EMI leaking down shaft of rotary switch

Grrr. Rev 2. Corrects brass bushing reference designator.(above)

James

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I've got it now. It=92s funny my brain starts down one path to a solution and tends to get stuck there.

I don't know how James makes the beautiful ASCII art, I haven=92t the patience nor the skill. Nothing beats a white board for getting ideas across.

George H.

cheap:

You could try a short length of straight wire spring under a local screw head bearing against the shaft.

Also check out Smalley wave springs.

John

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Thanks again for all the ideas. If Grayill doesn't come through I think I like the ideas that have a bit of side-loading on the shaft. I get ground contact in two places. On one side where the spring doing the pushing and on the other where the shaft is pushed into the inner side of the hole. Between the two the shaft should be grounded.

George H.

George,

I thought this was one of your side projects for students. I'd certainly go with one of the other suggestions in real life!

Cheers

Phil

Just a goofy idea, but can you find a way to insert a whole lot of graphite into the shaft bearing? Or maybe massively silver loaded lithium grease?

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Phil, My side projects are things like keeping my Ferguson TO-20 Tractor running. I build apparatus for students as a living.

Maybe You'll like this one,

I enjoy it though and that=92s all that really counts.

George Herold

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Yeah I thought about that, the bushing sits right in top of the shaft hole.... it's hard to see how I could inject anyting in there. And this knob is going to get a lot of action. I'd be afraid that after

But thanks,

George

Very pretty! I think that two photon Doppler-free spectroscopy is one of the most beautiful measurement ideas ever.

Cheers

Phil Hobbs

Thats about right, the anchor points in the Motorola design was the slot in the chassis the shaft of the PC board mounted pot went through. It was slotted because the chassis was soldered on after the parts were waved on. The slot was a convenient place the spring could grip, the ends of the spring were bent back to grip the wall of the chassis slot. Hard to describe but suffice to say, spring tension and the shaft held the part in place.

Brilliant idea! Still it would be good to see Grayhill stand by their specs!

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Yeah, Do you have any idea if whoever first figured this out found it by accident or on purpose. I've noticed that you can sometimes see a bit of Doppler-free absorption with a single laser beam and a bit of relection off the back side of the gas cell.

George H.

The reference I have for it is

L. S. Vasilenko, V. P. Chebotaev, and A. V. Shishaev, JETP Lett. 3 (English translation) p.161 (1970)

Russian papers in the Soviet era never admitted discovering anything by accident, so I don't suppose we're likely to find out. Of course the Lamb dip can show up the same way, and that was discovered by accident IIRC.

Cheers

Phil Hobbs

As a beyond-cutoff waveguide, maybe a disk attached to the shaft that is positioned close to the panel? Size of disk to be as large as practical; maybe a large one on the inside and a small one (size of knob so as to not show?) on the outside?

I *still* do not understand how signals get thru; the frequency must be quite high and thus easy to filter at inputs..

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Robert, The switch is connected to the resistor I'm looking at. If the shaft loses contact with ground it becomes an antenna. It 'transfers' the electric fields outside the box to the inside, where they capacitivily couple to the resistor. Perhaps you=92re confused because everyone knows you shouldn=92t =91hot=92 switch signals as I=92ve done. But it=92s just easy and it works=85. Most of the time.

George Herold

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Hmm too bad, maybe the story will come out later. I love stories of accidental discoveries. It gives us average chums (by =91us=92 I=92m only referring to myself and not you) hope that if we keep our eye balls peeled we might see something.

George H.