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

[dl2sba]

Hi Everbody

I'm running a Symmetricom 090-03861-03 since some days now. Where can I find detailled information on these status values:

• frequency correction
• temperature correction
• phase corrections
• gps phase correction

Why is the frequency correction value slightly but constantly rising, while the phase values stay more or less flat?

I've plotted them for some days - check http://dl2sba.com/index.php?option=com_content&view=article&id=268:measurement-on-gpsdo&catid=15:shack&Itemid=27


//Dietmar

[uncle_bob]

Hi Everbody

I'm running a Symmetricom 090-03861-03 since some days now. Where can I find detailled information on these status values:

• frequency correction
• temperature correction
• phase corrections
• gps phase correction

Why is the frequency correction value slightly but constantly rising, while the phase values stay more or less flat?

I've plotted them for some days - check http://dl2sba.com/index.php?option=com_content&view=article&id=268:measurement-on-gpsdo&catid=15:shack&Itemid=27


//Dietmar

Hi

The GPSDO acts as a PLL once things settle out. The phase is locked so it's not going to go anywhere. The frequency change shows up in the DAC values.

Bob

[dl2sba]

Hi Bob

thanks for reply - but I don't understand completely - when the frequency correction still increments, did this mean, that the output frequency is constantly increasing/decreasing or is this the ageing of the oscillator?!

 

[uncle_bob]

Hi Bob

thanks for reply - but I don't understand completely - when the frequency correction still increments, did this mean, that the output frequency is constantly increasing/decreasing or is this the ageing of the oscillator?!

Hi

Yes, the DAC is stepping to keep the OCXO on frequency.

As the OCXO comes out of storage and begins to operate it will "retrace". Generally this is a one way (frequency up or frequency down) process. The amount of frequency change is generally much greater than the aging rate of the OCXO. It will settle out in a few days to a few months. It is always best to keep an OCXO on power all the time. That eliminates this effect.

Bob

[dl2sba]

OK Bob

thanks for the information - I'll keep the GPSDO running and collect the data ... lets see how it works in longer terms ...

//Dietmar

[jkf1000]

Just a few pics of my distribution project so far. Photo 1 shows how the origional lower board was modified (butchered) to retain just the origional power supply circuitry and to accomodate moving the distribution boards down into the lower two positions. The distribution boards have been reconfigured for 50ohm impedance and when tested give a nice buffered unity gain sine wave output at around 1.8v P to P on all of the output BNC connectors no matter how many loads are connected.

The rest of the photos are just various stages of the project so far. As previously stated it is just missing PSU for the trimble, mains switch to enable switch off of the analog circuits when not required and a DB9 for the RS232.

Any thoughts or suggestions very much appreciated.. Karl

[jkf1000]

Rest of the photos so far.. Also forgot to mention a couple of changes I made which can be seen in the photos. Repositioning of one of the PSU filter caps to gain a little more space and the addition of a 4 pin header for the RS232 connection.. Karl

[ttipok]

Here is pinouts of 50-pin connector of both Symmetricom/Trimble UCCM.

I did some analyzing of debugging flags, avaliable on UART-debug port (called UART3). Also High-speed serial port is found (UART4). It sending time immediatly and synchronized with 1PPS edge.
More info at http://tipok.org.ua/node/53
Hope it will be useful.

[jkf1000]

Very useful information, all I need now is a consolidated list of all the serial commands if anyone has compiled it, I have quite a few which I have collected while reading through this thread but then someone else always finds more!! I have tried the UCCM- "?" but get no responce back..

[Macbeth]

Here is pinouts of 50-pin connector of both Symmetricom/Trimble UCCM.

I did some analyzing of debugging flags, avaliable on UART-debug port (called UART3). Also High-speed serial port is found (UART4). It sending time immediatly and synchronized with 1PPS edge.
More info at http://tipok.org.ua/node/53
Hope it will be useful.

Excellent work. Shame about that high speed UART4 not having the leap second byte. But did you check if it may be adding the leap second automatically so no need for the separate byte itself? The flag is there to let you know it's got it. It would seem odd not to incorporate leap seconds in some manner yet provide the flag?

[ttipok]

Just checked-out once more. There is no leap seconds addition on this port. Just raw GPS time. But, as work-around, there is flags transferred as well so from this flags we can determine that receiver got leap seconds amount and read them from another port (binary debug UART3).

[texaspyro]

Bit 1 (0x02) in the FL[0] word appears to be the leapsecond pending flag.  Back in June, before the leapsecond announcement it was always 0.  Now it is 1.

Edited to correct the bit number/mask...

[ttipok]

Yep, You are right, but seems like it's FL[0] bit1, if taking into account this and this logs.

