– the antenna for serious MW DX-ing
By Bjarne Mjelde, Norway
K9AY web group, September 19, 2000
Above is John Bryant’s 3D impression of a 2-loop K9AY.
K9AY loop is with little doubt the "hottest" DX gadget among serious
DX-ers today. The Wellbrook K9AY has been widely acclaimed by
many DX-ers, 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
for those not familiar with the Wellbrook Communications K9AY
The antenna uses two, or four, delta-shaped loops to provide a
steerable cardioid pattern in 90° or 45° steps.
A remote controled 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 quality.
The K9AY comprises of an Antenna control unit and two Antenna
head units. A 10-15dB 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
It is recommended that the loop be erected using a vertical support
7 meter high, the width should be 5 meters from the vertical support.
was made by Wellbrook Communications. Because I live only 4.5
km from a 250kW Loran C station on 100 kHz, I asked that the circuit
be made especially to meet the challenge from this extremely noisy
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
go round corners).
After 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 storms.
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 Communications.
– benefits and drawbacks
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.
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 be nonsense.
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.
comparisons are made with the loop’s amplifier ON, unless notified.
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:
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.
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 level:
Rossii Murmansk 657
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 3-5dB 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 has consistant
lobes as stated under "Comparison - …"? Evidently 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 loop’s 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 antenna’s
exact azimuth one would have to place it on a rotor and measure
every few deg. 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 to ambitious for me to enter).
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 –123dBm. I then connected the beverage on an empty frequency
(1500 kHz) at daylight. The readout was –122dBm. When I connected
the K9AY, readout varied between –119 and –120dBm on the 8 directions.
Considering that the 10-15dB amp was on, this is truly excellent.
With amp off, it was down to –123dBm. In comparison, the beverage
connected to Wikander’s preamp gave a readout of around –116dBm.
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
250kW 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 it’s just a pain. 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.
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.
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 aren’t 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 10dB 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 6-10dB 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 stand
difference in signal levels
by 1-3dB is, when using one’s 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
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 to speak.
is of course one other advantage with the beverage, as a two-three
beverage array towards one area (like North America for a European
DX-er) 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.
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 10dB 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 10dB preamp to the K9AY did not cause
any intermodulation problems. There is however a general rule
that signal level not be increased unless it’s 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.
ultimate test, as
I see it, would be the K9AY’s 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 stations.
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.
noise level was so low that I could actually hear stations with
100% readability at a –118dBm 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. Readabiltiy
enough, the beverage isn’t optimised for 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.
Communications claims nulls of typically 20dB, with up to 40dB
nulls in some cases. From what I’ve 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 40cm deep, certainly
inferior to the 1-1.5 meter rods into moist clay that I’ve heard
On daytime signals from local stations, I was first able to null
around 20dB. This didn’t seem satisfactory, so I recalled an article
written by Nick Hall-Patch some years ago about using salt water
to enhance short ground rod’s grounding abilities. This seemed
to help, as I did null the local NRK by 32dB (and later up to
47dB) at daytime. However nulls were less profound during darkness.
In general, I’m able to obtain nulls in the 10-20dB region on
skywave signals and 20-35dB 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 on Hard-Core DX.
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 don’t 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
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.
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 >40dB
easily, and had nulls of 10-30dB on several other frequencies.
Since a phaser (like the APU100 or the more widely spread MFJ1025/1026)
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 from Iran…OK
so conditions were extremely auroral at the time but still!
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. That’s 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.
be honest, I don’t 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 to test. For most
purposes the K9AY is excellent for SWL and probably for DX-ing
too, except it’s lack of directionality may give more noise than
a beverage antenna directed at a specific area. John Bryant has
an extensive discussion on this topic.
few words if you consider setting up the loop with a fiberglass
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 DK9SQ’s mast.
is without doubt the antenna for those who want to do serious
MW DX-ing 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 the four-loop version runs at GBP
165. 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, it’s 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, it’s 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 less room)
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
Well done, Gary Breed and Andy Ikin!
Internet mailing list
DX Internet mailing list
© Bjarne Mjelde, 2000. Reproduction is allowed,
provided credit is given to the author and HCDX.