DIY Faraday cage for a mobile phone

Hello -

I'm writng some software to run on a PocketPC with a built-in GPRS phone,
and I need to test the software when the GPRS signal is weak, intermittent
or non-existent. The cheapest way to do this seems to be to build a Faraday
cage with adjustable leakiness. It needs to have some holes in it so that I
can see the screen and tap it with a stylus. Unfortunately I'm working at a
location that has excellent GPRS coverage.

I've already confirmed that a metal tin that previously contained Marks and
Spencers chocolate biscuits is 100% effective, but I can't see through it or
operate the PocketPC. I've also tried making a cage out of a single sheet of
galvanized chicken wire with 12mm square holes, held together with plastic
cable ties, with overlapped joints. This only caused a small amount of
attenuation, the PocketPC hardly noticed. I'm guessing that it failed
because the diagonals of the holes are larger than 10% of the wavelength
that GPRS uses (1800MHz ?) or because the plastic cable ties don't provide
good conductivity at the joints.

Before I go out and buy some expensive perforated copper sheet, can anyone
offer advice on improvements?

Thanks

---

› See More: DIY Faraday cage for a mobile phone

> Before I go out and buy some expensive perforated copper sheet, can anyone
> offer advice on improvements?
>
> Thanks

Have you tried covering the open side of the tin with two layers of
chicken mesh slightly offset.

Dave

"Dave Stanton" <[email protected]> wrote in message
news[email protected]...
>
> > Before I go out and buy some expensive perforated copper sheet, can
anyone
> > offer advice on improvements?
> >
> > Thanks
>
> Have you tried covering the open side of the tin with two layers of
> chicken mesh slightly offset.
>
> Dave

Thanks for the reply. I did briefly try that, but it wasn't very successful.
I think part of the problem is that the biscuit tin appears to have a layer
of laquer on it, and the chicken wire has a slightly oxidized Zinc coating,
so it may be difficult to get a good electrical connection between the two,
which I understand is important. I think I will try this again.

Dave Stanton wrote:
>> Before I go out and buy some expensive perforated copper sheet, can anyone
>> offer advice on improvements?
>>
>> Thanks
>
> Have you tried covering the open side of the tin with two layers of
> chicken mesh slightly offset.
>
> Dave
would it help if you laid on your back and looking up at the P/PC
covered it with tin so you can still operate it inside the tin?

Simon wrote:

> I'm writng some software to run on a PocketPC with a built-in GPRS phone,
> and I need to test the software when the GPRS signal is weak, intermittent
> or non-existent. The cheapest way to do this seems to be to build a Faraday
> cage with adjustable leakiness. It needs to have some holes in it so that I
> can see the screen and tap it with a stylus. Unfortunately I'm working at a
> location that has excellent GPRS coverage.
>
> I've already confirmed that a metal tin that previously contained Marks and
> Spencers chocolate biscuits is 100% effective, but I can't see through it or
> operate the PocketPC. I've also tried making a cage out of a single sheet of
> galvanized chicken wire with 12mm square holes, held together with plastic
> cable ties, with overlapped joints. This only caused a small amount of
> attenuation, the PocketPC hardly noticed. I'm guessing that it failed
> because the diagonals of the holes are larger than 10% of the wavelength
> that GPRS uses (1800MHz ?) or because the plastic cable ties don't provide
> good conductivity at the joints.
>
> Before I go out and buy some expensive perforated copper sheet, can anyone
> offer advice on improvements?

Some fine wire mesh, such as:
<http://rswww.com/cgi-bin/bv/initSession.jsp?goto=/rswww/subRangeAction.do&catoid=-1600768109&store=uk>


--
Grunff

In uk.d-i-y Simon <[email protected]> wrote:
> Hello -
>
> I'm writng some software to run on a PocketPC with a built-in GPRS phone,
> and I need to test the software when the GPRS signal is weak, intermittent
> or non-existent. The cheapest way to do this seems to be to build a Faraday
> cage with adjustable leakiness. It needs to have some holes in it so that I
> can see the screen and tap it with a stylus. Unfortunately I'm working at a
> location that has excellent GPRS coverage.

Simply purchase a new large fridge, and open the door a crack.

