Mu Metal shield

[mac]

http://www.youtube.com/watch?v=Tqqqe7xReII

There are two tv stations in my block!!!
I wonder how much will it cost to shield my entire apartment   

mac

[PRR]

You stop TV frequencies with electric shielding. Copper mesh. Copper sheet. "Faraday cage"

Often you can get significant reduction with rather skimpy mesh like this:


But are you really picking-up TV signals on your pedals? Such high frequencies don't leak much into small metal boxes, are absorbed by non-RF circuitry.

[Hides-His-Eyes]

Mu metal is for blocking magnetism isn't it? Not RF?

[R.G.]

Mu metal is specialized toward low-ish M fields all right. It has a very high initial permeability, although it saturates more easily than other magnetic materials.  For RF shielding, the higher the conductivity the better, and the smaller the holes the better. RF is blocked up to the frequency where the biggest dimension of the holes is 1/4 wavelength, so wire mesh is pretty good for RF in the TV broadcast range.

[Earthscum]

I was asking something a bit similar in this thread: http://www.diystompboxes.com/smfforum/index.php?topic=93317.0

What would be the largest hole size to use for, say a clear window on an amp, or stompbox top?

[beans_amps]

1/4 wavelength for channel 13 is about one foot.  So any thing you would use for amp making is probably going to be good to screen that out.  UHF is another matter.  They are reallocated for cellphone use and whatnot.

I agree with everyones comments on the mu-metal.  Mu-metal has a high nickel content and is intended to 'filter' magnetic feild interference.  Originally intended to sheild CRT's in electric power stations from the heavy currents flying around in there.

Aluminum is quite effective at filtering electrical feild interference.  I worked for several years in a facilty using RF to weld plastics together.  We used aluminum or brass for all our sheilding.

Another thing to look into is an RF filter on the DC power connection.  This is if you are not using battery power.

Sean

[Earthscum]

I agree with everyones comments on the mu-metal.  Mu-metal has a high nickel content and is intended to 'filter' magnetic feild interference.  Originally intended to sheild CRT's in electric power stations from the heavy currents flying around in there.

Ugh... at my last job we had electric under-floor heating (electric cast into the concrete floors). I hated doing design in the winter. Whenever it would kick on, the monitor screens would float, wave, and flicker all over the place. The only one it didn't affect was the Mac blue monitor. Another monitor would be fine for about 10 minutes after you degaussed it, lol. Wish I had known about mu-metal before. I bet I could've got the boss to drop some money on it, he's an engineer.

[amptramp]

One point about mu-metal is that it is not intended to be bent or folded after it is annealed.  The shapes you see for conical CRT shields are fabricated and then the metal is annealed above the Curie point (where all magnetism is overcome by thermal energy) before the item can be used.  If it is flexed or bent, it has to be annealed again or you lose the magnetic shielding effect.  And mu-metal is expensive!

For our purposes, electrostatic shielding via aluminum or other non-magnetic materials is adequate.  The aluminum acts as a mirror that reflects the electric field and the magnetic field has to return with it.  Thus, electrostatic shields can eliminate magnetic interference, just like the shorted turn on a shaded-pole phono motor delays the magnetic field.  Similarly, shielded wire works perfectly well even though it has no magnetic component and the relative permeability is 1.0.

[runmikeyrun]

I used to live about 2 miles from a 50,000w AM station transmitter.  Everything I built had AM radio coming through it until I finally put it in a box.  Not to mention that it was a politically motivated station of which I was NOT a fan!  That was frustrating.  Aside from building a faraday cage around my work area there was really nothing I could do about it.  sorry about your luck.

[Paul Marossy]

I used to live about 2 miles from a 50,000w AM station transmitter.  Everything I built had AM radio coming through it until I finally put it in a box.  Not to mention that it was a politically motivated station of which I was NOT a fan!  That was frustrating.  Aside from building a faraday cage around my work area there was really nothing I could do about it. 

That would have drove me crazy!

[mac]

You stop TV frequencies with electric shielding. Copper mesh. Copper sheet. "Faraday cage"

But are you really picking-up TV signals on your pedals? Such high frequencies don't leak much into small metal boxes, are absorbed by non-RF circuitry.

IIRC using the wave eq and considering that in a conductor j=const*E one can calculate how much a wave can penetrate a metal as a function of the freq. This is stuff I didn't see in 25 years... I have to find and take a look at my notes...

Some months ago I did a funny experiment using thick stainless steel cookwares. I put my cell phone into one, called, and guess what? ring... ring.
I had to put a small cookware into a big one to isolate my cell phone.
I did the same thing with a small pocket radio, same results. One cookware wasn't enough.

When I have some free time i'm going to check if for example 1mm of solid metal is the same as 10 leaves of 0.1mm. I suspect that reflections and absortions between leaves can have some extra fx.

I used to live about 2 miles from a 50,000w AM station transmitter.  Everything I built had AM radio coming through it until I finally put it in a box.  Not to mention that it was a politically motivated station of which I was NOT a fan!  That was frustrating.  Aside from building a faraday cage around my work area there was really nothing I could do about it.  sorry about your luck.

Not only I have tv stations but street power transformers, public lights, traffic lights, motorcycles... Except for the lovely girls walking in the avenue, everything in the street makes noise.
The middle single coil of my guitar is useless   

mac

[mac]

Another use for mu metals,
speakers too close to power tubes,

http://www.chambonino.com/work/miscguitar/misc6.html

My LC30 does not have this problem but I should have to do some tests to be sure.

mac