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Categories | Antenna Rotators & Accessories | Prop pitch rebuilt by K7NV Help

Show all reviews of the Prop pitch rebuilt by K7NV

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AC8DE  Rating: 5/5 Mar 31, 2014 11:35  Send this review to a friend!
Better than the Best by Far  Time owned: 6 to 12 months
The Prop Pitch is the “holy grail” of rotators (short of industrial gearboxes), but they have a complex install and only make sense for those that have big heavy arrays… or have plenty of money and simply want the best. The prop pitch is an interesting and unique rotator with unique requirements and unless you've went through the motions of installing one, you don't know how unique it is. Kurt’s remanufacturing work is absolutely immaculate putting this rotator truly in a class all by itself. (It’s called a “rebuild” here on e-ham, but it truly is a remanufacture.) It is a serious piece of hardware for serious hams that have pockets deep enough to spend serious money on their equipment, but has serious install requirements as well.

Their HUGE gear reduction either 7,000:1 (medium or large size) or 9,500:1 (small size) and the fact they were built for military plane propeller pitch control (hence the name) makes them pretty special in many ways. Kurt’s rebuilds are not oil filled like they were originally, but rather grease packed for rotator service. They are true triple-stage planetary gear drives and have stupid high torque capability that puts their safety margin so high that they yawn at turning a large array. But they do turn slower than most other rotators due to the high gear ratio. An interesting fact is that if you adjust for the time value of money for when they quit making the prop pitch in the mid 1950's, if they still made it today, the SMALL unit would cost about $28,000! That gives you an idea of the kind of mil-spec build quality and capability it has, as there was no corner cutting in its design like other rotators.

The normal situation for installing a prop pitch is usually a high dollar large array installation and not just for a typical tribander due to its size and cost. The small prop pitch will fit in smaller towers like a crank up. (The smallest version of a prop pitch is larger than a Tailtwister, so it won't fit in compact crank-ups.) The medium size won't fit in anything smaller than Rohn 45. Even then you have to either cut out a cross brace or drop it in from the top, as it is physically long with the big motor on the bottom. And they are HEAVY! When I took delivery of the medium sized one from K7NV I was shocked at the weight when I tried to pick up the big tube it came in, as I hadn't considered how much it weighed. Packed, it weighed about 80 lb. Just the heavy mounting plate made to take the appropriate vertical loading and a heavy duty top bearing plate for the appropriate sized thrust bearing will set you back $500, not including the thrust bearing! If you add an intermediate plate, even more money is needed. It sure ain't no Ham IV installation! hi hi

The prop pitch requires higher amperage than other large standard rotators, so not just any controller can be used. A special Green Heron RT-21pp is what is normally used and is what Kurt supplies with a rebuilt unit. I hadn't considered the high current required by a prop pitch with a 280' wire run and how that affected voltage drop and wire gauge. The minimum wire I could go with was 10 gauge, which causes a 10% voltage drop at nominal current draw of 5 amps. At the peak amps of 8, it hits 17%, but I expect that we will never see that because we will keep the ramp rate pretty low. Jumping up to 8 gauge nearly triples the wire cost and does get the drop down to 10% drop at 8 amp peak current draw, but at nominal current draw it’s only a 3-4% difference, which isn't enough in speed/torque to worry about. A prop pitch requires 3 parallel runs of the heavy gauge wire and 2 conductors of small size for the feedback.

While not really a “negative”, if there is one thing I don’t like is that it still utilizes a terminal strip for electrical connection. A nitpick, I know. I’m sure this is to keep the connection universal and to follow the practices of most other rotators, but is a throwback to days gone by in my mind and doesn’t really suit this rotator with the connector options available today. I’d rather mount a weather proof Deutsch connector on it so that all connections are hermetically sealed from the elements without any goop and I don’t have to worry about a terminal screw coming loose. But that is just my preference and not really a negative.

If you can afford or need a K7NV rebuilt prop pitch, you’ll NOT be disappointed.
 
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