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GPSDO



Cluster Activity

Spots per uW band today:
UK spotter or spotted only.

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SFI
74
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11
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4
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3
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qui
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Date:21/11/17 Time:11:37
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UKHASnet
Symmetricom 10MHz GPSDO

I ordered a couple of these 10MHz GPS referenced OCXO boards from China after spotting them on ebay.
Basically a 10MHz Ovened oscillator referenced from GPS signal on one board, very handy!

Symmetricom UCCM-P



Bottom


A little googling returned a lot of info on the eevblog forum here
Warnings were given that the quality of the boards arriving from China were not good, mine both arrived faulty too.
One had missing MCX connector, part damage to U23 2.5v reference IC and some missing capacitors, the other had a faulty switching psu board to power the OCXO.

I managed to re-flow U23 and just add a coax for the missing GPS antenna MCX connector to make that board come to life, i have not replaced the two missing caps yet.
The second board has a faulty 5v>12v switching psu add-on board which is faulty, i have not looked at this yet, just applied 12v separately for the TCXO supply. The board with the working dc-dc converter sometimes screams badly from this converter even with psu current limit of 4A so i will probably supply my own 12v...

5v Current at startup should be about 1.5A dropping to about 600mA once hot and in an insulated box, if the switching supply is faulty it will be more like 180mA.

The main 5V supply is applied at the fuse near the header, Ground to the negative side of C11.

Power Connection



You can monitor the board activity on the serial port 4 pin header, it is RS232 voltages so can be connected straight to the com port of your pc.
57600 baud.

So far tests have been quite poor regarding GPS signal acquisition, but i may have too weak gps signal.
I have had full lock and it completed a site survey, the Reference at 144MHz vs GB3VHF and my home made GPSDO were within 0.1Hz, i have also measured against GB3CSB on 23cm and get within 0.5Hz there so i'm pretty happy with that.

I have replaced my GPS antenna and now find GPS lock is much better, it is now tracking 5 or more sats and has completed a site survey.


Surveying


Survey Complete



The TFOM and FFOM values indicate accuracy, TFOM is for the 1pps timing and FFOM is for the 10MHz, the lower the better...
From a similar user manual the TFOM of 2 means 10 to 100nS accuracy.
FFOM value of Zero apparently means "PLL stabilized ? internal 10 MHz signal within specification."

To make the initial startup faster you can set your location like this (you can get the values from a complete survey or some map software etc..):
GPS:INITial:POSition N,54,xx,xx.xxx,W,1,xx,xx.xxx,xx.xx

This has to be done just after power on to take effect so will probably need a pic to do this automatically, otherwise i find it takes a VERY long time to get GPS lock.














Last page added:16/08/17 15:45
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