If we're really looking for more things to worry about you could add
vertical loading caused by that heavy steel tubing, and colum strength. You
may eventually decide to stick with wires in trees. Isn't that where most of
started a few decades ago ?
Gene / W2LU
----- Original Message -----
From: "Gene Fuller" <w2lu@rochester.rr.com>
To: "Tower and HF antenna construction topics." <towertalk@contesting.com>
Sent: Friday, March 19, 2010 9:26 AM
Subject: Re: [TowerTalk] 2" OD pipe.. again
> Depending on where you live, to be really safe, add another0.5 " or so to
> the mast diameter for ice, although you're probably not likely to get ice
> and high wind at the same time.
> I've had "good luck" (after lots of calculation) with 2"dia x 0.25 wall
> seemless steel tubing, with large LP a foot or two above the top thrust
> bearing.
> Gene / W2LU
> ----- Original Message -----
> From: "Jim Thomson" <Jim.thom@telus.net>
> To: <towertalk@contesting.com>
> Sent: Friday, March 19, 2010 1:29 AM
> Subject: [TowerTalk] 2" OD pipe.. again
>
>
>> 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.
>>
>> ## You mean to tell us that you have 30' [thirty feet] of mast,
>> sticking out the top of the tower ??? Do you ever get ice...
>> or ice + wind ?
>>
>>
>>
>>
>> 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.
>>
>> ## 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? As far as wind speeds go....
>> unless
>> you
>> have a wireless wind speed indicator, at the top of the tower, you are
>> really
>> guessing. 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
>> earful.
>>
>> ## all of this mast issue is really a no- brainer. Stuff the numbers
>> into the
>> spread sheet, and see what spits out.
>> http://thebont.com/spreadsheets/AnalysisOfAntennaMastStrength.htm
>>
>> ## 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. 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. OK, so you buy a mast that's overkill, so
>> what?
>> Ham's spend $12K on a xcvr, without blinking an eye. When you get the
>> crane bill, to remove the destroyed ant's, coax, etc... the pricey mast
>> will look cheap.
>>
>>
>> later....... Jim VE7RF
>>
>>
>>
>>>
>>>
>>
>> 73
>>
>> Roger (K8RI)
>> _______________________________________________
>>
>>
>>
>> _______________________________________________
>> 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
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|