[TowerTalk] yagi f/b and rx s/n

[Patrick Greenlee]

It depends...

If reducing QRM and QRN from other directions than your beam heading 
produces a higher signal to signal plus noise ratio than optimizing for max 
forward gain then minimizing the side and back lobes is the best choice.

My personal "guess" is that minimizing reception in all unwanted directions 
is likely to produce better weak signal reception in the desired direction 
in the majority of instances of weak signal reception.

The above would not be the case if your noise level was quite low as 
measured with an omni-directional antenna (say a vertical) or when scanning 
by rotating the beam and getting low noise levels in all directions.  In 
this instance forward gain irrespective of side lobes or reception off the 
back of the beam would produce the best weak signal reception.

You have to be the judge of your expected circumstances.  Which of the above 
best describes your personal experience?  1.  The weak signal is in the 
clear but is so weak your receivers gain is insufficient to make it readable 
or  2.  is it that the signal is strong enough to read if it were not for 
the noise level being high enough to mask it? Situation 1 above calls for 
optimizing forward gain and situation 2 calls for reducing side lobes and 
increasing front to back ratio.

You pays your money and you takes your chances.

73 Patrick AF5CK


-----Original Message----- 
From: Barry N1EU
Sent: Sunday, January 13, 2013 5:08 AM
To: Tower Talk List
Subject: [TowerTalk] yagi f/b and rx s/n

I need to come up with some dimensions for 2-element yagis for 20-10M.
I wish to maximize ability to hear weak signals.  Does that mean
optimizing f/b ratio, rather than gain?  This will be assembled from
SteppIR components that I have on hand, so dimensions can be optimized
for each frequency once a boom length is chosen.

Thanks & 73,
Barry N1EU
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