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Message-ID: <72DDC8B018CB4996B1E7BB253B94C771@JimPC>
From: "James Moritz" <james.moritz@btopenworld.com>
To: <rsgb_lf_group@blacksheep.org>
References: <AANLkTi=j-Bp7+YC+527yQ6EBahLUdq6WqYXSGNTk33m7@mail.gmail.com> <59F87B1BA5D04A2F98902CF94C38DB30@JimPC> <000e01cbe589$d2324060$0401a8c0@xphd97xgq27nyf>
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Date: Fri, 18 Mar 2011 18:40:47 -0000
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Subject: LF: Re: Re: Re: Loop TX antennas at VLF?
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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 Moritz
73 de M0BMU