Receiving WSPR with the RTL-SDR
Recently RTL-SDR.com reader DE8MSH wrote in to let us know about his experiments with receiving WSPR with his RTL-SDR. WSPR is an acronym for “weak signal propagation reporter” and is a software program and RF protocol designed for very weak signal radio communications between ham radio users. With less than 5W of transmitting power, a WSPR signal could potentially be copied all over the world.
To receive WSPR, DE8MSH used a direct sampling modified RTL-SDR dongle together with a 9:1 unun, 10m RG58 coax cable from RTL-SDR to unun and a 12m wire antenna outside his house. Then by using SDR# together with the WSPR software he is able to copy signals from all over Europe and Canada/USA from his home in Germany.
A non’s comment about receiver drift is very important. I have an older RTL SDR with a separate upconverter that takes everything from about 10 KHz to 50 MHz and upconverts to 200 MHz. Unfortunately the 200 MHz oscillator of the upconverter is so susceptable to minor changes in temperature that it causes the WSPR signals to drift constantlly due to air currents in the room. Use a TCXO if upconverting amd keep the oscillator isolated from temperature changes. That should stabilize your WSPR receiver and allow decoding of the signals.
I have an upconvertor and a RTL dongle, and for ages couldn’t work out why I wasn’t able to ‘see’ WSPR signals, so here’s couple of key things to note:
-Make sure the dongle is well warmed up, not drifting, and most importantly use a broadcast station and the PPM setting to get the frequency spot on. If you are still a few tens or a hundred Hz out, make a note of how much and apply that amount to the tuning after setting SDRSharp to the WSPR frequency.
-Set your clock
-I couldn’t get WSPR-X to work whereas WSPR 2 works fine.
-In WPSR 2, set TX fraction to zero and de-select ‘idle’. Withing 2 minutes it will start receiving. Adjust the volume in SDRSharp so it reads around 0dB in WSPR 2.
-A lot of the time you won’t hear the signals so don’t bother trying to tune them by ear! If everything is setup correctly and your reception frequency is spot on it’ll work automatically.
Just use sdrharp to tune and demodulate. Then vbcable to trunk the sound to WSPR. Done! Have fun!
Great. Is there a link to more info on how he did it?
I can’t believe I still haven’t messed with WSPR. Guess that’ll give me something to do this weekend!