Date: Thu, 11 Nov 2010 19:47:30 -0600
From: "Stan Stockton" <k5go@cox.net>
Subject: Re: [TowerTalk] Prop Pitch Indicator
Roger,
I believe the best solution is to buy a Green Heron Engineering/K7NV
control box. Their indicator system uses a stationary reed switch and a
magnet that is on a piece that is mounted to the bottom of the motor
shaft. You set the gear reduction ratio in the rotator box - 9576-1 for
a small prop pitch - and as it spins it will count turns and give you a
very accurate digital readout. The point and shoot knob and electronic
limiting of rotation are other desirable features.
#### I forgot to mention the electronic limit switch feature of the
GH box. You can independently set the CW and CCW limits to
what ever you want..and they are capable of a lot more than 360 degs.
If the PP is a side mount set up, with a typ max of 300 deg rotation
limit, the CW /CCW limit is programmed in...so the PP stops just
prior to the boom smacking the tower. The GH box has other features,
such that if any shorted wiring, the PP won't run amok, and the fet is self
protected.
## Back in the 70's, MM station VE7WJ had several PP's in use. He had
no limit switch's on most of them. One day, the phone rang a few seconds
after he had started turning his 60' boom on 20m. He owned a real estate co,
and
was engrossed in the business call. He forgot all about the PP, that kept
spinning
round and round and round. The coax had ripped the DE right off the boom,and
the whole thing was a helluva mess!
## The GH box is not cheap, [it's no worse than a DCU-1] but kill's abt
10 x birds with one stone. I'd err on the side of caution and use the
ramp up/down feature anyway. You will spend more time and effort
with selysns, external gears, outboard limit switch's, hb pwr supplies,etc,
and maintenance frustration, than you ever will with the GH box.
later.... Jim VE7RF
If you have a big
antenna you can also ramp up the motor, ramp it down, and run it full
out in between. The control box is not cheap but in my opinion most
antennas that are big enough to require a prop pitch are worth spending
the extra money on that control box if you can afford it. I have one
and wish I had two more.
Stan, K5GO
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