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:

g4ilo said...

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.

Roger G3XBM said...

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