what enclosure to use ?

[Archimedes]

Hi All

I built a super-regen radio and want to enclose this in a box of some
sort. I have two options -

1. Plastic box
2. Aluminium Box

Now I want to listen to this radio when I am sitting next to my
computer. I know that the best option is to use the aluminium box as
it provides the best sheilding. However I dont understand how that
will help, when the antenna will be protruding out of the box and
therefore the radiation from the computer will be picked up from the
antenna regardless of which box I use. Is this a correct assumption ?
so should i just stick to plastic box ?

Thanks
Shelton.

 

[Bob Masta]

On Thu, 13 Mar 2008 21:10:30 -0700 (PDT), Archimedes
<shelton.dcruz@gmail.com> wrote:

Hi All

I built a super-regen radio and want to enclose this in a box of some
sort. I have two options -

1. Plastic box
2. Aluminium Box

Now I want to listen to this radio when I am sitting next to my
computer. I know that the best option is to use the aluminium box as
it provides the best sheilding. However I dont understand how that
will help, when the antenna will be protruding out of the box and
therefore the radiation from the computer will be picked up from the
antenna regardless of which box I use. Is this a correct assumption ?
so should i just stick to plastic box ?

Thanks
Shelton.

This is pretty easy to test before you build. The plastic case is
about the same as nothing for RF, so just place your naked radio
where you want it to be and see what happens. If that's
acceptable, go with plastic. If not, and you want to see if aluminum
would make any difference, try this trick: Put the naked circuit in
a cardboard box that is about the size of the alumimun box
you are considering. Then wrap the carboard with aluminum foil,
making sure you have crimped all seams to get good contact.
Use an alligator clip or even a screw and nut to connect to this
any ground you want to test,

Best regards,


Bob Masta

DAQARTA v3.50
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator
Science with your sound card!

 

[George]

Bob Masta says...

This is pretty easy to test before you build. The
plastic case is about the same as nothing for RF, so
just place your naked radio where you want it to be and
see what happens. If that's acceptable, go with
plastic. If not, and you want to see if aluminum would
make any difference, try this trick: Put the naked
circuit in a cardboard box that is about the size of the
alumimun box you are considering. Then wrap the
carboard with aluminum foil, making sure you have
crimped all seams to get good contact. Use an alligator
clip or even a screw and nut to connect to this any
ground you want to test,

I read somewhere that magnetic metals (i.e. - ferrous) are
much more effective in shielding from RF, and
electro-magnetic interference in general, than non-magnetic
metals like aluminum and copper. But not having been
formally educated in this stuff, I'm having trouble coming
up with an explanation for why that might be true. Can you
shed light on this?

 

[John Popelish]

George wrote:

I read somewhere that magnetic metals (i.e. - ferrous) are
much more effective in shielding from RF, and
electro-magnetic interference in general, than non-magnetic
metals like aluminum and copper. But not having been
formally educated in this stuff, I'm having trouble coming
up with an explanation for why that might be true. Can you
shed light on this?

To be a good shield, the material has to be several skin
depths thick at the frequency being shielded. High
conductivity thins the skin depth, but so does high
permeability. So if the ferrous metal has a permeability
(at the frequency in question) that more than offsets its
higher resistivity, then it will need less thickness to
provide the same shielding.

http://www.ndt-ed.org/EducationResources/CommunityCollege/EddyCurrents/Physics/depthcurrentdensity.htm

--
Regards,

John Popelish