Topband: K9AY Loop Revisited

[Tom Rauch]

I hope I don't get into trouble but....

> I'm looking for any helpful tips.  I did order the fiberglass mast, so
> the metal mast ? is solved.

There isn't any evidence that a short metal mast hurts performance, 
but there is strong evidence the antenna is dependent on a moderately 
good ground and that the feedline shield should NEVER be connected to 
the same ground as the antenna. Neither should the mast.  

Of course you can get lucky......
 
> 1.  Can I use high quality RG-58?  The coax run will be about 150
> feet. My gut feel is yes (low loss at 1.8/3.5 mHz), but does it lack
> the proper shielding for anti-noise pick-up?

Factually, almost any coax...even those with poor looking 
braiding....are very good on 160 meters. Terminated or unterminated, 
I've never had a length of cable with shield connections intact, 
grounded or ungrounded at the far end, that hears any signals on 
lower frequencies through signal leakage. I tie-wrapped 30 feet of 
cheap Radio Shack cable with a thin braid to another piece, ran 100 
watts through one cable, and connected a level meter to the other 
cable. I had considerably more problem with connection resistance on 
the shields than with actual cable crosstalk on 7MHz. 

The most important considerations are to not route the cable with 
things that will induce excessive unwanted noise on the shield, make 
sure shield connections are good, and to isolate the shield from 
antenna grounds. Especially with a ground dependent antenna like the 
K9AY. 
 
> 2.  What's preferred, being all things somewhat equal.  Mounting the
> antenna 40+ feet from an overhead powerline (house drop -- 22 foot
> high mast + safety factor) or mounting farther away from the power
> line, but closer to my Hy-tower? (I run 150 watts).

Anyone's guess. Have a look at www.w8ji.com in the article about 
noise and nearfields.

 
> 4. What type of ground does the K9AY loop need?  The installation
> manual says 4 or more 10 foot ground radials will help, other K9AY
> loop articles I've read says ground loss is part of why the antenna
> works.

Ground loss is deleterious to the K9AY, it definitely does NOT help 
it. The K9AY is another form of the EWE and other small terminated 
loops. All of these antennas benefit from good ground, because the 
vertical component of the wires actually receives signals. (In a 
Beverage, it is the voltage drop along earth from loss that lets the 
horizontal wire respond to vertical electric fields)  

The K9AY is especially ground dependent because the termination goes 
to a common ground with the source end of the antenna. Anything that 
disrupts that ground termination or "pumps" it with enough current to 
"wiggle" the ground voltage around will get right back into the 
feedline and eventually the receiver. 

Of course in cluttered environments, sometimes less than perfect can 
actually wind up helping because effects are random! 73, Tom W8JI
W8JI@contesting.com