And with the easy availability of powerful test gear at relatively low
cost, combined with AC6LA's fine Excel spreadsheets, it's easier than
ever to get good data for VF and Zo vs frequency from a few measurements.
The procedure is pretty simple. Make swept vector impedance (that is,
complex, magnitude and phase) of a convenient length of the line, one
with the far end open, again with it shorted. Export that data to the
spreadsheet, which will then compute and plot curves of VF, Zo, and
attenuation vs frequency. The AIM family of analyzers will do this, and
I believe the SARK will too. My weapon of choice is the VNWA 3e,
designed by German university EE prof DG8SAQ and built by some hams in
the UK.
The effect of a CCS conductor is clearly seen by comparing plots of mfr
data for CCS cables on the same graph as for cables with a solid copper
center. CCS line has more loss below 10 MHz than copper.
73, Jim K9YC
On Sun,2/5/2017 7:24 PM, Wes Stewart wrote:
If you follow this link http://k6mhe.com/n7ws/Ladder_Line.pdf to my
paper and look at Table 1, it gives the measured values of four
different Wireman P/Ns.
Note that these are 50 MHz values and transmission line Zo and Vp are
anything but constant at lower frequencies. Likewise, these
particular lines use copper-clad steel conductors that "misbehave" at
lower frequencies so Eq 4 somewhat falls apart when the conductors do
not have a well-developed skin effect. I mentioned this in the paper
but did not account for it in the equation.
Wes N7WS
On 2/5/2017 5:11 PM, Hardy Landskov wrote:
Hi Jim and all,
The email below reminds me of a problem I had some years ago with
"450 ohm
window line". Nothing seemed to work. I then found an article that
explained
how to measure the Zo of coax/ladder line. I measured a piece of
window line
and it was 374 ohms! I found out in the archives that W8JI had
measured 377
ohms with a piece of window line. We exchanged emails and he was
elated that
I had verified his results.
Here you have two different sets of equipments, two different runs of
ladder
line, and different times. I was very happy myself. I have an HP8753B
so it
was no problem to run through the numbers. It was a very eye opening
exercise!!
Bottom line: Use 375 ohms for matching tuners and other things when
using
this line.
73 Hardy N7RT/4
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