[Towertalk] Quad question for mechnical enginners

[Ed W4EP]

Hi Vaclav,

First of all I am NOT an engineer but I do have
40+ years of quads under the belt so this is free
advice based on lots of failures and successes
plus free advice is worth exactly what it cost ;-)

With a 40' boom and all those spreaders I would
never recommend using an aluminum mast up even
a few inches above the exit point of the tower.
It will fail...question is when.

Assuming your quad is only a couple of feet above the tower top,
with the tower only 35' high and two sets of guys, half your antenna
will be below the top of the tower I hope
you will consider non-metallic guys or I'm afraid you are
going to be in for some interaction problems with so
little height to work with and so much wire.

Lastly If you are in an area subject to icing You might consider
copper clad steel rather than #20 stranded. I wouldn't trust
bamboo either but I'm no expert on bamboo and ice loads.

My quad is also on a self supporting crank up tower and even
partially extended at 40' a four elements gets out like gang busters
so yours should really do a good job for you but when they break
they are so big and bulky they are frustrating to work on
so I'd suggest building it for long term survival.

GL es 73, Ed
W4EP




From: Vaclav Sal <VSal@teltone.com>
To: "'towertalk@contesting.com'" <towertalk@contesting.com>
Date: Mon, 3 Jun 2002 14:48:50 -0700
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