Don't forget Gary's article in this group's Files section, on PVC loop
antennas:
http://tinyurl.com/yjfd67e
This
calculator may also prove useful although it does not apparently take into
account "distributed capacitance" when the windings are closer together, but
with .5 inch spacing you are probably not affected that much:
http://www.angelfire.com/mb/amandx/loop.html
Tim
C.
--- In ultralightdx@yahoogroups.com,
"farmerik" .> wrote:
>
>
> Still
thinking! The circumference of a 30 inch loop is quite similar to the
perimeter of a 2 foot square, does changing the shape make much difference?
>
> If my memory of High school geometry is correct, a round
loop form could be made from a strip of Masonite 8 feet long which would be
close to 30 inches. Of course it would need 'spokes' or spreaders to KEEP it
round. A 2 foot square loop should be easier to make, if it is just about as
good.
>
> It's Electronics 101, but I still don't have a clear
understanding of the difference of Impedance and Inductance. Do you happen to
know of an Impedance calculator for loops this big? What I am wondering is
there transmission line I could use to mount the loops in the attic, pointing
in a few different directions, and choose the one I want by connecting it to
the radio separately. I just have no idea if that is possible or impossible. -
FARMERIK
>
>
> --- In ultralightdx@yahoogroups.com,
"farmerik" wrote:
> >
> >
> >
OK, now I am getting somewhere, at least in my mind. A 30 inch diameter, with
1/2 inch spacing [I think I need that to prevent capacitance between
windings?] gets me to 258 uH with 15 turns and the wire I chose.
> >
Now I need to think of a coil form that big. Sonotube? Made up from long
strips of Masonite? If I can't come up with a round form, would you happen to
know how to calculate for a square one?
> >
> > -
FARMERIK
> >
> >
> > --- In ultralightdx@yahoogroups.com,
"jim_kr1s" wrote:
> > >
> > >
> > > --- In ultralightdx@yahoogroups.com,
"farmerik" wrote:
> > > >
> > >
> Thanks for the additional explanation, it is clearer to me now.
>
> > > What sort of loop would I wind if I wanted to connect it
directly, and
> > > not use a torrid [or other]
transformer?
> > >
> > > In that case, the inductance
of the antenna has to resonate directly
> > > with the varactor
diode on the chip. Taking into account stray
> > > capacitance in
the connecting wires and the loop itself, design for
> > > about
240 uH. This calculator should get you close.
> > > http://electronbunker.sasktelwebsite.net/InductanceCalc.html
>
> > <http://electronbunker.sasktelwebsite.net/InductanceCalc.html>
It
> > > gives more accurate results for large air-loop coils than
the one called
> > > "Professor Coyle."
> > >
>
> > 73,
> > >
> > > Jim, KR1S
> > >
http://kr1s.kearman.com/ <http://kr1s.kearman.com/>
>
> >
> >
>
