Mar 30, 2008

K9AY in my backyard

Picture: K9AY in a field day setup during CQWW-CW-2003

The K9AY has clearly proved to be an ideal backyard lowband receive antenna.
With its small footprint of just 9mtr (30ft) and a height of only 7.5mtr (25ft), it will fit about anywhere. Although this is a directional antenna, its horizontal opening angle in the forward direction is e-x-t-r-e-m-e-l-y wide.
Its merit lies in how well it will attenuate local and medium distance signals from the backside.

Exactly what is the K9AY capable of ?
When switching to one of its four directions, you are focussing on finding the best s/n of the DX by choosing which other direction needs to be attenuated.
So in short; you steer the backside pattern to cancel out the interference.

The K9AY has been in many of our contest and/or fieldday setups. Compared to phased verticals and beverages the K9AY has one big advantage; its high angle front-lobe brings you 'little pistols' in the short to medium distance.

Building the K9AY double loop RX antenna
See ON4UN's Lowband Dx'ing about how to build this simple antenna.
Or visit Gary's website at :
So far I have build several versions of the K9AY steering box, using different (scrap)parts, transformers etc.
There is nothing critical in the design.
However make sure your vertical TX antenna is at a distance of about 0.3 wavelength.
If not, the pattern might be such distorted that you end up with no F/B.

A single ground rod about 1m (3ft) into the ground is ok.

We have successfully used a K9AY setup on a mountaintop 2013mtrs asl (6000ft) during our HB0-dxpeditions. As grounding was not possible at this rocky area, we simply used 4 radials under each horzontal loop. That antenna worked extremely well; even the smallest stations within the European area from 160mtrs up to 20mtrs could be heard on the K9AY. Other local antenna's were dipoles, verticals and two Spiderbeams.

Optimal termination
This can be useful if you have the time to adjust to the optimal F/B on a single situation. But at contesting this is not practical. The standard value per band delivers enough F/B already.

For a fixed direction single loop K9AY setup, I reworked the 4 position steering box to choose from 4 different resistance values. Each are optimized for 160/80/40mtrs and it works very well.

The K9AY in my backyard
Having 2 crossed loops in your backyard, taking up all available space is not feasible.
Tripping over the horizontal loop wires is another turn-off, especially when fetching a cold beer from the barn during the dark hours !

During my last Christmas holidays I re-measured the backyard and finally found a single hot spot where I could install the K9AY. I just had to try it; it did only just fit.

The 10m length/50mm dia/5mm wall thickness DJ6NI type fibreglass pole was placed in a large bucket, filled with cement sand. I used the ground connection of my "160m Reference Vertical"which I had temporally removed. The same coax and according heavy common-mode filtering was used.

That is me on the picture. It was pretty cold as you can see some thin snow.

How did the K9AY perform in my backyard?
Directivity was all there; I could easily eliminate some known 160mtr european beacons switching front/back.
But the total "F/B behavior" was not as good as I was used to. Perhaps being so close to the house the pattern wasn't optimal. But then again, almost any antenna out in the field works better.

My biggest concern was the large amount of close-in signals at night. All europeans were MUCH louder compared to the 160m Reference Vertical I was using for so many months now.
Since the vertical has a low-angle "doughnut" radiation pattern, its high angle signals are all attenuated. The K9AY however, does have high angle reception at max gain.
I could hear DX, but the band was constantly filled with strong EU signals :(
I should have realized that up-front.

After 3 days of trying and some further experimenting on fine-tuning the termination etc. I removed the K9AY from my backyard. It did not deliver the improvement I needed.

It is good to have a reference antenna.

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