Calibration on my Flex 6700 GPS seems off at 10 Meters?

Tim - W4TME

Yes.  Please use the Fldigi Frequency Analysis feature to determine the actual offset,  The display is not absolute because 1 pixel does not equal 1 Hz.

Roy Laufer

Okay, I've never really used this software before, so excuse any errors on my part.

Here is a screen grab when I have the slice set to 9.999.000 MHz USB


You may notice that the WWV signal line is to the right of the fldigi cursor. If I set the panadaptor to 9.999.028 - at which point the cursor lines up with the WWV signal detected:


Is that sufficient indication that my 6700 GPS is not correcting the TXCO's drift and that my 6700 seems off by approximately 2.8 ppm?

If not, please advise me on further tests that you would need.

Thanks.
Roy, AC2GS

Roy Laufer

Well, here's a new little wrinkle (as long as I seem to be "talking to myself" for the time being):

I disabled the GPS function. If I try to manually calibrate it to 25 MHz I get no where, primarily because propagation conditions limit my reception of that signal, BUT if I try to calibrate to 15 MHz I get a calculated offset of -2833 ppb, and the panadapter lines up the peak of the 15 MHz WWV signal at 15.000.000 as, I assume it is supposed to. Now, if I re-enable the GPS I get Sat Visible: 13, Sat Tracked:10, Status: Locked, and everything on 15 MHz stays the same, UNTIL I power down and restart the 6700 - then WWV peaks at 15.000.042 AGAIN.

I am getting the idea that the GSPDO is not disciplining anything on my 6700 - perhaps it only does it every X hours? Or perhaps once out a certain amount of ppb it doesn't correct?

Any suggestions? Any advice? Any anything???

Roy AC2GS

Duane_AC5AA

I just ran the FLDIGI routine on my one-year-old 6500 WITHOUT a GPSDO and at 10 MHz WWV I clocked it at .006 (6 Hz) high.  Guess I won't be spending cash on a GPSDO just yet.

  73, Duane

Walt - KZ1F

I recall the way Steve explained this in a recorded presentation that txco drift 'as they age' as in years. Duane's .6 may well be the rounding I spoke of. I don't recall how many zeros there were, seemed like a lot, I'd accept either 6 or 60 Hz.

Doug Hall

I don't think it's a rounding issue. A double precision floating point variable has 15 decimal digits of precision, way better than 1 Hz at 15 MHz.

Roy Laufer

While the wizards of FRS are off somewhere else, no doubt pondering something more interesting than my personal problem, is there a possibility that SSDR 1.4.x broke the disciplining aspect of the GPSDO? In other words, is there anyone out there with the GPSDO add-on, that notices ANY difference in the unit's accuracy with the GPS being disabled from when it is enabled?

The disciplining nature of the device is not obvious unless you apply a great deal of effort. At this point (of general silence) I am hoping that it was an unnoticed problem in 1.4 that will be resolved in 1.5...

It would be nice to hear from someone "in the know", rather than generate random possible causes for my present problem.

Roy AC2GS

k3Tim

Hey Roy,

Okay, I took the bait and tried this.  I had tried over the weekend but no interesting information found.  Today - it's a different story... 

Using the FlDigi Frequency Analysis Mode per Tim's post I experimented on a 6500 with GPS. With GPS, the signal is smack on +/- propagation effects.  Also, since FlDigi is measuring based on a CPU clock in the Flex, there is an expectation of a slight offset.  The internal clocks for CPU / FPGA are not derived from the GPS disciplined clock.  Not a deal breaker but something to keep in mind when going for sub-hertz resolution.

With GPS disabled, I set about to calibrate the radio in the standard way, except I put 15000 in for the frequency rather then 15, missing the "in MHz" in the menu.  Radio didn't like that and crashed.  Reboot and try again.  The s/w should have caught this, but....

With a calibration offset manually entered one could see and hear the effect in FlDigi in the tone of carrier that is offset by 1 Kc.  A calibration cycle removed the manual offset and radio was indicating 14999.000 Kc for WWV as expected (1 Kc offset).  

To test GPSDO an offset was manually entered at the calibraion menu of SSDR and GPS enabled. The GPS immediately started to nudge the frequency a small amount each time to bring it back to proper frequency (14.999 Mc).  This took about 30 seconds for an offset of about 500.

----ONE PROBLEM ----

When the offset had been adjusted by GPS, the panafall frequency was not updated and continued to be an indication in the panafall that frequency was off.  In other words the GPS bumping the main osc did not effect the frequency in the panafall.   Opening a new slice and closing the one used to calibrate, then opening the closed slice again resulted in proper frequency readout.  So one has to close the slice when the GPS bumps the osc (a large amount - ie. > 2 Hz) in order to have the proper frequency readout.  This is a "feature" we need to be aware of when calibrating.  At least that is my take on it.  The folks with GPS do not have to worry so much as the main oscillator won't be drifting enough to be noticed in the panafall.

After cal'ing you should close and reopen the slice to see final effect, at least that is my take in this.  BTW I have about 40 years in software programming and the day job is finding s/w bugs. 

Hope this helps, but I think you radio is looking for a trip home.

Note: I suspect one has to set the offset back to zero when enabling the GPS, not 100% sure but it can't hurt!

Best Regards,

K3Tim 

Walt - KZ1F

That crash was a good find Tim! Would you open a problem record explaining how to recreate so perhaps the fix can be in 1.5?

Roy Laufer

There also should be some documentation regarding what happens when you attempt to use a WWV signal that is too weak (it reports a 0 ppb error result).

k3Tim

Good idea Walt, will do.

Thanks,
Tim

Tim - W4TME

Tim - your defect report of the radio crashing when putting in a frequency value greater than the radio can tune is entered into our bug tracker.

For the others - the frequency calibration process has been completely reworked and is much more accurate with weak signals.  Once SmartSDR v1.5.0 has come out, I recommend that you re-run the frequency calibration.

Tim - W4TME

Roy - I am going to convert your Community post into a HelpDesk ticket so we can do one-on-one support.

Chris DL5NAM

... you forgot to say when the 1.5.0 will come :-)

Tim - W4TME

I didn't forget.  All I can say is "soon".

k3Tim

Tim
    Thanks for the heads-up on V 1.5 and some of the features and the
    defect report.  Feel free to delete the ticket I opened.

Release timing:
   As they say  "if it isn't tested it doesn't work".  
   Better to take extra time to test than let loose a problematic update.

Roy :
   How goes the  cal / GPS-DO ??

_..--

Chris DL5NAM

... i know you answer b4. It was a joke from my side .  73 Chris

Tim - W4TME

Doug is correct.  The error is too great to be a rounding issue.

Tim - W4TME

And my answer to to this "joke" will always be the same :-)

Roy Laufer

To K3TIM:

The FRS wizards are working on some log files, my GPS-DO is off and my 6700 is manually calibrated for now...

I'll let you know how it all turns out.

73,
Roy AC2GS

k3Tim

Hi Roy Very good and hope a remote fix is possible.. Tim. Aka. K3Tim