[TowerTalk] Matched "Bury Flex" cables

[Keith Dutson]

John W0UN wrote:
>Solid dielectric is much more controllable, but I even measure the actual
phase shift for each delay line of solid dielectric coax, if the application
is critical.

For HF, the delay is likely not critical.  From reading the ARRL Antenna
Book I understand phase errors up to 30 degrees for antenna phasing have
small effects on radiation pattern and TOA.

73, Keith NM5G

-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of W0UN -- John
Brosnahan
Sent: Thursday, July 14, 2005 8:49 AM
To: towertalk at contesting.com
Subject: Re: [TowerTalk] Matched "Bury Flex" cables

At 11:36 PM 7/13/2005, Al Toothaker wrote:
>Wouldn't the different electrical lengths indicate that the cable 
>manufacturing process is not consistent?  Any spec on a cable has a 
>tolerance and though they may wander in performance, it could still 
>meet their specs.


The velocity factor in foam coax is the most difficult thing to control,
since it is a function of the percentage of air bubbles in the dielectric.
Some manufacturers specify it for a range of values -- such as 0.78 -- 0.82
VF, others just give a nominal value.

Solid dielectric is much more controllable, but I even measure the actual
phase shift for each delay line of solid dielectric coax, if the application
is critical.

And with foam coax it is MANDATORY to TUNE (trim) each delay line to the
correct electrical length.

--John  W0UN



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