Message-ID: <004101cbe5a1$68069bb0$0401a8c0@xphd97xgq27nyf>
From: "mal hamilton" <g3kevmal@talktalk.net>
To: <rsgb_lf_group@blacksheep.org>
References: <AANLkTi=j-Bp7+YC+527yQ6EBahLUdq6WqYXSGNTk33m7@mail.gmail.com> <59F87B1BA5D04A2F98902CF94C38DB30@JimPC> <000e01cbe589$d2324060$0401a8c0@xphd97xgq27nyf> <72DDC8B018CB4996B1E7BB253B94C771@JimPC>
Date: Fri, 18 Mar 2011 19:19:30 -0000
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Subject: LF: Re: Re: Re: Re: Loop TX antennas at VLF?
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Jim
Now you have introduced another element into the argument ENVIRONMENT,
which is not applicable to the argument because each individual QTH will be
different. In a discussion like this,   one has to assume a level playing
field.
Discuss each antenna in the ideal environment THEN consider the X factor
depending on a specific QTH where a loop might have an advantage although I
doubt it.
also
the loops to which you refer in the USA used on 137 are fairly large
compared to what some intend to use on 9 khz in the UK, I doubt if they
would radiate over any distance even on 137.
Why are some reluctant to go for high power and bigger antennas, whereas in
EU balloons and kites are acceptable as the norm for those trying to cover
the maximum distance.
In the UK there are wide open spaces in the countryside plus beaches for
kite and balloon activities.
73 de mal/g3kev




----- Original Message -----
From: "James Moritz" <james.moritz@btopenworld.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Friday, March 18, 2011 6:40 PM
Subject: LF: Re: Re: Re: Loop TX antennas at VLF?


> 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
>
>