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Old February 28th 07, 08:11 AM posted to rec.radio.amateur.antenna
Owen Duffy Owen Duffy is offline
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First recorded activity by RadioBanter: Dec 2006
Posts: 1,169
Default tuner - feedline - antenna question ?

Richard Clark wrote in
:

....
I note you have no solution that answers for the loss in a fairly
typical instance for a fairly typical line condition. It couldn't
have been any more difficult than your former computations, could it?
(In fact it is, but not conceptually.) And yet the absence of that
effort is notable (OK, so you've been ambushed). I may have stumbled
on a novelty application but I didn't trip over a boulder of a common
usage.

....

Richard,

No, it is just that I have not posted a solution as yet.

Your problem was described as "Presume a source of 100+j0 Ohms impedance
sees a 50 Ohm line that is 5.35 wavelengths long and is terminated with a
load of 200+j0 Ohms. The normal attenuation of the line is 2.00 dB. What
is the loss in the line?"

Rather than sit down an write a bunch of stuff to calculate it, I took
the lazy way out and played with a scenario using Belden 8262 (RG58C/U)
in my line loss calculator that was pretty close to your scenario (Zo is
a touch different at 50-j0.24, most lines with loss will have a non-zero
jX component in Zo). My result for 15.8m of 8262 at 67MHz with a 200+j0
load is a transmission line loss (power into the load divided by power
into the line at the source end) is 3.3dB. This value of line loss is
independent of the source equivalent impedance.

If I reproduced the algorithms with the exact propagation constant and Zo
for your problem scenario, the answer would be more accurate, but I think
similar, and still obtained independently of the source impedance, and
not worth the time.

The figures from the calculator are below if someone wants to play with
it.

Now, are you prepared to post your solution?

Owen

Parameters
Transmission Line Belden 8262 (RG-58C/U)
Code B8262
Data source Belden
Frequency 67.000 MHz
Length 15.800 metres
Zload 200.00+j0.00 ?
Yload 0.005000+j0.000000 ?
Results
Zo 50.00-j0.24 ?
Velocity Factor 0.660
Length 1924.75 °, 5.347 ?
Line Loss (matched) 1.997 dB
Line Loss 3.279 dB
Efficiency 47.00%
Zin 30.48+j24.99 ?
Yin 0.019622-j0.016087 ?
VSWR(source end) 2.22
VSWR(load end) 4.00
? 1.46e-2+j2.13e+0
k1, k2 1.30e-5, 2.95e-10
Correlation coefficient (r) 0.999884