Metal RF shielding for plastic cases

[John_M]

Which one? :shock: :wink:

Your first post.

Click me.

Click me.

Click me.

Read through tells just about everything.

So it helps?

Yes. If you have an expensive receiver that you want to protect.
Read every one.

 

[Al42]

Al42:
1. The shield does not have to be grounded to stop EMF

Your degree in electrical engineering is from where? Mine's from CUNY. A magnetic shield doesn't have to be grounded - an emf shield does.

2. The original question was for any type of interference.
Do CRT's transmit an RF signal?

Everything with electricity flowing through a non-linear component radiates RF. The question is how much. In the case of a CRT, not enough to matter.

3. Power Supply not transmitting Broadband noise. The
purpose of the shield on top of the Powersupply is to stop the power supply from radiating EMF (60hz EMF)

Which wouldn't bother a scanner so, since that's what this discussion is about, who cares?

4. Poorly designed? After the design and testing was completed the Bubble Detector detected smaller bubbles with fewer miscues.

Poorly designed because it was susceptible to magnetic interference.

5. With any project there are time constraints and so much money available for a project. If the project takes more time than originally projected then you can ask for more money but sometimes it is not always granted. For the shield we used what was available to us.

You could have gotten a sheet of mu-metal for a few dollars in a few days. Unless you already hasd a CRT shield lying around that you could cut up.

We tried different types of sheet metal for the shield. We used what worked and it worked great. Sure you can find better metals to be used for the shield who's got time for this?

How long does knowledge take? It took me about 0.1 second to come up with mu-metal.

6. After a project is completed there are going to be people to criticize. Hindsight is always 20/20. I do not know why you even attempt to critisize when you are absolutely unfamiliar with the project I am describing.

Which had noithing to do with the original thread.

7. Call AOR up and tell them how they could have done better with the design of the 8200 and see what they say. The 8200 handheld is under constant developement. (8200MarkII 8200MarkIII)

Again - nothing to do with the current thread.

 

[Al42]

What a topic.

Lets take few steps back.

(OK, I know I am going to screw up a few things, so just chime in where you KNOW I am wrong)

RF or EMF radiation (Radio waves) are shielded by conductive material.

If the material makes a complete shell around the object, the interior of that shell is shielded whether or not the shell is grounded. If the shield is not complete it must be grounded to be effective.

Oopsies. The shell radiates the signal if the source is inside. It shields what's inside from what's outside only.

This is the type of shielding found in most radios

Depends. Some shields are to prevent signals from radiating outward. (Like, say, intermediate oscillator products.)

A unique type of magnetic shielding is the Faraday shield. This is a conductive band placed around a magnetic field source in a particular orientation to intentionally generating an eddy current in the conductive band (converting the magnetic energy into electrical energy). This current then dissipated as heat. You see this shields as copper bands around transformers and metallic tape or mesh loops around CRT monitor tubes.

And incomplete loops around search coils on metal detectors.

 

[John_M]

Al42:
1. The shield does not have to be grounded to stop EMF

Your degree in electrical engineering is from where? Mine's from CUNY. A magnetic shield doesn't have to be grounded - an emf shield does.

2. The original question was for any type of interference.
Do CRT's transmit an RF signal?

Everything with electricity flowing through a non-linear component radiates RF. The question is how much. In the case of a CRT, not enough to matter.

3. Power Supply not transmitting Broadband noise. The
purpose of the shield on top of the Powersupply is to stop the power supply from radiating EMF (60hz EMF)

Which wouldn't bother a scanner so, since that's what this discussion is about, who cares?

4. Poorly designed? After the design and testing was completed the Bubble Detector detected smaller bubbles with fewer miscues.

Poorly designed because it was susceptible to magnetic interference.

5. With any project there are time constraints and so much money available for a project. If the project takes more time than originally projected then you can ask for more money but sometimes it is not always granted. For the shield we used what was available to us.

You could have gotten a sheet of mu-metal for a few dollars in a few days. Unless you already hasd a CRT shield lying around that you could cut up.

We tried different types of sheet metal for the shield. We used what worked and it worked great. Sure you can find better metals to be used for the shield who's got time for this?

How long does knowledge take? It took me about 0.1 second to come up with mu-metal.

6. After a project is completed there are going to be people to criticize. Hindsight is always 20/20. I do not know why you even attempt to critisize when you are absolutely unfamiliar with the project I am describing.

Which had noithing to do with the original thread.

7. Call AOR up and tell them how they could have done better with the design of the 8200 and see what they say. The 8200 handheld is under constant developement. (8200MarkII 8200MarkIII)

Again - nothing to do with the current thread.

