Hello, All:
I have a Tashjian 472 with a flat top. I am using a 20ft 2 inch 0.25 wall
steel mast, 2ft inside the tower and 18 ft above, with a T2X rotator. I
bought the mast from one of the companies is NCJ. The tower with its BIG
concrete and steel reinforcing base was professionally installed.
I have from the top a 40M dipole, a 10M 8el, and a 15/20M 8el at the tower
top. I am usually not there, so I keep the tower down unless I am actually
operating, so the top is normally at 23 feet. That puts the top antenna
usually at 40 or 41 feet (with the truss cable above it). I don't operate
in heavy winds.
I am in Kerr County, central Texas, not tornado alley, and 150 miles or so
from the coast, so hurricanes don't bring big winds. I am of course subject
to thunderstorms.
Its been up for 2 years. So far no tower, mast or antenna problems. My only
problem has been a self induced (Don't ask!) rotator problem. Trust me:
Taking the antennas and mast down to be able to work on the rotator is a
pain. Think renting a cherry picker.
We shall see. If I have problems I will report. Stay tuned.
73,
Rusty, NA5TR
----- Original Message -----
From: "Jon Casamajor" <k6el@comcast.net>
To: <towertalk@contesting.com>
Sent: Tuesday, March 24, 2009 3:06 AM
Subject: [TowerTalk] Mast ratio in and out of the tower
Scott,
I've had mine up for over 20 years. The mast is Chrome Molly, 2"x 20'. I
have 4' of it in the tower below a large thrust bearing. The tower is a
Tristao HDX572 equivalent to the US Tower of the same model number. I've had
20²' on this tower for the whole time pretty much. I had a KT34-XA and the
402CD 40m Yagi, plus some other stuff with no issues. We do get some nasty
winds here, although not like the tornado country but occasionally 75 MPH.
I've had no problems with either the Tail twister that rotates the house
here or the mast. My current stack is a bit larger and you can see it at QRZ
on the K6EL page. I am confident that this stack will be here long after I
am. I've added 10' to the top of my mast and I think I'm still within a good
safety margin at least for my area assuming my stack is "parked" properly
when the winds kick up. We don't get many violent downburst type
thunderstorm stuff.occasionally, but pretty rare. Four or five feet inside
the tower, with a good thrust bearing would be fine in all but the most
violent conditions.
Regards,
Jon-K6EL
k6el@comcast.net
To: <towertalk@contesting.com>
Subject: [TowerTalk] Antenna Mast - guidelines for ratio in tower / out of
tower
From: "Scott Dickson, W5WZ"
Date: Mon, 23 Mar 2009 06:10:00 -0500
I've seen discussion on the importance of selecting the correct material for
a mast. I don't recall ever seeing a discussion on the ratio of mast in the
tower versus above the tower.
I have a 2" x 0.25" by 21 ft galvanized 1026 DOM mast. It will hold a Force
12 C-51XR, (weighs 250 lbs, wind load 18 sq ft, mast torque < 900 in-lbs)
installed 2 feet above the thrust bearing at the top of the Rohn 55G tower.
The rotor is M2 Orion 2800.
Currently, I do not have any other antenna that will be on the mast.
Perhaps I'll install a 6 meter beam above the C51 in the future.
It seems to me that the length of mast in the tower is as important as the
length of mast above the tower.
What rules / guidelines / best practices are used to determine where to
install the rotor?
--Scott, W5WZ
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