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

To: towertalk@contesting.com
Subject: Re: [TowerTalk] yagi f/b and rx s/n
From: Jim Lux <jimlux@earthlink.net>
Date: Sun, 13 Jan 2013 09:12:04 -0800
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
On 1/13/13 8:18 AM, john@kk9a.com wrote:
You can easily design a 2el monoband yagi with 50 ohms impedance and
reasonable gain.  Trying to design one for multiple frequencies using a
fixed boom length is more of a challenge.  I always focus my designs on gain
first and then SWR and F/B.  If you really want good F/B you'll have to add
another element to your beam.

I think the OP has variable length elements, so what's he presumably looking for is how to pick the boom length...


To:Tower Talk List <towertalk@contesting.com>
 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.


N1EU, you need to decide if you want to optimize for gain, or whether a dB is important, because that's really the tradeoff. All two element Yagis will have *about* the same gain, what changes is the depth and width of the null to the back.

You can make that back null narrower or wider by changing the element spacing.


Have you thought about driving both elements and doing a W8JK type antenna? (two elements driven out of phase and closely spaced) You can get a very narrow beam width, at the expense of low electrical efficiency so gain is somewhat below the directivity. And you get a beam in both directions. But up high enough, when the sunspots are right, maybe that's what you'd really want.. When 10 is hot, it seems like the directivity is what you want, to point to the side of a bunch of people you don't want to work.
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