[TowerTalk] [Bulk] Re: MASTS

Wed Mar 16 16:19:31 EDT 2016

15' mast...15 ft!  I don't know how that 4 snuck in. Musta fat fingered 
the keys.

Roger (K8RI)

On 3/16/2016 Wednesday 2:21 PM, Roger (K8RI) on TT wrote:
> Alternative materials for masts , or any material leave you playing 
> the odds. The stronger the materials the more the odds are in your 
> favor. An antenna of only 5 sq ft of wind area on a 145' mast become 
> the equivalent of  a 75 sq ft antenna.  Far, far beyond the ability of 
> water pipe, sked 40, or even 80.  Water pipe is the same material as 
> rigid conduit which is easily bent with hand tools although hydraulic 
> benders are used on larger sizes.
>
> EMT come in 10' lengths. I've never seen longer.
> For rotators mounted down in the tower, torque resonance is a real 
> thing.  The longer the mast, the lower the frequency.  Strength is not 
> a direct indication of spring
>
> Many materials have been used, but often the success is in spite of 
> inferior materials and a lot of luck.
>
>
> I'm surprised EMT would be rated near those specs as it's designed to 
> be easily bent with hand tools. Larger sizes are available in 90, or 
> sweep 45s and 90s as the would collapse  if bent.
>
> Just because something non standard worked for someone does not mean 
> it wioll work for you.
>
>
> 73
>
> Roger  (K8RI)
>
>
> On 3/15/2016 Tuesday 9:40 PM, Grant Saviers wrote:
>> Gerald,
>>
>> Could you point me to the 35kpsi spec?  I couldn't find a steel spec 
>> on the Wheatland EMT manufacturer site, or that matter on any other 
>> site I looked at that google turned up re conduit specs.
>>
>> Here is a section from a Q&A by the Steel Tube Institute re the 
>> controlling ANSI 80.3 standard for electrical conduit
>>
>> "Rigid conduit is intended for electrical applications, not 
>> structural ones. Its requirements are governed by UL and ANSI 
>> specifications, not by ASTM. The main issue here is that, whereas 
>> dimensions may be similar between the two, rigid conduit is not 
>> intended for, is not designed for, and is not tested for any strength 
>> or structural requirements."
>>
>> So while the yield number and wall thickness in the mast calculator 
>> turn out ok, YMMV.  And likely with the thin wall it will deform with 
>> boom and rotator clamps.
>>
>> Standard schedule 40 water pipe would be a much better choice for 
>> several reasons:
>>
>> 1. the grade steel is specified
>> 2. it is specified to withstand an internal pressure, which is a 
>> control on the seam weld quality
>> 3. it is allowable in structural applications, although used mostly 
>> in larger diameters.
>> 4. hot dip galvanized inside and out
>>
>> Caveat emptor.  Unless it falls down, and your insurance asks about 
>> the engineering and the plaintiffs attorney finds the statement to 
>> the effect "I don't care if it falls down."
>>
>> Grant KZ1W
>>
>>
>> On 3/15/2016 12:35 PM, TexasRF--- via TowerTalk wrote:
>>> Google says 1.5" EMT is actually 1.75" OD and .065" wall thickness and
>>> yield strength is 35,000 psi.
>>>   Putting these numbers in a mast analysis program and using a 7 sq 
>>> ft wind
>>> load 24" above top of tower, failure happens at a wind speed of 84 mph.
>>> Lowering  to 12" above tower top, failure is at 119 mph.
>>>   So, it could be useful in a modest installation.
>>>   73,
>>> Gerald K5GW
>>>       In a message dated 3/15/2016 2:01:59 P.M. Central Daylight Time,
>>> infomet at embarqmail.com writes:
>>>
>>> Let’s  not call names.
>>> An EMT mast is great, as long as you don’t get greedy and make it 
>>> too tall
>>> outside the tower.
>>> Mine is about 2’ above the tower top  and I think it will survive 
>>> any wind
>>> likely in my area.  And I really  won’t cry if the $150 beam is 
>>> damaged!
>>> It’s several years old and shows no  sign of deterioration. It cost 
>>> almost
>>> nothing and weighs next to  nothing.
>>> So I have a used tower, used tribander, used rotator, EMT mast, but new
>>> coax.
>>> I also have a HB amp made from used components, with an easy KW+ 
>>> output.
>>> It’s a rare pileup I can’t get through.
>>> I am VERY happy,  but may change to an LPDA so I can get the WARC 
>>> bands,
>>> someday.
>>>
>>> I also  use junk tubing from a kid’s swingset for Field Day. It’s 
>>> worked
>>> fine  for a decade or so.
>>>
>>> Successful systems can be designed around most any components, as 
>>> long as
>>> one doesn’t try to do too much!
>>> I’d far rather see a  ham put up 30-40 feet of used tower and a used
>>> tribander than envy those with  more elaborate, expensive setups!
>>> A few more hours on the air will make up  for a few dB of antenna
>>> performance and there will be money left for  beer.
>>>
>>> Wilson
>>> W4BOH
>>> _______________________________________________
>>>
>>>
>>>
>>> _______________________________________________
>>> TowerTalk  mailing  list
>>> TowerTalk at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/towertalk
>>>
>>> _______________________________________________
>>>
>>>
>>>
>>> _______________________________________________
>>> TowerTalk mailing list
>>> TowerTalk at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/towertalk
>>
>> _______________________________________________
>>
>>
>>
>> _______________________________________________
>> TowerTalk mailing list
>> TowerTalk at contesting.com
>> http://lists.contesting.com/mailman/listinfo/towertalk
>
>

-- 

73

Roger (K8RI)

---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus