[Elecraft] Balun with a G5RV?

[Ron D' Eau Claire]

> Look carefully at the tables for transmission line losses in the ARRL
> handbook. Note the losses in the table are for the MATCHED condition. A
> 450 ohm transmission line matches to a 450 ohm load. Because of this,
> significantly less current flows in a 450 ohm transmission line, leading
> to lessor I^2R losses.

Bill, I'm looking at losses for high SWR's, not "matched" conditions. This
data is published by the ARRL and a variety of others although the charts in
current ARRL publications require some extrapolation for really low loss
lines like open wire line.

For example, using 100 feet of feeder with SWR of 20:1 at 10 MHz, the losses
are approximately:

RG-58  = 6.5 dB

RG-8   = 5 dB

"Window" line = < 1 dB

Open Wire line = < 0.1 dB

While ohmic losses are a factor at the current loops, dielectric losses are
a damaging factor at the voltage loops. In lines that depend upon a short
insulator that is in contact with the full length of the wire, such as
coaxial cable with the solid dielectric around the center conductor, the
dielectric losses are typically the greatest factor in line loss. By
comparison, true open wire with a minimum of high-quality insulators will
suffer mostly ohmic losses. Because the losses are almost entirely ohmic,
open wire lines show very low losses even when mismatched at high SWR's.

Ron AC7AC
K2 # 1289