RadioBanter - shielding

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What material can be used for shield against potentially dangerous
levels of radio waves. Lets say outside my bedroom is a radio
communication device. What material could stop the waves from
entering. Cement? Lead? How thick?

Aluminium Siding -and- Aluminium Screened Windows

Speaking of aluminum screen, I previously tried a little experiment.
Just one layer of screen isn't enough, if I make a cylnder of screen,
5-6 layers thick, then place my cell phone inside the signal is lost
completly. 2-3 layers cause loss of a few bars. I'm not sure if it
is a result of blocking the signal or just scrambling it.

On Oct 9, 8:28 pm, wrote:
On Oct 9, 12:18 pm, RHF wrote:

On Oct 9, 10:00 am, billy wrote:

What material can be used for shield against potentially dangerous
levels of radio waves. Lets say outside my bedroom is a radio
communication device. What material could stop the waves from
entering. Cement? Lead? How thick?

Aluminium Siding -and- Aluminium Screened Windows

I have a MSEE, but E&M is not my specialty. However, since aluminum is
not a ferous material, I believe the H wave will penetrate it. RF
shielding paint is generally nickle for that reason. I don't recall if
"mu metal" is ferous or not.

Turn your degree in!

Faraday cages, AKA screen rooms, are used to isolated a space from the
outside
world. They use copper mesh, with the junctions welded, and achieve
isolations of
from 80dB up to ~120dB, more dB isolation requiring multiple "walls".
Think nested
Russian dolls.

A RF/EM "wave" consists of both E and H fields. Any conductive case
with completely
conductive seams and walls will stop any RF/EM field.

Take a cookie tin. With unpainted top and bottom join edges.
Put an FM radio inside tuned to the strongest FM local staiton.
As you put the top on the signal will go away.
Works for AM/MW/Cell phones as well.

Over in alt.survival we have several ongoing threads about how to
protect electronics
in a nuclear or solar EMP event.

The better answer would be "why do you think you have dangerous levels
of RF impinging
your home/bedroom?"
And
"What frequencies do you think are present?"

Higher frequencies mean shorter wavelengths, which mean any openings
have to become
smaller and minor joint imperfections become more important.

IE A friend has a home recording studio. He lives within a mile of a
pretty powerful AM/MW
station. He was getting some interference in spite of serious efforts
to filter the RF at the
input to his mixer. At my suggestion he built a screen room of
'chicken wire'. Rat wire
would have been better but the larger wire knocked the signals
intensity down enought
so it was not a problem. His room isn't really RF tight, a good radio
will still pick up the
stronger local MW stations, they are all very weak. A not perfect
screen room but effective
enough for his needs. Cellphones, TVs, FRS HTs and FM radio are fairly
uneffected. Rat
wire with it's 1/4" grid would kill everything below microwave, if you
could build a good enough
door.

Terry

On Oct 9, 6:37 pm, wrote:
On Oct 9, 8:28 pm, wrote:

On Oct 9, 12:18 pm, RHF wrote:

On Oct 9, 10:00 am, billy wrote:

What material can be used for shield against potentially dangerous
levels of radio waves. Lets say outside my bedroom is a radio
communication device. What material could stop the waves from
entering. Cement? Lead? How thick?

Aluminium Siding -and- Aluminium Screened Windows

I have a MSEE, but E&M is not my specialty. However, since aluminum is
not a ferous material, I believe the H wave will penetrate it. RF
shielding paint is generally nickle for that reason. I don't recall if
"mu metal" is ferous or not.

Turn your degree in!

Faraday cages, AKA screen rooms, are used to isolated a space from the
outside
world. They use copper mesh, with the junctions welded, and achieve
isolations of
from 80dB up to ~120dB, more dB isolation requiring multiple "walls".
Think nested
Russian dolls.

A RF/EM "wave" consists of both E and H fields. Any conductive case
with completely
conductive seams and walls will stop any RF/EM field.

[snip]

Not any. Skin depth comes into play so that any Faraday cage is going
to have a lower cut-off frequency below which attenuation falls off.
The size of holes set an upper cut-off frequency above which
attenuation falls off. A Faraday cage, therefore, looks like a band-
stop filter for RF/EM fields - the thicker the walls and the smaller
the holes, the wider the bandwidth..

Tom

On Oct 9, 1:42 pm, billy wrote:
Aluminium Siding -and- Aluminium Screened Windows

Speaking of aluminum screen, I previously tried a little experiment.
Just one layer of screen isn't enough, if I make a cylnder of screen,
5-6 layers thick, then place my cell phone inside the signal is lost
completly. 2-3 layers cause loss of a few bars. I'm not sure if it
is a result of blocking the signal or just scrambling it.

Why do you state "potentially dangerous levels of radio waves" ?

