All,

I have the opportunity to turn a walk-in closet with door into a ham
station. I'm thinking of turning the closet into a Faraday cage to
help in reducing common-mode QRM. To this this, I will need to line
the entire inside of the closet, including the door, with some type of
metal, and then connect that metal to my ground system.

Question is this: what type of metal would provide acceptable results:
aluminum foil, copper foil, or tin-plated zinc sheets nailed
overlapping along the closet inside?

Thanks in advance,

The Eternal Squire

wrote:
All,

I have the opportunity to turn a walk-in closet with door into a ham
station. I'm thinking of turning the closet into a Faraday cage to
help in reducing common-mode QRM. To this this, I will need to line
the entire inside of the closet, including the door, with some type of
metal, and then connect that metal to my ground system.

Question is this: what type of metal would provide acceptable results:
aluminum foil, copper foil, or tin-plated zinc sheets nailed
overlapping along the closet inside?

Thanks in advance,

The Eternal Squire

Just as important as the conductivity and thickness of the shield is
the continuity. Nonconducting seams can act as slot antennas. So
aluminum, though it is a very good conductor, is very difficult to
seam in a conductive way. Well connected, galvanized chicken wire
(with 1 inch or so holes) may work as well as aluminum foil that has
non conductive seams, as long as the holes are much smaller than the
shortest wavelengths you are trying to shield.

On 18 Oct 2005 22:13:36 -0700, wrote:

All,

I have the opportunity to turn a walk-in closet with door into a ham
station. I'm thinking of turning the closet into a Faraday cage to
help in reducing common-mode QRM. To this this, I will need to line
the entire inside of the closet, including the door, with some type of
metal, and then connect that metal to my ground system.

Question is this: what type of metal would provide acceptable results:
aluminum foil, copper foil, or tin-plated zinc sheets nailed
overlapping along the closet inside?

Thanks in advance,

The Eternal Squire

There are very few good reassons for doing this. There are also
considerations such as any thing that comes in must be bypassed
and filtered (I really mean everthing) so that none of the offending
signals arrive. AC power is the hardest to filter.

The best material and common most one is Copper screening.
Note ALL joints must be soldered or otherwise have a non corroding
and solid joint. The door also must have a 100% contact joint all the
way around (bottom too). The door will usually have phosphor bronze
allow fingers to allow contact around the periphery. What your
attempting to make is a box that has no openings that are
significant till you reach the microwave range.

Why is common mode QRM a big problem?

Allison

Out here in the this trailer park, we have both dirty power coming from
the AC, and air-conditioning motors from a whole bunch of trailers.
These are problems that cannot be fixed, so I would rather use
defensive techniques such as a Faraday cage

A Faraday cage is an electrostatic shield, not a shield for
electromagnetic fields(*). There would be no advantage to shielding your
equipment from external electrostatic fields.

Shielding your station from electromagnetic fields probably won't solve
any perceived problems, either, and is a much more difficult job. As
others have pointed out, it's often much more difficult to prevent
energy from getting through the shield via power and other conductors
and through seams and door fittings than it is to make the shield
itself. If you don't pay proper attention to the sneak paths where
energy can get in, you're wasting your time making the shield in the
first place.

(*) I found "Faraday cage" in the index of only one of a half dozen
electromagnetics texts. It's not in Terman's _Radio Engineering_ or the
rather old IEEE dictionary I have, either.

Roy Lewallen, W7EL

"John Popelish" wrote in message
...
wrote:
All,

I have the opportunity to turn a walk-in closet with door into a ham
station. ...
Question is this: what type of metal would provide acceptable results:
aluminum foil, copper foil, or tin-plated zinc sheets nailed
overlapping along the closet inside?

Thanks in advance,

The Eternal Squire

Just as important as the conductivity and thickness of the shield is
the continuity. Nonconducting seams can act as slot antennas. So
aluminum, though it is a very good conductor, is very difficult to
seam in a conductive way. Well connected, galvanized chicken wire
(with 1 inch or so holes) may work as well as aluminum foil that has
non conductive seams, as long as the holes are much smaller than the
shortest wavelengths you are trying to shield.

Lungren screen rooms use a copper screen which is just like screen door.
However, they are rated up into the GHz range. You'll also need some type
of "finger stock" around the door to provide an electrical seal. The
Lungren screen rooms have a brass-like finger stock all around the door.
The grounds _ALL_ go to one single point and only one single point

However... I'm not sure what this buys you for a ham shack...unless you want
to do receiver design and testing and need the quiet, RF free environment.
Connecting the antenna eliminates all your work, so to speak.

73, Steve, K,9.D;C'I

I'm sorry to mention this, but yes, I am a builder, and its very hard
to do low-level measurements. I was hoping that feeding my antenna
connection through a bypassed and filtered port would allow my signals
in but without the common-mode AC and motor noise.

The Eternal Squire

On 19 Oct 2005 09:57:51 -0700, wrote:

Out here in the this trailer park, we have both dirty power coming from
the AC, and air-conditioning motors from a whole bunch of trailers.
These are problems that cannot be fixed, so I would rather use
defensive techniques such as a Faraday cage

Won't work. Most of the noise is radiated and the point of
interaction is the antenna not the power cord for the most part.

If the power source really is dirty try running on isolated battery
or from the mobile rig in the car. IF you hear it there then you need
to get away from the area.

FYI: the motors used for air conditioning and refigeration are least
likely noise sources. Most are capcitor start induction types, arcing
or other raditional likely sources are not common to them.

Electonics such as TVs, Computers, Electronic Games, Lamp
dimmers and touch switches are your enemies.


Allison

Okay, I'll try it first without the cage. I do have my wife's
electronics going through a 30 amp CORCOM filter.

The Eternal Squire

Check this article out.

http://www.qsl.net/n9zia/wireless/pd...ug1998-p64.pdf

It's an article about making a shielded room from foil covered foam board.
You'd still have the problem of getting your power in, and signal cable out.
Actually, the signal cable out would be fairly easy. Bulkhead mounted
type-N or SMA connectors are made just for that purpose. The power would be
slightly more difficult. Not only do you want to keep stray RF from leaking
through the hole, but it would require filtering to reduce conducted noise
on the lines also. One of my first real jobs was at an commerical two-way
dealer. The shop, and tower were really close (less than a mile) to a 50 kW
AM broadcaster (WTOP 1500 kHz). Guess how I discovered 60 volts AC between
the cases of two AC outlets. I also learned that a 3 dB reduction in
reciever sensitivity makes a big difference, but reducing the noise level by
3 dB doesn't.

Come to think of it, of all the screen rooms, and sheet metal shielded rooms
I've ever been in the biggest problem was ventilation.

Robert N3LGC