----- Original Message -----
From: "Richard Karlquist"
Sent: August 10, 2002 2:30 PM
Subject: RE: [Towertalk] Bury - Flex Information
> I bought some bury-flex and the
> velocity factor was out of spec
> (they claim 85%; it was less than
> 80%). They sent me some more,
> and it was still out of spec. I
> see that the link you posted still
> claims 85% velocity factor. Note
> that lower velocity factor typically
> is associated along with higher loss.
>
> Rick Karlquist N6RK
I have noted the same thing Rick -- with just about every other type of coax
I've ever tested. It does not surprise me that BuryFlex follows suit. From
my experience, any coax, from any vendor, and sold under any type or quality
description, needs to be tested when you intend to use it in a VF critical
application.
Think about it. The VF is related to the physical dimensions of the coax,
tollerance on the center conductor, the braid, the dielectric, etc. It is
impossible to control the subtle nuances of the various factors accross a
length of coax. Grab a spool of house wiring (or any other wire for that
matter) and measure with a micrometer. Compare to the wire tables. Try
various samples from the same spool, they will vary slightly. They are
without exception, always out-of-tollerance--generally erring on a larger
diameter. Coax is VF is tough to control. If it matters, check it first
and use the actual VF instead of the "target" specification.
Another related issue: When you test a coax that is new, remember that it
has not been aged, flexed, or stretched. Now hang the 200' (or whatever)
hank between two trees and leave it supporting its own weight for a week.
Now test it again. It will not be the same.
By the way, when you need to test the losses in a cable, don't use VF as a
predictor of loss. Better to look at the loss of the coax.
My $0.02
Ford-N0FP
ford@cmgate.com
|