The Wellbrook K9AY Antenna
Text by Guy
Atkins, photos by Don Nelson
K9AY is a commercial version from Wellbrook Communications
in the UK. The total loop circumference is determined
by the user; I sized this K9AY as 86 ft. loops.
Shorter circumferences could be used for shortwave-only
Wellbrook K9AY antenna I purchased incorporates
a low-noise 15-dB preamp; a version without the
preamp is also available. The preamp circuitry is
of excellent quality, with very high IP2 and IP3
specifications. The model with the preamp sold for
140 GB Pounds at the time of writing, including
shipping to the USA. This price was $230 US at time
of purchase. For current pricing, see their website.
For MW DX it performed admirably
and equalled the performance of Beverage antennas
at times. However, it was easy to miss a het or
audio on a split frequency because of the controls
need critical adjustment (i.e. it's not a good antenna
to use while scanning for hets between domestics).
An email received from Andy Ikin of Wellbrook suggests
that bandscanning with the K9AY on mediumwave can
be improved by disconnecting the antenna from ground
and turning the null control (pot) fully clockwise.
Alternatively, a relay controlled jumper could be
used to connect the ends of the loops, essentially
turning the K9AY into an omnidirectional longwire.
Modified in the above fashion,
the DXer would seek out hets or audio using the
K9AY in omnidirectional mode, and then switch to
high directionality to optimize reception and reject
K9AY's directionality--considering its size--is
remarkable. Front-to-back ratio of 30-40db is typical,
which is enough to completely eliminate many co-channel
stations on mediumwave. There occasionally seems
to be a slight reduction in domestic channel splatter
when using the K9AY for trans-Pacific MW DX targets.
On shortwave the K9AY is a low
noise omni-directional antenna, filling in the gaps
between the Beverages' coverage. For my afternoon/evening
Indian and African loggings, the K9AY was consistently
the best antenna (often the *only* antenna hearing
the DX). "On target" Beverages, such as
those we aimed due west for Papua New Guinea, always
gave clearer signals on PNGs than the K9AY. It's
tough to beat looking "down the barrel"
with a Beverage antenna!
I used a fiberglas telescoping
mast from German amateur DK9SQ to support the K9AY.
It extends to approx. 33 feet, but I only used 26.5
ft of the height for the antenna. Further information
on the DK9SQ mast and pricing can be found at Kanga.
Wellbrook supplies the interface
box (attached to mast), approx. 100 ft. of 2-conductor
wire for loop selection, and the control box which
sits next to the DXer's operating position. The
DXer supplies a 12vdc regulated linear power supply
or battery (300ma draw), coax (50 or 75 ohm will
work) between the interface and control boxes, loop
wire, a supporting mast or other structure, and
miscellaneous hardware as needed to complete the
K9AY. Clear, detailed instructions are provided
by Wellbrook Communications.
Further information on the K9AY
are found on Wellbrook's website. The article reference
for the K9AY design is QST, September 1997, p.43-46
with additional commentary on p. 77-78 of QST, April
photo shows the relative height of the mast when
used for the K9AY during a recent Grayland (check
out the 360 degree
panorama image of the site, 550k), WA DXpedition.
The motel building shown on the left is a weather-beaten
structure within 1000 ft. of the Pacific Ocean.
The picture is touched up to indicate the two opposing
loops and their support ropes. The DK9SQ mast is
extended to 26-1/2 feet, although it can be increased
to approx. 33 feet. Each section of the mast is
triple-reinforced fiberglas, with black UV resistant
coloring. The sections are carefully hand made,
and the fit of each piece is very precise. Note
that this mast is a separately purchased item, from
the Kanga website.
I chose to use a painted, round
board as a transportable base for the K9AY. A rubber
"pipe cap" from a plumbing supply house
provides a cushioned surface for the bottom of the
DK9SQ mast. Tent pegs hold the board to the ground,
and elastic rubber "bungee" cords keep
the mast vertical during 1-man antenna deployment.
