Hey Garry:
Interesting! I don't know enough ferrite-core antennae, although in
a way the idea of less turns the better makes sense, in that large
ferrite rods with smaller lengths of wire have more gain than the
tiny ferrites, which must put on more turns to get enough
inductance. In your scenario, might there there still be more gain
by laying on a few more turns of wire, in that the additional turns
would more than make up for their copper losses?
I have a 28" x 42" box loop (essentially a slightly-squashed three
footer), with 10 turns of 16 gauge for 540-1700+ khz and an
additional 17 turns for 150-700 khz. I use two DPDT switches to make
it work, along with a 3-gang (15-450 pf per section w/ceramic posts)
cap. Putting my Quantum Loop in the middle of it makes for some
incredible gain or passive phasing, depending on the circumstances.
I have noticed that, on MW, I have to short out the LW coil in order
to prevent it from de-Qing the MW coil and adding unwanted
inductance.
Kevin
--- In ultralightdx@..., "sloshatron" <wa1gwh@...> wrote:
Kevin;
Interesting situation on the MW vs LW windings used with the same
variable. I know that more turns and less C create a higher
voltage
at the loop terminals. This is handy with crystal set loops
because
the higher performance diodes will work more efficiently with
higher
voltage. But I think this should not make any difference with a
magnetically coupled arrangement like you describe. In fact, if
the
wire sizes for both windings are the same and the windings are the
same size I would think that the shorter winding would be superior
because the total copper losses would be lower in the shorter
length
of wire. And, the capacitor would be used at a higher value to
resonate the pair at the same frequency. Unless the capacitor is a
high quality one (ceramic insulators, no corrosion at joints) it
will
have a higher Q at higher capacity settings. This idea is (once
again!) from a Ben Tongue paper where he documented that a small
receiver type phenolic insulated variable had lower losses at
higher
settings of C.
I suspect that having two loops on one frame might be the answer to
this situation. I believe that unused windings and tapped windings
are usually avoided in constructing high performance loops. Guess
it
depends on convenience and what is desired for efficiency.
How big is your box loop? My current crystal set is a 3' x 3' box
loop of #14 bare solid wire. In the last listening contest in
January I logged about 90 stations with it in a week or so. I
don't
use a spotter radio -- I like to do it all with the crystal set.
Just nuts I guess. Ought to fit in well here!
Garry
near Syracuse, NY
