I ran a program written by K6STI, which computes coil losses and the results
are interesting.
Using 28 mhz, the highest frequency of the normal amp, I looked at a 4 turn
coil made of #14 wire with 4 turns on a 3" diameter form and 2" long.
Form loss was calculated as:
Dielectric Loss in %
Air 0
Air Dux .1
Polystyrene .2
Teflon .3
Steatite 3.0
Glass 3.8
Polycarbonite 18.9
PVC 17.0
Porcelain 21.2
Bakelite 24.7
Nylon 28.2
Douglas Fir 31.3
QST in September, 1931 reports on the new National SW-3 receiver. James
Millen notes that bakelite is often made with wood flour (perhaps Douglas
Fir) and has very high losses - especially on 10 and 20 meters. He
recommends the use of National R-39 material.
Colin K7FM
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