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Topband: semi-variable Spacing and phased arrays

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Subject: Topband: semi-variable Spacing and phased arrays
From: (Tom Rauch)
Date: Tue, 30 Jul 2002 10:39:36 -0400
> I'm attempting to put up two 580 foot Beverages spaced 200 feet 
> (compromise for 80/160) and have a spacing question.

Hi Ted,

First, a small meander like you described would be fine. You'd never 
notice the difference.

Second, you'd have virtually no change in directivity or S/N of the 
array with 200-foot spacing on 160. You can read about this on my web 

With a 500 foot antenna and 200 foot spacing, the best case receiving 
improvement at 25 degree wave angle would be about 1dB over a single 
antenna. That's true even though signal level increases about 3dB. 

Here is the 160 meter directivity (not GAIN) referenced at 25 degree 
signal arrival at each spacing:

One antenna =8.8dB
200 ft spacing = 9.7dB
300ft spacing= 10.6dB
380ft spacing= 11.4dB

Don't be misled by the absolute "gain" shown in the model, thinking 
it means you will see that change in S/N improvement. The gain change 
actually just reflects the addition of two signals with the same S/N 
ratio from each antenna, and can be 3dB with absolutely no change in 
receive performance. We are often misled by folklore into thinking 
more absolute gain means better receiving.

73, Tom W8JI 

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