[TowerTalk] Stinger & Jin-Pole Tubing

[K7LXC@aol.com]

In a message dated 97-04-09 14:54:25 EDT, wdfuller@themall.net (Don Fuller)
writes:

> My new jin-pole hardware and thrust bearing need 2-inch OD mast...I am
>  having trouble finding 2-inch OD hardware for this.  2-inch EMT is 2-1/8"
>  OD and won't fit. EMT is probably strong enough for the jin-pole but not
>  the stinger.  I can get rigid conduit which is 1-7/8" OD and probably OK
>  but heavier for the jin-pole handling up the tower. I have seen some
>  negative comments here on Tower Talk about using normal water pipe for
>  stingers, but those making the comments have had multiple large yagis
>  mounted above the tower.  I will only have one TA-33 and one 440 yagi
above
>  the tower.  Question-  will 1-1/2" schedule 40 galvanized water pipe be ok
>  for my installation?  I would also appreciate comments on spacing of my
>  yagis above the tower (by the way Rohn 25 with flat top). Your comments
and
>  ideas would be appreciated.  Thanks in advance.
>  
Don --

       A ginpole is an erection fixture that attaches to the tower and has a
pulley at the top with the haul rope running down to the ground.  The pulley
is typically in a small fixture at the top of the ginpole mast called a
'rooster head' because the pulley is held away from the ginpole mast slightly
so it clears the ginpole mast and fixture and looks like a rooster head.  The
ginpole mast for amateur ginpoles is typically aluminum for a good strength
to weight ratio.  Ham ginpole  loads are generally less than 100 pounds.
 Don't use a steel pipe for the ginpole mast; it's way too heavy.

      A mast is a 'pipe' that sticks out of the top of the tower and has the
antennas mounted to it.  The bottom end is attached to a rotator.   Is that
what a stinger is?

     You are describing 'pipe'.  For safe reliable mast installations you
need 'tubing'.  It's dimensions are OD where pipe is measured by ID.  A 1.5
inch ID pipe has an OD of approximately 1.9 inches.  Two inch tubing is 2
inches OD.  

     The topic of masts is fairly involved.  For a discussion of it, consult
Dave Leeson', W6QHS's book "Physical Design of Yagi Antennas" or send me an
SASE for a reprint of the landmark W7NI mast article.

       While your antenna load is relatively small, you should still have an
idea what the wind forces on your system are.  What state and county are you
in?  I'll look up what the wind speed zone is.  To answer you question about
mast suitability, I'll give you a definite maybe.  More info on request.

73,  Steve  K7LXC

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