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The Wellbrook K9AY Antenna


Text by Guy Atkins, photos by Don Nelson

This particular 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 performance.

K9AY Antenna Control UnitThe 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 co-channel interference.

K9AYThe 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 1998.

K9AYThis 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.

774 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 degrees)

0-15 Seconds: K9AY (optimum setting)
16 -25 Seconds: Flip of Beam Reversal switch of K9AY
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 of K9AY
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 K9AY Antenna Head Unitmast 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 interface box.

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.

K9AYA 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).

Would you like to comment on the article or ask a question? You can continue discussion on the article and K9AY antennas at the DXing.info Community Forum for antennas.

Published on DXing.info on September 29, 2002
originally published in Dec. 1999 on Numero Uno

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