> I have heard this point argued for years. "Does trimming the
> coax affect the SWR?"
The answer is NO!!!!!!
> If the length of coax has an affect on
> impedance, then how could it not affect power out?
Changing the length of the line changes IMPEDANCE at the source end
(assuming the VSWR isn't 1:1).
Changling the length of the line DOES NOT change the VSWR on the line.
Both of these statements ignore feedline losses, which are negligible when
we're talking about adding or subtracting a few inches or a few feet of
cable at HF/VHF/UHF frequencies for the kinds of cable we normally deal
with. The more cable loss, the lower the VSWR will be at the source end.
Likewise, the longer the cable, the closer the Z at the source end will be
to the cable's characteristic impedance.
> We strive
> to maintain 50 ohms at the tail of all devices to match the
> end load. GE puts matching networks in their Mastr II's. I
> have taken a MFJ-259 and soldered a PL259 only at one end and
> then started trimming the coax down and watched the impedance
> change significantly with each cut. Duplexers come with
> precise lengths of cabling. I have heard that trimming coax
> only fools the meter. Not being an engineer with millions
> worth of equipment I can only make a SWAG (scientific wild
> ass guess) as to whether coax length makes a difference in power out.
Everything you just said above is right. I think what has you confused is
that you're thinking that Z and VSWR are interchangable. They aren't. Z
changes with coax length. VSWR does not.
--- Jeff