"Simon" <[email protected]> wrote in message
news:[email protected]...
> Hello -
>
> I'm writng some software to run on a PocketPC with a built-in GPRS phone,
> and I need to test the software when the GPRS signal is weak, intermittent
> or non-existent. The cheapest way to do this seems to be to build a
Faraday
> cage with adjustable leakiness. It needs to have some holes in it so that
I
> can see the screen and tap it with a stylus. Unfortunately I'm working at
a
> location that has excellent GPRS coverage.
>
> I've already confirmed that a metal tin that previously contained Marks
and
> Spencers chocolate biscuits is 100% effective, but I can't see through it
or
> operate the PocketPC. I've also tried making a cage out of a single sheet
of
> galvanized chicken wire with 12mm square holes, held together with plastic
> cable ties, with overlapped joints. This only caused a small amount of
> attenuation, the PocketPC hardly noticed. I'm guessing that it failed
> because the diagonals of the holes are larger than 10% of the wavelength
> that GPRS uses (1800MHz ?) or because the plastic cable ties don't provide
> good conductivity at the joints.
>
> Before I go out and buy some expensive perforated copper sheet, can anyone
> offer advice on improvements?

As a general rule of thumb, grid spacing should be less than (or equal to)
1/10 the wavelength of the highest frequency you are interested in blocking.

Marcus

>> Have you tried covering the open side of the tin with two layers of
>> chicken mesh slightly offset.
>>
>> Dave
>
> Thanks for the reply. I did briefly try that, but it wasn't very successful.
> I think part of the problem is that the biscuit tin appears to have a layer
> of laquer on it, and the chicken wire has a slightly oxidized Zinc coating,
> so it may be difficult to get a good electrical connection between the two,
> which I understand is important. I think I will try this again.

What you need to do is use plenty of nuts and bolts with large washers to
hold the mesh in place and yes, scrape the laquer off. Blimey this is
taking me back a few years to Amateur Radio days.
RF will leak around holes so good firm electrical contact is essential.

Dave

"Simon" <[email protected]> wrote in message
news:[email protected]...
> Hello -
>
> I'm writng some software to run on a PocketPC with a built-in GPRS phone,
> and I need to test the software when the GPRS signal is weak, intermittent
> or non-existent. The cheapest way to do this seems to be to build a
Faraday
> cage with adjustable leakiness. It needs to have some holes in it so that
I
> can see the screen and tap it with a stylus. Unfortunately I'm working at
a
> location that has excellent GPRS coverage.
>
> I've already confirmed that a metal tin that previously contained Marks
and
> Spencers chocolate biscuits is 100% effective, but I can't see through it
or
> operate the PocketPC. I've also tried making a cage out of a single sheet
of
> galvanized chicken wire with 12mm square holes, held together with plastic
> cable ties, with overlapped joints. This only caused a small amount of
> attenuation, the PocketPC hardly noticed. I'm guessing that it failed
> because the diagonals of the holes are larger than 10% of the wavelength
> that GPRS uses (1800MHz ?) or because the plastic cable ties don't provide
> good conductivity at the joints.
>
> Before I go out and buy some expensive perforated copper sheet, can anyone
> offer advice on improvements?
>
> Thanks
>
>
========================
Have you considered using a box made from the reinforcing mesh used with car
body filler? It's very easily shaped and reaily available.

Cic.

Or find a friend with a steel Narrowboat or just take the whole lot to
Braunston, Northamptonshire. The signal is next to nothing by the canal
there.
Brian

"Simon" <[email protected]> wrote in message
news:[email protected]...
> Hello -
>
> I'm writng some software to run on a PocketPC with a built-in GPRS phone,
> and I need to test the software when the GPRS signal is weak, intermittent
> or non-existent. The cheapest way to do this seems to be to build a
> Faraday
> cage with adjustable leakiness. It needs to have some holes in it so that
> I
> can see the screen and tap it with a stylus. Unfortunately I'm working at
> a
> location that has excellent GPRS coverage.
>
> I've already confirmed that a metal tin that previously contained Marks
> and
> Spencers chocolate biscuits is 100% effective, but I can't see through it
> or
> operate the PocketPC. I've also tried making a cage out of a single sheet
> of
> galvanized chicken wire with 12mm square holes, held together with plastic
> cable ties, with overlapped joints. This only caused a small amount of
> attenuation, the PocketPC hardly noticed. I'm guessing that it failed
> because the diagonals of the holes are larger than 10% of the wavelength
> that GPRS uses (1800MHz ?) or because the plastic cable ties don't provide
> good conductivity at the joints.
>
> Before I go out and buy some expensive perforated copper sheet, can anyone
> offer advice on improvements?

