Author Topic: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)  (Read 192056 times)

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Offline NivagSwerdna

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #950 on: December 06, 2017, 04:18:06 am »
I'm getting less optimistic... I powered the board from 6V but without the 12V boost converter in place and although I get flashing lights I am just getting garbage out of the serial pins... I thought this was 57600 8-N-1 but it seems to be not quite right... just gibberish.  I guess I will have to supply 12V and hope the behaviour changes.
 

Offline cdev

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #951 on: December 06, 2017, 10:11:35 am »
Maybe try a slower speed.. my GPSDO's default is 9600 baud.
"What the large print giveth, the small print taketh away."
 

Offline NivagSwerdna

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #952 on: December 06, 2017, 11:18:23 am »
Maybe try a slower speed.. my GPSDO's default is 9600 baud.
I tried all the baud rates I could imagine.  This is very strange.  I know there is a binary output mode... *(irig?) maybe it has switched.
 

Offline cdev

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #953 on: December 06, 2017, 11:24:37 am »
Do you have a logic analyzer you can throw on it? Also, take a look at that huge header, there are multiple UARTS on some of those huge headers. There is a web site in the Ukraine which has traces of the header on the UCCM GPSDOs. You may have spare UARTS, or like ublox, different kinds of output might be redirect-able to different outputs, i.e. reconfigurable. That is quite likely.

Look at what Ublox does to get an idea of how they do it.
"What the large print giveth, the small print taketh away."
 

Offline NivagSwerdna

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #954 on: December 06, 2017, 10:51:02 pm »
Do you have a logic analyzer you can throw on it?
I have a scope which I should attach at some point.  The GPS is outputting sensible data and the on-board LEDs seem to be doing something.  I'm wondering if the CPU clock is derived from the OCXO... if so applying 12v will fix it.  This will have to wait... life is getting in the way.
 

Offline cdev

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #955 on: December 07, 2017, 03:04:09 am »
Could you paste in a sample of what the GPSDO is outputting along withe the parameters its being captured at? Maybe its something we can figure out?
"What the large print giveth, the small print taketh away."
 

Offline Helix70

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #956 on: December 27, 2017, 06:26:45 pm »
Hi Everyone,

Got myself a Trimble UCCM based GPSDO for Christmas (eBay auction: #252162780444). Had it running for a few hours, and it seems to be doing its thing correctly, does it all look normal to you guys? Any idea why the oscillator step changed in the plot window? Everything else seems stable at that time, not sure what happened.

Thanks,

Josh
« Last Edit: December 27, 2017, 06:28:28 pm by Helix70 »
 

Offline Bryan

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #957 on: December 27, 2017, 07:12:56 pm »
The survey data progress shows 99% complete, so suspect it is part of the process. Did it complete?
-=Bryan=-
 

Offline Helix70

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #958 on: December 27, 2017, 07:47:40 pm »
Yes, it completed. So perhaps thats when it locked the PLL for the oscillator? The parts per trillion dropped to -38ppt at that stage, from what looks like -6890ppt..
 

Offline Bryan

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #959 on: December 28, 2017, 02:39:04 am »
I suspect so, if you select I believe ! it can show you the status of the ocxo
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Offline Helix70

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #960 on: January 04, 2018, 11:55:12 am »
Why does the Oscillator signal "spike" and resettle once an hour? As can be seen on the screenshot, on every division there is a 20ppt or so spike on the OSC plot. Are other people seeing the same thing?
« Last Edit: January 04, 2018, 12:13:01 pm by Helix70 »
 

Offline texaspyro

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #961 on: January 04, 2018, 12:04:31 pm »
Why does the Oscillator signal "spike" and resettle once an hour?

It could be the discipling algorithm periodically updating its loop parameters or measurements.  Heather's plotting functions tend to uncover lots of weird things GPSDO's do.
 
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Offline Macbeth

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #962 on: January 05, 2018, 08:21:43 am »
I'm getting less optimistic... I powered the board from 6V but without the 12V boost converter in place and although I get flashing lights I am just getting garbage out of the serial pins... I thought this was 57600 8-N-1 but it seems to be not quite right... just gibberish.  I guess I will have to supply 12V and hope the behaviour changes.

Noooo! There is no need to force 12V on a board that expects 5V (ok maybe 5.5V - 6V). The Texas Instruments CSA boost module powers the OCXO and the GPS antenna. I replaced my fried one with a much cheaper Aliexpress XL6009 IIRC.

One thing I noticed was that any serial comms using a cheap shit CH340/USB was full of noise and I had to lower the comms to 19400 baud using the 'SCPI' commands of the Symmetricom. You probably have the same problem only worse. Try a real TTL/RS232 port if you still have one, otherwise try genuine FTDI or at least alternative USB/RS232 adapters. 
 

Offline PA0KTF

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #963 on: February 14, 2018, 12:03:02 am »
I have a Trimble board 57963-80A. I am missing L4. It looks similar to L11. Can somebody tell me the value of this component ? Thanks !
 

Offline ghulands

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After getting distracted for a couple of years, I finally got around to putting this together - though still on the bench.

I hooked up a raspberry pi to it so I could have a local ntp server running. I was having issues with gpsd so I modified it to allow it to process the $GPGSV message and then have it convert the $PFEC,GPtps to a $GPRMC message. The diff is attached.
 

Offline NivagSwerdna

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Noooo! There is no need to force 12V on a board that expects 5V (ok maybe 5.5V - 6V)...
One thing I noticed was that any serial comms using a cheap shit CH340/USB was full of noise and I had to lower the comms to 19400 baud using the 'SCPI' commands of the Symmetricom. You probably have the same problem only worse. Try a real TTL/RS232 port if you still have one, otherwise try genuine FTDI or at least alternative USB/RS232 adapters.
I had a brief look at this at the weekend.... I feed the Symettricom RS232 output to a cheapo RS232 to TTL level converter attached to an Arduino2560 and I noticed that the MAX3232 or whatever it is on the converter was REALLY REALLY hot so I disconnected it.... still getting garbage from the Symmetricom.  I will replace the MAX3232I on the board (it is an irritating form factor that I don't have) and see if that helps but I am losing hope.  There is definitely some life in the board though... the LEDs flash various colours so the FPGA core must be doing something useful.  The GPS receiver appears to have some life too as I can see the output from that.  I guess 12V to a MAX3232 was out of spec; most of the expensive components are on the other side of LDOs so fingers crossed for that side of the board... (they measure the correct voltages now).
« Last Edit: May 19, 2018, 07:10:49 pm by NivagSwerdna »
 

Offline NivagSwerdna

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Eventually got around to this again... I replaced both the MAX3232I (in a TSSOP package) and it still didn't work but eventually traced the problem to a tiny short on the edge connector pads (I don't have an edge connector as I hot aired that off originally whilst probing the board) due to a bit of stray solder from when I replaced the 12V boost regulator (I replaced the regulator with the correct part as they are available in Farnell).

All well again now.  I really need to box it properly and stop tinkering.

 
 

Offline NivagSwerdna

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I hooked up a raspberry pi to it so I could have a local ntp server running.
Did you get the PPS signal working with the server? I thought it would be too narrow so built a pulse stretcher. 
(Previously I did have a similar NTP server working using an old VP Oncore receiver for which I followed the instructions at http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html)

Thanks for the diff.  :-+
 

Offline ghulands

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It was working for 24 hours but then it got confused and couldn't see the pulse. I had a gps unit from Adafruit lying around so I put a splitter on the antenna line and hooked it up along with the GPSDO. So now the ntp is essentially a separate system, all contained in the same box.
 


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