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4.5 - Tuning Accuracy

4.5.1 - SDR-IQ, SDR-14

If you observe that the SDR-IQ's or SDR-14's receive frequency is inaccurate (when tuning to WWV or WWVH, for instance), you can adjust it.

When you initially install SdrDx, it looks for a file called sdr-fparms.sdr in your home directory. It won't find it, and consequently it will set the SDR-IQ or SDR-14 up assuming that the SDR's internal frequency standard is perfect. If that were the case, then when you go to 10 MHz (10,000.000) and check the frequency of WWV with the FFT set for 32678, the peak will be just about exactly (within one pixel) on the 10 MHz frequency mark.

Note: "Hey, I run Windows! Where's my home directory?" Uh, yeah. I actually have no idea. But you can find it. Here's how: After quitting SdrDx, go searching for the "sdr-fmems.sdm" file. When you find it, wherever it is, *that* is where Windows told SdrDx "home" is.
Note: A user tells me "Under XP, home is found at... C:/Documents and Settings/username ...where "username" is your user name."

But most likely, when you go look at 10 MHz WWV or WWVH, it'll read off frequency. Close, but no cigar, as they say. My own SDR-IQ unit reads 10,000.175 as WWV's frequency under those circumstances... when I first got it, it was 10,000.156, so there has been a little drift.

All you have to do to correct this is create a textfile named sdr-fparms.sdr in your home directory with one line in it that has this "drifted" value in it. So again in my case, the file contains one line...


...which you'll recall is what my SDR-IQ read when started with no file present. Yours will be different, but not by a large amount.

Save the file, quit and restart the software twice, and you'll see that the unit is now precisely on frequency. Note that depending on the behavior of the IP server software, it may take TWO startups before the value takes effect.

You should be aware that the PC version of the net-server saves the offset, so if you've set your frequency offset using, for instance, SpectraView or SDR-Radio, your unit may not appear to be off in some cases. Unless you experience incorrect frequency readouts, you can skip setting this up in SdrDx.

Think you might have drifted a little? Set your FFT for 16384 points, and your span to just a few KHz. Set the file to 10000000 and then quit and restart SdrDx twice. Measure WWV at 10 MHz again, adjust the file value to the new readout value, save it, restart SdrDx twice, and you should be good to go.

4.5.2 - FUNcube Dongle

If you observe that the FUNcube Dongle's receive frequency is inaccurate, you can adjust it to about the nearest KHz. Right-click FCD and tweak the "Freq Correction" value while you observe the registration of the signal with the corresponding signal frequency readout.

4.5.3 - Anything else

See the note on PPM Correction

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