I have recently been experimenting with an low power amateur radio beacon kit that helps monitor and study HF radio wave propagation. The beacon is a low power transmitter that sends out a small digital packet that tells anyone who receives and decodes it: who sent it (call sign), where the sender is (maiden head grid square locator) and finally the transmit power level (in dBm).The digital protocol I’ve been using most is called WSPR is Weak Signal Propagation Reporter (pronounced: wisper), and was invented by Joe Taylor K1JT of WSJT/JT65 and Nobel Prize in physics fame.

You may be wondering how I know who’s copying the beacon and that’s where the WSPR software and the internet comes in. The WSPR software uses a sound card connected which is to a radio transceiver to send and receive WSPR packets over HF radio. Any received packets/spots can be uploaded to http://wsprnet.org, and since there are hundreds of participants all over the world you can observe radio propagation patterns real time. The wsprnet.org site has a nice map view and a straight text view with good basic filtration options. They also have downloadable logs if you were interested in doing some in depth analysis. You can find my beacon by searching for the callsign W5BIT (10BitWorks’ ham radio club callsign).

Being someone interested in QRP and QRSS low power sorta stuff (I’ve built a few other kits) I decided to get one of Hans Summers new Ultimate3S QRSS/WSPR kits with a bunch of filters, a GPS module (I used this GPS module, an OCXO kit, and enclosure. The kit went together easily, the documentation and instructions are top-notch. I did try a variation on the OCXO kit with advanced thermal stability however I think have a bad Si5153 clock synthesizer chip and was exhibiting “clicking” each time it shifted frequencies when in MFSK/WSPR transmit mode. More on that experimental part of the build in a different post though.

I finished the kit enough to operate on just 30m and without the OCXO in April of 2015. Within the first few hours of operation I had copy from YV4GJN in Venezuela at a transmit power level of 100 mW a distance of 2,336 mi and 23,360 mi/W (miles per Watt)! The next crazy distance was JQ2WDO in Japan at 6,598 mi and 65,980 mi/W! Then the next day Austrailia VK4RV and VKDOI the furthest being 8,426 mi and 84,260 mi/W! At times I’ve dropped the power down to just 10 mW and was regularly copied in the US at 116,507 mi/W!  I have plans to get it on 6 bands including 6m once I finish testing and assembling the OCXO kit (but I’ve put that on hold and have only been operating on 30m). Oh and I forgot to mention the GPS makes it GPSDO, so in theory if I designed and built a low pass filter it should be good (stable) enough to operate on 2m but I don’t have much interest frequencies that high at the moment.

Pic of some of the 100 mW spots incl Japan and Australia:

Between April 2015 and October 2015 there have been 96,873 spots of W5BIT reported to wsprnet by 487 unique stations. The furthest station was VK6TU at 16,768 km (10,419 mi) at 20 mW (13 dBm) for 838,400 km/W  (520,958 mi/W). The average distance to spotting stations was 1,615 km (1,004 mi). Keep in mind that the furthest point on earth from San Antonio, TX (the antipode) is 19,928 km (12,382 mi) and is somewhere in the Southern Pacific Ocean where there are no people. The best way to exceed 838,400 km/W distance to power ratio would be to be to reduce the power level to 10dBm or below since there are so few really far away stations and most spots for the beacon are in the 1,600 km range.