[Lowfer] UWL's new loading coil

[Lyle Koehler]

That's a pretty classy looking coil!

When you wind a coil with #14 plastic-insulated house wire, the
center-to-center spacing of the coil comes out pretty close to twice the
diameter of the copper conductor. However, the thickness of the plastic
insulation is probably not proportional to the copper diameter as you go to
larger wire sizes. Then, too, when a coil is basket-wound, it is possible to
push the turns closer together than if it were wound on a cylindrical form.

Yes, the turns will need to be spread if the length is shorter than the
design value. In fact, you may find that the inductance is still too high
when you stretch the coil to its design length, because AWG-COIL is based on
the formula for the "true" inductance of the coil, and doesn't take the
distributed capacitance of the windings into account. A cylindrical coil
with your dimensions would have a distributed capacitance of nearly 50 pF.
At 185 kHz, the "apparent" inductance might be more than 20 mH!
Basket-winding reduces the distributed capacitance effect, but won't
eliminate it completely. So be prepared to do some coil stretching.

I intended AWG-COIL to provide a starting point for coil design, so that the
parameters could be fine-tuned using more sophisticated coil-modeling
software such as Reg Edwards' SOLENOID or Brian Beezley's COIL programs. The
effect of distributed capacitance is fairly small for a "full-sized" LowFER
antenna and a modest-sized loading coil. However, when the antenna
capacitance is small, the loading coil must be larger, which means that its
distributed capacitance is larger, and this in turn will be a very
significant portion of the total circuit capacitance because the antenna
capacitance is so small to start with. In other words, the antenna/coil
calculations go to Hell in a handbasket (or perhaps in a basket-wound coil).

Lyle, K0LR