arrl fmt

Joseph

K5CG

Logan KE7AZ

Joseph

Logan...thanks for the reference.  I may have this figured out (or not!). I have measured the error on WWV 10MHz and 15Mhz and get reasonable results.  I have an old HP 8640B signal generator that hasn't been calibrated in 20 years and I picked a freq and measured that like I think I would go after the ARRL frequencies.  You tell me:

1. Set up the radio (6600m) near the carrier, USB.

2. Set up WSJT-X in freq calc mode on that frequency, Frequency Tolerance = 20, offset = 1500, T/R = 30s.  (Not sure why on any of these.)

3. Set up SpecLab to measure the frequency of the audio.

4. Set the dial on my radio to get as close as I could to 1500 on the sidetone (SpecLab).

5. Cleared the WSJT-X window and let it run for a bit.

6. Followed the instructions in the reference you provided to get the average measured sidetone frequency.

7. Teleneted to the radio and got the Rx frequency error.

8. Plugged that into the formula in the reference (F= dial freq+ average offset - freq error) to get frequency.

Does that sound right??

For WWV the radio says the received error is -.22882 mHz (what the radio reported, which seems low.  It onced reported +0.000000...is that even possible?)

When calculating the signal generator frequency, the calculated error was 0.658913 Hz, but like I said, it hasn't been calibrated in eons.

Comments??

Logan KE7AZ

k3Tim

Joseph

I may understand...we'll find out Thursday.  One more question: the avg freg (measured) is totally dependent on WSJTX.  Is the frequency calibration described in the manual sufficient?  When I repeat that exercise, back to back, using 5, 10 , and 15Mhz WWV,  I get values ranging from -.0108 ppm/.11Hz int, to -.0078ppm/-.04Hz int.  Is this as expected?

Logan KE7AZ

Thank you for your comment.  Sampling rate error would probably have been a better term rather than PC clock.  My comment was based on my experience with SpecLab that has a calibrate function for the sampling rate.  As you suggested I ran a couple of quick tests using WSJT-X and Flidigi.   I used  WSJT-X to measure the 100Hz sideband on WWV  since it is present all of the time (albeit pulsing) and came up with an average of 99.830 Hz.  I did the same test with Flidigi and came up with an average of 99.519.  Now these were short tests, less than a minute, so more averaging is needed for more accuracy but it does show that some systematic errors may be present.  However, each time we move one digit to the right of the decimal point, the sampling/averaging time goes up by a factor of 10. So, to borrow from a phrase from college:  "Further investigation is obvious and left as an exercise for the reader."     Except for the FMT and some other high accuracy applications, this level of accuracy is not needed for most ham activities.
Logan, KE7AZ

k3Tim

No problem with the sampling rate error Vs. PC clock as the meaning was understood.

Very interesting about the fldigi and SpecLab tests. Since the tone is pulsing, that may thru some problem into the measurement.  I tried fldigi with the 500 and 600 tones on WWV (2.5Mc) using AM demodulation. These were within about 1/100 cycle but did bounce around. Since the tone is AM modulated not sure the propagation would affect the frequency of the tone.

With the new feature of Smart-SDR allowing two PC's to connect at the same time, a simulated FMT was run on  WWV @ 2.5Mc using separate slices and fldigi on two PCs. The floating scopes showed the exact same frequency excursions due to propagation. This result seems to indicate the PC decode of the DAX stream is not dependent on super accurate clocking (within the PC). 

Tim - k3Tim

Logan KE7AZ

Tim,
Interesting test results, especially the two PC test and I agree with your conclusion.

I did another test on the 10 MHz WWV carrier offset by 1500 Hz Monday night using WSJT-X, Fldigi, and SpecLab (uncalibrated).  I was able to isolate about 2 hours of data where the Doppler was minimal.  All three packages gave basically the same average result: 1499.97 Hz offset.  If I had the proper test equipment and reference sources, I'd take a hard look at my external 10 MHz source, a Leo Bodnar GPDSO.  However, I recognize that I am pushing the limits of what might be expected from a consumer product.

I have a BG7TBL GPSDO, as well.  Guess I'll have to hook it up, let it stablize, and re-run my test.

Logan

Logan KE7AZ

Joseph,
Could you explain what you meant by "described in the manual?"  Is this the procedure for the FlexRadio or a feature in WSJTX?
Logan

Joseph

Sorry...as described in section 13.1 of the WSJTX user guide.

Logan KE7AZ

Joseph,
Thanks for the clarification.  I ran the test with my radio and got -.015 ppm for the slope and .04 Hz for the intercept.  So it looks like your numbers are reasonable.  It appears to me that this calibration also accounts for the "Get_Error" value.  Good Luck with the FMT.
Logan, KE7AZ

Mike-VA3MW

Logan KE7AZ

K1FR

Bill W2PKY

Noticed almost 30 Flex radios were entered and most did very well. Used FLDIGI, also monitored WWV 2.5, 5, & 10Mhz to attempt to get some idea of any Doppler shift. WWV errors were slightly negative where K5CM signals were slightly on the positive side. Massaging the data is the key to entering a very close value. Wish these events were more frequent. Too bad the League doesn't incorporate something like this into code practice runs simply posting the frequency so Ops get more practice.