It is not so much a matter of wind loading as cable gallop. The twists
create periodic turbulence over much smaller sections of the feed line
making it very unlikely to create a condition of mechanical resonance with
the feedline. This same principle is used in most modern car antennas to
reduce the wind noise in the audible range. It has also been use for years
in the form of T-2 electric distribution cable.
As far as comparing amateur radio practices with commercial broadcast
stations we must be cafeful to remember that the technical requirments to
operate an amateur station are now higher than those to build or operate a
commercial broadcast station. Many facilities are built by the lowest bid
contractor and overseen by a non-technical contract administrator or an
engineer more familiar with video and audio than rf. Some of the finer
points of station construction may be lost in construction, especially if
the station designer is not envolved in the construction phase.
-----Original Message-----
From: Carter Grabarczyk <k8vt@ameritech.net>
To: Paul Christensen <paulc@mediaone.net>
Cc: Ten-Tec Reflector <Tentec@contesting.com>
To: <tentec@contesting.com>
Date: Sunday, April 02, 2000 1:27 PM
Subject: Re: [TenTec] Re: Ten Tec antenna tuners (ladderline lore)
>
>
>
>Paul Christensen wrote:
>>
>> Well, since posting my inquiry yesterday, I received a lot of expanations
>> for the practice of twisting balanced transmission line. Here is a
summary
>> of the majority of replies:
>>
>> 1) Twisting the lines reduces motion due to wind loading effects.
>
>Wouldn't twisting make the wind loading WORSE? Take a hundred foot run
>of ladder line to your antenna without any twists. Now use a twisted
>ladder line to go to the same antenna the same 100 feet away. Because of
>the twist, you will actually have used some amount of cable GREATER than
>100 feet. Now, instead of 100 feet of cable in the air, you will have
>101 or 105 feet or whatever in the air (depending on how tight the
>twist). In any event, you will have MORE wire in the air and thus MORE
>wind loading and more motion due to a larger target.
>
>This twist issue probably has its roots in the very early days of
>telephony when the open wire telephone lines were regularly transposed
>to reduce/cancel noise. Whether this has any (practical) effect today on
>ham transmission lines is open to debate, but it certainly has nothing
>to do with decreasing wind loading.
>
>73/Carter/K8VT
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