[Elecraft] Need advice on Small Tower

Wed Jul 13 20:09:07 EDT 2016

I guess since the thread is still alive, and because I use my Elecraft rigs 
 with said tower :) I'll wade in here, because I spent a fair amount of 
time  researching this two years ago before reinstalling my Wilson TT-45, which 
is  very similar.

Everyone is right, one way or the other.  The tower wind curve I have  
shows 3 square feet of wind load for a total tower height of 43 feet in a  78 
mph wind.

Another 50 mph curve supplied with the rotating base is done at 50 mph, and 
 says 12 square feet at a total height of 45 feet.

But both curves, as well as the more recent US Tower data, rely on the use  
of a house bracket in the analysis.

A much more recent US Tower doc shows 4.8 square feet of wind load, for 85  
MPH 3 second gusts, but with the tower at a height of 21 feet.  This was  
from a California PE analysis, and it also referenced the house bracket.

So the answer, "it depends" depends on at least wind speed (or gust) used,  
what base, the use of a house bracket, height of the mast in the top 
section,  and what the current sq ft numbers for your antenna happen to be, which 
seem to  be changing in some cases :).

After crunching some numbers, I decided to limit my use to 34 feet  
self-supporting with a hex and a rotating base .  It's definitely worth  doing the 
math.

I'm happy to share PDF's of the reference stuff with anyone that needs  it.

Scott ka9p (sorry Eric)

In a message dated 7/13/2016 5:08:53 P.M. Central Daylight Time,  
w6vyred at gmail.com writes:

Hi  Mike,
I don't know where the 3 SQ-FT comes from.  US Tower does not  publish 
ratings for the MA series any longer.  I have had an MA-40 since  1982 and at 
that time the rating was 10 SQ-FT @ 50 MPH winds fully  extended.  I have 
confirmed this with US Tower in the past. I was also  told at that time that 
they do not rate the tower retracted.  There have  been some new regulations 
concerning tower ratings in the past couple which is  probably why they do not 
list it now.  I have had a 3 Element SteppIR on  this tower since 2006. The 
HRO website still lists the rating at 10  SQ-FT.

That being said, I do retract the tower if winds of  50 MPH are predicted 
or if I am leaving for any length of time.  My base  is 3 X 3 X 5 which was 
recommended at that time and I have the drawings for  that.

I think the 3 SQ is indicating the size of the extended portion  which is 3 
inches square.

Date: Wed, 13 Jul 2016 04:01:47  -0700 (MST)
From: Mike  K2MK<k2mk at comcast.net>
To:elecraft at mailman.qth.net
Subject: Re:  [Elecraft] Need advice on Small  Tower
Message-ID:<1468407707184-7620050.post at n2.nabble.com>
Content-Type:  text/plain; charset=us-ascii

Hi Terry,

I'm moving and I've just  sold my MA40 with the MARB40 tilt over/rotator
base. It's a fine tower for  small loads. Be careful, it's only rated at
3sqft load when the tower is  cranked down to the 21 foot level. I had a 2
element SteppIR yagi on it and  I would crank it down if winds over 20 or 30
mph were  forecasted.

Cranking it up and down is very easy on the arm. It cranks  easily but
requires 100 cranks. Tilting it over and cranking it down and  back up
requires much greater effort until the mast is at the 45 degree  angle. I
would have liked to have a power driven winch for that  operation.

The foundation for this mast is substantial with lots of  rebar. I'm selling
my house and just had the top 12" of concrete removed so  that I could
replace it with grass. It took a crew longer to remove the 12"  then it did
for the crew to dig and pour the foundation in the first place.  I'm 
thankful
I didn't have to any of the work.

This mast can  actually be handled by one person if you have moderate
equipment to help. I  had a wheeled lawn cart for rolling it around and a
Harbor Freight 1 ton  shop crane for taking it off of the flat bed delivery
truck and helping to  engage and dis-engage the mast into the MRB40 unit.
With two people it's a  very simple job. All of my experiences were good and
given the opportunity  I would not hesitate to purchase another one.

I have a personal website  with lots of photos. Contact me directly if you
want the link.
k2mk at  comcast dot net

73,
Mike  K2MK

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