How about putting it in a microwave oven (with the microwave off,
obviously!)

You could control it with PocketVNC with a cable connected to it if you need
to operate it with the door closed.
You could just open the door a bit the get the required signal strength.

Sparks...

In article <[email protected]>, Simon
<[email protected]> writes
>Hello -
>
>I'm writng some software to run on a PocketPC with a built-in GPRS phone,
>and I need to test the software when the GPRS signal is weak, intermittent
>or non-existent. The cheapest way to do this seems to be to build a Faraday
>cage with adjustable leakiness. It needs to have some holes in it so that I
>can see the screen and tap it with a stylus. Unfortunately I'm working at a
>location that has excellent GPRS coverage.
>
>I've already confirmed that a metal tin that previously contained Marks and
>Spencers chocolate biscuits is 100% effective, but I can't see through it or
>operate the PocketPC. I've also tried making a cage out of a single sheet of
>galvanized chicken wire with 12mm square holes, held together with plastic
>cable ties, with overlapped joints. This only caused a small amount of
>attenuation, the PocketPC hardly noticed. I'm guessing that it failed
>because the diagonals of the holes are larger than 10% of the wavelength
>that GPRS uses (1800MHz ?) or because the plastic cable ties don't provide
>good conductivity at the joints.
>
>Before I go out and buy some expensive perforated copper sheet, can anyone
>offer advice on improvements?
>
>Thanks
>
>

You'll need quite a fine mesh to do that!. And no gaps either. Solder
all of them and operate the keys with non conductive rods of a very
small diameter.

Try the lower sub basement floors of a car park or concrete building.

Or failing that take the whole shooting match out into Norfolk where
you'll fine a lack of GSM GPRS UMTS and much else!....
--
Tony Sayer

The message <[email protected]>
from "Simon" <[email protected]> contains these words:

> Before I go out and buy some expensive perforated copper sheet, can anyone
> offer advice on improvements?

Door from an old microwave should make a nice seethrough radio-opaque
wossname.

--
Skipweasel
Pay no attention to that man behind the curtain.

In an earlier contribution to this discussion,
Simon <[email protected]> wrote:

> Hello -
>
> I'm writng some software to run on a PocketPC with a built-in GPRS
> phone, and I need to test the software when the GPRS signal is weak,
> intermittent or non-existent. The cheapest way to do this seems to be
> to build a Faraday cage with adjustable leakiness. It needs to have
> some holes in it so that I can see the screen and tap it with a
> stylus. Unfortunately I'm working at a location that has excellent
> GPRS coverage.
>
> I've already confirmed that a metal tin that previously contained
> Marks and Spencers chocolate biscuits is 100% effective, but I can't
> see through it or operate the PocketPC. I've also tried making a cage
> out of a single sheet of galvanized chicken wire with 12mm square
> holes, held together with plastic cable ties, with overlapped joints.
> This only caused a small amount of attenuation, the PocketPC hardly
> noticed. I'm guessing that it failed because the diagonals of the
> holes are larger than 10% of the wavelength that GPRS uses (1800MHz
> ?) or because the plastic cable ties don't provide good conductivity
> at the joints.
>
> Before I go out and buy some expensive perforated copper sheet, can
> anyone offer advice on improvements?
>
> Thanks

I've got an excellent Faraday Cage. It's better known as a caravan!
--
Cheers,
Roger
______
Please reply to newsgroup.
Reply address IS valid, but not regularly monitored.

"Simon" <[email protected]> wrote in message
news:[email protected]...
> Hello -
>

>
> Before I go out and buy some expensive perforated copper sheet, can anyone
> offer advice on improvements?

Try a old biscuit tin (a metal one)- you may find just putting the top in
with a "crack" open is enough.

--
73
Brian
www.g8osn.org.uk