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[TowerTalk] Yagis and Receive Strength

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Subject: [TowerTalk] Yagis and Receive Strength
From: (Tom Rauch)
Date: Fri, 23 Jul 1999 21:14:58 -0400
> So heres my ignorant question (kind of embarrassing too), does a larger
> yagi, i.e. going from 2 elements to say 4 elements improve receiving as
> well as transmitting? 

There are no ignorant questions.

Here's how it works. Most low-band systems are noise or QRM 
limited, so we can ignore the rig and absolute signal level fed to the 

1.) If the noise (and QRM, consider that noise also) that limits your 
reception is from the same direction as the desired signal, you can 
stack a million antennas and nothing will change for receiving!

2.) If the noise comes from a direction where the stacking reduces 
response, the S/N will improve by the ratio of that null to the 
forward lobe increase. That can be many dB with a very small gain 

3.) If the noise is evenly distributed all around the antenna, the S/N 
will improve by the same amount as the directivity increased.

Since we don't know about your situation, we don't know which is 
fits best. It will be somewhere between no improvement and a large 

The main problem is probably your high power. With only four 
elements and high power and absolutely no local noise, I have the 
same situation. Dozens of stations call that I can't copy. That's 
despite an S2 noise floor.

Very few DX stations have 1500 watts, and most run 100 watts. 
Either you need a very special receiving array that has much more 
directivity than the transmitting antenna, or your transmitting will 
out do your receiving with the QRP stations calling you.

73, Tom W8JI

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