On Sun, 11 Dec 2005 17:22:16 GMT, "Greg Ordy"
wrote:

[snip]

Good job Greg. Also thanks for the work on the N2PK VNA software.

By inspection of the loss figures for Buryflex on Davis' web site one
can note that the loss at lower frequencies is higher than other RG-8
type cables.

Importing their data into Dan's (AC6LA) "bestfit.xls" spreadsheet
shows very poor correlation with theoretical k1, k2 coefficients. I'm
observing something similar on some RG-142 that I am measuring with my
N2PK VNA. The '142 has a silver-coated, copper-plated steel center
conductor and I believe that the skin depth encompasses the steel at
lower frequencies.

Anyway, that might be a factor, assuming of course, that their data
are valid.

On Sun, 11 Dec 2005 15:29:20 -0700, Wes Stewart
wrote:


Importing their data into Dan's (AC6LA) "bestfit.xls" spreadsheet
shows very poor correlation with theoretical k1, k2 coefficients. I'm
observing something similar on some RG-142 that I am measuring with my
N2PK VNA. The '142 has a silver-coated, copper-plated steel center
conductor and I believe that the skin depth encompasses the steel at
lower frequencies.

I noted when I imported Davis' Bury Flex data to tllce that the
regression model correlation coefficient was lower at 0.9918 than most
other data which tends to come in better than 0.997 and mostly 0.998
or better.

One of the reasons that some lines show a very good fit to the model
(eg 5 nines) is that the measurement data was fitted to a model, and
the published figures are from the model, not the original
measurements, and the error in deriving a model from the published
figures is principally caused by rounding of the published figures.

A possible explanation of Greg's observation of low Zo is that the
foam is more dense than intended, increasing C, lowering Zo, and
increasing loss at higher frequencies.

Owen
--

Wes Stewart wrote:
. . .
Importing their data into Dan's (AC6LA) "bestfit.xls" spreadsheet
shows very poor correlation with theoretical k1, k2 coefficients. I'm
observing something similar on some RG-142 that I am measuring with my
N2PK VNA. The '142 has a silver-coated, copper-plated steel center
conductor and I believe that the skin depth encompasses the steel at
lower frequencies.
. . .

I've definitely seen this in RG-174 and some similar diameter 75 ohm
cable, at 7 MHz. The problem with those cables is that the center
conductor is made of very fine strands of Copperweld. While the fraction
of copper relative to the wire diamter is large, the actual copper
thickness is small due to the very small diameter wire, allowing current
to penetrate into the steel at lower frequencies.

I've also seen the effect in the time domain when using RG-174 type
cable but with solid silver-plated Copperweld center conductor. The
increased loss at low frequency actually improves the step response
somewhat because of the disproportionately higher loss at lower frequency.

Roy Lewallen, W7EL