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Author Topic: Clark Masts QTM Series  (Read 1764 times)
KD0AFK
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Posts: 245




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« on: December 02, 2007, 08:21:21 PM »

Is anyone familiar with this company? They sell air actuated extendable masts that extend to 30 feet and collapse to 3 feet. This would be perfect for a mobile mast mounted on the back of my sleeper for a beam. Here is the link. http://www.clarkmasts-usa.com/QTM.html The only problem is that they are located in the UK and I know shipping will probably be just as expensive as the mast itself. Is there anyone in the US that sells the same kind of item? I am working on a beam that will lie flat against the back of my sleeper and with a motorized head, rotate it into place once it is hoisted up into place. A "V" beam made out of hamsticks seems like the way to go on this. Any and all comments are welcome.
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KD0AFK
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« Reply #1 on: December 02, 2007, 09:10:44 PM »

As a follow up to my question, what I envision for the beam is a 20 meter yagi that opens up sort of like an umbrella so that it would lie close to the mast like a closed umbrella and when the mast is hoisted up I could flip a switch and a motor would pivot the closed antenna 90 degrees to horizontal and a second motor would wind a cable tight and the elements would open up to form a yagi.
I am trying to work on an animation to demonstrate this and will post it if I get it finished.
I am thinking that as long as all of the elements are grounded or connected or isolated the way that they should be, and the cable that actuated the extending of the elements is insulated from the elements themselves it shouldn't be a problem. I would like something that I wouldn't have to climb a ladder or take a half an hour assembling to be able to get on the air with.
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KD0AFK
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« Reply #2 on: December 02, 2007, 09:57:04 PM »

here is a crude animation of what i want to do.
http://truckerham.com/animations/yagianimation.gif
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W5CPT
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Posts: 561




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« Reply #3 on: December 03, 2007, 05:44:18 AM »

There are a few US manufacturers that make pneumatic masts. All the news trucks have them and the EMS here in Paducah KY has one mounted in their converted bus. The down side of these things is the cost. They costs tens of thousands of dollars. Hardly worth the advantage on HF that you get. If you were using a microwave link where you had to have line-of-sight yes, but for 14Mhz no. And the air pump must run the entire time the mast is up.

More time and money than it is worth.

Clint - W5CPT
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KD0AFK
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« Reply #4 on: December 03, 2007, 07:22:15 AM »

The pneumatic masts that I have seen that are made in the US are huge things like you see on broadcast vans and yes they more than likely cost thousands of dollars but what I saw on the Clark site is nothing more than an extendable mast with an air chuck maybe seals for the air, couldn't cost more than a couple hundred dollars. If they cost too much, I'll just have to make my own.
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KD0AFK
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« Reply #5 on: December 03, 2007, 01:24:45 PM »

their cheapest one is almost $900. Seems kind of a rip-off to me. I'll see if I can't build one for a fraction of that. Being in a big truck I have an on board air compressor at my disposal. with a little ingenuity, aluminum pipe, a welder and rubber o-rings I think I can build one for less than $100.    
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W5CPT
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« Reply #6 on: December 05, 2007, 03:18:10 PM »

I (and others I am sure) would be very interested in seeing what you come up with.

Clint - W5CPT
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NA0AA
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« Reply #7 on: December 06, 2007, 09:58:57 AM »

That will be interesting.  We have a pneu mast on our RACES vehicle [old TV remote van] and provided the seals are lubed, and clean, the compressor does not run all the time to keep it erected.

BUT, it's a good 15-20 minutes to raise/lower the mast.

How about a crank-up tower?  The shortest ones are about 11' collapsed, if you put an electric winch on it you are good to go.

Personally, I believe you are over-thinking this just a bit.  Check out the MFJ extendable masts in their current catalogue - they have a couple of versions now at various price points.

I'm using their cheap 33' fiberglas with a wire taped to it for a vertical with a SG-230 antenna coupler - maybe you could use something like that?

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