Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: Glen Martin Roof Top Question  (Read 660 times)
AF5LO
Member

Posts: 40




Ignore
« on: August 15, 2001, 08:02:53 AM »

I have mounted a 4.5' rooftop tower on my garage.  As it turned out, the lag bolts (not the big ones supplied by Glen Martin) went into the rafters on both sides of the tower.  Once I drilled the pilot holes, I realized that I was into the rafters, so I could not use the 5 inch lag bolts from GM.  The rafters are 2x4 construction.  What sort of additional bracing do I need?  I do not believe we are in a high-wind area, but some thunderstorm gusts can reach 60 mph.  I have a maple tree screening the antenna (Cushcraft MA5B) from the west wind.  Located in Brunswick, Ohio (20 miles SSW of Cleveland).  Mast is Rohn 2"x10'.  
Logged
N4UM
Member

Posts: 466




Ignore
« Reply #1 on: August 15, 2001, 11:14:11 AM »

I'd consider putting some 2x6's at right angles to the rafters underneath the roof. Make them long enough to overlap at least 4 of the rafters.  The idea is to distribute the stress from the tower over a relatively large portion of the roof so that it is not all concentrated in a small area.  I think Glen Martin's  advertising brocure illustrates how to do this.
Logged
AC5E
Member

Posts: 3585




Ignore
« Reply #2 on: August 15, 2001, 12:26:16 PM »

Hi: I had much the same problem, but I'm down here in the hurricane belt.

  I put 2x4 "bridges" between the rafters, positioned directly under the tower legs, and connected to the rafters with the metal L brackets called "hurricane clips." Then I put 60" 2X6 bracing across bridges, rafters, and all to spread the pull on the roof out.

  It's been up several years, through one hurricane and several storms with 80 MPH gusts, and it's still there.

  73  Pete Allen  AC5E
Logged
AF5LO
Member

Posts: 40




Ignore
« Reply #3 on: August 15, 2001, 01:16:41 PM »

What about lightning protection?  Did you ground the roof-mounted tower, or just use lightning suppressors on the coax?
Logged
AC5E
Member

Posts: 3585




Ignore
« Reply #4 on: August 15, 2001, 02:44:22 PM »

  Hi again Lenny: I run the coax to ground level, where I have an Alpha Delta lightning arrestor mounted directly to the center lightning rod of a three rod array. That is, there are three 8 foot lightning rods on 8 foot centers, connected with #2 copper wire tied to the rods with multiple clamps. If I have ever been hit, I don't know it - but my neighbors have had to replace televisions, TV dish's, etc..
  73  Pete Allen  AC5E
Logged
AF5LO
Member

Posts: 40




Ignore
« Reply #5 on: August 15, 2001, 08:48:45 PM »

OK, I have installed an arrestor, but haven't yet connected it to ground rods.  I wanted to get a sense of what to use first.  Sounds like you trenched the #2 wire between rods.  I now have everything connected but antenna (MA5B) does not perform on 12M at all.  FIne everywhere else.  O'ell.  Tnx es 73, Lenny
Logged
AC5E
Member

Posts: 3585




Ignore
« Reply #6 on: August 15, 2001, 10:17:30 PM »

 Hi again. Lenny, the wires between my ground rods are in the ground, but they didn't start that way. I drove the rods down about 7 feet.

  I clamped the inter-ties to the rods with small diameter hose clamps (4 per rod, close spaced, as best I remember) and drove the rods down until the wire was on the ground, leaving just a nub sticking out on the ends, and just enough of the center rod to mount the lightning arrestor on. The grass has grown up and captured enough soil, so the end two rods are under the surface, and the arrestor is right at ground level.
 
   By the way, the object of the three rods is to absorb a lot of energy fast. Three rods gives three low resistance paths to ground. It seems to work since I have had no lightning damage.


   I wish I could help you with the 12 Meter problem - but I don't remember even seeing one of those antennas.

  73
Logged
AF5LO
Member

Posts: 40




Ignore
« Reply #7 on: August 16, 2001, 07:57:19 AM »

I see that you live in MS.  I think you get more lightning there than we do.  Turns out we have severe WX predicted for today.  Guess I get to see how well this baby is bolted to the roof!  Still haven't grounded it yet.  I'll just disconnect the coax and put it in a glass jug for now until I getthe arrestor hooked up.  Mine had to go 7 feet abover the ground.  I'll relocate it when I get time to cut the coax (it's 9913, nasty to work with for installing connectors).  As far as 12M goes, I have a wire up that works there.  It's a quiet band anyway and usually dead by the time I get home.  

From what I understand about lightning, it prefers to strike the best available path to ground.  My antenna right now, is not the best path.  Sometimes I often wonder why we ground... seems like we are just inviting a strike.  
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!