Impressions and a field test
K9AY loop antenna
The K9AY loop is with little doubt
the "hottest" DX gadget among serious
DXers today. The Wellbrook K9AY has been widely
acclaimed by many DXers, and several articles have
been written about it, among others by Guy Atkins
and John Bryant. Having proved brilliant performance
despite its size, I felt tempted to buy one of these
A brief introduction for those
not familiar with the Wellbrook Communications K9AY
loop: The antenna uses two, or four, delta-shaped
loops to provide a steerable cardioid pattern in
90° or 45° steps. A remote controlled variable termination
allows the user to optimise the null during changes
in the arrival angle of interfering signals, and
provides a considerable improvement in reception
The K9AY comprises of an Antenna
control unit and two Antenna head units.
A 10-15 dB broadband amplifier is selected by a
front panel switch on the control unit. In addition,
the control unit consists of a direction switch
(8 directions, 4 directions for the 2-loop version),
an Omni switch to select all loops, and a nulling
It is recommended that the loop
be erected using a vertical support 7 meters high,
the width should be 5 meters from the vertical support.
Above is John Bryant’s
3D impression of a 2-loop K9AY
was made by Wellbrook Communications. Because I
live only 4.5 km from a 250 kW Loran C station on
100 kHz, I asked that the circuit be made especially
to meet the challenge from this extremely noisy
RF source. I ordered the vertical support from Germany;
the radio amateur DK9SQ Walter Spieth manufactures
a black fiberglass mast 10 meters high that is just
about perfect for this. My loop was made with a
height of 8.5 meters, width 5 meters, grounded with
a single copper pipe and counterpoises under each
loop. The distance to the nearest building (and
RF source) is some 30 meters. The coaxes run some
50 meters each (they had to round corners J
some trial and error during the setting up of the
loop, I finally made it stand rather perfectly vertical.
I used guys at 1 meters and 6 meters. In addition,
the loops themselves are fastened in a way that
brings additional support to the mast. I think it’s
fairly solid and it has survived its first gale.
The truth will emerge with the autumn and winter
The equipment used for testing
and comparison were the following:
- The Kneisner & Döring
KWZ-30 broadband receiver. This excellent receiver
has one feature not found on other receivers in
its price segment – a very accurate field effect
digital readout in addition to the usual S-meter.
Thus I’m able to detect differences in signal
levels not measureable when using an S-meter.
- A 200-meter bidirectional
beverage. It is directed towards ENE-WSW and is
very efficient with regards to signals from Asia
and Western Europe/South America.
- The K9AY loop
- A broadband ultra-linear combined
2-way splitter/preamplifier/wave trap made by
Stefan Wikander of Sweden.
- A broadband ultra-linear combined
4-way splitter/preamplifier made by Wellbrook
Comparison – benefits
The beverage has a distinct front
and back lobe, while it attenuates signals from
the sides quite well. Of course, the lobes are not
consistant throughout the MW spectrum, as its 1-wavelength
lobe at 1500 kHz is considerably sharper than its
½-wavelength lobe at 750 kHz. Since the K9AY have
consistant lobes, this indicates that comparisons
be made with that in mind.
Because of the beverage’s lobe
properties, any comparison between that and the
K9AY has to be done with stations being within the
beverage’s front or back lobes. Comparing the K9AY
with the beverage in the latter’s side null would
Of course one should have had
3 or 4 beverages to compare with. Since that is
not the case, we can only do the best out of it.
All comparisons are made with
the loop’s amplifier ON, unless notified.
For those not familiar with how
field effect in dBm is related to the usual S-meter
readings: Approx. 6dB is one S-unit. The table below
may serve as a guide:
It has been said that the K9AY
has a uniform nearly 270-degree main lobe, and a
sharp, V-shaped back null. Mark Connelly once described
it as "heart-shaped". This may be true
for the 2-loop K9AY, but the 4-loop K9AY seems to
have a different signal pattern.
