Message-ID: <000001c3789a$752bb040$6507a8c0@Main>
From: "Alan Melia" <Alan.Melia@btinternet.com>
To: rsgb_lf_group@blacksheep.org
References: <3F604383.4358.5B6012@localhost> <001e01c37852$deaf7d00$6507a8c0@Main> <004201c3785b$e01167e0$3704210a@Hugh>
Date: Thu, 11 Sep 2003 14:53:46 +0100
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Subject: LF: Re: Re: Re: re EWE aerials
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Hi Hugh, thanks for that I don't have that book but that is what I have
"believed" to be a Beverage. However being cantankerous ( as a G3 I am
entitled to that condition ;-))  ) It occured to me that like your book a
lot of these text-books are simply repeating the content of older tomes, and
possibly perpetuating some myths. It does not say why the aerial has to be
longer than a wavelength....is it just the case that it needs that length to
really show the effects? I can see this in directionality as longer aerials
have narrower main lobes. But I would have thought that a travelling wave
aerial should work (to some extent) whatever its length since it is
aperiodic, may be the longer it is the bigger the "aperture" hence the
bigger the signal-voltage at the terminals.  In fact a lot of us pick up
very big signals with aerials at 10m which are less than 100m long. I really
wonder whether anyone has done proper measurements....it is obviously
difficult. I must try and contact a ex-BT wireless man who was involved in
long-distance short-waves before the war.

Terman (1943) for instance refers to it as being between half and several
wavelengths long. He also quotes a height of 10 or 20 feet. I guess to show
directionality it would need to produce a much great voltage from the
travelling wave effect than from its low effective height as a top loaded
vertical (which would be almost omni-directional) Terman does quote a couple
of references from 1923/4 and these might be worth me ferreting out.

Another though is that since the aerial is so critically dependent upon the
slowing of the phase-front, the use of insulated wire may well nullify the
effect, by causing the velocity in the wire to be much less than that of the
wavefront.

Now, anybody got a spare 20 miles or so of old telephone pole-line in the
middle of a desert??

Cheers de Alan G3NYK
alan.melia@btinternet.com


----- Original Message -----
From: "Hugh M0WYE" <m0wye@thersgb.net>
To: <rsgb_lf_group@blacksheep.org>
Sent: 11 September 2003 12:57
Subject: LF: Re: Re: re EWE aerials


> Alan, et Group,
> The Services Textbook of Radio (1958) Volume 5, (page 336) says that "a
> Beverage, or wave aerial, is a straight wire several wavelengths long,
> usually carried by insulators on telephone poles at about 30 feet above
the
> ground..."
> Further on it says "Such aerials should be at least one wavelength long,
so
> that for the very low frequencies involved, several miles of line are
> required. They are therefore only suitable when a large area of poor