Oops; some corrections to words needed in my post as
sent, corrections below. Also, note my correction to make Bill's,
N3RR, title accurate for what he posts.
Jim
At 00:21 6/28/98 +0100, Bill Hider, N3RR wrote:
>Gentlemen,
>
>Yes, it's true. Sometimes it makes a difference. Sometimes it's significant.
>And there is a reference to go to to determine what it is!!
Unfortunately, the reference you site below, is too a completely
different "it" (loss mechanism)! See on below.
>
>Per the ARRL Handbook, 1994, Chapter 16 (Transmission Lines), page 16-14
through
>16-15, the following is a summary of Fig 26, a graph showing on the x axis: %
>relative power delivered to the antenna; and y axis: VSWR at input end
(i.e., at
>the transmitter) of the transmission line, and a family of curves
depicting the
>transmission line loss at the frequency of interest if the load is matched to
>the line (i.e., the manufacturer's spec dB/ft times # of feet used):
>
>For 1:1 VSWR (at xmtr) and lossless transmission line, % power delivered
to the
>antenna = 100%
>For 1:1 VSWR (at xmtr) and 1 dB loss in transmission line, per mfg., % power
>delivered to antenna = 80%
>For 1:1 VSWR (at xmtr) and 2 dB loss in transmission line, per mfg., % power
>delivered to antenna = 63% (eyeball interpolation)
>For 2:1 VSWR (at xmtr) and 1 dB loss in transmission line, per mfg., % power
>delivered to antenna = 73% (eyeball again)
>
>The "lost" power is dissipated in I Squared R losses (H E A T) in the
copper (or
>other metal) in the transmission line.
BUT, Bill, you are talking apples, my post is/was about oranges!
I presented NO argument against the "copper losses", I-squared-R
losses, which is what the ARRL tables/graph you refer to is all about.
My argument is to refute Robert's assertion that there is also real,
meaningful loss/distortion/per him, noise, caused by the reflected
power exiting the cable later than the non-reflected power. A
completely different phenomena, and a false idea/notion which
must be stopped from spreading, as it just t'aint true.
In fact the "problem" which Robert addresses is even less than
my suggestion, as I didn't make a point about the continual
diminution of the energy being re-reflected to form his
asserted after "dit" echo. Obviously after 10 or so round trips
up and down the line, the "echo" will be many, many dB
down from the initial impulse of which Robert was sounding
the alarm. My post simply refutes the importance of that
phenomena.
And good that you post info about losses to your web site,
but certainly do not confuse reflection phase (time) distortion
with copper losses and their increase with vswr on the
transmission line. Totally separate issues.
73, Jim, KH7M
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