Nulls are present not only in
the back of the loop, but on the sides too. The
below table shows the signal levels of daytime signals
from NRK Vadsø 702 and Radio Rossii Murmansk
657 when using the null control to minimise signal
NRK Vadsø 702
R. Rossii Murmansk 657
This not only shows that
one can null a signal on the 90° and 135°
sides of the loop (in addition to the 180° null),
but it seems to confirm a finding made at a Grayland,
WA DX-pediton, namely that the loop has a distinct
and relatively sharp front lobe that is more sensitive
than settings 45° away. The South-East position
(in bold) is the approximate bearing of the stations.
We see that 45° away, the signal is 3-5 dB weaker.
Not a substantial amount I admit, but nevertheless
quite interesting. The difference in gain seems
to increase with wavelength, as tests on stations
below 600 kHz suggested even greater differences.
Above 1300 kHz the difference is difficult to measure.
So, does the loop have consistant lobes as stated
under "Comparison -
not! It seems to have a narrower lobe with increasing
wavelength, contrary to the beverage which has a
narrower lobe with decreasing wavelength.
The table seems to suggest that
using the nulling control, the loop has a 90°
(or possibly even <90°) front lobe, approximate
nulls of 15-20dB at 90°, approximate nulls of
>20dB at 135°, and nulls >25dB at 180°.
In other words, nulling increases with angle from
the loops plane.
The null levels 90° away
from the bearing are not uniform, as one would expect
them to be. This could be because the bearing of
the stations are not exactly aligned with the plane
of the loops, and that the side null is rather sharp.
To find the antennas exact azimuth one would
have to place it on a rotor and measure every few
degrees. The coarse 45-degree steps are insufficient
in finding exact null values or any "hidden"
side/back lobes (except if using mean values of
a large number of stations covering all directions.
That project would be too ambitious for me to enter).
The K9AY is claimed to be as
silent as a T2FD, and more silent than an ordinary
longwire. To find out about this, I first measured
the signal reading of the KWZ-30 with no antenna
load. This read as 123 dBm. I then connected
the beverage on an empty frequency (1500 kHz) at
daylight. The readout was 122 dBm. When I
connected the K9AY, readout varied between 119
and 120 dBm on the 8 directions. Considering
that the 10-15 dB amp was on, this is truly excellent.
With amp off, it was down to 123 dBm. In comparison,
the beverage connected to Wikanders preamp
gave a readout of around 116 dBm.
Another aspect of the noise problem
is the Loran C. Some of the readers may be informed
about what this 260-meter high tower, equipped with
a 250 kW transmitter, operating on 100 kHz only
4.5 km away does to my beverage antennas. The only
remedy that partially cures the pain is a wave-trap
designed for attenuating signals on 100 and 200
kHz. Several attemps to make highpass filters to
attenuate signals below 500 kHz have fallen short.
The noise makes DX impossible
in the 550-590 kHz range, and is a major disturbance
to DX between 890 and 1100 kHz. On other frequencies
its just a pain in the as sorry, neck.
I have noticed that the noise level increases with
the length of the antenna. Hence, I had hopes that
the short wires of the K9AY could have a positive
effect on the Loran C noise. A test of the Wellbrook
ALA100 loop (16-meter circumference) in 1999 proved
that this could indeed be the case.
And it did. Surely, the Loran
C is noticeable on the frequency ranges mentioned
above. However, the noise level is significantly
lower than with the beverage. And more: It is possible
to null the noise completely with some of the direction
settings. That alone nearly justified the cost and
labour with the K9AY. A test with the Iceland 189
kHz station comes to mind; with the beverage one
could barely hear that there was "something"
behind the noise. With the loop, Iceland was totally
in the clear with practically no noise.
Local or semi-local daytime signals
are roughly equal level on the loop and the beverage
on the lower part of MW, slightly higher advantage
loop on the higher part. Now, since local MW stations
arent the reason why I bought the K9AY, I
did a sunset/post-sunset comparison with long-distance
signals (mainly from Japan, China, Taiwan and The
Philippines). Comparison was difficult because the
beverage signals fluctuated as much as 10 dB while
the loop signals were extremely stable. Conditions
were generally poor, with an A-index of 16 and unsettled/minor
storm geomagnetic levels.
