elfa, wrote:

All the devices that have been described by you draw the magnetic
component of the radio wave out of the air, and concentrate it in a core
that has a coil mounted on it. This induces RF voltage in the coil. In
most of these, that coil is connected to a variable capacitor. Both the
coil and the capacitor have a property called reactance, which resists the
flow of RF current. But the two components have reactances of opposite
signs (one positive, one negative), so when you adjust things so the
positive & negative numbers are equal at your frequency of interest, the
reactances cancel, and a large RF current flows. While this does bring in
one more control, the ability to 'peak' the coil to work best ay only one
frequency is usually worth it.

The trick to using this to boost reception is to have a coil that
intercepts more energy than your naked radio does. Ferrite has a high
permitivity (take my word for it), which causes the magnetic field that
would have flowed near the rod to go through it; the rod picks up energy
from a physical space larger than the rod.

Another approach is to build an air-core coil that encloses a lot of area.
This gives up compactness, but is well-suited to home construction with
balsa & plastic.

Unfortunately, another poster was right, unless you can give us some
quantative data about your rod & capacitor, we can't help with a
recommended turns count. To try a guess, start with 40 turns, tune
through your frequencies while tuning your loop's capacitor. When you
find a frequency where the capacitor can peak the signal (orthe noise),
adjust things: remove turns to move the loop's range to higher
frequencies, add to bring down.

Good luck.

--

R F Wieland Newark, DE 19711-5323 USA 39.68N 75.74W
Icom R75 Heathkit GR-81 Inverted-L in the attic
Reply to wieland at me dot udel dot edu