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Re: Topband: big K9AY-loop + MFJ 10126

Subject: Re: Topband: big K9AY-loop + MFJ 10126
From: K4SAV <>
Date: Sun, 23 Dec 2007 10:44:11 -0600
List-post: <>
Johan de Vos wrote:

>Hi all,
>In have set up a loop which is twice as big as the normal K9AY loop; a
>little more noise, but signals are much louder. I was able to work V8 and
>could hear AH2L easily. Question is, what will be best size to have the
>optimum S/N. Does anyone has experience with this?
>Another experiment is 2 verticals spaced ¼ wave (40m apart) tuned for 160m.
>The verticals are 6 mtrs long and in use with the MFJ 1026. It works, but
>not as good as the K9AY loops. So next experiment will be 2 x k9ay loops
>spaced 40m in combination with the 1026. 
>I also tested beverages here, but K9AY was still the winner at my location.
>3Y0X was better to hear on the K9AY then on the 300 mtr beverage! I live
>near a river, so to much reflections to have proper working from the
>Conclusion: to improve the gain here, I have to work further with the K9AY
>73'Johan PA5A   

The best size for a K9AY (or EWE, pendant, flag, etc) is a compromise 
between gain and lobe shape.  As you go down in frequency the shape of 
the lobes of these antennas gets better but the gain drops very 
quickly.  The size recommended for the K9AY is a good compromise for 
160, 80, and 40.  Making a K9AY twice as large will give more gain on 
160 but the pattern will be a little worse.  You will probably find that 
this antenna will be very poor or useless on 40. 

There are many ways to mess these antennas up so that they don't perform 
properly.  The most common problems are insufficient transmission line 
decoupling and interaction with other antennas.  The lower the antenna 
gain, the tougher these problems become.

To answer your question, the optimum size is as small as you can get it 
without having insufficient preamp gain, intermod problems in the 
preamp, and common mode transmission line problems.

Two verticals spaced 1/4 wave apart and properly phased endfire should 
out perform a single element K9AY.  If it doesn't then something is 
wrong in the vertical phasing.  In the horizontal direction performance 
should be very close, but in the vertical direction the phased verticals 
will be much better, so the signal to noise ratio should be better on 
the verticals.

Two K9AY loops (or two EWEs, flags, pendants, or other similar loops) 
phased end fire, will be a very large improvement over a single 
element.  It is also more difficult to build these and make them work 
properly.  Because the front to back and front to side is much greater, 
it takes a lot less stray signal to mess them up.  It really doesn't 
matter which of these loops you use.  If properly constructed, the 
performance will be essentially identical.  There will be some 
differences in managing some of the parameters, since some are more 
sensitive to ground impedance, and some are more sensitive to feedline 
coupling, but if these problems are managed properly, the performance 
will be the same.

A Beverage antenna constructed properly will easily beat a K9AY.  The 
break-even point on 160 meters for a single element K9AY and a Beverage 
occurs at a Beverage length of about 100 meters.  As frequency goes up, 
the Beverage gets better and the K9AY gets worse, so at higher 
frequencies the break-even point is a much shorter Beverage.  This is an 
approximate break-even point because the shape of the curves isn't 
exactly the same.  When you try to make them the same performance, 
typically the loops will be slightly better in the vertical direction 
while at the same time the Beverage will be slightly better in the 
horizontal direction.  If your 300 meter Beverage is being beaten by a 
K9AY, then something is wrong with the Beverage.  I would suspect 
insufficient transmission line decoupling, improper termination, or a 
very poor ground connection.  It is unlikely that a river will upset the 
Beverage, unless it contains salt water.  It may also be that the signal 
you are listening to is out of the beamwidth of the Beverage.  The 
beamwidth of a 300 meter Beverage should be about 56 degrees azimuth.

Jerry, K4SAV
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