12 Sep 2013

TXing tonight with a 472kHz "in the air" loop

As the next stage in my experiments from the new QTH at LF and MF, this afternoon I converted my earth-electrode antenna into a complete "in the air" loop by removing the earth connections and joining the wires with a length of wire along the grass. The DC resistance of the loop is 0.9ohms and the enclosed area somewhere around 60-100 sq m although the loop is far from vertical and the bottom wire actually runs along the grass rather than up in the air. The measured loop current is around 0.9A and tuning very sharp with around 1.7nF in series and matched with a 3C90 step down transformer. According to my calculations of radiation resistance, the ERP should be in the 20-40mW region, considerably greater than with the earth-electrode antenna.
630m WSPR spots of G3XBM so far this evening
My first report this evening was from PA3ABK/2  at -28dB S/N but I am hopeful of a few more 472kHz spots tonight. I expect that the results with the loop will be better than with the earth-electrode system, but the loop can be further improved by raising the upper wire (bigger vertical enclosed loop area) and thickening up the lower wire to reduce resistive losses further.

I am doing things one step at a time so I can assess the difference.

UPDATE 1800z:  M0PPP has spotted me several times this evening but had failed to copy me in the last 2 weeks, so this is encouraging. Also reports from G8HUH and G6AVK.

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