L. B. Cebik wrote:
>
> scenario: cut your line with precision to keep the equipment adjustments
> flat and minimal or use transformers with attention to proper wx treatment
> for your area and climate for the same purpose, with comparable
> losses--which are negligible in either case relative to all the other loss
> sources that might enter such systems. No wonder folks have claimed
> success for both ways of doing things.
just another thing to throw a monkey wrench in the works...
do some rough calculations:
compare wavelengths at the two busiest frequencies on 80m in contests
300/3.5mhz = 85.7m
300/3.8mhz = 78.9m
difference = 6.8m
shorten by velocity factor 6.8*.66(?)=4.5m
so the wavelength changes by 4.5m in the hardline (even assuming the
smallest
velocity factor i know off hand) from 3.5 to 3.8 mhz. this ammounts to
about
an 8% or an almost 30 degree change for a one wavelength line. go to 2
wavelengths
and the shift is almost 60 degrees.
so cutting to a half wavelength multiple is not so easy, unless you are
restricted
to a narrow bandwidth. similar effects can be calculated for other
bands, just
remember that the same physical length 'contains' more wavelengths as
you go up
in frequency.
i use random lengths of 75 ohm hardline (cut to fit and never measured)
with no
matching transformers. i do have a couple pieces of rg-11 that i use to
balance
out some bands inside the shack where its easy to play around with
them. and
the losses i have with 50 ohm loads plus home made plumbing fitting
connectors
is so low i could not measure it for sure with amateur grade meters at
hf. i
could see a measureable loss on 2m, but no more than i could attribute
to the
predicted losses from the cable itself.
--
David Robbins K1TTT (ex KY1H)
k1ttt@berkshire.net or robbins@berkshire.net
http://www.berkshire.net/~robbins/k1ttt.html
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