Jim Thomson wrote:
> Date: Thu, 18 Mar 2010 19:12:25 -0400
> From: "Roger (K8RI)" <K8RI-on-TowerTalk@tm.net>
> Subject: Re: [TowerTalk] 2" O.D. Pipe???
> Stan Stockton wrote:
>> Just my opinion.... 1.5 inch schedule 40 may be fine if you have some
>> big tribander or 35 foot monobnder and it is mounted right above the
>> top bearing. If you are stacking antennas on the mast, forget it.
> http://www.rogerhalstead.com/ham_files/Tower29.htm shows a tribander at
> 100', 7L 6-meter Yagi at 115 and a 14' cross boom at 130' holding a pair
> of 11L on 440 and pair of 12L 144. That all on 2" schedule 40 but it's
> structural steel. It's a bit flexible with the top looking like a blue
> gill rod that just tied into a big Bass, but it's withstood over 70 mph
> winds and many occasions.
> ## sched 40 pipe doesn't come in a 2.0" OD. It's is 1.9" OD,
> with a .145" wall.
This is structural and it's approximately 2". To me, 1.9 is 2" unless
working with close tolerances.
> ## You mean to tell us that you have 30' [thirty feet] of mast,
> sticking out the top of the tower ???
Yes, with antennas as shown in the photo.
> Do you ever get ice...
Lots of it.
> or ice + wind ?
if 70 MPH plus qualifies, then yes.
> I'm going to a heavier wall DOM so it doesn't beat the antennas to
> death, but strength wise it seems to have been more than sufficient.
> OTOH it's not ordinary schedule 40 pipe which is relatively soft and
> easily bent.
> ## Regular sched 40 pipe would have been toast, long b4 now.
As I said, it's structural steel, but still listed as schedule 40.
> ## 1026 DOM comes in 60 ksi, to as high as 90 ksi.
> ## IMO... for ants mounted way up a mast, you had better [A] run the
> numbers through the spread sheet.. and [B]
> make sure the mast you buy
> has paper work with it.
> Inform your steel supplier, that it's a legal liability
> issue... and guess who's liable?
Liable for what? My roof? Then I'd agree.
> As far as wind speeds go.... unless you
> have a wireless wind speed indicator, at the top of the tower, you are
I did, but right now it's at 30'
> If it's 56 mph at grnd level, it could easily be 70 mph at the
> top of the tower. Talk to anybody who has a wireless wind speed indicator
> at both the top of the tower.. and also at the 15' level. You will get an
I'm a pilot. I'm well aware of the differences in wind speed between
ground at altitude. *although* nature is not consistent and occasionally
puts the strong gusts down low.
> ## all of this mast issue is really a no- brainer. Stuff the numbers into
> spread sheet, and see what spits out.
> ## estimate the max wind speed gusts for your area.... then add a MIN
> of 25% " to the speed [and pref a lot higher... like 30-50%]. Then procure
> the correct mast.
The antennas are still up there. Unfortunately the flexibilty of the
mast is beating the snot out of the 144 and 440 antennas which is why
I'm going to DOM, but they've been there quite while now. I'm amazed
the 17 visually verified lightning strikes haven't removed something
important, even more so than the wind.
> These 1 in a 100 yr wind storms are too plentiful these days
> and ditto with ice storms, seismic events, and heavy rains. WX patterns are
> changing.. for the worse.
I'm not sure I'd say for the worse, but they certainly are more varied.
Ours has become much more mild...so far., but the weather if becoming
much less predictable.
> OK, so you buy a mast that's overkill, so what?
I agree and said so earlier.
> Ham's spend $12K on a xcvr, without blinking an eye.
I don't have that much in my whole station including a custom amp.
> When you get the
> crane bill,
Never happen. They can't get one on the property without taking down the
power lines and shutting down the whole subdivision, plus ruining my
wife's yard. The first we could pay for. The second I'm not willing to
risk. It'd have to stay there bent up and all. Either that or cut the
guys on one side and pull it over.
> to remove the destroyed ant's, coax, etc... the pricey mast will look cheap.
I also said that in an earlier post.<:-))
> later....... Jim VE7RF
> Roger (K8RI)
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