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K9AY
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Basics
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info on the K9AY loop
Performance
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How to make your own K9AY
Grounding
The importance of good ground
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Remote
Remote control
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Modifications
to the K9AY loop
By Al Merriman - K4GLU
July 4, 1998
Over the past few months Andy Ikin and myself have been experimenting
with these fantastic antennas.
Between myself and Andy Ikin of Wellbrook in the UK a number of
changes have been made.
Here is a quick rundown.
1. Variable termination using a Vactrol or some other method
is an absolute must! Peak performance cannot be realized with a
fixed resistor.
This is very easy to do. All that is needed is a Vactrol or Andy's
unit that was described recently in MWC mounted in the termination/relay
box in place of the termination resistor; an additional control
line running from the in shack control box to the termination/relay
box at the antenna and a 1K pot mounted in the control box to vary
the voltage.
2. Use of a "magnetic" matching transformer in place of
the one used by K9AY to reduce local noise pickup.
Among other designs the transformer designed by Nick Hall-Patch
years ago works fine. Both Andy and myself came up with this at
about the same time.
3. Ground. For a portable setup a 4 wire counterpoise system
with a wire running under each leg of the antenna works well. For
fixed home use a ground rod is the easiest way to go but the counterpoise
will also work - in fact it is what I use. Suggested by Andy.
4. Separate feedlines for each loop. This was done by me
so that I could use the 2 loops in a phasing setup against each
other in the the few instances where phasing is still necessary.
Although the two loops can be successfully phased against each other
I'm not totally satisfied. I am currently playing with a active
whip antenna - MFJ1024 at the moment but a Dressler ARA60 is ordered
- mounted at the top of the mast just above the loops.
Phasing one of the loops against the whip is working extremely well
so far and will probably be my final setup. I then may revert to
a single feedline for the two loops per the original K9AY article.
I had concerns that the active antenna feedline running down through
the middle of the loops might mess up their patterns but so far
that does not seem to be a problem.
5. Ground disconnect. Discovered by accident that in some
instances nulls could be greatly improved by disconnecting from
ground. So I have added an additional relay to do this.
I have a difficult time describing this, as it is very random. Don't
know for sure why this is, but it seems to be caused by a interaction
between the two loops when ground is removed.
In some cases nulls can be improved on one loop by varying the termination
resistance on the other. Don't ask me to explain it any further
- I can't.
To get the full benefit of this I'll have to continue using two
feedlines instead of going back to one because with a single feedline
a single termination resistance is used used for both loops.
6. Modified the control box so power could be fed to remotely
sited amps. This is not needed if you don't use remote amps.
A 10db or so amp is needed but in shack units - such as the Kiwa
work very well. 7. Separate RF and DC grounds are used in the relay/termination
box. This is to minimize the possibility of noise getting into the
antennas from the power supply. Suggested by Andy.
Of the above listed changes only number one is absolutely
required for maximum performance. |
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