WSPR Modulation Movie

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Last seen: 3 years 2 months ago
Joined: 2012/03/04 - 09:52
WSPR Modulation Movie

I use 3 Ensemble RXTX alternately to transmit WSPR on 80-10 meters. In addition I use an Ensemble RX and separate laptop as a return monitor, frequency verification, etc. While using Bob's (G8VOI) excellent frequency calibration tutorial and monitoring on the Ensemble RX with HDSDR I noticed the frequency kept "jumping" 1-2 Hz and I could not get the +- 1Hz calibration that I expected.

Then the light went on! Of course, this is exactly what 4FSK modulation SHOULD do. Bottom line on that is "Use the "tune" mode to calibrate your frequency, not simply engaging "transmit"...... patently obvious after the fact but I am a little slow sometimes.

Anyway, putting HDSDR in the CW mode, transmitting in "tune", and using "CW Zap" will put you dead on the signal and you can read your frequency from the HDSDR display. This assumes, of course, you have previously calibrated your HDSDR to WWV or comparable..... here in China it is BMP. Then, if you put your mouse wheel in the 1 Hz step mode, HDSDR in AM mode, you can move up/down 1 Hz and confirm the phase meter rotates one direction when you are one Hz high and the other direction when you are 1Hz low. When you are less than 1 Hz away you can count the number of rotations per minute, divide by 60, and this will tell you what fraction of a Hz you are off frequency by. AGAIN, assuming that the HDSDR receiver has been calibrated against a known standard using the same procedure.

Then the learning begins....... put the WSPR rig in transmit and watch the display expanded spectrum display. I zoomed mine so it would encompass the entire 200Hz WSPR band. You will see your signal "moving 1-2 steps to the right, then 1-2 steps to the left.... all on approximately a one second beat. There is is! 4FSK modulation right there on your screen. If you wanted to dig deep enough into Joe Taylor's documentation I suspect you might even be able to decode the characters by simply watching the screen.

So I shot an iPhone movie of an entire transmit sequence and uploaded it to Youtube at

Very very cool.

Warren Allgyer
Stealth Amateur Radio from Beijing
CW, BPSK31, and WSPR on 40/30/17/15/12/10 Meters