[texaspyro]

Yep, You are right, but seems like it's FL[0] bit1, if taking into account this and this logs.

Oops,  I was working off my re-formatted log dump and not my actual code...

FL0 went from 0x60 pre-leapsecond announcement to 0x62 afterwards.

BTW, if you have a Z3801A, it says the leapsecond will happen on Sept 30 and not Dec 31.  Also, sometime in the last couple of weeks, lots of them have GPS receivers that hit the GPS week rollover point and started reporting it was 1997.  Lady Heather automatically detected that anomaly and corrected the date by adding 1024 weeks to the time.  Thunderbolts will hit the rollover point in the middle of 2017.

   

[Bryan]

All:

Would appreciate some help. Needed to resolder some new connections to the RS232 header pins and something must have messed up the unit. It keeps reporting a GPS engine failure. Not sure if it was stray electricity, static, but at a loss where to go from here. Have tried to enter a location manually, no luck. I am certain the antenna is ok. Looked over the board with a loupe in the event I broke a component off, but can not find anything. Everything responds fine using a terminal program.

Code: [Select]

UCCM-P > system:status?
-------------------------------------------------------------------------------
090-03861-03   serial number W561020383   firmware ver 1.0.0.2-01     LINK mode
-------------------------------------------------------------------------------
Reference Status __________________________   Reference Outputs _______________
   Ref 8KHz 0: [LOS]
                                              TFOM     9             FFOM     3
                                              UCCM-P Status[OCXO WARM]

>> GPS: [no ref]
ACQUISITION .............................................. [ GPS 1PPS Invalid ]
Tracking: 0 ____   Not Tracking: 0 ________   Time ____________________________
                                              GPS      00:27:45 [?] 06 JAN 1980
                                              GPS      Invalid: GPS rcvr failed
                                              ANT DLY  +0.000E+00
                                              Position ________________________
                                              MODE     Survey:      0% complete
                                                       Suspended: no track data
                                              INIT LAT     0:00:00.000
                                              INIT LON     0:00:00.000
                                              INIT HGT           +0.00 m  (GPS)




ELEV MASK  0 deg
-------------------------------------------------------------------------------

Code: [Select]

UCCM-P > posstatus
-----------------------------------------------------------------------------
1/6/1980 00:35:46
-----------------------------------------------------------------------------
 Position : LAT( LON( H(0.00 m MSL)
-----------------------------------------------------------------------------
 Geometry : PDOP(0.0) HDOP(0.0) VDOP(0.0)
-----------------------------------------------------------------------------
 Channel Status
   num of visible sats > 0
   num of sats tracked > 0
   ------ Receiver Channel State ------
     CH 0 >  SateID(0) TrackMode(code search) SigValue(0)
     CH 1 >  SateID(0) TrackMode(code search) SigValue(0)
     CH 2 >  SateID(0) TrackMode(code search) SigValue(0)
     CH 3 >  SateID(0) TrackMode(code search) SigValue(0)
     CH 4 >  SateID(0) TrackMode(code search) SigValue(0)
     CH 5 >  SateID(0) TrackMode(code search) SigValue(0)
     CH 6 >  SateID(0) TrackMode(code search) SigValue(0)
     CH 7 >  SateID(0) TrackMode(code search) SigValue(0)
     CH 8 >  SateID(0) TrackMode(code search) SigValue(0)
     CH 9 >  SateID(0) TrackMode(code search) SigValue(0)
     CH 10 >  SateID(0) TrackMode(code search) SigValue(0)
     CH 11 >  SateID(0) TrackMode(code search) SigValue(0)
-----------------------------------------------------------------------------
  Rcvr Status(0) :
-----------------------------------------------------------------------------
  Antenna Voltage: 4637 mV,  Antenna Current: 17 mA
-----------------------------------------------------------------------------


Code: [Select]

UCCM-P > status

                 - UCCM Slot STATE -



1-1. #Now ACTIVE STATUS ---------------- [OCXO Warm]
1-2. #Before ACTIVE STATUS ------------- [Wait for GPS]
2-1. #Reference Clock Operation -------- [Not Used]
2-2. #Current Reference Type ----------- [LINK]
2-3. #Current Select Reference --------- [LINK0]
2-4. #Current Reference Status --------- [NOT SELECTED]
     #GPS STATUS ----------------------- [Unavailable]
     #Priority Level ------------------- [LINK > GPS]
     #ALARM STATUS
     #H/W FAIL ---------- [ GPS_COMM ]
     #Bad Quality ------- [ LINK ]
3-1. PLL STATUS ------------------------ [Enable]
3-2. Current: PLL MODE ----------------- [OFFSET OBSERVATION MODE]
Command Complete

