22 Jan 2010

ERP calculation on 500kHz

I've recalculated my ERP based on a better measurement of antenna current. I was using a dust iron core for my current transformer, so swapped this for an FT37 ferrite toroid today and got a lot more current measured now. My antenna current is actually around 0.12A. My antenna is 5m long with a small spiral top so the effective height must be <5m. Even putting in 5m into the classic formula I cannot make my ERP exceed 1mW. I make it more like 600uW. Interestingly this is 20dB more than the original estimate from M0BMU and since then I'd increased the ERP, I believe, by around 20dB which would also make it 600uW. Of course the margins of error must be large.

2 comments:

  1. I suspect that you must be one of very few people to compute your ERP and send it in your WSPR transmission, Roger. I think most people just send the power into the antenna.

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  2. This is common practice on 136 and 500kHz Julian as the ERP is well below the TX power output.

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