K7LXC@aol.com wrote:
>
> In a message dated 5/25/2008 5:05:48 A.M. Pacific Daylight Time,
> kc4pe@mindspring.com writes:
>
>
>> Great Steve .. beautiful illustration .... Be sure and let all know when
>>
> your book will be ready for sales....I'm sure it will be a "Must" for all
> folks with a tower. Steve what is your feeling of the "Dual Tram" .... seems
> it
> requires more set up etc....but their must be reasons of a dual vs the
> single
> tram as you describe..??
>
>
> A tram is where the load is under one tramline. What you're describing
> is a trolley system where the load rides on top of 2 lines. It is a real
> PITA
>
DISCLAIMER
Please note these are suggestions and not a "how to" for beginners<:-))
I always hang the antenna under the line using pulleys for support, not
on top be it one or two lines. BTW good pulleys rated up to 700# run
between $30 and $40 each. Depending on the weight and length of the
antenna and the width/spacing of the two tram lines a little inequality
is permissible. The farther apart the better (within reason) If and I
emphasize the IF you can get about a 10' spacing AND use a good non
stretch line with little catenary the tension only needs to be nearly
the same. Close enough that you can test it by feel or at least many
can. This is one spot where I do not like heavy steel cables. Too much
catenary which means too much give, which means much less tolerance to
tension differences. It's expensive, but this is a great spot for
Phyllistran however even good 1/2" or 5/16" braided poly rope can work
depending on the weight of the antenna. Don't use Nylon, it's too
stretchy. Using good pulleys, a bit of care, and I've never even nicked
a line...Yet.
10 foot spacing is about as far as most can use. Even at 5'7" I can
reach 5' out from the top of the tower and do so safely with the proper
rigging.
That means most normal size antennas up to around 40 to 50' booms can be
handled in calm conditions. It's still a good idea for tag lines off
each end of an antenna that size though.
Three important points are keeping the tram lines tight, and hanging the
antenna close to the lines (within inches) with the attachment to the
antenna made in such a manner that it can not move and particularly not
inward. This lets the antenna serve as a spreader for the lines as it
travels along.
> since you have to rig it so that the 2 lines are spread apart, it's
> difficult
> to tension them equally, the antenna has to be balanced just right and then
> you've got tons more friction trying to slide the load up
That's why I hang the antenna under the lines using pulleys. Little
friction and little problem balancing if the attach points are properly
rigged and far enough apart. Another reason I don't like antennas
riding on the lines is the tendency for the antenna to cut into
synthetic lines or ropes and for metal lines to damage the antenna.
The main drawback to the dual lines is the strength required for the
cross bar they attach to at the top. That means it's going to be heavy
and must attach to the mast above the point where the antenna will
attach. Two lines means about twice the side force applied above the top
of the tower which can be considerable with properly tensioned lines.
Don't drill holes in the pipe or angle so a U-bolt can be used for
attachment to the mast. Use a mounting plate with saddle clamps or
U-bolts "around" the mast and "around" the spreader. The leverage can be
tremendous at this location when tension of the lines AND the weight of
the antenna is taken into consideration. HOWEVER with the addition of
tag lines off each end of the antenna and proper rigging you can get
away with *relatively* little tension on the tag lines be it a single or
double tram.
Don't work alone and always use a crew who know what to do and how to
follow directions<:-))
73
Roger (K8RI)
www.rogerhalstead.com
> the lines. Not
> worth the effort IMO.
>
>
>
>
> Cheers,
> Steve K7LXC
> TOWER TECH
>
>
>
> **************Get trade secrets for amazing burgers. Watch "Cooking with
> Tyler Florence" on AOL Food.
> (http://food.aol.com/tyler-florence?video=4&?NCID=aolfod00030000000002)
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