What's in a Whisper?

A while ago I set up a WSPR, or Weak Signal Propagation Reporter at home. Before I go into the details, WSPR is an amateur radio protocol that allows stations to transmit their callsign, location and power level and for receivers around the globe to decode those and upload the results to a central database. It's a great way to see what you can hear and what propagation is like.

A couple of months ago the regulator changed the Australian License Conditions Determination, the rules of engagement around amateur radio and now all licensed amateurs in Australia can even set-up a transmitter although I haven't yet. Receiving is plenty of fun and anyone can do that.

Initially I used a piece of Windows software to track the contacts but to me it was like ordering a courier with an 18-wheeler to pick up a postage stamp. I looked around an found a piece of software that runs nicely on a single board Raspberry Pi computer. The software is called rtlsdr_wsprd, it's a mouthful, but it works nicely on a Pi with an RTL SDR dongle. The dongle I have is capable of using all HF frequencies up to 1766 MHz, so I can technically hear the 23 cm band, though I haven't actually heard any stations there.

I created a list of all the published WSPR frequencies and I listen to a frequency for fifteen minutes, pick another frequency at random and do it again, all day, every day. My log for this installation goes back about eight months and I get about a hundred contacts every month or so.

You might think that's a lot of contacts, but really it's not. The antenna is indoors, it's under a metal roof and while it's on the second floor, it's far from ideal, but it works surprisingly well.

What have I learned from this experience?

I've heard 36 different stations, across 11 countries and 23 grid squares, the furthest was G0CCL, a club station in Cambridge in the United Kingdom which was transmitting on 20m with 5 Watts. I heard it 14750 km away.

There are plenty of other things that I can extract from this. The most popular band is 20m, it accounts for nearly 70% of the contacts I heard. Surprisingly, I am also hearing contacts on 80m, as well as on every other amateur band that my receiver can hear. The 6m band is pretty popular too, nearly 13% of the stations I heard.

For my receiver, between 4am and 6am in the morning was the best time to hear something, together they account for just under 20% of the contacts. Locally the worst time is 8am in the morning.

From the data I've collected, April and May were the most active, accounting for nearly 70% of the contacts.

I must point out that the log is not continuous, there's gaps when the logging station wasn't switched on and when I was switching antennas and locations, so using the statistics I've given you here for your own station are probably not going to work quite the same.

The WSPR mode isn't perfect. It will happily decode rubbish and report on that, so I've manually filtered out the bogus information, like for example a grid square XI97LK, or callsign 3KE/21XWK, where neither the location or the prefix are real.

I can tell you that I was surprised that my station can hear 80m on the little telescopic rabbit-ear antenna supplied with my dongle. That same antenna is also fine at hearing 6m, so I'm pretty happy with that.

One thing that this little experiment reveals for me is that a cheap dongle is a perfectly fine way to start playing with a limited budget. It offers the opportunity to explore the RF spectrum using modern tools and techniques. Much of what I describe is absolutely possible with a traditional radio. Originally I had my station set-up like that. It consisted of my Yaesu FT-857d, a 12 V power supply, a CAT cable, an audio interface and a computer.

In stark contrast, my current set-up consists of two things. A Raspberry Pi with an RTL SDR dongle plugged in.

While this set-up cannot transmit, neither could I at the time. Since then there have been advances in both. There are all-band WSPR transmitters for a similar cost to a Pi and a dongle. Power it up, configure it and you're good to go. I'm eyeing off that as a future project, since it's perfect to use to see what bands are open for your station at any given moment.

If you've never had a go, you should. I've documented how my monitor station works and you can find it on the projects page on my website at vk6flab.com.

WSPR is a really nice way to get into many different aspects of our hobby and the barrier to entry is your imagination.

I'm Onno VK6FLAB

• This article is the transcript of the weekly 'Foundations of Amateur Radio' podcast, produced by Onno Benschop, VK6FLAB who was licensed as radio amateur in Perth, Western Australia in 2010. For other episodes, visit http://vk6flab.com/. Feel free to get in touch directly via email: cq@vk6flab.com

• If you'd like to join a weekly radio net for new and returning amateurs, check out the details at http://ftroop.vk6flab.com/, the net runs every week on Saturday, from 00:00 to 01:00 UTC on Echolink, IRLP, AllStar Link, Brandmeister and 2m FM via various repeaters, all are welcome.