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

[ekyle]

I would check and see what the diagnostic log file says. DIAGnostic:LOG:READ:ALL? It might offer some clues.

[digital_dreamer]

I'm building a monitor for my Trimble GPSDO based on a STM32F4 driving a 3.5" screen at 480x320. What a lot of fun.

So far, I'm receiving the TOD from the dedicated TOD USART entirely via DMA and interrupts - no loop. The alternate/fake seconds are filled in via counter/interrupt, as well. The most time consuming portion, besides waiting for data, is drawing to screen, obviously. But, I have it down to less than 240 microseconds per clock digit change and only updating the digits that changes.
The time is computed on the fly, converting the GPS seconds to UTC via Modified Julian Date. I'm amazed that the math to convert to MJD and back is only a few hundred cycles on the 168MHz MCU - hardly any time at all.
Leap seconds are added when available on the TOD stream.

I'm updating to the screen the PPS and DAC values each second, as well. The Sat data is split between POSSTAT and SYST:STAT?, alternating on each second. It seems the El and Az data is only available from SYST:STAT?, so you have to match the Sat ID/PRN from POSSTAT to the SYST:STAT? data. Can create messy issues if the data changes between the two USART transfers.

I'd like to create a plot of the DAC, PPS, and OSC, as well as a scattergram/skyplot as texaspyro has done in LH, but haven't quite got that down yet. texaspyro has done some amazing work with his software.

However, I got a whole bunch of questions to ask those that would know:

• I'm confused by the definition of “Tracking”. What does “tracking”, as provided by POSSTAT mean compared to “tracking” in SYST:STAT? I found out the hard way that the actual tracked sats should be parsed from “position available” 
• There are supposedly 10 different TFOM values (0-9). I’ve seen the first 4 and the last one described, but not 4 through 8. When I try to interpret it and break it out, it doesn’t end as “9 = > 1ms”. Below is what I break it down to. Clearly something is not matching up:
  “0 = < 1ns", “1 = 1-10ns", “2 = 10-100ns", “3 = 100ns-1us", “4 = 1-10us", “5 = 10-100us", “6 = 100us-1ms”???, “7 = 1-10ms”???, “8 = 10-100ms”???, “9 = 100ms-1s”???, “10 = > 1s”??? Do we skip the “100ms-1s”?
• Where does OSC data come from and how is it calculated? Next to the PPS, this is the most valuable piece, as it relates to the GPSDO's performance.
• What does a negative DAC % value mean? This one I have now is at -11.30 %. The previous one was 5.xx %. Don’t remember if it was negative. It's a percentage of the 5v, correct (for UCCM-P Trimble)? So, what does negative mean?
• Is the info from DIAG:LOOP? of any value to monitor? If so, what part?
• What is referred to by phase in SYST:STAT? and is it related to SYNC:TINT? Haven’t been able to determine that it IS actually the PPS Time Interval
• Building Skyplot/scattergram: Is there a good reference/source for computing the spot based on EL/AZ. Google hasn't been helpful. This isn't a popular topic, apparently. 

best regards,
MAJ

[texaspyro]

I just added the capability of Heather to monitor and control a GPS device while simultaneously calculating ADEVs from an external time interval counter like the TAPR TICC  (it can also work with the time interval analyzer only).  This mode lets Heather calculate true adevs instead of "bogo-adevs" derived from the GPSDO self-reported control loop statistics.

As a test.  I connected Heather to a Trimble "UUCM" GPSDO and a TICC.  The TICC channel A is the UCCM and channel B is a Oscilloquartz Star-4 GPSDO.  The TICC reference is a ERC-130 rubidium (uses an LPRO-101.  Attached is a screen dump of a 12 hour run.  The UUCM beats the Star-4 at tau<20 seconds.

[Bryan]

Wow, that's excellent. How does the external counter connect?

[texaspyro]

Wow, that's excellent. How does the external counter connect?

The TAPR TICC (https://www.tapr.org/kits_ticc.html) is a small, cheap ($200) two channel time interval counter with 60 ps resolution.  It uses an Arduinio 2560 for its processor and outputs data via USB.   A commercial, single channel counter with that kind of resolution will set you back a few grand.

Heather now supports time interval counters.  It can either run the TICC as the main input device (instead of a GPS receiver) or as an auxiliary input device (while monitoring and controlling s GPS receiver).  The code supports up to 4 TICC channels simultaneosly.  Currently it works with either time stamping counters or time interval counters.  The TICC reader code can handle the TAPR TICC,  the HP5313x, or a generic time interval/time stamping counter.

Here is screen dump of it running in stand-alone mode and displaying the four different adev type of an Oscilloquartz Star-4 GPSDO.

