With an ERP of less than 10mW from my earth-electrode "antenna" in the ground I get spotted in Norway most nights on WSPR.
I use my FT817ND and my transverter. The output from the transverter into 50 ohms is about 12W, but the measured ERP is only about 10mW (i.e. the "antenna" gain is about -32dB). A "proper" antenna and ground could be several dB more efficient. Most nights on 472kHz WSPR I get over 20 stations spotting me and on the better nights 30 stations! Neither my XYL or the neigbours are aware it is even being there!
This "antenna" also works pretty well on 160m. On 472kHz and 1840kHz it is an almost perfect match with a small 3C90 step-up transformer. At the old QTH I did not need this at all. I suspect it would be quite good on 137kHz TX, although I have not (yet) tried it on this band.
My theory is on LF and MF bands it works as a sort of loop in the ground. If this is correct, the loop would be bigger as you move down in frequency. It could even be quite effective at VLF.
WSPR does not really allow chats, but works with very weak signals. It is ideal for me on this band. From the old QTH I have had JT9 472kHz QSOs with stations in the UK and Belgium with a similar set-up at my QTH.
2 comments:
Hello Roger,
Excellent experiments on MF. I have copied you several times on 474 khz on WSPR recently. At present I am experimenting on 160m using an indoor Magnetic Loop. I initially started with 700 milliwatts transmitter power and have gradually increased power to 10 watts. I can send you a picture of my Loop, which is located indoors, in our garage, which is built with concrete blocks. The diameter of the loop is about 8 feet. How can I send you a picture of my Loop ?
Kind regards and a Happy New Year to you and the family
Finbar EI0CF
Thanks Finbar and a happy new year to you too. You can send me the photo of the loop as an email or message.
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