Jorge,
Depends how big your 'big yagis' are, what wind speed you'd like the
mast to survive. You have to do some calculations.
For your existing mast, the tricky part can be to identify what material
the mast is made of. Makes a huge difference to the mast's ability to
survive in strong winds, so it is important/essential that you know what
the mast is made of.
Here I have an Optibeam OB4030 and an Ultrabeam 4-el (like Steppir 4-el,
but stronger). That's a total of about 20 sq ft of antennas.
When I did the calculations, it showed that for a 15ft mast and antennas
separated by 10ft, 2inch diameter 0.25in wall S355 steel would fail at
a wind speed of 63mph. Too low for my risk tolerance.
To get 100mph wind survivability, I had to go to 2.5in diameter S355
with 0.25 in wall. (I used S355 because that's what I could get with a
minimum strength certificate. It is similar to, but slightly lower spec
than DOM1026 - I can't get steel to the US DOM 1026 spec in UK).
If you have even medium sized yagis, I suspect your 0.125 inch mast will
fail at quite a low wind speed. Not surprised you see it bending!
Some resources for learning more:
http://www.arraysolutions.com/images/KT9OMpartI.pdf Part 2 is also on
the Array Solutions site.
K7LXC's MARC mast calculator program from Champion Radio Products.
Dave Leeson's (W6NL now, W6QHS when he wrote the book) 'Physical Design
of Yagi Antennas' has excellent coverage of materials and mast
calculations.
Hope that helps,
Dave G3WGN WJ6O
-----Original Message-----
From: Jorge Diez - CX6VM [mailto:cx6vm.jorge@gmail.com]
Sent: Thursday, December 27, 2012 14:13
To: towertalk@contesting.com
Subject: [TowerTalk] mast for two big antennas
Hello
Wich type of mast do you use when you have 2 big yagi?s on the same
mast, maybe 10 ft of separation?
Mine 0.125 inch wall mast bend a little with strong winds
73,
Jorge
CX6VM/CW5W
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|