I found that a capacitive shield plate connected to ground through a 100 Ohm resistor would eliminate the VFD noise effects. Changing the resistor to 1000 Ohms started to show some interference. I'm hoping that a flimsy Mylar conductor (around 1 Ohm per square) would be a sufficient shield for the electrical field coupling (the gap between the 2 coils is a couple of mm).
As the old guy in the ESI repair department would say . . . "One experiment is worth a thousand expert opinions."
Thanks
Carl
Carl B. Van Wormer, P.E., AE7GD
Senior Hardware Engineer
Cipher Engineering LLC
21195 NW Evergreen Pkwy Ste 209
Hillsboro, OR 97124-7167
503-617-7447x303
[log in to unmask] http://cipherengineering.com
-----Original Message-----
From: Louis Hart [mailto:[log in to unmask]]
Sent: Wednesday, August 10, 2016 7:28 AM
To: TechNet E-Mail Forum <[log in to unmask]>; Carl Van Wormer <[log in to unmask]>
Subject: RE: [TN] looking for medium resistance material
Carl, if the conductor thickness is less than the skin depth, would that mean the magnitude of the evanescent wave electric field would be great enough to allow propagation outside the shield? Sorry to say, my understanding of electromagnetic field theory is a lot less than what I think it should be, but I am curious.
Regarding aluminum and soldering, I knew a guy who had a roll of 'aluminum solder' on his desk although I never saw him use it. The wire was several millimeters in diameters, so may not have been for electronic purposes.
On the subject Drew brought up of mu-metal, I inherited a microwave spectrometer long ago which had a klystron housed in the stuff. The fellow who bequeathed it to me said the metal was great for shielding, but its desirable properties were degraded by mechanical forming.
Nice to see good activity on TechNet. (I may qualify as one of the old-timers, having joined when it first appeared back in 1994 or 1995.) Louis Hart
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Carl Van Wormer
Sent: Wednesday, August 10, 2016 9:16 AM
To: [log in to unmask]
Subject: Re: [TN] looking for medium resistance material
My next attempt will be to try a metalized Mylar, hoping that the thin conductor (much thinner than the skin effect depth) will be good enough for the capacitive shielding, but too thin for significant eddy current flow from the magnetic field. If that work, I will be left with the "simple" matter of connecting to the shield. How do you solder a wire to a party balloon?
Thanks,
Carl
Carl B. Van Wormer, P.E., AE7GD
Senior Hardware Engineer
Cipher Engineering LLC
21195 NW Evergreen Pkwy Ste 209
Hillsboro, OR 97124-7167
503-617-7447x303
[log in to unmask] http://cipherengineering.com
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