have a frequency error? Last time I tested one
of his units the frequency was wrong by about 1e-11 due to a software bug.
(Other people on the Internet have observed the same, e.g.
https://blog.febo.com/?p=636) I was briefly in contact with the designer
via email a couple years ago and he promised a fix but then stopped
replying to my emails.

On Mon, Apr 15, 2024 at 8:29 AM Zen via time-nuts time-nuts@lists.febo.com
wrote:

hello David,

Both Samsung UCCM I own are not satisfied with a 5 V supply, the need 5.5 V. So I advise a bit more than 5 V. There is a LDO on the Samsung UCCM so it will do its own onboard power cleanup.

One of them is equipped with a OrangePi (RaspberryPi lookalike) which runs Linux with LadyHeather. This makes for a standalone unit that, once connected to the LAN, can be monitored via the network/LH.

For a house standard this works quite nicely, not needing an always-on PC, but rather a low power *Pi taking care of the monitoring chores.

Wilko PA1WBU