Generally, the beverage had a
1-4 dB higher signal level on the middle and higher
parts of the MW band, while on the lower part the
difference was around 6-10 dB or roughly 1 S-unit.
Comparing a (although modest length) beverage directed
at its main target, and observing the K9AY playing
practically at the same level was most rewarding.
Of course, one should expect that the difference
in signal level would increase with the length of
the beverage, and that e.g. a 1000-meter beverage
would outperform the K9AY by a solid margin. Will
all owners of an array of 1000-meter beverages please
A difference in signal levels
by 1-3 dB is, when using ones ears, nothing.
I was unable to detect any differences in audio
that would suggest that the two antennas performed
differently. Had I not had the measuring equipment
to help me, my conclusion would have been that there
was no difference at all.
Other users (such as participants
to the Newfoundland and Grayland DX-peditions) have
reported that a beverage directed to a specific
area will perform better than the K9AY for stations
from that area. This corresponds with my experience,
but will not play a major role until the beverage
reaches a length well above 200 meters. However,
a long beverage with a narrow lobe will leave areas
uncovered. Unless one has a large beverage array
(such as Lemmenjoki, Finland), the K9AY will do
very nicely in "filling the gaps", so
There is of course one other
advantage with the beverage, as a two-three beverage
array towards one area (like North America for a
European DXer) will have the ability to separate
stations from different parts of the continent,
while the K9AY will tend to hear all parts at once.
Possible result: Fewer stations to reach a readable
level than with the beverages.
Will the K9AY permit further
amplification? During winter days here in the Arctic,
signal levels are often low, and beverage antennas
are often amplified to let that rare DX come through.
As far as I can tell, the K9AY can stand another
10 dB amplification in the form of an excellent
quality preamp without problems, provided that signal
levels in general are on the low side. Intermod.
from the Loran C appears very quickly if linearity
is compromised; connecting the Wikander 10 dB preamp
to the K9AY did not cause any intermodulation problems.
There is however a general rule that signal level
not be increased unless its necessary. One
should comply with that. For all I know, K9AY users
in RF-plagued parts of the world, such as Central
Europe or North America, may be best served by having
the amp switched off altogether.
The ultimate test, as I see it,
would be the K9AYs sensitivity in a low-noise,
ultra-low signal level environment, as one often
experiences during winter days here in the Arctic.
I had a chance to find out as the geomagnetic field
finally settled to "quiet" with an A-index
of 5. This would enable loggings of North American
I pulled out of bed just at sunrise,
to discover that there were weak East Coast signals
on frequencies like 1520, 1500, 1200, 1150, 950
and some others. I first used the loop with the
KWZ-30 and the beverage with the AR7030+, and then
swapped receivers since the AOR is slightly more
sensitive than the KWZ-30.
The noise level was so low that
I could actually hear stations with 100% readability
at a 118 dBm signal level. No European interference
was present on the frequencies I checked. I was
very surprised to learn that the K9AY played at
equal terms with the beverage on all frequencies
down to around 900 kHz. Below that the K9AY was
less sensitive than the beverage, but still only
marginally so. In fact, since I could null the Loran
C so effectively, readability was on several occasions
better than with the beverage. The stations were
audible (though still at a very low signal level)
well past sunrise. When connected to the AR7030+,
I could use the internal preamp in addition to that
of the loop without any problems. Readability improved
True enough, the beverage isnt
optimised for East Coast North America (ECNA) reception
with its direction somewhat to the South of the
continent. But it was the best ECNA performer in
my previous 2-beverage array towards North America,
so I feel that the comparison was pretty fair.
Wellbrook Communications claims
nulls of typically 20 dB, with up to 40 dB nulls
in some cases. From what Ive learned, a proper
ground system is critical for this to take place.
This is a problem here where the ground is generally
rocky and/or stony beneath a 10-20 cm thin layer
of soil. My original ground rod was 40 cm deep,
certainly inferior to the 1-1.5 meter rods into
moist clay that Ive heard some have.
On daytime signals from local
stations, I was first able to null around 20 dB.
