[SEDXC] [SECC] K9AY Loops

[Bill Coleman]

On Oct 2, 2007, at 4:27 PM, Hal Kennedy wrote:
> Its interesting how some subjects that have been around a while  
> sometimes suddenly pop up and become ‘in vogue.”  NN4ZZ and K4DLI  
> have just added K9AY loops for receive, and three different groups  
> and/or individuals have been over to my QTH in the last two weeks  
> to inspect mine.
>
> As far as I’m concerned, you can’t get a better bargain than a K9AY  
> if you don’t have room for beverages.  They are thirty feet in  
> diameter and 25 feet high and they do work.

Hal, you can add me to the list of folks who have recently put up a  
K9AY. Last year, grabbed some spare parts and put up a single half- 
sized loop. Last month, I added a second loop and added relay switching.

Our own Gary, K9AY, was extremely helpful with this project. The  
standard design uses 85-foot loops and requires a 25-foot high  
support. Gary indicated that shorter loops would work as well. I had  
a 44-foot piece of wire available, so I hooked it up and it worked  
great.

Gary's original loops were around 110 feet long, which were too long  
for 80m. My half-size design works pretty well on 80 and 40m, but it  
a bit short on 160m, so signal levels are pretty low there (about 35  
dB down from the vertical).

My support is an oak tree -- passing over a branch about 10 feet  
high. The wires are spread out by draping over the outer branches.  
Ground connection is two counterpoise wires about 10 feet long right  
under the antennas.
> You can buy the one from Array Solutions for significant bux or you  
> can build your own for around $10.  Mine is home brew.
Me, too. It's interesting to put an antenna analyzer on the loop. The  
SWR is flat from 160m up to nearly 30m with a termination resistance  
of 390 ohms (in my case).

I built my loop almost entirely from the junk box. I think the only  
thing that was bought was some stainless hardware for connecting the  
wires.
>   Gary does not recommend decoupling beads on the feedline, but I  
> believe they are a useful precaution to keep common mode current  
> off the shield.
I pretty much followed Gary's original relay switching design, except  
for the matching transformer. Gary used a trifilar-wound 9:1  
autotransformer. Following some tips on the hard-core-dx.com site, I  
opted for a magnetically-coupled 9:1 transformer instead, with the  
windings separated as much as possible.

I used three stacked FT37-43 toroids with 8 turns in the primary and  
24 in the secondary, separated as much as possible on the cores.   
After putting an antenna analyzer on the loop, I ended up pulling one  
turn off the secondary for better match. The FT37-43 toroids are  
pretty small, but they were in the junkbox. Something like an FT80 or  
FT114 would work better, and you wouldn't need three of them.

The magnetically-coupled transformer allows you to electrically  
separate the antenna ground from the feedline sheild, which reduces  
the chance of any coupled noise. Decoupling beads should be unnecessary.
> It’s worthwhile reading.  I have spare cores if folks want to wind  
> transformers – it takes 5 minutes to make one.  I use 2 turns and 6  
> turns, Gary uses 3 turns and 9 turns but our results are the same.   
> Ill be adding a second K9AY soon and phase them with an MFJ noise  
> canceller.  Can’t work ‘em if you can’t hear ‘em.
W8JI has some interesting information on the K9AY loops here:
http://www.w8ji.com/receiving.htm

By Tom's analysis the K9AY Loops have a higher figure of merit than  
either the EWE / Pennant, and are just about 1 dB less than a one  
wavelength Beverage.

So, if you don't have room for a Beverage, the K9AY seems like your  
best bet to improve your receiving antenna.

I know that my loops made the difference between working 3B7C on 80  
and 40m and not working them at all. They were in the noise on my  
transmitting antenna, but copyable on the loops.



Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr at arrl.net
Quote: "Not within a thousand years will man ever fly!"
             -- Wilbur Wright, 1901