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Re: Topband: Caged Inv-L - Pros and Cons ?

To: <N8DCJ@YAHOO.COM>, <topband@contesting.com>
Subject: Re: Topband: Caged Inv-L - Pros and Cons ?
From: "Bill Wichers" <billw@waveform.net>
Date: Wed, 25 Jan 2012 00:38:27 -0500
List-post: <topband@contesting.com">mailto:topband@contesting.com>
My vertical (without toploading) is a 6-wire cage. I used the 18awg insulated 
copperweld and spreaders I made form aluminum sheet and extrusions. It tunes 
well, although I can't compare it to a single wire since I've only ever used 
the cage.

The big downsides I have with my setup:
1 - there is much more weight involved so it sags down from the tree branches 
more. This limits the max attainable vertical height (I have about 85 feet of 
radiator as I was going for a 5/8 wave on 40m and use it on 80 and 160 as well).
2 - there is a lot more wind and ice load to worry about. The ice loading makes 
#1 more of an issue. Ice/snow sometimes makes it heavy enough that the 
feedpoint lays on the ground and the antenna is unuseable until the snow/ice 
melts off. Windload mostly just bows the antenna into a bannana shape and maybe 
affects tuning a little but that's about it.
3 - the design of the supports becomes more of an issue and you need to provide 
a means to limit the amount of twisting the vertical can do in the wind. I did 
this in my setup by machining an aluminum center piece for the top with two 
stainless eyebolts on the sides for a horizontal support rope and one for the 
vertical radiator. The antenna is suspended between two large oak trees. The 
horizontal rope's tension going through the top bracket makes a sort of spring 
that keeps the antenna in one position axially. This has worked well for me and 
the antenna does not get twisted and tangled as it blows around in the wind.
4 - grape vine loves to climb the wire spreaders! Be warned! I swear it reaches 
out from nearby low trees longing to climb into the clear sky on my innocent 
antenna system :-)

The cage is a *lot* more work to erect than a single wire would be. I'm not 
sure I'd do it again. I am able to tune over a large amount of the band (a 
little mfj autotuner can easily tune the entire band), but the structural 
issues are much more involved than they'd be for a single wire. 

I also had an issue with keeping the wire tension balanced between the 
spreaders. The top and bottom spreaders are made of aluminum bar stock in a 
hexagonal spoke configuration. They are *strong*, but they took some effort to 
build. The top assembly takes all of the weight and the top and the bottom 
together maintain the general shape of the wires and their individual tensions.

The spreaders along the vertical at 10' intervals are open hexagons made of 
.080" thick aluminum sheet cut into 1/2" wide strips and bent into shape. The 
hexagon is "closed" by a small aluminum piece reveted to the ends of the 
hexagonal hoop. The strips present little area for ice to accumulate which was 
a concern for me (there is some buildup though). I put small brackets at the 
corners of the hexagon using pop rivits and then three wires in an "every other 
wire" pattern around the spreader are laced to the bracket with small stainless 
wire. The remaining three wires slide in polyethylene tubing (raindrip vertical 
pipe which has about a 1/8" center bore and maybe 3/32" thick walls) pieces 
that are laced to the remaining three brackets. The three sliding wires are 
fixed only at the top and bottom of the entire antenna while the three fixed 
wires are attached to every spreader. This allows the spreaders to be set in 
the horizontal plane without any tensioning issues. Originall
 y I fixed every wire to every spreader but I ended up with some tight and some 
slack wires as it proved impossible to balance the tension between each wire 
segment and each spreader. In a 4-wire setup you may have a similar issue.

You can get good results with the cage but I'd be most concerned with the 
additonal weight (and resulting sag of your supports) and complexity of 
construction of the cage over anything else. I've had mine up for two years now 
and most of my maintenance issues have been clearing off grape vines and 
installing additional radials (I have around 33 right now and enough more wire 
to get up around 70-80).

-Bill KB8WYP
[Sent using Blackberry Messaging]

----- Original Message -----
From: topband-bounces@contesting.com <topband-bounces@contesting.com>
To: topband@contesting.com <topband@contesting.com>
Sent: Tue Jan 24 21:29:57 2012
Subject: Topband: Caged Inv-L - Pros and Cons ?

I am considering modifying my Inverted L such that the vertical part (~ 70 ft) 
is a cage of say 4 wires , purely for bandwidth. Besides BW any Pro's and or 
Con's to this idea ? my current configuration allows me to use from about 
1800-1860

Dan N8DCJ
_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK
_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK

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