Testing WSPR mode

WSPR How low can you go? (And still be heard)

As part of my Flying Squirrel project, I wanted to know, “Would my little Si3551A based telemetry transmitter,sending WSPR,  ever be heard by anyone?” So I conducted the following test.

  1. I configured the Radio gear to send the absolute minimum signal possible, on the 20m WSPR frequency:
    Icom 746 Transmitting at min power.
    ICom 746 transmitting a WSPR signal at the lowest possible transmit power. Notice the red circles. The radio shows no power out. The SignalLink interface has the tx turned almost all the way down. And the power meter’s needle is barely deflected, about the width of the needle on the 20 watt scale. (See the inset at the top left corner for a close up)



  2.  A picture of the WSPR software transmitting at 20:40 UTC. 1:40PM Pacific
    WSPR Transmitting on June 18th at 20:40 UTC
    WSPR Transmitting on June 18th at 20:40 UTC


3. And finally WSPRNet.org confirming reception by two monitors.

Reception reports from, WSPRNet.org


The total power out of the radio is just a few milliwatts and I am being heard across the US continent! (I live on the West coast in the Greater LA area). I should add that my coax run, is about 150ft of coax, so even less power is reaching the HF vertical antenna in my yard.

I left the experiment running for a while and almost every transmission cycle on WSPR, had at least one station hearing my station. WSPR has an amazing ability to pull signals out of the noise. In the case above I was heard at -23db and -25db.

This is good evidence my SI5351A will be heard!

73s de KJ6FO



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