Gary,
Most rotator manufacturers publish "square foot" ratings for their
rotators. This rating does not fully account for the wind dynamics of
very large Yagis where much of the wind load is developed at a large
radial distance from the mast.
For example, the square footage of a MonstIR is similar to the square
footage of a large triband Yagi stacked with a 2 element shorty
forty; however, the MonstIR develops much more torque and momentum because much
of the wind load is at much larger radial distance from the mast.
Full size -- or near-full size -- 40 meter 3 element Yagis (including
the MonstIR) develop very large torque and momentum that cannot be
reliably handled by anything but a large rotator.
73!
Frank
W3LPL
---- Original message ----
>Date: Tue, 9 Jan 2007 07:24:30 -0600
>From: "Stone, Gary R." <Gary.Stone@va.gov>
>Subject: RE: [TowerTalk] Rotor Selection Advice Wanted - Heavy Duty
>To: <donovanf@starpower.net>, <towertalk@contesting.com>
>
>Then I have a question. The M2 2800 is rated to handle the MonstIR
>stated load. And if the M2 2800 can't handle it (as appears to be the
>case over and over - which is incorrectly rated - the M2 or the MonstIR
>or am I missing something?).
>
>Gary, N5PHT
>
>-----Original Message-----
>From: towertalk-bounces@contesting.com
>[mailto:towertalk-bounces@contesting.com] On Behalf Of
>donovanf@starpower.net
>Sent: Monday, January 08, 2007 11:14 PM
>To: towertalk@contesting.com
>Subject: Re: [TowerTalk] Rotor Selection Advice Wanted - Heavy Duty
>
>Rick,
>
>I installed two M2 Orion 2800s in 1998, they've very reliably turned
>a 48 foot boom 15M Yagi on a 200 foot tower, and a 48 foot boom 20M
>Yagi on another 200 foot tower. Both of these rotators take a serious
>beating in the wind with no difficulty at all, and there's no reason to
>baby sit them by pointing the antennas into the wind etc.
>
>I use a "small" prop-pitch on another 200 foot tower. It easily turns a
>full size 3 element 48 foot boom Yagi. The wind load of this large
>antenna is slightly larger than the wind load of a MonstIR. I wouldn't
>even consider trying to turn this antenna with a M2 Orion 2800, it
>produces far too much wind load for a mid-sized rotator.
>
>The initial symptom of an undersized rotator is boom slippage in
>moderate winds. Redesigning the manufacturer's mounting clamps will
>reduce or eliminate the slippage, but result in destruction of the
>rotator in high winds.
>
>None of the above suggests that there's a problem with the M2 Orion.
>I own four M2 Orion 2800s, and I'd purchase more in a flash when I need
>them. Its an exceptionally reliable rotator for all but the very
>largest antennas, for which it was never intended.
>
>The MonstIR is in this class of very large antennas that requires a
>large rotator, such as a small prop-pitch, or -- based on favorable
>reports here -- a large rotator such as the Prosistel 67 or the
>Yaesu 2800.
>
>On a related note, the 2 inch mast commonly used with MonstIR
>installations presents a serious mast slippage problem for almost any
>clamping system. If you can substitute a 3 inch mast, you'll have a
>much improved installation.
>
>73!
>Frank
>W3LPL
>
>---- Original message ----
>>Date: Mon, 8 Jan 2007 16:36:36 -0800 (PST)
>>From: "Rick Karlquist" <richard@karlquist.com>
>>Subject: Re: [TowerTalk] Rotor Selection Advice Wanted - Heavy Duty
>>To: donovanf@starpower.net
>>Cc: towertalk@contesting.com
>>
>>donovanf@starpower.net wrote:
>>> I should have been clearer in my reply to Rick's e-mail. Rick
>discussed
>>> using an M2 Orion 2800 or a prop-pitch rotator with the MonstIR.
>>>
>>> The M2 2800 Orion rotator has insufficient capacity to hold the
>MonstIR in
>>> a moderate wind, while a prop-pitch will handle the MonstIR easily
>under
>>> any conditions that the MonstIR can survive.
>>>
>>> I did not intend to make a comment regarding the Yaesu G2800DXA, and
>I'm
>>> sorry my e-mail wasn't specific enough to avoid unintentionally
>>> interpreting it that way.
>>>
>>> 73!
>>> Frank
>>> W3LPL
>>
>>That's really helpful, Frank. I had no idea how inadequate the Orion
>>was. On K7NV's web site, he talks about "small, medium, and large"
>>prop-pitch units. Is the "small" one adequate for the MonstIR? I am
>>not sure if the "medium" one can fit into my 15" top tower section.
>>
>>Rick N6RK
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