Dick-
Insofar as supporting antennas in the trees, I used to use a line from
the antenna through a pulley and then down to ground level. At the
bottom, I hung a weight to keep the tension on the antenna but which
allowed the line to "stretch" as the tree moved under windy conditions.
A bucket of rocks (holes in the bucket for drainage) will do the trick -
and you can position the pulley far enough away from the tree so that
the weight doesn't rub against the tree and get caught.
73-
Fred, W6TKV
Dick Green wrote:
>
> I've had an 80m delta loop suspended at about 75-feet from a tall spruce
> tree for three years and the wire keeps breaking at the corners or at the
> apex. I'm probably putting too much tension on it, so when the tree bends in
> the wind the wire breaks. But I need to put a fair amount of tension on the
> loop to keep the base wire from drooping too close to the ground. I've been
> using #12 stranded insulated THHN, which seems like it should be strong
> enough for the application. I'm wondering if I would be better off using a
> different kind of wire -- perhaps #12 insulated Flexweave or # 10
> Copperweld. Does anyone know the relative breaking strength of these wire
> types?
>
> Another approach might be to find a way to keep tension on the wire, but
> provide enough give to compensate for tree movement. I'd be interested in
> any recommendations or ideas from people who have successfully kept
> tree-supported delta loops up for a long time -- what kind of wire did you
> use and how did you support the apex and corners?
>
> Here are the construction details of my loop:
>
> Originally I had a friend shoot a pull rope over a high branch of the spruce
> tree -- about 75 feet up. I pulled the # 12 THHN up and across the branch
> with the pull rope (i.e., the apex was supported by a branch. Per W4RNL and
> others, the feedpoint balun is inserted in the loop about a 1/4-wave down
> from the apex, about 12 feet from one of the corners. I supported the
> corners with glass dogbone insulators attached to 1/4" black dacron rope
> which runs to pulleys that are mounted in trees about 15 feet up. The loop
> doesn't hang quite symmetrically: one corner is higher off the ground than
> the other.
>
> In this configuration, the loop broke at the lower corner several times over
> a period of three years. It was easy to lower the insulator, grab the rope
> ends, slip the insulator back on, and solder the wire back together. At one
> point I got tired of this and replaced the dogbone insulator with one of
> those heavy black rubber bungee straps. This provided a little strain relief
> and a gentler interface with the wire. I have successfully used these straps
> with my 160/80 inverted vee, which is also suspended from a tree. This
> configuration lasted about a year, then a month or so ago the loop broke at
> the other corner (still had a glass insulator there.) It was not possible to
> reach the free end of the wire -- it was too high up. I tried to snag it
> with a pole saw (blade removed) and pull it down, but the wire was stuck in
> a crotch of the branch. I had pulled a backup rope up with the wire, but
> pull rope was stuck in the crotch, too!
>
> Determined to provide a reliable backup pull rope and minimize the
> possibility of breaks at the apex, I hired a tree climber to go up there,
> cut down the old rope and wire, install a double-wheel pulley, and thread a
> couple of pull ropes through the pulley -- one to pull the wire and another
> for backup. I used one pull rope to raise a replacement wire and connected
> it to the balun. I used a single-wheel pulley at one corner and the same
> heavy black rubber bungee strap at the other corner. I figured a pulley at
> one corner would provide some give for the wire and a gentler interface, but
> thought that pulleys at both corners and the apex would allow the wire to
> reorient itself too much -- it might start rotating around the tree! So, I
> used the bungee strap at the other corner to keep the wire from slipping.
> BTW, I actually got the tuning right on the first try!
>
> This configuration lasted all of one week. At the first moderate windstorm,
> maybe 25 MPH, the wire broke at the apex. I guess when the wire ran over a
> branch there was more give. The pulley seems to have eliminated the strain
> relief at the apex, so I need to either provide more strain relief at the
> corners or use stronger wire, or both. What's a good way to provide some
> give at the corners without letting the loop sag too much? Springs? weights?
> Is THHN not a good choice for this application? Any other ideas?
>
> I'd appreciate any comments from those who have been down this road.
>
> 73, Dick WC1M
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
> Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
> questions and ask for Sherman, W2FLA.
>
> _______________________________________________
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_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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