A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)

[PE1DHI]

Building my own at the moment and came across this thread.

Where did you get the distribution amp as I'm probably not using the correct search terms...

thanks in advance.

This HAM makes them for a low price:

https://telecom.tweedehands.net/accessoires-diversen/10-mhz-distributieversterker-1-10.html

[PE1DHI]

I just looked at your drawing again and I think I see the problem. the connection marked VREF (on the pcb) is the output of the built-in voltage reference and should have 5V on it, and you also marked the EFC as being ground. That's not going to work

Paul,

Mmm, I connected the CTI TXCO with wires, because it did not fit straight on to the PCB. I "thought" that I had figured out the connections (without any documentation).
Could you enlighten me with the right connections, please? Or are these connections somewhere in the past 57 pages?

Jugo

[PA0PBZ]

They are probably somewhere in this thread but it's simple because they are all marked on the PCB

GND, +5V (not used), PWR and RF are obvious. VREF (Voltage reference) is an OUTPUT of the TXCO used by the DAC. If the CTI doesn't have this (looks like it doesn't) you have to provide it somehow, but it needs to be stable, voltage about 5-5.5V. EFC is the tuning voltage, the output of the DAC.

I hope this helps.

[wkb]

If this is the same CTI OCXO as I have lying around then it does not produce a Vref.

In addition it has a square wave output, not a sine wave. Not sure if the Symm
likes that; originally it has a sine wave OCXO.

Wilko

[PE1DHI]

After directions from PA0PBZ it starts to work, but....
Actually it did work before when I reconsider the post and pictures from 29-1-2022.
PA0KTF told me that the Symmetricom TXCO is 1 Hz per Volt and CTI TXCO about 7 Hz per Volt.
A voltage divider and R-C combination for damping give sometimes a proper valid output.

At least some progression and work to be done.

[LukGasp]

Hi there!
Its been over two years since I got my Symmetricon working flawlessly, but two weeks ago I had to switch it on again to hook it up to a frequecymeter and what a surprise to realize it cannot update to the proper date, altough it shows the time and location.
Any hints that may lead me to get a proper date, plase?

Thanks in advance!

[bingo600]

You are probably being hit by GPS WRO (Week Rollover)
A lot of the older receivers are hit by that one.

If the GPS manufactor hasn't released a newer firmware , there's nothing you can do.

But your 1-PPS + 10MHz will still be as accurate as before, as the date isn't used for these functions.
It's just the "cosmetic" date what will show (a multiple of 1024 weeks - ISTR) wrong.

/Bingo

[LukGasp]

Do you know if Symmetricom has released a newer firmware? Is there a such a thing that may be found online?
I still need the GPSDO for my frequency meter.
Also, upon inspection, it was noted that the 10MHz isn't behaving properly as before. It varies constantly. I can observe that with the assistance of  an oscilloscope.

Cheers

[ZigmundRat]

These are all units built for a specific customer and no information on them or firmware has been released by Symmetricom, Trimble, or any other OEM. So while the community has done a pretty good job of reverswe engineering and detective work, ultimately you have what you have.

The WNRO (week number roll over) problem should not affect the GPSDO operation - only the displayed date. If your 10MHz is unstable there is another problem. Maybe time to buy another one.