14 Jan 2013

An INDOOR loop on 472kHz TX?

Over the last few days I have been receiving quite strong WSPR signals on 472kHz from Richard G4KPX who is in Ely, some 14km north east of me.  Looking on the WSPR database I see he has been copied up to 573km on the band using WSPR. Now, in a email from Richard today he revealed his secret: he is using just 1W RF into an indoor 3m x 2m single turn loop made of 10mm pipe leaning against the wall of his spare bedroom!  The EIRP is at most 100uW and probably a lot less because of the losses with mounting it where he does and the capacitors used to resonate it. This is a pretty amazing set of results.

Richard has been spotted across the Atlantic on 160m using the same indoor antenna and has similar magnetic loop antennas for all HF bands I believe.

So, if you believe you have no space for an MF band TX antenna, and you don't even have a garden to put a couple of earth-electrodes in the ground, you could always follow Richard's example.

Some months ago I believe one of the German 136kHz stations (DF6NM?) tried something similar using a large coax as a big indoor loop on 136kHz and also got some quite decent results. Never say you cannot erect an antenna!  What you need is a bit of ingenuity.


David Cope said...


Not knowing much about WSPR how does one determine the validity of these reports, how does the system cope with false positives?

I must obviously read up on the system, but I'm not really sure it's for me, but maybe I should give it a go. Is there such a thing as a WSPR "keyer" e.g. something like a DDS which can generate WSPR into an RF amplifier controlled by a microprocessor? That would get me interested.

Cheers. DAvid. G8JGO.

Roger G3XBM said...

David, the WSPR software is pretty error proof. Occasionally noise will produce garbage but if a genuine signal is received it decodes solidly and accurately. Honestly, WSPR is truly amazing software for experimenters. There are some WSPR beacon kits I believe but you do need PC clock accuracy: I use a package (free) called Atomic (Google it) that sets the PC to internet time every few minutes.

David Cope said...

That's interesting Roger. I did just dive off for a quick look at the WSPR site and noticed WPSR 2.11 beta has support for a softrock SDR TRX - WSPR has built in I/Q encoding/decoding so that's a step forward. If I could get WSPR running on something like a Raspberry PI then that would be a nice, dedicated project.

Ouch! these Capchas, my poor eyesight :-)

Cheers. David.