On Fri, 01 Jul 2005 04:30:00 GMT, Owen wrote:

On Thu, 30 Jun 2005 21:07:20 -0700, Roy Lewallen
wrote:

I saw this apparent discrepancy many years ago, and wondered the same
thing. I've come to believe that the extra loss is due to the braided
shield, not some unknown additional dielectric loss. There's very little
quantitative information about that loss mechanism, but from time to
time I've come across comments that it can be substantial.

Roy,

I thought about the effects of through braid loss. I guess any loss
that increases proportionately to f will be captured in the loss model
and allocated against k2.

Below are k2 factors for a few cables of interest. The first three use
PE dielectic, and there is a big difference between RG58 and RG213
where the dimesions of the dielectric are quite different. A small
difference between RG213 and RG214 with similar dielectric size, but
214 has double braiding, suggesting that braid loss / leakage may one
of the factors.

Belden 8262 (RG58C/U) 2.95e-10
Belden 8267 (RG213) 8.23e-11
Belden 8268 (RG214) 7.17e-11

The next bunch don't use braid, but use a corrugated solid outer
conductor. Not a dramatic change in k2 considering how much larger
6-50 is compared to 4-50.

LDF4-50 6.15e-12
LDF6-50 4.60e-12

Could the distribution of the electric field intensity in the
dielectric be a factor, will the dielectric exposed to the highest
field intensity dissipate the most power?

I'm a little late on this as my news service just hiccupped.

Without wading throught the ASCII math, a couple of thoughts.

1. As Tom said, most references give the D of poly as 0.0002,
although the "Handbook of Coaxial Microwave Measurements" by General
Radio gives it as 0.0003.

2. Again, without having followed the derivation, I find the k2
values to be different from those given by the handiwork of Dan,
AC6LA, in his XLZIZL.xls workbook or his TLdetails program. Dan used
published attenuation values and Excel regression analysis to
determine the values of k1 and k2. See:

http://www.qsl.net/ac6la/bestfit.html

3. Also, General Radio says, "alpha(diel) does not depend at all on
the dimensions of the line..." This suggests that there should be no
difference in k2 between LDF4-50 and LDF6-50. Dan's numbers show that
to be the case.

4. Any loss that doesn't follow the sqrt(f) rule (radiation,
wire-to-wire resistance of braid?, etc) as you suggest falls into the
k2 term.

5. High-quality, high-frequency (microwave) flex cables do away with
braid, or at least solder fill it, and use tape-wound shields.