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| To: | [email protected] |
|---|---|
| Subject: | RE: LF: Ground loss |
| From: | "john sexton" <[email protected]> |
| Date: | Tue, 14 May 2002 08:53:32 -0400 (EDT) |
| Reply-to: | [email protected] |
| Sender: | <[email protected]> |
|
Hi Sasha,
I'm afraid this formula gives a result which is an order of magnitude less than measured here. Soil conductivity is about 0.002 Siemens/metre (chalk). From notes of one of my test configurations, I had C =233pF, lant = 40.5 metres, lcp = 100 metres. With these figures the formula gives R = 7.7 ohms, whereas the measure value was 93 ohms. Most probably you are considering a flat surface and perhaps an entirely vertical antenna? This may be all well and good for a commercial antenna, but amateur antennas like mine are not on a flat surface, are surrounded by leaky capacitors like trees, buildings, etc. and are only partly vertical. It is common experience among this community that increasing the coverage of ground with wire only works up to a point and beyond that no gains are achieved. See G4FGQ site http://www.g4fgq.com for several useful free programs which include information about values of conductivity for different ground. If your advanced formula takes into account the environment, trees, buildings, etc., non flat ground and antennas that are partly horizontal and partly vertical it could be very useful. 73, John, G4CNN Join Excite! - http://www.excite.com The most personalized portal on the Web! |
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