Topband: The K9AY on 160

[Gary Breed]

Ford

Comments inserted below...73, Gary, K9AY

> Does anybody have experience with the K9AY (specifically the one sold by
> Wellbrooke out of the UK) on 160?  I would be interested in comments.
>
> My specific questions:
>
> A reference on the Wellbrooke web page that the distance to the antenna
> can't be more than 50 meters.  What's up with that?  I need to run 225' or
> so.  What happens?

As I understand from Andy Ikin, Wellbrooke is making the antenna pretty much
identical to my QST article (Sep '97). Their distance limitation might be
for voltage drop in the control cable. Just use larger wire!  A preamp located
at the antenna will help overcome coax losses and swamp out noise pickup on
the coax itself.  Don't elevate the coax run, bury it or lay it on the
ground to minimize its effect on noise pickup and pattern distortion.

> Can the support be a metal support?  I can place a 30' pole up made of old
> well casings in about 10 minutes.  Plastic or wood turns into a real problem
> for me.  Additionally, does 40' equate to better performance or is the 9
> meter height important?

Metal is OK since it is electrically short at this frequency. For added
"insurance" against interaction, insulate the support pole from ground.

> Are there favored directions?  They talk about 360 degree coverage with
> selectivity between 4 favored directions.  Is it continuously variable or
> should the antenna be oriented precisely to obtain good directivity at NE
>SE NW SW?

A terminated loop is unidirectional with a cardioid pattern. The original
design uses two loops with switching to get four directions. The forward
lobe is very broad, so the value of switching is to move the null for best
noise/QRM reduction.  There have been writeups describing a method that uses
the same two loops to get eight directions.  It works, but adds complexity
to the switching system to get a small benefit.

> How does performance of the K9AY compare to other systems?  Specifically,
> pennants, loops, and beverages.

The pennant, flag, EWE and K9AY loop are different mechanical
implementations of the same principle and will work similarly.  Most of them 
are 20-30 dB down in signal strength from a beverage and need plenty of preamp
gain.  Also, remember that the amount of signal captured is proportional to
the area enclosed by the loop. For example, as published, the EWE is much
larger than the K9AY loop, and will deliver more signal without a preamp.
You can make any of these antennas larger or smaller (within limits) as long
as you accommodate the required change in termination value and feedpoint
impedance.

> Any other observations may be important as well.

The K9AY loop has become popular with low frequency SWLs (or is that LWLs?).
There is a lot of information on the K9AY loop from this perspective on
WA1ION's web sites -- http://members.aol.com/MarkWA1ION/weblink.htm
and http://www.qsl.net/wa1ion/index.html



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