[Bryan]

I got a full refund when the trimble unit I ordered from him didn't show. It did arrive after 2 + months finally, and had a few small caps ripped off the board.

Well against my better judgment I went and ordered a 65256 from this seller. Arrived yesterday, poor condition, dirt and oil all over it, OCXO is speckled with rust and corrosion. Hooked it up to 5.5v to start with, nothing from the output either 10MHZ or 1pps ( well ok 20mv on the 10MHz output), let it sit for awhile, current dropped from about 2 amps to over 1 and still nothing.Then I noticed the DSP TSM320 was just cooking. Yup, it's probably dead. Didn't even bother with seeing what it shows up on the PC as it surely will be a disappointment.

[digital_dreamer]

Got a question regarding the UCCM-P Trimble GPSDO, if you guys don't mind.

When up and running the TFOM is typically at 2, which is 10-100ns.
Now, I've noticed the PPS time interval will frequently get much better than that, usually around 1ns or better. So, why does't the TFOM drop down to a lower number, like "1" during this time?
I notice during a reset, the TFOM is well in line with the PPS Time Interval. But, once the TFOM gets to 2, it'll never go lower, even if the time interval is 1ns or less.

Any insight on this? Is my understanding woefully incorrect and off in another galaxy?
Would it be proper to override this if developing a GPSDO software monitor?

best regards,
MAJ

[lachesis]

I think mine is dead too. I bought it back in January but didn't get around to testing it until this week, so it looks like I'm out of luck with eBay. The seller listed it as "tested working" as well. I hook it up and let it complete its survey of the sky, but it never enabled the output. Oddly, it reports that everything is fine (except LINK is unavailable).

I can get the output to come up if I do DIAG:OUTP ON, at least sometimes. This makes the left LED switch to flashing GREEN & YELLOW. My scope thinks this is a 10MHz output, but since it wasn't autoenabled, I suspect the reference is not happy with the output.

The OXCO has a nice 1.5V P-P signal on its output pin. The board looks alright - no obvious components ripped off or anything like that.

My suspicion is that the OXCO has drifted outside its range, but I'm not 100% sure about that. Does anyone know which pin I should measure to find its adjustment voltage, and what the relationship between that voltage and the change in frequency should be? The OXCO is labeled Trimble 65256.

Here's some logs:

Code: [Select]

UCCM >DIAG:LOG:READ:ALL?

Log status:  14 entries

L00:17/05/10.01:53:25 Reset board by preset command
L01:99/08/22.00:00:01 Output mode: Alarm
L02:99/08/22.00:00:01 Power up start
L03:99/08/22.00:00:01 A/S change: Slave(HIGH)
L04:99/08/22.00:00:01 REF_SEL change: LINK(HIGH)
L05:17/05/10.01:59:13 Ref available
L06:17/05/10.02:00:14 Ref Change: GPS
L07:17/05/10.02:00:15 Ref chang: External PPS
L08:17/05/10.02:04:00 Reset board by preset command
L09:99/08/22.00:00:01 Output mode: Alarm
L10:99/08/22.00:00:01 Power up start
L11:99/08/22.00:00:01 A/S change: Slave(HIGH)
L12:99/08/22.00:00:01 REF_SEL change: LINK(HIGH)
L13:17/05/10.02:05:02 Output mode: Active                            <-- here's where I did DIAG:OUTP ON


Code: [Select]

UCCM >STAT

               - UCCM Slot STATE-

1-1. #Now ACTIVE STATUS ---------------- [Alarm]
1-2. #Before ACTIVE STATUS ------------- [OCXO Warm]
2-1. #Reference Clock Operation -------- [Not Used]
2-2. #Current Reference Type ----------- [GPS]
2-3. #Current Select Reference --------- [GPS 1PPS]
2-4. #Current Reference Status --------- [Ref LOS]
     #GPS STATUS ----------------------- [Available]
     #Priority Level ------------------- [LINK > GPS]
     #ALARM STATUS
     #H/W FAIL [ GPS LINK ]
     #OPERATION ALARM ------------------ [GPS LINK ]
3-1. #PLL STATUS ----------------------- [ENABLE]
3-2. #Current PLL MODE ----------------- [ENABLE]

Command complete
UCCM >SYST:STAT?

