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Message-ID: <$RGBICAM3vd4EwmE@telemetry.demon.co.uk>
Date: Sat, 8 Jan 2000 09:05:16 +0000
To: rsgb_lf_group@blacksheep.org
From: "Tom Boucher" <tom@telemetry.demon.co.uk>
Subject: Re: LF: Re: AMRAD Antenna ?
In-reply-to: <3876554B.72D98BF3@bellatlantic.net>
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>From Tom, G3OLB

Andre

I'm not at all clear how this antenna is matched and fed. I am
particularly interested because I currently use an 1100 ft end fed wire
which I could conceivably extend to a full quarter wave. Like yours it
is suspended from a number of trees but high voltages are not a
particular problem because I have it well insulated with some good
ceramic insulators (thanks Dick!) There are also cows in my field but
they are a well insulated breed.

Your 1600 ft antenna is approaching a quarter wavelength long and, as
Dave says, opposite ends of a quarter wave antenna will present opposite
impedances i.e. if you leave the far end open, the near end will look
like a low impedance and conversely if you ground the far end, the near
end will be high Z. So I cannot reconcile grounding BOTH ends and being
able to resonate it.

73, Tom G3OLB


In message <3876554B.72D98BF3@bellatlantic.net>, Andre' Kesteloot
<akestelo@bellatlantic.net> writes
>Wooops,
>I guess I did not express myself quite clearly enough.
>The far end of the wire terminates in a field , (and specifically near a pond)
>visited by many cows.  In order to avoid any possible unpleasantness (wire
>falling on the ground if broken by the wind, etc.), we decided to ground that
>end.
>It may well be that the whole thing operates as a loop of sorts, as there is a
>non-zero resistance between the two grounds (the one at the Tx site, and the one
>at the pond end)
>73
>Andre'
>
>Dave wrote:
>
>> Surely the Voltage gradient is just the same but the other way round? High
>> current point at the earthed end and high Voltage point at the TX site as it
>> is about a quarter wave....
>> The "earthed at the far end" idea has been used with topband antennas for
>> years in order to get the current into the vertical drop.
>>
>> 73 Dave G3YXM.
>
>
>
>