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

[Don Wilhelm]

  Wayne,

I understand your reasons for putting an antenna in the attic, but that 
will offer no additional lightning protection over putting it outside.

An outside antenna will pick up more noise from the house wiring, so why 
go to the trouble.  Even if you mount your loop antenna on short 
standoffs just above the roof (look for electric fence insulators if you 
want to do that, they work very well). it will work better than it will 
inside.

Your idea of just bringing the ends of the wire loop into the shack 
using two pieces of conduit to maintain the spacing between the wires 
will work very well - you would be creating an open wire feedline, which 
is quite efficient.

You will need a balun between the coaxial output from the tuner and any 
parallel transmission line.  Use a current balun.  Many use a 4:1 balun, 
but in many cases (most cases), a 1:1 balun will be better.  If the 
impedance at the shack end of the balanced line is low, a 4:1 balun will 
make it even lower.  You might want to consider the Elecraft BL2 which 
is switchable between 1:1 and 4:1 so you can choose the best ratio for 
each band.

On 4/11/2011 7:11 PM, Wayne Conrad wrote:
> My radio (K2 with the internal ATU) hasn't shipped yet, but that
> shouldn't stop me from putting up an antenna, right?  If only I knew
> what to put up, that is.  That's where I'm asking for help.
>
> 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).  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.
>
> The house is the usual ~60' x ~30 feet and "L" shaped, single story, and
> the major axis is North/South.  The attic is full of trusses and
> fiberglass, but I can get to most of it, sometimes slithering on my
> belly like a snake.  There are the usual electrical wires, network
> cabling (OK, maybe not everyone has CAT6 in their attic), TV coax, and
> AC ducts going hither and thither.  My shingles are asphault.
>
> I have no idea what band or bands I'll be on.  I don't even have my
> license yet.
>
> 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.
>
> I was thinking of open-wire feeder, because I "read on the internet"
> that it might be better for this application.
>
> 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.
>
> I don't know if I need a balun, or even what kind.
>
> 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.  Nor do I know if the
> answer to that question changes if I eventually go QRO.
>
> I don't know if the length of the loop matters.
>
> 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?
>
> Thanks, and best regards,
> Wayne Conrad
>