-------------------------------------------------------------------------------
57964-05     serial number  86855225     firmware ver  1.0.0.2-01 W-CDMA  mode
-------------------------------------------------------------------------------
Reference Status __________________________   Reference Outputs _______________
XX Ref 8KHz 0: [LOS]                                                           
XX Ref 8KHz 1: [LOS]                          TFOM     2            FFOM      3
XX Ref 8KHz 2: [LOS]                          UCCM A Status[ALARM]             
XX Ref 8KHz 3: [LOS]                                                           
>> GPS: [phase:+0.0E+00, settling]                                             
ACQUISITION .................................................[GPS 1PPS Invalid]
Tracking: 0 ____   Not Tracking: 12 _______   Time ____________________________
PRN  El  Az  C/N   PRN  El  Az                GPS      00:00:22 (?) 22 Aug 1999
                     5  -- ---                                                 
                     6  -- ---                ANT DLY  0 ns                   
                    17  -- ---                Position ________________________
                    15  -- ---                MODE     Survey:    1.0% complete
                     4  -- ---                         Suspended: no track data
                    29  -- ---                INIT LAT S   0:00:0.000         
                    20  -- ---                INIT LON W   0:00:0.000         
                    22  -- ---                INIT HGT           +0.00 m (MSL)
                     2  -- ---                                                 
                    31  -- ---                                                 
                     7  -- ---                                                 
                    28  -- ---                                                 
ELEV MASK  5 deg                                                               
-------------------------------------------------------------------------------

Command complete

UCCM >ALARM:OPER?
NONE
Command complete

UCCM >ALARM:HARD?
NONE
Command complete


[NivagSwerdna]

If you are feeling down because your ebay junk doesn't work then...

http://www.ebay.co.uk/itm/10MHz-GPS-Disciplined-Oscillator-GPSDO-GPS-antenna-included-/182145209432?hash=item2a68b35458:g:JWoAAOSwNsdXRBph

If I hadn't already bought two Symmetricom and two Rb frequency references I would probably get one of those... the differential outputs are rather nice... 

[PA0PBZ]

I think mine is dead too.

Can you post the output of POSSTATus after it's been on for a few minutes?

[texaspyro]

My suspicion is that the OXCO has drifted outside its range, but I'm not 100% sure about that.

Lady Heather works with these.  Run it and see if the DAC voltage is near +/- 100% or if any alarms show up.

[PA0PBZ]

My suspicion is that the OXCO has drifted outside its range, but I'm not 100% sure about that.

Lady Heather works with these.  Run it and see if the DAC voltage is near +/- 100% or if any alarms show up.

According to the STAT? output it is not tracking any satellites, so I wonder if the antenna is working, therefore my request above.

[lachesis]

Here's the POSSTAT, STAT, and SYST:STAT? outputs again, after running for 10 minutes or so. I'll leave it running today and see if it ever eventually locks, but I kinda doubt it. It certainly knows the GPS time and position.

Code: [Select]

posstatus

---------------------------------------------
 05/12/2017  19:41:43
---------------------------------------------
 Position: LAT(N  37:XX:XX.XXX) LON(W 122:XX:XX.XXX) H(         -11.20 m MSL)
---------------------------------------------
 Geometry: PDOP(4.8) HDOP(3.4) VDOP(3.3)
 num of visible sats >  6
 num of sats tracked >  6
  -------- Receiver Channel State --------
 CH  0 > SateID(28) TrackMode(pos avail) SigValue(38)
 CH  1 > SateID(30) TrackMode(pos avail) SigValue(39)
 CH  2 > SateID(13) TrackMode(tracking ) SigValue(20)
 CH  3 > SateID(19) TrackMode(tracking ) SigValue(21)
 CH  4 > SateID(17) TrackMode(tracking ) SigValue(23)
 CH  5 > SateID(07) TrackMode(pos avail) SigValue(50)
 CH  6 > SateID(09) TrackMode(tracking ) SigValue(24)
 CH  7 > SateID(05) TrackMode(tracking ) SigValue(23)
 CH  8 > SateID(08) TrackMode(pos avail) SigValue(35)
 CH  9 > SateID(11) TrackMode(pos avail) SigValue(35)
 CH  10 > SateID(15) TrackMode(tracking ) SigValue(20)
 CH  11 > SateID(01) TrackMode(pos avail) SigValue(40)
---------------------------------------------
 Rcvr Status(0):   
---------------------------------------------
 Antenna Voltage:  5000.00mV   , Antenna Current:    32.12mA

Command complete
UCCM >stat

               - UCCM Slot STATE-

1-1. #Now ACTIVE STATUS ---------------- [Alarm]
1-2. #Before ACTIVE STATUS ------------- [OCXO Warm]
2-1. #Reference Clock Operation -------- [Not Used]
2-2. #Current Reference Type ----------- [NONE]
2-3. #Current Select Reference --------- [X1PPS]
2-4. #Current Reference Status --------- [Good Accuracy & Stable]
     #GPS STATUS ----------------------- [Available]
     #Priority Level ------------------- [LINK > GPS]
     #ALARM STATUS
     #H/W FAIL [ LINK ]
     #OPERATION ALARM ------------------ [LINK ]
3-1. #PLL STATUS ----------------------- [ENABLE]
3-2. #Current PLL MODE ----------------- [ENABLE]

Command complete
UCCM >syst:stat?

