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Re: Topband: Non-resonant receive antennas

To: "'Top Band Contesting'" <>
Subject: Re: Topband: Non-resonant receive antennas
From: "Tom W8JI" <>
Reply-to: Tom W8JI <>
Date: Thu, 18 Dec 2014 13:53:03 -0500
List-post: <">>
" Since Rick correctly stated that RDF doesn't account"


RDF is  everything !   The RX antenna system is the only way to improve
signal to noise ratio. All electronic device is not perfect and introduce
noise and deteriorate the signal to noise ratio, including your radio too

RDF is one way to measure directivity .

I'm a little tied up with other things like paying work, but I see this is still going on.

RDF is directivity, I just called it that to not confuse it with gain that is important to transmitting. I suggested it as a factor in deciding if an antenna is **likely** to be an improvement or not because:

1.) Front gain to rear wide area ratio, based on the null width of the entire rearward pattern, was being used. This method was rarely effective, unless noise largely existed only in the entire rear hemisphere. It is very unlikely to have grossly dominant noise exactly fit a rear hemisphere, and it is impossible to have that condition in more than one direction.

2.) People were using gain as a measure, specifically with closely spaced non-staggered Beverage antennas. If two Beverages are paralleled so close as to not change pattern one bit and not change S/N ratio one bit, gain increases 3 dB! Gain is a useless parameter until the receive system internal noise affects S/N ratio.

There certainly are other things that are important, and I weigh more than raw RDF into my selections. (Someday when I have time I may publically document things.) Removing signal from directions where there is no noise or where there is very little noise can make things seem better by RDF when they are really not better, as can RFD improvements by reducing side or back response to levels below where noise or QRM detracts from copy.

My preference with large area (not tall height) vertical arrays and Beverage arrays is a very clean pattern with deep nulls elevated above the horizon and maximum overall area removed from the pattern, but I always want to be sure the next direction selected does something useful before I lose too much from the presently selected array.

What I have and use is the result of almost 40 years of reading and experimenting, but it only came together here because I have the room I always needed. Most of my life I lived on small lots, and what I did then was ideal.

All antennas are compromises, and RDF might be the best (far above gain or other methods) going at the moment, but distribution of noise and QRM has to factor in by looking at the pattern.

73 Tom
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