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
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.
>Sent: Jan 23, 2007 7:44 PM
>To: email@example.com, firstname.lastname@example.org
>Subject: [TowerTalk] Why a Prop Pitch?
>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).
>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
>summarizing - Power (torque) and Size.
>From: John Cowan <email@example.com>
>Subject: [TowerTalk] Prop Pitch Motor
>Why would you use a prop pitch motor as opposed to a regular rotor?
>Subject: Re: [TowerTalk] Prop Pitch Motor
>To: firstname.lastname@example.org, email@example.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
>73 Mark W0NCL
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