[TowerTalk] Biggest rotor that will fit in a Rohn 25G

[Roger (K8RI) on TT]

Don't forget to multiply the wind area 6-meter antenna by the height 
above the top of the tower. Even a small antenna can rapidly gain 
resistance with height.  A 3 sq ft antenna, 10'bove the top of the tower 
become 30 sq ft.

73

Roger (K8RI)


On 7/20/2016 Wednesday 8:39 PM, Jeff AC0C wrote:
> Thanks for the guys who have replied so far.
>
> The top section is a flat top with a bearing.  The rotor would sit 
> down at the junction of the first and second section point.
>
> The antenna under consideration is probably something like a Tennadyne 
> T12 covering 10-30m, 36 foot mast, 53' max element and about 150 lbs.  
> 16 sq ft if I remember right.  I may stick a small 6m beam up above 
> the T12 but that would not offer much in the way of wind loading 
> compared to the LPDA, other than the contribution to torque felt by 
> the top mast bearing.
>
> 73/jeff/ac0c
> www.ac0c.com
> alpha-charlie-zero-charlie
>
> -----Original Message----- From: Steve Maki
> Sent: Thursday, July 21, 2016 5:34 AM
> To: towertalk
> Subject: Re: [TowerTalk] Biggest rotor that will fit in a Rohn 25G
>
> On 7/20/2016 17:26 PM, Bill Tippett wrote:
>> K8RI:  > A heavy duty rotator with a large antenna should be mounted 
>> well
>> down into the tower. Mounted at the top, in the tapered section would
>> likely put very high stress at that point.
>>
>> I mounted my rotator at the same point in 45G and had no problems for 
>> >10
>> years with the antennas/wind speeds in Colorado described 
>> previously.  If
>> still concerned, you could mount a straight 25G section above a straight
>> 25AG4 and install the rotator in the 16" window.  Of course this would
>> require a long mast (~15').  I don't know which LPDA Jeff is considering
>> but I doubt it's >32 sq. ft.
>
> And besides, the rotational torque will be resisted by z-braced sections
> below the rotator.
>
> The only concern with the normal R25 rotator mounting position is
> lateral loads encountered with tall masts. I've seen pointy top sections
> fold over in that scenario.
>
> -Steve K8LX
>
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-- 

73

Roger (K8RI)


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