Re: Don't throw out the oven!

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Sunday, October 20, 2002 4:38 PM
Subject: Re: Don't throw out the oven!


> Original poster: "Mr Viggy by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<LittleViggy-at-alum.manhattan.edu>
>
> But, wouldn't a microwave oven be designed to keep microwaves inside,
> not the complete RF range?
>
> Viggy
> > > Since the oven part is designed to keep the R.F. inside, it should
> > do an equally good job of keeping R.F. out.  In other words, it is
> > a ready made faraday cage!  A great place to put anything that you
> > don't want zapped while firing your Tesla coil!
> >
>

A good point, but bear in mind the following:

Microwave ovens are designed to keep the field at the outer surface of the
microwave below around 5 mW/cm^2 at 2450 MHz...

1) Tesla coils run at hundreds of kHz, many, many decades below 2.4 GHz....
what makes a good shielded box at 2.4 GHz won't do so at 100 kHz.

2) It turns out that you don't need all that great a shielded box to keep
the flux below the limit... Say the box is a cube 31.6 cm on a side.. the
total surface area is 31.6x31.6x6 cm^2, or about 6000 cm^2.. that's
5E-3W*6E3 cm^2 or 30W total leakage... Assume now that there's 1000W
inside.. The microwave oven box only needs attenuate around a factor of 33,
or less than 20 dB... which is not a very good shielding...

(A note.. I read somewhere about someone who put their cell phone in a
microwave to protect it from EMI during a Tesla coil test... they were much
surprised when the phone rang!)*


>>*That was me and it does work! - Terry<<