I feel kind of obligated to respond to the question regarding "450" ohm
"window" type ladder line, since we are responsible for some of the
error. The earlier models were solid, 19% copper clad steel. We insisted
on 30 %and a better polyethylene jacket, and supplied the wire for a
stranded 18 gauge model as well, which was actually 40% -as a pilot run.
The stranded was so successful that we contracted for a 16 gauge model in
reworked dies, and a bit later, 14 gauge. The only way that the MFR could
see their way to do this on a relatively low volume operation was to use
the same machinery for all of them, modifying only the extrusion orifices
- not the width set. Obviously, then, as the wire gauge got larger the
error from the original years ago design at 450 ohms, nominal, increased
downward.
We never objected to this for two reasons: The great majority of the
amateur usage is not at all sensitive to the problem since, as a tx line,
a transmatch and balun is usually employed. Secondly, to make new
equipment to a true 450 was cost prohibitive - the $ write off over the
volume produced would have made the stuff cost more than the amateur
community would pay.
The few designers and builders who required critical value had only to
alter length to suit, and a purist could still "roll his own"
Keeping the cost down has made the resurge of balanced line use a real
exciting phenomenon, and the growth still escalates. Problems due to the
big stretch of the "nominal" expression on the 14 gauge model have been
rare.
Our market still is afflicted by the "if a little is good, more must be
better" disease, so a major share of the 14 and even 16 gauge stuff is
gross overkill for what it's used for, but there isn't too much wrong
with the "if it feels good, do it" attitude, either, I guess.
The stuff still reigns supreme as the best buy in transmission line for
HF, bar none - nothing ready made has a better db/dollar ratio!
The minor inconvenience of reactance change due to water and dirt is
easily minimized by cleaning and waxing it every so often, just like
one's car(except the definition of reactance changes to esthetics!).
We're pretty proud of the 6 choices instead of one that we have been a
part of.
Hope this is of interest.
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!
On Fri, 10 Jul 98 10:41:36 -0400 "Lowell, Mark"
<mlowell@noclant.navy.mil> writes:
>
>Reply to the message of Friday July 10, 1998 09:49 -0400
>-----------------------------------------------------------------
>
>>The early charts had gross errors in attenuation for these line
>types,
>>I have no idea if the later ones do. The error was in the direction
>of
>>much to little loss.
>
>Tom, I have the 1996 edition ARRL Antenna Handbook. It shows open
>wire types as having much lower loss than hardline. Starting with
>which
>year's edition were the loss charts corrected?
>
>>Remember MOST 450 ohm ladder lines are not 450 ohm at all. Some 450
>>lines are as far off as the upper 300 ohm range.
>
>I had no idea it was that far off. I wonder why they call it 450 Ohm?
>
>>TV twinlead is pretty
>>good for dry weather impedance, but ALL of these unshielded lines
>have
>>high wet weather loss at VHF and above. Mounting is also critical, as
>>is current balance and physical balance to surrounding conductors.
>
>Right. Twisting it and installing it inside pvc seemed to be a
>reasonable
>amount of work to get a super-low loss feedline, but now that the
>chart is
>in question, I'm not so sure. I guess if it was a really good thing,
>everybody would already be doing it.
>
>
>Mark, N1LO
>
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>
>
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