I have used nothing but quads for the past 30
years. I see a lot of problems in what you are doing:
A quad in a diagonal or square configuration will clear guy wires that are
about 4 to 5 feet down from the top of the tower. Draw a picture on paper
and you can see that you will have about 18 inches clearance. I have never
used anything but 3/16ehs or 1/4ehs guys for my towers from 64 to 100 feet,
but always wanted to put up Philystran guys, but they were simply too
expensive.
I never put the quad mast plate more than a foot above the top of the tower
and highly recommend that you do not either. A thrust bearing made from
wood, phenolic, or most anything will work just fine. The quad only turns
at 1 rpm. The mast would be better made from either 1/4 inch wall aluminum
tubing in a T6 configuration or simply from 2 inch thin wall galvanized
steel electrical conduit if you are not going more than a foot out the top
of the tower. You DO NOT need more than 10 feet of mast, and if you will
probably wind up using only about 6 feet.
The rotator shelf should be inside the tower, but the standard heights of 2
or 3 feet inside the tower will work just fine.
You will regret the rotator with no brake about 5 seconds after the first
wind gust above 20 mph which means you can only operate on perfectly still
days. You will NOT be able to keep the antenna mast from turning in the
rotator for high wind gusts.
Spreaders of 3/4 inch aluminum will not work for anything larger than a 2
meter quad. You need at least 2x2x 3/16 inch aluminum spreaders 3 feet long
tied to a 3 inch heavy wall aluminum boom with muffler clamps.
Do not use Insulated wire. Use only bare of enamel (formvar) covered wire,
or remove the insulation from the wire you have. Do not use smaller than
#14 for a KW input. Aluminum welding wire is used by some manufacturers
because it is much lighter although all joints must be bolted and there will
always be a dis-similar metal corrosion, but it works.
You can buy an inexpensive 2,3, or 4 element quad for 20 meters from
Lightning Bolt that also includes good protection for joining the elements
to the poles. Their elements are fiberglass and are considerably stronger
than bamboo. Actually Calcutta bamboo is much stronger than standard bamboo
and I have reinforced them with a layer of fiberglass and resin, but they
get heavy quickly.
If you have never done this before, build a two elements first, then add the
additional two elements as a second project. Any boom over 30 feet is very
difficult to handle. You will find that 10 feet is difficult to handle on a
quad much less 40 feet.
Ice will take down most quads at one time or another, but they sustain wind
pretty well if designed properly and the elements are joined to the poles
with flexible attachments. Mike, at Lightning Bolt would be a good person
to call BEFORE you start this project.
Enginner is spelled Engineer.
-----Original Message-----
From: towertalk-admin@contesting.com
[mailto:towertalk-admin@contesting.com]On Behalf Of Vaclav Sal
Sent: Monday, June 03, 2002 4:49 PM
To: 'towertalk@contesting.com'
Subject: [Towertalk] Quad question for mechnical enginners
Being ignorant in the subject I need some professional opinion on this
mechanical problem.
I am building 4 element 20 meters quad with the following physical
characteristics:
Boom length - 40 feet
Boom diameter 4 inches
Elements - spreader made from two 2 feet long aluminum angle ( ¾ by ¾ inch)
Elements - bamboo
Wire - 20 gauge stranded plastic coated ( surplus )
Each element weight is approximately 10 pounds - this is educated guess on
my part.
I have a crank up tower ( two sections approximately 35 feet high extended)
with two guy wires sets - one attached to the stationary part which I assume
will be the main ones to keep the thing from falling over. The top guy wires
are just to keep the top section in place.
Since my element spacing is approximately 10 feet, I will need some
clearance for the top guy wires and the boom must be mounted some distance
above the top guy wires.
The question is :
If I use thrust bearing on the 2 inch aluminum conduit mast ( two coupled 10
foot sections) - what should be the SAFE height of the mast above the top of
the tower?
I am guessing that the mast could act as a spring and the section inside the
tower should be as long as feasible. I just do not want to bend the section
above the bearing if it is made too long.
My rotator is garden variety Ham rotator - no brake. I am not too concerned
if the rotator cannot handle the start/ stop . My main concern is not to
bend the mast above the bearing.
I am no looking for detailed analysis, that would be waste of time. I just
need some expert opinion.
PS The monster is in the back yard with plenty of clearance to land "safely"
if necessary. Hi Hi.
73 Vaclav AA7EJ
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