Re: [TowerTalk] Delay Lines useing 9913 TRUE or FALSE

[Jim Lux <jimlux@earthlink.net>]

The velocity factor is primarily a function of the dielectric material, 
which doesn't change from physical configuration.  There is a small effect 
from the ratio of L and C (which determines the nominal Z) which might 
result from deformation.There is 1000 ohm TL made for delay line use that 
has a coiled center conductor, resulting in very high L).  It's hard to 
imagine that any coiling/wrapping, etc. that doesn't result in an impedance 
bump would materially change the delay.

If you had an egregious mismatch somewhere, the vector combination of 
reflected and forward waves might result in some weird changes in apparent 
phase shift as a function of frequency; this is, after all, how swept 
frequency pseudotime domain reflectometers work (as used in many network 
cabling testers) (or for that matter, how Vector Network Analyzers do time 
domain displays)


Given that in a phasing harness, you're probably going to have significant 
reactive circulating power (from one element to another), the low loss of 
9913 would be a "good thing".

At 09:35 PM 10/30/2003 +0000, RCARIELLO wrote:
> Hello to all.
> I have been told not to use an air dielectric coax such as Belden 9913 for
> delay lines. It seems the velocity factor changes as the cable is
> tie-wrapped or coiled which would effect its electrical length.
>
> Rich AA2MF
>
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See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.

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