Revisiting this thread, I've taken the liberty of copying and pasting the
comments posted this AM into one post in which I'll insert brief comments
in caps:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
<So, if I understand this correctly, the 14 gauge, nominally 450 ohm line
that I bought is actually something other than 450 ohms
CORRECT - SOMETHING LESS
; and rather than
being less sensitive to environmental conditions (the reason other than
physical strength that I bought the heaviest) it is more sensitive?
NO
So if it is carrying ice, in a heavy rainstorm, exposed to ash or other
pollution, it is likely to underperform relative to the 18 gauge 450
line?
I SEE NO REASON FOR SIGNIFICANT DIFFERENCE IN PERFORMANCE DUE TO THESE
FACTORS AMONG ANY OF THE 4- NOMINAL450 OHM MODELS.
Please clarify. It is helpful to know when odd tuning circumstances
occur
where the likely source might be found (e.g. when the line is iced or it
is
raining or snowing heavily here in New England I should probably expect
it
to behave badly).>
OF COURSE - THIS IS AN OBVIOUS VARIABLE IN ANY ANTENNA OR TWIN LEAD
SITUATION, AND AN EXCELLENT REASON TO HAVE A TUNER IN THE SHACK FOR
MAXIMUM PLEASURE AND SUCCESS AT HF.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
<OK Press, pretty good explanation. Now all we need is the dialectric
constant, and we can figure out for ourselves the impedence of the
line.>
POLYETHYLENE HAS A DIELECTRIC CONSTANT OF 2.25 @ 10MHz - READ ON, THOUGH,
AS I THINK TOM, W8JI, HAS DONE WORK ON THE SUBJECT AND PLANS MORE. WE
HAVE HAD MANY REPORTS FROM QUALIFIED USERS WHO HAVE DETERMINED AND CITED
91% AS A GOOD MEAN VELOCITY FACTOR FOR THIS TYPE OF MATERIAL.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
<I wouldn't apologize for making the line better!
HEY, I DIDN'T THINK I HAD! JUST WANTED TO SHARE THE HISTORY OF THE STUFF
SINCE 1980.
1.) Larger conductors generally have less loss for a given spacing and
dielectric.
2.) Lower impedance generally means less weather effects for a given
spacing
3.) Lower impedance line often means less impedance extremes at the far
end
in many applications.
4.) Larger conductors mean more power handling.
5.) Larger conductors mean less breakage.
NO ARGUMENT ON ALL 5, ASSUMING TECHNIQUE APPLIED IS CONSTANT THROUGHOUT.
This type of line is very poor at VHF, at least the samples I've
measured.
I'm sure you've seen the effects of periodically repeating "bumps" on
VHF
or UHF performance.
DEFINITELY - AND WE'VE COUNCILED AGAINST IT WHENEVER ASKED.
THERE HAVE BEEN LOTS OF NIFTY VHF J POLE DESIGNS OVER THE YEARS THAT
EMPLOY ALL 6 VERSIONS - BUT THEY ARE NOT "LINE" APPLICATIONS, AS YOU
MENTION.
IMO, the problem is misapplication of what amounts to a good line for HF
(except for weather and routing problems) to VHF "matched" applications.
Dean Straw seems to feel the new ARRL Chart is correct, and the old one
wasn't that far off. My measurements disagree with that.
DEAN AND I HAVE DISCUSSED THIS IN DETAIL, AND FOR WANT OF GOOD
EXPERIMENTAL DATA, THE DATA PRESENTED IN THE NEXT ISSUE IS PRESENTED AS
CALCULATED, SUBJECT TO CORRECTION AS BETTER INFORMATION IS COLLECTED. THE
TABLES IN THE ARRL TEXTS HAVE BEEN SERIOUSLY IN NEED OF RE-WORK FOR
YEARS, AND THE UPCOMING ISSUE'S INFO IS A LOT BETTER. I'M LOOKING FORWARD
TO YOUR WORK ON THE SUBJECT.
When we sort that out off-line, I'll post a correction or clarification.
Have you ever measured VHF performance Press, (ON THE TWINLEAD)
NO - NEVER CONSIDERED IT TO BE WORTHWHILE PAST CHANNEL 13.
and do you recommend this line over hardline?
FOR HF, I SURE DO, WHEREVER PRACTICALLY POSSIBLE AS A STOCK ITEM OR HOME
BREW. THE MAJORITY OF THE AMATEUR COMMUNITY INVOLVED IN HF ACTIVITY DO
NOT SPEND MEGABUCKS ON ANTENNAS AND TRANSMISSION LINE, NOR TO THEY NEED
TO, TO THOROUGHLY ENJOY THE HOBBY. THE SERIOUS SERIOUS DX'RS ARE NOT TO
BE MOCKED OR CRITICIZED, HOWEVER, FOR THEIR HARDLINE, EITHER ANDREW'S
BEST OR SURPLUS CATV - IT'S A GREAT HOBBY AND A GREAT FREE COUNTRY.
Since you sell the stuff, you see more than Dean or I do.>
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Press Jones, N8UG, The Wireman, Inc., Landrum, SC, 29356
Sales (800)727-WIRE(9473) or orders@thewireman.com
Tech help (864)895-4195 or n8ug@thewireman.com
www.thewireman.com and the WIRELINE bargain page
Our 21st year!
_____________________________________________________________________
You don't need to buy Internet access to use free Internet e-mail.
Get completely free e-mail from Juno at http://www.juno.com
Or call Juno at (800) 654-JUNO [654-5866]
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|