arrl fmt

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I am trying to understand the ins and outs of the ARRL Frequency Measurement Test (Nov. 11) using just my GPSDO equipped 6600M and no other lab equipment.  Predictably, I have many questions. 

First off, is using the WSJTX Frequency Calibration mode to accumulate the measurement data sufficiently accurate?  If so, does this methodology make sense:
   1. delete all FreqCal mode frequencies in the WSJTX settings
   2. create a FreqCal mode entry for the next test frequency.
   3. Run FreqCal for the duration of the run...3 minutes I think it is.
   4. Use the WSPR 2.12 command line utilities to analyze the data.
   5. Edit the FreqCal setting for the next run and repeat.

It appears that the batch file method for controlling the radio outlined in the https://physics.princeton.edu/pulsar/k1jt/FMT_User.pdf article doesn't work with the 6600M unless you also have a com port like CAT control (no option for TCP/IP CAT control).  Hence the method above.

If there is a how-to somewhere that I have missed, please pass on the link.


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Joseph

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Posted 4 weeks ago

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Danny K5CG

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I'm sure there are many ways up the mountain but that seems like a lot of work when you could more simply read the offset error over the API. Considering that you have a GPSDO.

All you have to do is search for "FMT" on this site and there are many articles. But this one is most pertinent.

https://community.flexradio.com/flexradio/topics/arrl-fmt-tonight-getting-the-most-accurate-frequency

The tests are on November 8th, results submission deadline is the 11th. http://fmt.arrl.org/


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Logan, KE7AZ

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Here is a link to an excellent presentation that shows how to setup
Spectrum Lab and Flidigi.  It has step by step screenshots that show
exactly what fields need to be addressed.

www.ve2azx.net/technical/FreqCal.pdf

Sorry for the delayed response but life gets complicated at times.

Logan, KE7AZ


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k3Tim

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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
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Logan, KE7AZ

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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
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Logan, KE7AZ

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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
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Joseph

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Sorry...as described in section 13.1 of the WSJTX user guide.
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Logan, KE7AZ

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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
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Michael Walker, Employee

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How did everyone make out?  

Unfortunately, I had a different priority, so I missed it.

Mike
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Logan, KE7AZ

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The results have been posted and I am happy with my efforts.  My 80M freq was off by .11 Hz and my reported 40M frequency was off by .56 Hz.  When I went back to my data, I discovered that Murphy got me in the end and I mis-typed my 40M entry with an extra zero in the middle!  My measured (vs reported) frequency was only off by .01 Hz!  Next time I need to be more careful with all of the digits and decimal points.  Rookie mistake.

I have a 6600 with a BG7TBL GPSDO (the $100 version) for a 10MHz reference. DAX allowed me to use SpecLab, WSJT-X, and Flidig at the same time to collect data. I initially had a slice for 40M and one for 80M.  But I found it easier to retune a single slice than start a second instance of all of the apps. I also had a slice recording 5MHz WWV data.

WSJT-X and Flidigi each were less than .1 Hz on 40M.  The first run on 80M did not yield good data due to poor S/N ratio.  The second run was better but there was a lot of variation in the data that I averaged. The measurements were .within .08mHz to .13mHz of the correct result.

SpecLab was marginally useful because the 23mHz bin size for the FFT needed 44 seconds to collect the data.  SpecLab allows a 50% overlap in successive data collections so you get an effective collection time of  22 seconds.  However, in 2 minutes you only get 6 sets of data towork with.  Next time, I'll try a bin size of 43mHz and increase the overlap to get more data points.

I am going to go back and take a look at the WWV data that I also collected and see if it could have helped refine my results on 80M.

All in all, a lot of fun, and very doable with a Flex and a GPSDO.

Logan KE7AZ
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K1FR

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My first FMT and did better than expected. Probably beginner's luck!

A quick scan of the results shows Flex was very well represented.

73, Tom
K1FR

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Bill W2PKY

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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.