[TowerTalk] K9AY performance expectations/help

[Doug Turnbull]

Pete,
     Thank you for this thought provoking e-mail.   I had never thought of
using a common mode current choke.   Is this choke mounted at the K9AY or
close to the shack?   I will give this a try.   Another point you mention is
counter to what I had been told previously but you have tried it so perhaps
I should as well.   I have eight short radials running beneath the
horizontal runs of the K9AY previous information was that there was no point
going beyond the perimeter of the two loops.

     In my case the K9AY is mounted in woods about two hundred fifty feet
from the transmit antenna.  I have five short ground rods of only one meter
length each as I hit rock.   The soil is quite wet during our 160M season
this being Ireland and sad to say it has been pretty much saturated though
our summer though the trees do a job of drying the land.  It works for me
and I would not be without the K9AY but your idea of the longer radials
interests me and the use of the choke is something I want to try.   How many
fifty foot radials did you use?   Where is the choke located?   Thank you
for the information.   I appreciate it.

                     73 Doug EI2CN

-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of Pete Smith N4ZR
Sent: 29 August 2009 11:18
To: TowerTalk
Subject: Re: [TowerTalk] K9AY performance expectations/help

After several winters experimenting with K9AY loops here, I have reached 
a few conclusions that others haven't touched on yet.  I can't comment 
on interaction, because my RX antenna is over 300 feet from my TX antenna.

  -- the quality of the ground is quite important.  Your marshland 
should be pretty good, as long as you have a good connection to it.  Try 
laying down a few 50-foot radials in addition to your ground stake.

-- the feedline *must* be decoupled for common mode currents, or else 
pickup on the shield may negate the directivity of the loop itself.  I 
have had very good luck with the ON4UN center-tapped bead choke 
described on the Contesting Compendium at 
<http://wiki.contesting.com/index.php/Common_mode_chokes>.

-- the best indicator of whether the K9AY is "working"  is the signal to 
noise ratio.  Since the rear null is so narrow, you won't often hear big 
differences in signal strength when you switch directions, but for 
signals that are anywhere in the "front 180 degrees", you should hear a 
significant improvement in the SNR.  I just don't think there is any way 
that your vertically-polarized loop should be able to compete as a 
receiving antenna.

-- The rear null is pretty "selective" not only in direction but in 
arrival angle.  This could be the reason that you get seemingly good 
directivity on the ground weave from a local station but not on skywave 
signals.  You might try finding a broadcast signal on the high end of 
the band and a few hundred miles away, and checking the directivity on 
that signal.  The K9AY loop is much beloved by MW DXers because of the 
deep and narrow null, which allows them to listen for weak signals on 
the same frequency as stronger ones.

73, Pete N4ZR
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On 8/29/2009 5:40 AM, Doug Turnbull wrote:
> Scott and Jerry,
>       I am most interested in this thread so thank you for starting it.
> Scott, I find that my Array Solutions K9AY gives me about a 6 to 15 db
> directivity between front and back. Some signals show little directivity
> difference while with others changing the direction is most noticeable.
My
> antenna has proven invaluable in contests to null Europe and listen to the
> States on 160M.   I also find it useful to listen on 80M and find the same
> relative front to back ratio.
>
>       I have never found much difference in adjusting the terminating
> resistance.
>
>       I have a friend, who is a first class 160M operator and EU pioneer
on
> this band, GW3YDX who has never been able to get satisfactory performance
> from his K9AY so I suppose performance is variable but in my case the
> antenna is most useful.
>
>               73 Doug EI2CN
>
>
>
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