Sunday, July 12, 2009

Listening on WSPR...

I spent the weekend trying out WSPR......'Weak Signal Propogation Reporter'. It's a new type of mode which was only developed in April 2008 and allows users to detect very weak signals with the soundcard on their PC's. I saw this mentioned on the Soldersmoke Blog recently so I downloaded the software.

It basically works as follows.....
1) You tune to a specific frequency on each band. On 30 metres, the most popular band for these kind of signals, you set your rig to 10.138700 MHz on USB.
2) The software listens to the received audio from 1.4 to 1.6 khz. This equates to 10.140100 to 10.140200, a 200 Hz wide section of spectrum.
3) For a basic receive set-up, just put the microphone from your PC next to the loudspeaker of your rig and run the software.

There are a few issues that still need to be resolved. You need to set the time on your PC so that it is accurate to within 1 sec. You also need to find out where 10.138700 MHz is! You can't assume that your rig is accurate. I found that on my rig, I had to set it to 10.138778 MHz.

There is a nice short explanation of WSPR on the G4ILO website.

The main website for WSPR reports is WSPR Net which lists all the WSPR spots and can also display them on a map.
The picture above is a screenshot of the WSPR screen. The horizontal waterfall displayat the top shows the signals heard in the 200 Hz band split up into 1 minute segments. In the data section below it, the 2nd column is how far below the noise floor the signal is. The last 3 columns on the right are callsigns heard, their locator square and their power in dBm (20 dBm=0.1 watts, 27dBm=0.5w, 30dBm=1w, 33dBm=2w, 37dBm=5w, 40dBm=10w).
Most stations seem to be running around 1 to 5 watts and over the space of a day, I was hearing signals from both sides of the Atlantic. The activity level seems a little low so perhaps it is still a mode that is only growing? Still, I was suprised at what was heard with the WSPR software digging out signals buried in the noise. Here is a map of what was heard in 30 minutes on a Sunday afternoon in July. Note that the antenna in use was a low doublet antenna only about 4-5 metres above ground level.

As a mode, WSPR has a lot of potential. Some of the advantages might be....
1) You can automatically see if various propogation paths are open although a lack of global receiving stations might make this difficult?
2) Within minutes of sending out a signal, you can see what type of signal you have at various receiving stations.
3) By using very low power, you should be able to see roughly how you are getting out. Then if you make any major antenna changes, you should be able to get instant feedback on your signal strenght?

For anyone interested in very low power operation, this mode has obvious attractions. I tried messing about with QRSS (slow speed CW.....a dot = 3 seconds!) and I found it difficult to find let alone read the signals. WSPR seems to have a lot more potential.
I can feel myself at the edge of a slippery slope with this one ;o)

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