[TowerTalk] Why a Prop Pitch?

Tue Jan 23 23:09:15 EST 2007

For many years, I've seen one of the small prop-pitch rotors under a home-brew 3-element 10-Meter beam on a local building. The rotor and beam look like they have been abandoned many years ago. Judging by the bent, rusted boom of the beam, the two element halves that have fallen off, no feedline, and some other tell-tale signs, I would bet money that it was put up in the mid-late 1950's, when prop-pitch rotors were easily and inexpensively obtained (I still have the conversion info from a 1950's CQ Magazine), and when 10-Meters was open around the clock.

I've been meaning to stop and ask the people that have the building if they'd consider letting it go, or ask what they might want for it. It evidently has been forgotten about and ignored for many years, along with a TV antenna and some kind of small heavy-duty looking parabolic dish, which is just lying on the roof - neither hooked to any feedlines. 

On the prop-pitch setup, I don't see any selsyn with sprockets (like I used with the prop-pitch rotor I had back in the 60's/70's to turn my Telrex TB6EM yagi) or other direction indicating device hooked to the prop-pitch or mast, so I have no idea how they might have determined the yagi's direction.

Until just a week or two ago, K7NV had some pictures on his site that showed the insides of a prop-pitch rotor that had suffered significant water damage after being up for many years without being properly sealed when it was installed. So there's a chance that this abandoned one might not be in restorable condition, either. But maybe I'll stop and see if they want to get rid of it, just so I can see how it might have survived, probably after about 50 years in the weather. I was hoping to take the building owner some pictures of what happens to these units out in the weather, to make my case of "doing him a favor" to offer to get rid of that old "junk" for him! Maybe I'll email K7NV and see if he still has those pictures and can email them to me.

Larry

-----Original Message-----
>From: NPAlex at aol.com
>Sent: Jan 23, 2007 7:44 PM
>To: towertalk at contesting.com, w0tmm at yahoo.com
>Subject: [TowerTalk] Why a Prop Pitch?
>
>John,
>I can only guess from your comment that you have not had any experience  with 
>a prop pitch motor used as a rotator.  There are several reasons that  one 
>would use a prop pitch motor.  
>One was cost, as surplus motors were available at very reasonable prices.  
>They bring some premium now do to limited availability.  
>Another reason was power, or Torque. They can handle very heavy  loads.  
>Another reason is size and shape.  They fit inside relatively small  tower 
>cross sections, with no projections beyond the tower sides as some of the  new 
>models do.  This makes them very ideal for crank-up towers as all is  within 
>the tower envelope.  
>The electric motors (nom. 24vdc) are held in place with a large castle ring  
>nut, spin that off and the motor unplugs for easy maintenance.  The gear  box 
>removal is on a par with most rotator types.  
>One of the drawbacks however is direction sensing.  That has to be  added.  
>Historically that was done by use of Selsyn tx/rx coupled to the  mast.  Today 
>both M2 and Green Heron Engineering provide controllers with  pulse counting 
>direction indication.(K7NV design used with GHE, check out his  web site).  The 
>GHE controller has many features and provides ramp up and  down which is 
>useful with large arrays.
> 
>I have had the same prop pitch motor in service for nearly 40 years,  trouble 
>free.  
> 
>summarizing - Power (torque) and Size.
> 
>Norm W4QN
>==============================================================
>Message:  3
>From: John Cowan <w0tmm at yahoo.com>
>Subject: [TowerTalk] Prop Pitch  Motor
>To: towertalk at contesting.com
>
>Why would you use a prop  pitch motor as opposed to a regular rotor?
>John  W0TMM
>-----------------------------
>
>Message: 4
>Subject: Re:  [TowerTalk] Prop Pitch Motor
>To: w0tmm at yahoo.com,  towertalk at contesting.com
>wasnt he going to turn some serious snort? After  making about 6 trips 
>up the tower to work on rotors this last year Ive  wondered why I didnt 
>go to them in the first place. A new spid is working  great for me know 
>though.
>73 Mark W0NCL
>
>
>
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