Good Source for Insulators for Quarter Wave Stub?

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Good Source for Insulators for Quarter Wave Stub?

Post by DelD » Sun Aug 21, 2016 12:33 am

I'm wondering if anyone knows of a good source for the typical insulators used for a 1/4 wave stub (about 3" long iirc). They are used to support the insulated portion of the vertical run of FM transmission line on a tower to the bonding point approximately 1/4 wave from the base.

Hoping to find an alternative to Kintronics. They can provide them, but they are very expensive compared to those Andrew used to provide (no longer available).

Good used insulators in known good condition would also be great.
Del Dayton
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Re: Good Source for Insulators for Quarter Wave Stub?

Post by Deep Thought » Sun Aug 21, 2016 10:21 am

Other than RF Parts in San Marcos, CA (who may or may not have the correct size) you might try your local power company. Most of the insulators used for this sort of thing came from that application anyway. You may have to improvise the tower connection bracket from the coax clips but usually you can take those apart and insert the insulator between the two halves.
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Re: Good Source for Insulators for Quarter Wave Stub?

Post by ChuckG » Mon Aug 22, 2016 12:25 am

ERI sells them: ... 037547.pdf

Looks like nothing but a round member adapter/standoff + insulator + butterfly hanger tossed in a bag. Could probably roll your own if you had to.
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Post by RGORJANCE » Mon Aug 22, 2016 8:29 am

These insulators are the same ones that Andrew had been supplying for a very long time. They will suit your needs. Just be sure to configure them for your specific tower mechanical construction for either round member, or angle iron members.


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Re: Good Source for Insulators for Quarter Wave Stub?

Post by BigRed » Wed Aug 31, 2016 3:57 pm

Check with Phasetek in Quakertown, PA. They're straight shooters and build one hell of a good phaser and ATU product. Nice people to deal with too.

And then there's these guys in New England:
They stock all those old transmitting mica and newfangled vacuum capacitors that Radio Shack doesn't seem to have anymore. They also have a large stock of insulators. Just be willing to wait for a callback from the guy that owns the company. Fortunately they're also nice folks to deal with.

And then there's The RF Connection. If he doesn't have it in stock he'll probably know where to get it, new or surplus (and he's good people too).

And sometimes when I've REALLY been in a bind I've been known to use Schedule 80 PVC pipe (gotta order it from someone like McMaster Carr Supply, the local Home Despot won't know what you're talking about) as replacement for bowl insulators. Should be able to fabricate something from the various fittings and the pipe itself (flanges and endcaps along with "conventional" transmission line hangers). Don't know how that will hold up structurally for the long haul but I've had a couple of glass bowl substitutes made from 2" schedule 80 PVC parts that look just fine after 5-years. McMaster also has fiberglass-reinforced resin shapes (tubing, solid rounds and sheets) that could be used to fabricate such insulator stand-offs. Just a thought . . .

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