The ground wire is shown attached to a brass stake,
from which four counterpoise wires fan out beneath
the two 90-degree opposed loops. The far ends of
the four insulated wires are wrapped around the
loops' support rope tent pegs (metal), but are not
electrically connected. If better grounding is desired,
the wire ends could also be grounded via the metal
tent stakes. I used a black plastic film cannister
to help protect the BNC coax fitting from the elements.
To hear the K9AY in action,
click on the file name. If the file will not
play directly, download to your computer by
right-clicking (PC) on the filename, choosing
"Save Target As.." and then play
the audio clip.
kHz JOUB, Akita Japan, 1100 UTC Dec. 19, 1999.
Heard at Grayland, Washington State, USA.
Equipment: JRC NRD-535GS (Gilfer) receiver
with full Kiwa modifications. Recording: Sharp
MD-R1 Minidisc. Alternate antenna: 1000 foot
terminated Beverage antenna (oriented 290
0-15 Seconds: K9AY (optimum
16 -25 Seconds: Flip of Beam Reversal switch
26-40 Seconds: K9AY (optimum setting)
41-50 Seconds: 1000 Ft. Beverage antenna
51-60 Seconds: K9AY (optimum setting)
1:01-1:10 Seconds: Flip of Beam Reversal switch
1:11-1:25 Seconds: K9AY (optimum setting)
1:26-1:35 Seconds: 1000 Ft. Beverage antenna
Note that adjacent channel
splatter is slightly reduced with the K9AY
compared to the Beverage antenna.
This view shows how fishing swivels
are used to attach the loop ends to the mast via
"D" rings from a hardware store. A hose
clamp (carefully tightened, not too much) attaches
the strap-ends of the "D" rings to the
itself. A long cable tie keeps the interface box
in place on the mast. I also put a few wraps of
friction tape between the mast and the interface
box to help keep it from slipping. The coax lead-in
and 2-conductor control wire can be seen exiting
from a weatherproof fitting on the bottom of the
Not shown in any of these photos
is the method I chose for attaching the apex of
the loops to the top of the eighth mast section.
I plugged the top of the eighth section with a 5/8"
rubber stopper (cork), and then slipped a 2"
length of 5/8" rubber heater hose over the
top of the mast section. A thick-walled PVC tubing
"end cap" (plumbing store) is slip-fitted
over the rubber tubing. Two small but sturdy metal
eyelets are screwed into the thick sides of the
end cap; these provide attachments for the loops'
apex via more fishing swivels. The purpose of the
rubber tubing and the stopper is to protect the
thin fiberglas mast section from distortion, crushing,
or breaking from lateral forces on the mast. Overall,
the DK9SQ mast seems sturdy and flexible but I didn't
want to take chances in the high winds often encountered
at the Washington State coast during DXpeditions.
close-up shot of the base and counterpoise. Rather
than using the bungee cords to assist during setup,
the DK9SQ mast could easily be configured with a
set of guy wires at the bottom, or second from bottom,
mast section. Care should be taken to avoid excessive
strain on the mast so that the sections are not
crushed by hose clamps nor distorted by tension
from the supports or guys. The sections of the mast
are manufactured to close tolerances, and excess
force on the tubes could affect the telescoping
of the mast.
The control unit features
a switch to choose between loop A or B, a switch
to reverse the beam (directionality) of each loop,
and a null control (potentiometer). (NOTE: Wellbrook
has changed the design of the control box recently.
New versions used a rotary switch to select directions.)
Received signals and variable DC voltages travel
on the coax which enters the box at a BNC connector
on the left. A length of coax with BNC connector
on the right of the box carries the final signal
to the receiver. A coaxial style female jack is
also on the right side for powering the unit, and
two screw terminals are on the rear (for connecting
the 2-conductor wire).
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originally published in Dec. 1999 on Numero Uno