[Top] [All Lists]

[TowerTalk] low band receiving antennas options

To: <>
Subject: [TowerTalk] low band receiving antennas options
From: (Tom Rauch)
Date: Mon, 14 Jan 2002 12:55:46 -0500
> IMHO, the best length for triband (160, 80, 40) use
> is 500 to 600 ft.  I gave up trying to maintain terminating

I use my phased 800 foot long Beverages (three wide with 350 foot 
spacing) all the way up to 40 meters and higher.

The reason they work when they are so long is the far ends don't 
carry any current anyway because of losses. 

> I realize that unterminated and / or Bidirectional
> receiving antennas are not quite as good as a properly
> terminated and properly fed Beverage.  That said,
> my unterminated and bi-directional wires DO hear

You can obtain valid numbers by plotting the pattern, determining 
average gain, and subtracting actual gain in the desired direction 
from average gain. My Web page describes that, and gives some 
values for various antennas.

> For 160M,  I found a 1000 ft Beverage sometimes
> provided as much improvement over my 500 footer
> as the 500 footer provided over my vertical. 

In hundreds of A-B tests over the past few years, where both 
antennas were available at the same time, I've almost never found a 
case where a properly terminated 1000 foot Beverage beats a 
shorter Beverage...say one around 600-700 feet long.

Because there is so much loss along the length of the wire, all the 
extra length does is add minor lobes and extra unwanted nulls. I 
measure only about 50-70% current remaining after 600 feet. With 
70% current remaining, it is like feeding that last area of the 
antenna through a 3dB pad. This loss causes poor null formation, 
and the result is little improvement in directivity factor. It's like 
stacking two beam antennas with one robbed of 3dB power!   

Not only that, a second effect comes because the phase of arriving 
signals is very unstable when the distance between two points is 2 
wavelengths or more. It is impossible to keep the ends of the array 
in-phase. This effect increases fading, and decreases reliablility of 
the antenna.

That is why all my arrays are limited to about 800 feet long or 
shorter, and 700 feet wide. That is also why I run diversity receivers 
in stereo on wide-spaced arrays, because my "brain" can ignore 
the phase errors and add the signals. 

The more compact the array for a given directivity or pattern width, 
the more reliable the array will be in daily use. A compact array will 
also have less QSB than a similar pattern but physically more 
"spread out" array.    

As a matter of fact, I soon hope to shorten my last and final 
attempt at using long phased Beverages. A pair of 1000-foot west 
antennas will be shortened to 780 feet or so, because an existing 
pair 780 feet long are better than the 1000 footers about 95% of the 
> 80M, the 1000 footer seemed 'dead' in the early
> evening but 'came to life' several hours later.  My
> guess is that waveangles at / after sunset are
> higher and the long Beverage was not hearing 
> those higher angles.

It doesn't hear low angles either, because of phase errors caused 
by the velocity factor from earth losses below the antenna. If you 
want to hear low angles, you need phased verticals like those on 
my web page. 

One thing that saves the antenna on 80 meters is the high loss-per-
wavelength along the antenna. The loss effectively divorces the far 
end of the antenna from the system, so phase errors inherent on 
ionospheric paths with a spatial separation of a several 
wavelengths do not increase fading or produce significant deep 

Another common case where long Beverages work better than 
shorter counterparts is when the shorter Beverages are improperly 
terminated. Longer antennas self-terminate because loss along the 
antenna helps correct termination errors. As a matter of fact the 
unterminated F/B is a bit more than half of the unterminated return 
loss of the antenna. The very fact you see F/B ratio in an 
unterminated wire clearly illustrates how the far end is severely 
restricted in power from loss along the antenna!

When there is more than a few dB of loss, the extra length can't 
help the signal. It can only make things worse. John Kuecken 
discusses this in his book "Antennas and Transmission Lines. 
While his subject is transmitting longwires, it obviously applies to 
receiving systems as well. Kuecken, in actual antenna 
measurements for commercial communication systems, found that 
long  wires 1/3 of their height above ground reach a point of 
maximum gain when just over 3 wavelengths long, and gain 
decreases beyond that length. Of course that point would occur 
much sooner with a wire close to earth because losses would be 
much much higher.      

Another factor in observed improvements could be the user's luck 
in just by chance placing a null in the direction of a dominant noise 

By the way, remember whatever we do the electrical length of the 
wire is always longer than the physical length might lead us to 
believe. You can measure the electrical length with something like 
a MFJ259, using the "distance-to-fault" mode.

Anyway, enough of this. Most of it is detailed on 
anyway, complete with patterns and other visual aids.

73, Tom W8JI 

Where do you get ICE bandpass filters & beverage matching boxes?  The
same place that pays for the hosting of this list:  The eHam Store.
Order online at

FAQ on WWW:     
Administrative requests:

<Prev in Thread] Current Thread [Next in Thread>