Message-ID: <3877AF3D.47A84B20@netscapeonline.co.uk>
Date: Sat, 08 Jan 2000 13:42:21 -0800
From: "g3kev" <g3kev@netscapeonline.co.uk>
Organization: Netscape Online member
MIME-Version: 1.0
To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: Re: AMRAD Antenna ?
References: <29188.200001071140@gemini> <3875F52A.3AF2D67@bellatlantic.net> <00dc01bf594c$7f1a9ba0$0600a8c0@main> <3876554B.72D98BF3@bellatlantic.net>
Content-Type: text/plain; charset=us-ascii; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Sender: <majordom@post.thorcom.com>

Hello All.
Your comment about your antenna maybe operating like a LOOP is probably correct.
I would suggest it is performing like a grounded quad. Similar systems used on 160
and 80 metres where one cannot get a full size quad up.
At 1600 ft long and 50 ft high, think that is what you said, its natural resonant
frequency used as a grounded quad would be 296 khz. I expect there is some sort of
loading to resonate on 137 khz.
It would be interesting to check whether it radiates better as a loop or a long wire
with the grounded far end disconnected. Judging by experiments in the past using
loops v verticlals, I think the vertical/long wire approach would be better for low
angle.
I have tried a variety of loops in the past for 160 metres ie 40 m loop resonated on
160 and although it was quieter than my full size quarter wave on 160, it was not as
sensitive and did not pull in the long haul low angle dx, in fact there were signals
that  I could not hear that I was able to copy solid on the vertical, although at
times probably noiser. Small loops for short/medium distances of several hundred
miles are acceptable but for low angle long haul poor on mf/hf.
A full size loop ie quad or delta etc resonant at the operating frequency and
preferably at least a quarter wave above ground is a totally different story.
In the UK stations using loops have poor signals compared to those using verticals,
even low verticals heights with top loading. A couple of stations that have been
using loops have changed over to verticals and although not very high made a hugh
difference to their signals received at my qth.
The so called long wire, just a few feet above ground and fed with a drop wire is
really a top loaded vertical or inv L.
The above comments are a result of experiments and observations, especially on 137
khz and 1800 khz bands
73 de Mal/G3KEV
Andre' Kesteloot wrote:

> 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.