[Elecraft] K2 + ATU + Loop antenna in the attic

[Fred Jensen]

On 4/11/2011 4:11 PM, Wayne Conrad wrote:

> I want to start out with an loop antenna in the attic.  Why loop? Mostly
> the very American idea that more wire must be better, plus it's
> balanced--I hope to not need a separate RF ground, or counterpoises, or
> any of that jazz).

You need a safety ground on your radio, a loop antenna does not normally 
care about ground, except in what ground does to the radiation elevation 
angle.

> Why the attic?  So I don't have to worry about
> lightning protection, and because it ought to be incredibly cheap to put
> up.  I've spent every dime I have on the radio, you see.

Is it the K2/10?  Anything outside will be better.  Trees?  Even 
something laid over the roof will probably work better for you.
>
> I have no idea what band or bands I'll be on.  I don't even have my
> license yet.

That will be a necessity :-)
>
> My thought is that I run the loop around the perimeter of the attic, as
> close to the eaves as possible.  Over the radio bench, I'll punch a hole
> in the ceiling and drop feedline down the wall.

Elevating the wire above the ceiling joists might help some.  Many of 
the "Attic Designs" that have been published seem to use the "open 
space" of the attic rather than out near the eaves.
>
> I was thinking of open-wire feeder, because I "read on the internet"
> that it might be better for this application.

A balun is probably going to be important, the K2 output is inherently 
unbalanced.  Since you will have the ATU, putting the balun at the radio 
will eliminate any losses on the coax.
>
> It occurs to me that I could omit the 4' of feedline and just drop the
> two wires down.  Using the self-adhesive conduit that the hardware store
> sells, I could keep those two wires at "an appropriate distance" from
> each other, and white conduit looks better against a white wall than a
> black cable.  I don't know if that's a good idea, or what "an
> appropriate distance" would be.

2 or 3 cm is probably just fine.
>
> I don't know if I need a balun, or even what kind.

See above
>
> I don't know whether I need to keep the antenna wire off of the rafters
> with insulators, or can I just let it lay there.

That would be a good idea.  Electric fence insulators are cheap and 
would work.

   Nor do I know if the
> answer to that question changes if I eventually go QRO.

I don't know what you mean by QRO, but if it is anything over 10 or so 
watts, with such an antenna, you will likely not like the results :-) 
You also need to do a radiation safety survey which you can find on the 
ARRL web site.
>
> I don't know if the length of the loop matters.

Basically, you're just putting up some conductor and attempting to load 
power into it.  It's a "more is better" situation.  The KAT2 will stuff 
power into some pretty weird impedances, but not all possible weird ones.
>
> As you can tell, the ratio of things I know to things I don't know is
> pretty small.  Can you please help me improve that ratio?

Hope this helps.  Anything you can do outside will probably be better 
than anything you can do in the attic, unless you have CC&R's.