On Oct 9, 3:37 pm, wrote:
On Oct 9, 8:28 pm, wrote:

On Oct 9, 12:18 pm, RHF wrote:

On Oct 9, 10:00 am, billy wrote:

What material can be used for shield against potentially dangerous
levels of radio waves. Lets say outside my bedroom is a radio
communication device. What material could stop the waves from
entering. Cement? Lead? How thick?

Aluminium Siding -and- Aluminium Screened Windows

I have a MSEE, but E&M is not my specialty. However, since aluminum is
not a ferous material, I believe the H wave will penetrate it. RF
shielding paint is generally nickle for that reason. I don't recall if
"mu metal" is ferous or not.

Turn your degree in!

Faraday cages, AKA screen rooms, are used to isolated a space from the
outside
world. They use copper mesh, with the junctions welded, and achieve
isolations of
from 80dB up to ~120dB, more dB isolation requiring multiple "walls".
Think nested
Russian dolls.

A RF/EM "wave" consists of both E and H fields. Any conductive case
with completely
conductive seams and walls will stop any RF/EM field.

Take a cookie tin. With unpainted top and bottom join edges.
Put an FM radio inside tuned to the strongest FM local staiton.
As you put the top on the signal will go away.
Works for AM/MW/Cell phones as well.

Over in alt.survival we have several ongoing threads about how to
protect electronics
in a nuclear or solar EMP event.

The better answer would be "why do you think you have dangerous levels
of RF impinging
your home/bedroom?"
And
"What frequencies do you think are present?"

Higher frequencies mean shorter wavelengths, which mean any openings
have to become
smaller and minor joint imperfections become more important.

IE A friend has a home recording studio. He lives within a mile of a
pretty powerful AM/MW
station. He was getting some interference in spite of serious efforts
to filter the RF at the
input to his mixer. At my suggestion he built a screen room of
'chicken wire'. Rat wire
would have been better but the larger wire knocked the signals
intensity down enought
so it was not a problem. His room isn't really RF tight, a good radio
will still pick up the
stronger local MW stations, they are all very weak. A not perfect
screen room but effective
enough for his needs. Cellphones, TVs, FRS HTs and FM radio are fairly
uneffected. Rat
wire with it's 1/4" grid would kill everything below microwave, if you
could build a good enough
door.

Terry

Like I said E&M isn't my thing; rather I know analog IC design.
Somehow managed to pass two classes in E&M, and even knew how to do
Smitch charts.

I'm not quite convinced that aluminum shielding is all you need. Good
audio transformers use mu-metal shields. I thought the Faraday shield
only blocks the E, not H. Doing some googling, this website agrees
with me:
http://www.williamson-labs.com/480_shi.htm

This is the nickle spray I use for shielding:
http://www.mgchemicals.com/products/841.html
There is a chart of non-ferous and ferous shielding, with the ferous
shield being 20db better at times.

On Tue, 09 Oct 2007 17:00:13 -0000, billy
wrote:

What material can be used for shield against potentially dangerous
levels of radio waves. Lets say outside my bedroom is a radio
communication device. What material could stop the waves from
entering. Cement? Lead? How thick?

You need to fabricate one of these devices ............. immediately!

http://zapatopi.net/afdb/

On Oct 10, 1:15 am, RHF wrote:
On Oct 9, 12:18 pm, RHF wrote:

On Oct 9, 10:00 am, billy wrote:

What material can be used for shield against potentially dangerous
levels of radio waves. Lets say outside my bedroom is a radio
communication device. What material could stop the waves from
entering. Cement? Lead? How thick?

- Aluminium Siding -and- Aluminium Screened Windows

Follow-up Comment :
These are a beginning and most likely the lowest cost
first step. Plus they are the least intrusive and when
viewed from the exterior will not look like urban blight.

M...Sushi suggests
"This is the nickle spray I use for shielding:http://www.mgchemicals.com/products/841.html
There is a chart of non-ferous and ferous shielding, with the ferous
shield being 20db better at times."

CAUTION - Before using it on Interior Walls in Living Spaces
be sure to consult the MSDS Information for the Product and
the contact the Manufacture as to it's Safe Uses.

~ RHF
.

That paint is used for shield small plastic cases, not walls, though
it is available as a brus hon product. My comment is the ferrous
shielding is more effective. This again goes back to E&M,but my
recollection is a non-ferous shield only stops E, not H. A ferrous
shield, being electrically conductive as well, stops both fields.
Like I said, E&M is not my field of specialty, just my 2 cents.

billy wrote:

What material can be used for shield against potentially dangerous
levels of radio waves. Lets say outside my bedroom is a radio
communication device. What material could stop the waves from
entering. Cement? Lead? How thick?

simple copper screen (like screen door stuff) properly bonded and grounded
would do the trick nicely.

cement is partially effective (you need truckloads to do any good though )
and don't even talk about lead (the EPA would have you for lunch).

lets see, copper screen (.05 inch thick) completely around the room (plus
ceiling) properly grounded = 99% effective

cement: 1 foot thick, 10%
Lead? not sure