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Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061
Hi all.
Just found a circular biscuit tin-like tube of mesh, with caps at each end. It looks about 25cm diameter and has 2mm mesh size.
Would this be OK for use as a Faraday cage for a small SSTC to limit RF interference? plan is to have it arcing in all directions from a point to the edges and lid of the cage
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
NeilThomas wrote ...
The coupling from a cyclinder large enough to contain the SSTC as a cage and the SSTC itself will be pretty low, so it sounds ideal.
Yes, from my experiments conductive metal (copper, brass, aluminium) seems not to waste significant amount of power, especially in CW, since it's impedance is mostly dominated by inductive reactance, ohmic resistance is very low and little power is dissipated on it.
So all it would practically do is decrease the inductance a bit.
I could put PCB's right under the primary and get really no observable effect. On almost all my coils I happily use large brass bolts to fix my secondary base.
Stay away from iron though, and maybe take more care for it with disruptive coils since ohmic losses increase with duty cycle.
Making the cage too narrow might actually be a much bigger problem because of increase of capacitance and subsequent drop in Q factor.. so give the coil some room in the cage.
One weird thing I noticed, linked to this, when I have two air-coupled coils, putting a copper sheet under one seemed to *increase* coupling between them a bit!
Since I used tuned circuits at first I thought this must be due to shift in resonant frequencies, but when I made the receiver circuit untuned the effect was still there!
Also, if I put receiving coil above and bit on side of the transmitting coil turned by 90 degrees, I'd get very little power transferred, but if I put a sheet of copper by 45 degrees against them, power transfer would increase dramatically. :O
Can sheet of metal really be increasing coupling between coils or I'm getting something terribly wrong there?
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Circular Faraday cage?