This didnt seem satisfactory, so I recalled
an article written by Nick Hall-Patch some years
ago about using salt water to enhance short ground
rods grounding abilities. This seemed to help,
as I did null the local NRK by 32 dB (and later
up to 47 dB) at daytime. However nulls were less
profound during darkness.
In general, Im able to
obtain nulls in the 10-20 dB region on skywave signals
and 20-35 dB on local/semilocal signals. This is
good, but you need to work on the grounding systems
to maintain this level. I have heard other K9AY
owners having a problem with nulling, and I suspect
that insufficient grounding may be the problem.
I modified the ground somewhat by introducing another
rod, and connected the counterpoises and ground
lead to the head unit for two loops onto each rod.
I also interconnected the counterpoises at the far
end. Anything better than this is hard to get. It
remains to test the Bentonite solution suggested
Unlike a phasing system, when
you have obtained a null from a station in a specific
direction, the null is consistent over a large bandwidth.
This means that you dont have to retune the
loop when you move to another frequency, given that
interference comes from roughly the same direction.
Scan the MW band with the null on and the noise
level on every frequency is like if you switched
on an attenuator. Compared to an antenna phasing
system, nulling on the K9AY is much less time consuming.
I have also fed two receivers
with output from the K9AY via splitters. I tested
two different active splitters with this setup,
and there was no noticeable difference from using
only one receiver.
Phasing? With a K9AY loop? Well
yes, actually. The Wellbrook K9AY has an Omni switch
to select all loops instead of only one. I thought
that in its Omni mode the K9AY should behave rather
like a vertical antenna, such as an Inverted-L.
To put this "theory" to test I connected
the K9AY and the beverage to a Wellbrook APU-100
antenna phaser. And it worked! I nulled the local
NRK 702 by >40 dB easily, and had nulls of 10-30dB
on several other frequencies.
Since a phaser (like the APU100
or the more widely spread MFJ 1025/1026) is not
only capable of nulling, but enhancing as well,
I also achieved considerable gain increase on many
frequencies. I used the AR7030+ for this test so
I have no exact numbers except the general term:
It works! The most stunning example was eliminating
the semi-local NRK-702 kHz to bring a clear signal
OK so conditions were extremely
auroral at the time but still!
One may ask why one would use
an expensive antenna like the K9AY as a noise antenna
with a phaser, when one can be perfectly well covered
with a simple design like an Inverted-L. Thats
not really the question. It simply adds versatility
to the K9AY and reduces the need for putting up
more antennas. On the other hand, adding boxes like
the K9AY control unit, the phaser control, preamps,
antenna switches etc. really messes up your radio
shack. Or so my spouse says.
To be honest, I dont tune
the SW bands very much, except for the odd newscast
from BBC World Service. Compared to the beverage
again, the signal level is very much higher
so high that one should switch off the amplifier.
I have detected mild directionality on SW up to
the 49 meter band propagation has left the
lower bands empty so there was really nothing much
For most purposes the K9AY is
excellent for SWL and probably for DXing too, except
its lack of directionality may give more noise
than a beverage antenna directed at a specific area.
John Bryant has an extensive discussion on this
A few words if you consider setting
up the loop with a fiberglass mast:
The DK9SQ mast have a tendency
of de-telescoping if too much load is applied. This
may happen with the combination of four loops, guys
and heavy wind. It is recommended to use strong
tape or hose clamps to fasten the telescope elements.
Alternatively, one can go for the fiberglass mast
from Von der Ley Kunststofftechnik in Germany; the
elements are locked mechanically instead of having
to rely on friction alone. Alas, the mast is considerably
more expensive than DK9SQs mast.
This is without doubt THE antenna
for those who want to do serious MW DXing and do
not have the space to erect multiple long beverage
antennas. It will null local or semi-local stations
quite effectively, probably far more than any beverage
can do, and with an ability to steer the null as
well. Its gain makes it very effective for any kind
of DX be it nighttime, greyline or daytime.
It is expensive currently
(June 2002) the two-loop version runs at GBP 200
(plus postage and packing GBP 15). You also need
to cash out for wires, coaxes, vertical support
(unless you have a nice-fitting tree). But expense
is a relative term. It is expensive compared to
the random longwire, or one or two beverages, but
compared to many active antennas that are commercially
available, its really cheap. The price/performance
ratio is truly excellent. And compared to the GBP
1000+ receivers we love to buy, and considering
that the antenna system is the truly critical part
of our listening station, its definately cheap.