-------------------------------------------------------------------------------
57964-05     serial number  86855225     firmware ver  1.0.0.2-01 W-CDMA  mode
-------------------------------------------------------------------------------
Reference Status __________________________   Reference Outputs _______________
XX Ref 8KHz 0: [LOS]                                                           
XX Ref 8KHz 1: [LOS]                          TFOM     9            FFOM      1
XX Ref 8KHz 2: [LOS]                          UCCM A Status[ALARM]             
XX Ref 8KHz 3: [LOS]                                                           
>> GPS: [phase:+1.3E+01, settling]                                             
ACQUISITION ...................................................[GPS 1PPS Valid]
Tracking: 6 ____   Not Tracking: 6 ________   Time ____________________________
PRN  El  Az  C/N   PRN  El  Az                GPS      19:41:48     12 May 2017
 28  73 330   38    13  40 306                                                 
 30  71  58   39    19  15 193                ANT DLY  0 ns                   
  7  37 101   49    17  38 182                Position ________________________
  8  14  39   35     9   7 161                MODE     Survey:   65.0% complete
 11  26  81   35     5   7 252                                                 
  1  11  98   40    15   8 320                AVG LAT  N  37:XX:XX.XXX         
                                              AVG LON  W 122:XX:XX.XXX         
                                              AVG HGT           -11.22 m (MSL)
                                                                               
                                                                               
                                                                               
                                                                               
ELEV MASK  5 deg                                                               
-------------------------------------------------------------------------------

Command complete
UCCM >


[Bryan]

Hmm, is there a setting you are missing. Most others are

2-2. #Current Reference Type ----------- [LINK]
2-3. #Current Select Reference --------- [GPS 1PPS]

yours is

2-2. #Current Reference Type ----------- [NONE]
2-3. #Current Select Reference --------- [X1PPS]

I believe X1pps means it is using a external 1pps source when it should be using the GPS 1pps to discipline the OCXO....I think

[cdev]

Can Heather be told what "pin" of a USB to UART chip to expect to see a 1PPS pulse on? Not many USB GPSs connect the pin but many can be converted with a soldered wire. (Of course the timing is still USB so not very accurate but on a lightly loaded machine its still better than no 1PPS and much more convenient)

[texaspyro]

Can Heather be told what "pin" of a USB to UART chip to expect to see a 1PPS pulse on? Not many USB GPSs connect the pin but many can be converted with a soldered wire. (Of course the timing is still USB so not very accurate but on a lightly loaded machine its still better than no 1PPS and much more convenient)

No,  Heather does not use or assume that a 1PPS signal is in use.

Heather does have compensation for the offset between the time code in the receiver time message and when the message arrives.   The /tsx command line option lets use set the offset (+/- milliseconds).  If no /tsx is specified, Heather uses a typical value for the receiver type.

[SHF]

My finished GPSDO

[cdev]

Nice job!
What kind of processor does it run on? AVR or something else?

Also:
What kind of case is that?

Its very nice.

[Nuno_pt]

Well today I open Putty to see the status of the board it it only give me rubbish, no prompt UCCM command.

Looking at the board the DS3 red led is on, so checking the board I trace it to no power on the antenna, the center trace of the antenna is loose, it was fragile on arrival, and it broke with time, I can't find another point to feed the antenna or trace the rubbish coming from the RS-232.

So time for a new board, this time a Trimble one, let's see how that goes.

[NivagSwerdna]

So time for a new board, this time a Trimble one, let's see how that goes.

I like the look of... eBay auction: #252610556561

[Nuno_pt]

I was looking at that one to, but 92€ + 13€ for shipment, I think I'll go for a trimble unit, but if this NEC start to come down a bit I'll be force to hit the buy button. 

[SHF]

--> What kind of processor does it run on? Arduino or something else?

PIC18F2620
https://www.eevblog.com/forum/projects/a-look-at-my-symmetricom-gpsdo-(ocxo-furuno-receiver)/msg891389/#msg891389

[metrologist]

I was looking at that one to, but 92€ + 13€ for shipment, I think I'll go for a trimble unit, but if this NEC start to come down a bit I'll be force to hit the buy button. 

It was just under 100 free shipping last week! They are going up, you time nuts are driving the market.

I got a Trimble version with dead comm port. 

[NivagSwerdna]

It was just under 100 free shipping last week! They are going up, you time nuts are driving the market.

Someone just bought one and the price went up!  $109+$15 now!

[metrologist]

Because they know someone will talk about it on a forum and then someone else will want one.