Roy Lewallen wrote in news:13cid39fvvdsk28
@corp.supernews.com:

....
1. Belden 9204, like a lot of other 75 ohm cables, has a copper-plated
steel center conductor for strength. At 3.8 MHz, depending on the
copper
thickness, current might be entering the steel. If it is, the loss will
be a lot more than a simple model for solid copper would predict. I
notice that the statement at the bottom of the data you posted says
"Loss model source data frequency range 10.000 - 1000.000 MHz". You're
well below that. A good reason for a lower limit on the model would be
not accounting for current penetrating into the steel.

Roy, the reason I show the freq range on which the model is built is for
exactly the case you are discussing. It makes it clearer when the model
is an extrapolation, and confidence limits should be wider.

One of the things that I have done when doing the regressions on the
source data is to discard low frequency points that have high error wrt
the regression. This effect occurs almost intirely with CCS centre
conductor type cables.

Not all RG59 and RG6 type cables have CCS, and the worry with low cost
CCS is whether the coating is even thinner than the 9204.

I use RG6 quite a bit for ham work, and the cable I buy uses a HDC centre
conductor. I would avoid CCS for lower HF.

Back to the original problem, it would take a huge loss to deliver an
input impedance of just under 75 ohms from a 54 ohm load and a quarter
wave of nominal 75 ohm line. The Zo looks low.

Owen

PS: The quoted output from TLLC is somewhat hard to read due to the Greek
characters and some other symbols not copying to plain text.