Calibrate Sound Card

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There are two easy ways to calibrate your sound card sampling rate. This assumes you have the audio from your radio fed into your PC sound card.

WWV provides the precise timing. Tune in WWV on your HF radio. WWV uses DSB-SC, so AM RX will work. Check out the reference for more info.

My 11025 sample rate was off be a lot - about 6800 ppm. So this is worth doing.

I discovered Method #3,using Ham Radio Deluxe, DM-780. You don't need a radio for this one. Just run the calibration routine.

Contents

Method 1 - MMSSTV

This came from NMC MARS info. Download MMSSTV. From the MM Ham Soft page. This program is free.

  • Start MMSSTV and choose, Option/Setup MMSSTV.
  • Choose the Misc tab.
  • Click on the Adj button under 'Clock'
  • Follow the on screen instructions

This will bring up a screen with instructions with a waterfall. You'll see a line develop and it may not be anywhere near vertical. Mine was diagonal. When you have about a half a screen worth of data, click on the bottom of the line, then the top. The new clock sample rate will show in the Clock window of the Misc tab. This is your calibrated sound card Sample Rate. You can use this number in MT-63.

Method 2 - Spectrum Lab

This is a lot simpler, quicker and highly accurate.

For this method, you need:

  • A copy of Spectrum Lab from DF1YHF.
  • Radio that is on frequency.

WWV will output a 500Hz tone and a 600Hz tone. You can use either one. I used the 500Hz tone. Or you can use the 1KHz TIC from CHU. Or - you can detune your rig by 1KHz and use the WWV carrier.

You should see the waterfall display and the various WWV tones. If not, then you need to figure out how to set up the sound card interface and choose the right source. (e.g. line in)The tones are available every minute of the hour, so some patience is required.

Set the FFT parameters to provide sub-Hz accuracy. (e.g. 65536 sampling rate)In SL, choose Options/Audio Settings. Then using the peak detector on the spectrum display, coupled with the cursor, check the frequency of the reference tone.

Back in the audio settings window, enter the correct frequency under the Samplerate Calibrator box. (e.g. 500.0) and then enter the displayed frequency. Press the Calibrate Input SR button. This will adjust the sound card time rate. Then use the corrected value in the other sound card programs.

You can track the drift, permanently using the Drift Calibrator. However, this requires a constant input signal, which obviously can't be used while you are working the sound card modes.

Click on the '? about SR calbi.' button for more info.

For reference, mine ended up as 110099.49Hz, which is substantially different than 11025Hz.

Method #3

Install Ham Radio Deluxe Digital Master 780. This has one of the best user interfaces of any free package! Under Tools/Program Options - choose Soundcard and press the soundcard calibration button. Choose your sound card, press Start and let it run for a couple of minutes. Simple!

References