Losses? I just ran 1/2 wave of generic 450 at 3700 khz through Transmission Line Details and it came up with a .245 db loss.....what am I missing?
First, it does require that you use a 50 ohm load, and
choose the proper feedline type. The old ARRL
"generic" loss values for open wire line were rather
optimistic - it looks suspiciously like they ran the
calculations using the resistance of a single wire
rather than two wires. That's important, as wire
resistance is the primary loss factor at HF (at least
with air or polyethylene insulation).
Types with CopperWeld® conductors will have higher
losses on the lower bands than for pure copper, due
to the copper coating being to thin to keep the RF
out of the steel core. And that effect is particularly
bad with stranded CopperWeld®, where the effective
copper thickness is that of a single strand.
Meanwhile, Owen Duffy's
Transmission Line Loss
Calculator may be more accurate than TLD for open
wire lines - they use different formulas for the loss
calculations. While I'm certainly not in a position
to explain which is better than the other, some of the
plots I've seen show TLLC to map more closely to
measured results.
With a 50 ohm load, TLLC shows 120' of Wireman 551
with a loss of 0.47 dB at 3.7 MHz, and an impedance
of 55 ohms. (The matched line loss is 0.12 dB.)