Go buy yourself a DX-One Pro at double the price
and I predict utter disappointment if you compare
it with the K9AY (but I admit it takes up a lot
Hardly! I and many other K9AY
users will undoubtedly gain a lot of experience
during the coming autumn and winter. Hopefully,
by the coming spring, we will have found out a lot
more about this fabulous tool. Well done, Gary Breed
and Andy Ikin!
ADDENDUM: THE "TRUE" BEVERAGE TEST
Those who have read the above
article will have noticed that the K9AY vs. beverage
comparison was rather incomplete, in that I only
had one relatively short (200 m) beverage to compare
with. Hence, the results from that comparison would
not necessarily be valid for longer beverages. I
discussed this in my paper.
Eager to find out more about
how a K9AY loop works compared to beverages, I went
to my resort in Kongsfjord, 34 km SE of Berlevag.
The location there is extremely quiet with 250 m
to the nearest neighbours (actually only three homes)
and no other manmade noise within a 1.5 km radius.
Topographically it's only seconded by the endless
Arctic inland tundra found in Canada, Northern Scandinavia
In Kongsfjord I have erected
four beverages: 380 m beamed at the US West Coast,
450 m beamed at Alaska/Hawaii, 570 m beamed at the
Far East/Western Pacific, and finally 400m beamed
at South East Asia/Australia. Although a comparison
with beverages still leave the really long ones
(1000m +) untested, I feel that with this array
it is possible to make a more valid test. Two reasons:
I have four bearings, and the beverages themselves
are 2-3 times the length of my Berlevag beverage
(which by the way has been discontinued since it
was never able to really outperform the loop). The
K9AY used in Kongsfjord is more or less identical
to that used in Berlevag.
One may remember
that in my article, I measured the difference in
signal level on a no-signal frequency. The beverage
was 2-3 dB quieter than the K9AY with the K9AY amplifier
on. A comparison in Kongsfjord with the 380 m "US"
beverage revealed that the beverage was only 0-1
dB quieter. With the K9AY amplifier off, the loop
was 1-2 dB quieter. It would be fair to say that
the two antennas play at equal terms in this respect.
To control that there was nothing wrong with the
"US" beverage I also tested the "Far
East" beverage. The signal level was identical
with the "US" beverage.
High signal level
During periods of high signal
levels, i.e. during darkness, the K9AY compares
quite well with beverages. The beverage has the
edge with regards to stations in the bearing of
the beverage, but the loop plays at equal terms
with stations located 30-40° away from the beverage's
The beverage lobe is however
sharper and produces less interference from stations
30-40° and more from its bearing. The K9AY has
a broader pick-up zone. In our setting, the beverages
made it possible for us to separate stations from
Japan and the Philippines by selecting the appropriate
beverage, while the K9AY brought both. In several
instances, the K9AY was able to reduce interference
"from the back", sometimes resulting in
increased readability of the desired station.
This is where -
not unexpectedly - the beverage excels. As mentioned
in my previous paper, local interference is often
not a problem during daylight DX, and the desired
DX often have signal levels down in the -100 to
-110 dBm range. There is really no contest in these
instances. If you want to track down these stations,
there is no alternative to long beverages. It should
be mentioned however, that very few DXers are in
the position (geographically speaking) to be able
to DX rare stations on MW during daylight. Mostly
such DX is confined to areas where the angle of
the sun is very low, and the distance to darkness
is short. The Polar regions experience this during
late autumn and winter.
The results reported under
"Low Signal Level" should not scare anyone
from trying the K9AY. It simply states that no antenna
will be able to perform best under every circumstance.
The K9AY will work brilliantly in a number of settings
- though not in every instance.
K9AY Internet mailing list
HCDX Internet mailing list
W1WCR/Victor Misek (literature)
ON4UN/John Devoldere (literature)
First written in
2000, with addendum in 2001
published on DXing.info on June 16th 2002