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The
more rods, the better
Patrick Martin, USA
K9AY
web group, September 22, 2000
I just added two more ground rods to the termination point, I I
now have eight.
In checking the S Meter readings during the day, I find the gain
is going up. When I had two, many stations like KORC-820, Waldport,
was almost non-existant. Now KORC is fair during the day much of
the time.
I find the difference between the EWE and K9AY is about 8 DB now.
It used to be more like 20 DB.
So the school of thought of adding more rods and the gain increasing
is right.
I still have three more I can add if I want. I haven't had
the chance today to check out the nulls to see if they changed.
I am wondering what number of groud rods you really need before
it is over kill: 10, 20,30,50?
At the moment I have not installed the var.
termination for the K9AY. The 5K ohm pot I have been using works
OK.
I will be adding a var. termination in time though.
Yes, you need a separate lead to run the power, but I have four
pieces of coax out in the same area anyway. It would be easy to
check out the system using one of the other coax pieces.
Since I don't have the var. resistor installed as yet I need something
more stable, so I want enough rods in the ground that I can set
the poy for the null and leave it there.
I don't have to adjust it often. The null adjustment is "right on
the money" across the whole band.
When I had only one or two rods, depending on what frequency I was
on, the pot had to be adjusted.
Patrick
Martin, K9AY web group, September 22, 2000
George Maroti: What Patrick Martin describes
doing was the very reason for using a Vactrol for the remote termination
resistor. In the original K9AY article, Gary mentions experimenting
with different values of termination resistance, depending on one's
ground conditions and particular frequency of interest. By adding
so many ground rods, Patrick has completely stabilized that parameter,
and can now use a fixed resistor. For those in "average" soil conditions,
a single ground rod with counterpoise wires should be sufficient,
provided a variable termination is used.
Regarding the comparisons between the K9AY and beverages
out on the West Coast (read
more here);
beverages work better over poor ground, so I think when those comparisons
are being made, it may be that the beverages were poorer performers
over the wet ground conditions, not necessarily that the K9AY was
a better performer. It seems that if they were to set up both types
of antennas on the next DXpedition, they'll always have an optimum
antenna for whatever ground conditions they encounter.
If you read Joe Buch's original article, he describes that the K9AY
loop is effectively working as both a loop and ground plane vertical
whip, and the key to obtaining a null is to be able to have the
"vertical whip" voltage cancel the "loop" voltage. The ground conditions
will effect the "whip voltage", so depending on your ground conditions
and termination resistor, you may not be able to cancel the "loop"
voltage.
Another source for differences in performance may be due
to the fact that we all are not using the same model Vactrol. I
recall that some are using a model that is less than a hundred ohms
on the low range. I use a model that is about 200 ohms on the low
range, but is fairly linear between 200 and 800 ohms. Again, depending
on your ground conditions, you may be in a situation where you need
the lower range Vactrol. I'm not sure how linear that particular
model is, it might be better for some, and not for others. It would
be ideal if there were a Vactrol from 0 to 5 kohms, completely linear
in response.
One way to quantify some of these variations would be for
those who are on "good" ground to measure their Vactrol resistance
for deep nulls, and then compare these resistance values with those
who are on "poor" ground. Since I think most of us would rather
be DXing than conducting these science experiments, it would be
interesting to at least hear from various users how much variation
in "tuning" of their Vactrol is required, either depending on changes
in ground saturation, or when changing bands. In Pat Martin's case,
he's pretty much at the point where he can used a fixed resistor.
But, since he's primarily a MW DXer and concentrates on that band,
he might have to change that resistance when he ventures into the
tropical bands.
Still, even with some observed inconsistencies in performance, it's
an impressive antenna for its size.
George Maroti, k9ay web group, November
14, 2000
Patrick Martin: George has some good points
there.
Yes, I am sure by adding the extra rod rods I have stablized the
antenna.
I can still adjust the pot, but with the high winds on the coast
and all I wanted to beable to keep my adjustments stable. I only
need a single loop and to have the pattern directional to the West.
Since I rarely DX the Tropical Bands or any other band, the K9AY
works well as it stands. I do want to add the Varatol in time though.
I still have a couple extra Ground rods I can add it I want, but
the eight I have are doing fine. In comparing the K9AY with the
EWE I have, the K9AY does a better job on cutting down the splatter
on many frequencies, even though the gain is a little less. It is
nice to have both antennas for comparison though.
Patrick Martin, K9AY web group, November 15, 2000
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