Ladder Line and wind
 

I'm putting up a doublet centerfed by 450 ohm ladderline. It will be about
50ft away from the house to the feedpoint of the antenna. We live on top of
a hill and winds here are often gusting to 60mph. The typical direction of
the wind is perpendicular to the ladderline and I'm concerned about it
whipping itself to death.

The ladder grabber at center of the doublet will be supported by a line
running from the house to a tree so I'm considering attaching the ladderline
to the support line leading to the house to minimize the whipping. The
ladderline has to come this way anyway. This support line will be
perpendicular to the axis of the antenna.

I briefly thought about threading the house line through the ladder windows
but that seemed likely to spoil the impedence especially if wet.

Any concerns or recommendations?

tnx
jtm

Jim Miller wrote:
Any concerns or recommendations?

Use the #14 stranded ladder-line from The Wireman.
--
73, Cecil http://www.qsl.net/w5dxp


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hi cecil

wireman was my assumed source. are you suggesting that the #14 won't
need any additional support?

tnx
jtm

On Fri, 18 Feb 2005 12:11:05 -0500, "Jim Miller"
wrote:

Any concerns or recommendations?

Hi Jim,

The whipping action is due to vortex shedding - an imbalance of wind
pressure on each side which is oscillatory in nature. To cure it, the
simple resolution is to twist the line so that the face of the line
rotates every 12 to 18 inches.

73's
Richard Clark, KB7QHC

On Fri, 18 Feb 2005 12:11:05 -0500, "Jim Miller"
wrote:

I'm putting up a doublet centerfed by 450 ohm ladderline. It will be about
50ft away from the house to the feedpoint of the antenna. We live on top of
a hill and winds here are often gusting to 60mph. The typical direction of
the wind is perpendicular to the ladderline and I'm concerned about it
whipping itself to death.

The ladder grabber at center of the doublet will be supported by a line
running from the house to a tree so I'm considering attaching the ladderline
to the support line leading to the house to minimize the whipping. The
ladderline has to come this way anyway. This support line will be
perpendicular to the axis of the antenna.

I briefly thought about threading the house line through the ladder windows
but that seemed likely to spoil the impedence especially if wet.

Any concerns or recommendations?

tnx
jtm


My ladderline seems to do fine on windy days, and I did nothing
special to limit movement. You might bring it directly to your shack,
and if the wind bothers it, just twist it as someone else has
suggested.

On your other question, about doublet length, if you make it 102 feet,
it'll be G5RV-length, and there are plenty of articles on how those
perform on the various bands.

bob
k5qwg

wrote:
wireman was my assumed source. are you suggesting that the #14 won't
need any additional support?

Jim, I think you could practice your Tarzan act
using that stuff to swing on. It is stranded
copperweld and extremely strong.
--
73, Cecil http://www.qsl.ner/w5dxp


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On Fri, 18 Feb 2005 10:06:15 -0800, Richard Clark
wrote:

On Fri, 18 Feb 2005 12:11:05 -0500, "Jim Miller"
wrote:

Any concerns or recommendations?

Hi Jim,

The whipping action is due to vortex shedding - an imbalance of wind
pressure on each side which is oscillatory in nature. To cure it, the
simple resolution is to twist the line so that the face of the line
rotates every 12 to 18 inches.

Dear Richard,

I haven't heard about vortex shedding since 1960 when I was working on
the sonar system that measured the flow over the Polaris Missile Hatch
Doors on the Polaris boats. Bad News!

Bob, W9DMK, Dahlgren, VA
Replace "nobody" with my callsign for e-mail
http://www.qsl.net/w9dmk
http://zaffora/f2o.org/W9DMK/W9dmk.html

In article ,
Bob Miller wrote:

On Fri, 18 Feb 2005 12:11:05 -0500, "Jim Miller"
wrote:

I'm putting up a doublet centerfed by 450 ohm ladderline. It will be about
50ft away from the house to the feedpoint of the antenna. We live on top of
a hill and winds here are often gusting to 60mph. The typical direction of
the wind is perpendicular to the ladderline and I'm concerned about it
whipping itself to death.

The ladder grabber at center of the doublet will be supported by a line
running from the house to a tree so I'm considering attaching the ladderline
to the support line leading to the house to minimize the whipping. The
ladderline has to come this way anyway. This support line will be
perpendicular to the axis of the antenna.

I briefly thought about threading the house line through the ladder windows
but that seemed likely to spoil the impedence especially if wet.

Any concerns or recommendations?

tnx
jtm


My ladderline seems to do fine on windy days, and I did nothing
special to limit movement. You might bring it directly to your shack,
and if the wind bothers it, just twist it as someone else has
suggested.

On your other question, about doublet length, if you make it 102 feet,
it'll be G5RV-length, and there are plenty of articles on how those
perform on the various bands.

bob
k5qwg

what happens to the impedance of ladder line when you put a few gental
twsts?

anything significant

ml wrote:
anything significant

Nope, not very...
'Doc

Use heavy duty fishing line threaded through the feedline windows.

--
Dan Roth, N9NO


"Jim Miller" wrote in message
...
I'm putting up a doublet centerfed by 450 ohm ladderline. It will be about
50ft away from the house to the feedpoint of the antenna. We live on top
of
a hill and winds here are often gusting to 60mph. The typical direction of
the wind is perpendicular to the ladderline and I'm concerned about it
whipping itself to death.

The ladder grabber at center of the doublet will be supported by a line
running from the house to a tree so I'm considering attaching the
ladderline
to the support line leading to the house to minimize the whipping. The
ladderline has to come this way anyway. This support line will be
perpendicular to the axis of the antenna.

I briefly thought about threading the house line through the ladder
windows
but that seemed likely to spoil the impedence especially if wet.

Any concerns or recommendations?

tnx
jtm