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| To: | [email protected] |
|---|---|
| Subject: | Re: LF: IK2DED beacon and E field probe. |
| From: | [email protected] |
| Date: | Thu, 19 Sep 2002 04:47:08 EDT |
| Reply-to: | [email protected] |
| Sender: | <[email protected]> |
In a message dated 9/19/02 6:57:02 AM GMT Daylight Time, [email protected] writes:
For ERP calculation antenna curent is needed. I think Your curent is about Hmmmm, "poor earth on a rocky mountain" I think there maybe errors in the estimation of earth resistance. To give 3 measured examples: In good old London clay with 5 x 1.5m copper rods at the property boundaries all interconnected by 'radials' just under the surface I manage 150 Ohms at best going to 190 on the odd wet day. My radio club has a similar installation but with a much larger ground area, we have also made a connection to the electricity board earth at an official grounding rod. It measures at a total of 85 Ohms The best I've ever measured was between 12 and 15 ohms when using a wire from the top of an apartment block when the earth was connected to 22mm copper pipes in the central heating system - probably a kilometre or two of copper pipe which extended underground to other buildings. From the above estimate of the beacon; if 40W RF = 300mW ERP then 133W = 1W ERP or a total antenna system efficiency of -21.23dB. (which is most unlikely due to the rock) Reading the odd report of other portable operations from rocky sites, an estimate of 200 Ohms may be closer to reality. In that case a quick scribble shows that a 2.94 degree high antenna (18m effective heght) will have a Rrad of 0.025 Ohms and that for 40W of RF the output will be around 5mW ERP and the efficiency will be -39dB. My conclusion: The original estimate is too high and my estimate is probably too low and the only sure way is to spend some time measuring. Computer off, scope on, cornflakes finished and off to work. 73 David G0MRF www.g0mrf.freeserve.co.uk |
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