Topband: K3NA Loop Array

[Milt, N5IA]

In the most simple explanation of the theory of operation of the  Beverage 
antenna you must understand that the single wire above (or on) the ground is 
1/2 of an unbalanced transmission line.  The earth conductivity is the other 
"wire" in the transmission line.

When the earth 1/2 of the "transmission line" becomes very conductive, the 
whole array approaches being an actual 2-wire transmission line (perfectly 
balanced).  When that happens there is near ZERO signal received.

The more unbalanced the line is, the more signal level is impressed on the 
wire which can be detected by proper impedance matching to a coaxial 
feedline going to your receiver.  That is why the Beverage works well over 
poor earth.

I have posted this before, but it bears repeating the practical experience.

At XZ0A on Thahtay Khun Island in January, 2000, the Beverages installed 
over land on the island worked very well.  They worked so well that 
electrical noise from the mailand, more than 5 miles distant in the 
direction of JA, was preventing us from hearing well the bedspring ops.

I constructed a Beverage oriented in the JA direction, in a secluded 
location which would isolate the view of the mainland.  The intent was to be 
able to hear the weak JA signals without the electrical noise from the 
mainland.

The only place this could be done was right at shore level on the west side 
of the island.  A good portion of the antenna had to be over the sea water, 
in particular at high tide.  Suffice it to say, the antenna heard 
NOTHING!!!!  It was essentially a 2-wire transmission line terminated in its 
characteristic impedance; that is, a dummy load.

This post is not meant to be a treatise on Beverage antenna theory. 
Hopefully the simple explanation of how and why its works over poor earth, 
and conversely why it DOESN'T work over high conductivity soil or water, 
will be of use to some out there in radio land.

GN de Milt, N5IA

----- Original Message ----- 
From: "Nick Hall-Patch" <nhp at ieee.org>
To: <topband at contesting.com>
Sent: Wednesday, June 23, 2010 12:16 PM
Subject: Re: Topband: K3NA Loop Array


> Consider me to also not be an expert either in Beverage antenna theory, or 
> in
> wave propagation.    I wonder however whether some of the idea that the 
> Beverage
> works best over poor ground dates back to the original development of the
> antenna, when it was used for low frequencies that were propagated by 
> ground
> wave that had no horizontal component to the wavefront.  This would not 
> produce
> much signal on a Beverage antenna that is dependent upon that horizontal
> component, unless the wavefront was passing over a poor ground that would 
> cause
> it to tilt, introducing a horizontal component.
>
> Most of us use Beverage antennas for DXing on medium frequencies, and the
> signals we receive are skywave.  Even if the original wavefront had no
> horizontal component, by the time the ionosphere has finished with it, and
> delivered it to our receiver, there may be quite a reasonable horizontal
> component to it.  One would expect that a Beverage antenna should 
> therefore be
> able to generate a signal, even with quite a good ground underneath.
>
> Standing by for corrections to my perception...
>
> 73,
>
> Nick
> VE7DXR
>
> Quoting rfoxwor1 at tampabay.rr.com:
>
>>
>> ---- Greg - ZL3IX <zl3ix at inet.net.nz> wrote:
>> > Hi Eric,
>> >
>> > I am interested in a statement in your paper, "Beverages don't work 
>> > over
>> > high(ly) conductive earth"
>> >
>>
>> This may be very simplified. I am far from a Beverage expert, but it was
>> explained to me once that the Bev works well over poorly conducting
>> soil because the wavefront is no longer just vertically oriented, as it
>> travels down the length of the antenna wire; but rather is retarded,
>> causing a forward tilt in the wavefront. This forward tilt then will
>> induce a RF current down the length of the wire, which sums up at the
>> end (where the RX is). IOW instead of just a vertical field, there is
>> both a vertical and a smaller horizontal field, and the poorer the soil,
>> the greater horizontal field induces the antenna current you need.
>
>> -Bob k2euh
>>
>
>
> -- 
> Nick Hall-Patch
> Victoria, BC
> Canada
>
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