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| To: | <[email protected]> |
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| Subject: | LF: Re: Re: Re: Loop TX antennas at VLF? |
| From: | "James Moritz" <[email protected]> |
| Date: | Fri, 18 Mar 2011 18:40:47 -0000 |
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| Reply-to: | [email protected] |
| Sender: | [email protected] |
Dear Mal, LF Group,You are ignoring the fact that a number of amateurs have used loops quite successfully in the LF range, particularly in the US for 136k and "Lowfer" operation. The type of situation where loops can be more efficient than verticals of a similar size seems to be where the antenna is in a location with many tall trees. The trees can be used to support a large antenna, but also bring about high losses due to dielectric losses in, and the screening effect of, the poorly conducting wood. Loops, with generally reduced electric fields, are less adversely affected, it would appear. In the VLF range, using the same size of antenna and current level, the voltage on a vertical antenna is much higher, so one would expect extreme levels of loss of this type. So while on paper, and in the middle of a nice flat field, the vertical would be more efficient, the loop might actually be better in a practical situation with less than ideal locations. Loading coils are also a significant factor - it seems to be difficult to make a reasonably sized VLF loading coil for a small antenna that does not add significantly to the overall loss. The previous calculation shows that the requirements for a low-loss loop capacitor should not be too difficult. Cheers, Jim Moritz73 de M0BMU |
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