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K9AY terminated loops
for 75m |
It is very compact, low noise and directive with an impressive 20 to 25 dB front to
back. You need only a 25 ft high by 30 feet horizontal space for one loop, using a 25 ft
mast.
I attached the mast to one of my fence 4 x 4 post, 45 ft of speaker wire spliced
in two, a small pulley at the top of the mast to lower or raise the wire, two small eye
bolt on the fence, fishing line and two small weight et voilą.
It took more time to make a small PCB with the switching circuit. When I
connected the coax I could hear VK and Japanese stations that were inaudible on my
vertical due to background noise.
Elevation pattern (Termination not tuned properly)
Building details
By switching coax and load you change the direction of max gain. With two loops
you can beam in four directions using a relay switching box and control box.
The relay box will switch the load and feed point (with transformer) in the
branches of the loop. Directivity toward the source. In the picture above the antenna is
beaming toward the right. The crude schematics below will give you an idea if the circuit
needed for two loops.
K1 switches between loops, K2 switches R and feed point. The circuit is powered
via the coax as 0V, -12V and +12V and AC (AC will energize both relays).
I built a K9AY loop for 75m three year ago . I couldn't put the two loops and
made only one toward JAs/VKs and Africa. Results are excellent! It is very low noise
and even if signals are an average 2 S-Units below compared to my 75m linear loaded
vertical, I hear on the loop DX stations that I can't hear on my vertical because they are
buried in noise.
It is an excellent receiving antenna, taking limited space and with the
performance of a beverage.
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