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Author Topic: Sched 40 PVC for coil form on 160M  (Read 2919 times)
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WD8BIL
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« on: February 02, 2020, 12:20:55 PM »

OK Guys, get them arrows ready!  Grin

What are thoughts on using sked40 PVC as a coil form in a KW amp on 160 meters? It'll be @ 13uh and after the 40/80 Meter coil wound on 1 3/4"dia G10 Stock. I just don't have enough G10 for the entire coil.


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W1ITT
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« Reply #1 on: February 02, 2020, 02:13:51 PM »

I don't know what the loss tangent of PVC is at 160 meters, and it wouldn't surprise me if PVC plumbing parts from different manufacturers used differing recipes.  Aside from the pressure specifications, the stuff isn't highly specified, at least not the stuff we get at Home Desperate.  Those oft repeated advice  is to put it in the microwave oven, along with a cup of water to serve as an absorptive load.  If the PVC heats up at 2.4 ghz you might want to reconsider its use at 160m...or not.
However, I have been using a 4 inch white PVC coupling as the coil form for my 160m through 40m input link on a balanced tuner for decades, most often at a kilowatt or better and there is no sign of deformation or discoloration.  Certainly there's plenty of RF flux under there.  My coil is quarter inch copper tubing, so there would be little heat loss in the copper.  If you use thick wire or tubing, keeping the ohmic (heat)  losses down, it will probably be OK.  But I don't have the numbers to prove it. 
The thought occurs to me that those green fiberglas (?) military masts that come in four foot sections might be worth looking into.   They are close to your 1 3/4 OD G-10 in dimension.   A few years ago I chopped off a piece of that to use as the base for a ground mounted vertical.  In the end, there's only one way to find out...
73 de Norm W1ITT
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Jim, W5JO
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« Reply #2 on: February 02, 2020, 03:39:44 PM »

Check Schedule 80 too.  Right now I forget what Gary, W7FG used to make the spacers on his ladder line but it did not react with RF.  Someone still sells that antenna so you might drop him a line and ask what is being used.  Just be sure to tell him it is for a coil and not a competitor for him.
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WD8BIL
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« Reply #3 on: February 02, 2020, 05:40:51 PM »

All good thoughts.

Norm.... I'm thinking the only heating will be from RF current in the wire. I'll be using #8 copper so it should handle the current well. The famed microwave oven test is useless to determine reaction at 1.8MHz! Your experience with it in your tuner is the best news. It kinda supports my suspicion that it'll do fine.

Thanks Jim. Another data point confirming my suspicions.
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KD6VXI
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« Reply #4 on: February 02, 2020, 10:23:46 PM »

I stopped using spacers.

I wind the cool on a form then mount it.  If there is any sag I take a piece of copper flashing and wrap it around the coil like I'm making a tap.  Except I mount the psuedo tap to a ceramic spacer.

No pvc to melt / smoke / etc and the coil doesn't have anything to mess with Q or other properties.

I do have quite a bit of ceramic spacers.  If you don't, maybe another idea.

--Shane
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W7TFO
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« Reply #5 on: February 03, 2020, 12:21:59 AM »

I've seen PVC pipe used in a BC 1kW AM TX. 

It was superseded by plates of plexiglass at 90deg, for a square coilwind, but the old way still worked.

It was wound with heavy litz wire.

73DG

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Just pacing the Farady cage...
km6sn
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« Reply #6 on: February 03, 2020, 04:40:35 AM »

ABS pipe has less RF loss than PVC
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Patrick J. / KD5OEI
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« Reply #7 on: February 07, 2020, 11:02:04 AM »

PVC stinks in a Tesla coil secondary.
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Radio Candelstein
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