Code: [Select]

UCCM-P > GPS:SATellite:TRACking?
"Data corrupt or stale"
UCCM-P >

Code: [Select]

UCCM-P > DIAGnostic:LOG:READ:ALL?
Log status: 4 entries

L1:1980-01-06 00:27:05:Log cleared
L2:1980-01-06 00:27:05:SYST:PRESET performed
L3:1980-01-06 00:00:02:Power On
L4:1980-01-06 00:00:17:GPS Engine Alarm
Command Complete
UCCM-P >

[Bryan]

Hmm, just occurred to me, if I check the output of the GPS pin 3(tx) and it is spitting out NMEA like messages than that should confirm the receiver is ok?

[Macbeth]

Hmm, just occurred to me, if I check the output of the GPS pin 3(tx) and it is spitting out NMEA like messages than that should confirm the receiver is ok?

I was going to suggest just that!

[Bryan]

No NMEA output from pin 3 on the Furuno receiver. Soldered the receiver off the GPSDO board, but haven't had time to test the receiver yet. Did manage to find a users manual on K04BB's site. One thing I did notice when checking the voltages on the Symmetricom board is the voltage to the receivers antenna preamp (pin 10) is 4.7v, yet 5v almost everywhere else on the board. I think it should be closer to 5v, something maybe dragging it down, but it's difficult to trace back as it appears to be a multilayer board. Although I do note that there is supposed to be a 15 ohm current detection resistor across the antenna so perhaps that accounts for the voltage drop. The 3.3 supply to the receiver is a correct 3.3v. Beginning to think it's the Furuno receiver that is toast.

Just to confirm what voltages do other owners see from running the posstatus? command

[Macbeth]

That's normal with the antenna voltage. It's the CR1 Rectifier causing the voltage drop.

[NivagSwerdna]

When the GPSDO starts it initialises the GPS receiver, you should be able to observe that via the pins.  If you can't see that initialisation sequence then it is getting lost somewhere... I would suspect something has fallen off

You can listen to both pin 3 and 4 (https://www.eevblog.com/forum/projects/a-look-at-my-symmetricom-gpsdo-(ocxo-furuno-receiver)/msg905470/#msg905470) and should see something.

[Bryan]

When the GPSDO starts it initialises the GPS receiver, you should be able to observe that via the pins.  If you can't see that initialisation sequence then it is getting lost somewhere... I would suspect something has fallen off

You can listen to both pin 3 and 4 (https://www.eevblog.com/forum/projects/a-look-at-my-symmetricom-gpsdo-(ocxo-furuno-receiver)/msg905470/#msg905470) and should see something.

No parts have fallen off. Stupid mistake and tried to solder a broken wire on the serial connection. Forgot to power it off and I suspect some type of ground issue and a ungrounded soldering iron. There was a Arduino project connected to pin 3 of the GPS receiver and powered from the computer USB port. Saw the Arduino rapidly resetting itself. Wondering if it blew the GPS receiver, although thought they were protected?.

No output from the Furuno, just stays high. I also can't see any input going to pin 4 either on reboot. Oh well, sounds like it's toasted. Suspect strongly the receiver

Anyone have a dead board they want to sell the Furuno receiver off of.

[PA0PBZ]

Anyone have a dead board they want to sell the Furuno receiver off of.

If you don't see any initialization sent to the receiver even when you took it off the board I strongly suspect you have bigger problems.
Having said that, if you are sure it is the receiver I can send you one.

[Bryan]

If you don't see any initialization sent to the receiver even when you took it off the board I strongly suspect you have bigger problems.
Having said that, if you are sure it is the receiver I can send you one.

I will have another look at pin 4 and see if there is anything there, I just had a quick look on the scope, after not seeing anything on pin 3 just figured it was toast, but yes the main board could have issues as well, although only the one hardware error reported. Thanks for the offer of the receiver, will contact you via PM. Thanks

[texaspyro]

I have not looked at what/when the main board sends stuff to the receiver.  It may only send a few commands when you power up.

[NivagSwerdna]

If you look at... https://www.eevblog.com/forum/projects/a-look-at-my-symmetricom-gpsdo-(ocxo-furuno-receiver)/msg896223/#msg896223

You will see the kind of messages sent at start-up

The $PFEC,GPint,... commands are setting the interval the GPSDO wants to see various messages

I seem to remember that the output of the MCU on the GPSDO board is directly wired (presumably a UART) to the GPS receiver so if you are seeing nothing at the MCU then it is well broken.  You could test continuity from the GPS receiver to MCU pins... can't remember exactly and I don't have my notes to hand.