[TowerTalk] Coil Antennas

[Brian Beezley]

I've added a feature to my coil inductance and Q calculator that can 
help you evaluate a coil as a multiturn loop antenna. The program 
calculates reception factor, a figure proportional to the signal voltage 
a coil produces when resonated with a capacitor. You can experiment with 
coil dimensions to see the effect on receive signal level. The program 
can model circular, octagonal, hexagonal, or square solenoids that use 
solid or Litz wire.

Originally I used the automatic optimizer that normally maximizes coil Q 
to maximize reception factor. However, optimal coils turned out quite 
long and used large amounts of wire. Reducing coil length by a large 
factor often lowered performance only a dB or two. I'd never want to 
build one of the optimal designs so I removed the optimization function. 
It's easy to design a suitable receive loop by hand. Bigger is better, 
but maximum diameter is limited by practical considerations. Wire size 
is often determined by what's on hand or what's economical. That leaves 
coil length and number of turns. You can vary each with the mouse wheel 
and watch the reception factor change.

Reception factor is useful when you want to minimize reception. For 
example, you can first optimize a 160m matching network coil for highest 
Q and then adjust it to lower direct pickup. This might help maintain 
deep nulls in a directional receiving array or minimize troublesome AM 
broadcast signals.

Recently I greatly improved program accuracy for very short coils. I 
also updated the skin effect and proximity loss calculations so they are 
good down to DC. These changes increase accuracy for coils used as 
low-frequency loop antennas, especially on the 2200m band.

Windows program:

http://ham-radio.com/k6sti/coil.zip

Reception factor reference:

https://rudys.typepad.com/files/coil-antennas-1919.pdf

Brian