Al42 No, your right, it had nothing to do with the original thead.
But you did attempt to criticize the project. Again, you are absolutely unfamiliar with the Bubble Detector project. So why did you attempt to criticize? Give me a break!

Radiated EMF from a Power Supply could very well cause problems if close to scanner boards.

Read through Poltergeisty's first post. In case of a CRT
not enough to matter. Tell that to the guy who made up custom steel
side, top, and back panels to protect his receiver. To tell you the truth I don't see any need to ground it. Nor was grounding mentioned in Poltergeist's post. What school did you go to?

 

[poltergeisty]

Ah, the first one ok just wasn't sure. :wink:

 

[Al42]

Al42 No, your right, it had nothing to do with the original thead. But you did attempt to criticize the project. Again, you are absolutely unfamiliar with the Bubble Detector project.

All I have to be familiar with is that it's susceptible to interference from a part of itself. That spells poor design regardless of what the project is. Even birdies in scanners are evidence of design that could be improved.

Radiated EMF from a Power Supply could very well cause problems if close to scanner boards.

Since a properly designed power supply doesn't radiate any appreciable emf in the RF range (which is the only thing that would interfere with a scanner), no it couldn't.

Read through Poltergeisty's first post. In case of a CRT
not enough to matter. Tell that to the guy who made up custom steel
side, top, and back panels to protect his receiver.

The fact that someone thinks that a shield is needed doesn't mean that one is. Plenty of people "fix" things that aren't broken, or fix the wrong thing.

To tell you the truth I don't see any need to ground it.

If it's a magnetic shield there is none. If it's an emf shield it'll radiate the signal if it's not grounded. We're talking about shielding the source, here, remember.

What school did you go to?

As I said, CUNY. (Back when it was CCNY, but shilelding hasn't changed since Faraday's day.)

 

[John_M]

Al42: The power supply manufacturer their stupid because they put out a power supply that radiated a little 60hz EMF
The scanner manufactures are stupid because of a few birdies that they have been trying to get rid of for years
The guys who shield there Receivers are stupid. I thought that
that it was pretty well documented. I am not going to argue with you anymore about the grounding of a shield designed to protect an expensive sensitive receiver from EMF's and noise. Which is what the Topic
was about.

 

[N_Jay]

. . . . I am not going to argue with you anymore about the grounding of a shield designed to protect an expensive sensitive receiver from EMF's and noise. Which is what the Topic
was about.

Good,

Because you were the first to first to bring power suppy isues into the conversation, which is EXACTLY the type of interference issue that this type of sheilding will do little to help. (and the most unlikely for anyone to have)
:roll: :twisted: :twisted: :wink:

 

[John_M]

I did bring it up. Because we were talking about interference. Sorry :lol: I also knew that this type of shielding would do nothing for a power supply inside of a radio. A power supply near the outside of the scanner, this type of shielding would provide protection if the power supply is radiating strong EMF.

 

[N_Jay]

I did bring it up. Because we were talking about interference. Sorry :lol: I also knew that this type of shielding would do nothing for a power supply inside of a radio. A power supply near the outside of the scanner, this type of shielding would provide protection if the power supply is radiating strong EMF.

Seems like you were bit by a MAGNETIC field problem ONCE, and it has colored you view of shielding.

Very few power supplies put out enough 60 Hz EMF to bother ANYTHING.

Very few products are sensitive to 60 Hz EMF.

 

[Al42]

Al42: The power supply manufacturer their stupid because they put out a power supply that radiated a little 60hz EMF

EM or magnetism? An ungrounded "shield" won't stop EM radiation.

I am not going to argue with you anymore about the grounding of a shield designed to protect an expensive sensitive receiver from EMF's and noise. Which is what the Topic
was about.[/quote]
Don't argue - just show how an ungrounded shield can sheild against ignition noise or eadiation from a PC - which is what the topic is about. Or don't you have any idea which formulas are involved?

 

[Al42]

Very few power supplies put out enough 60 Hz EMF to bother ANYTHING.

Most power supply radiation is due to the diodes or a bad connection, which is in the RF range. 60Hz EM? Probably masked by all the 60 Hz EM floating around from line cords, power lines, etc. The "signal" from the power supply is probably far below the "noise".

Very few products are sensitive to 60 Hz EMF.

Stands to reason, since there's so much of it in the air. An electronic product sensitive to 60 Hz EM interference would be something like a water soluble fish.

 

[John_M]

If we must keep this childish behavior up I want no part of the
conversation.
Once again: The power supply radiated 60hz Emf period. Not a magnetic field. No ground needed to shield. Why would a shield have to be grounded in order to stop EMF and noise from a computer from penetrating through steel whether grounded or not?? Do you really need formulas? I say no.

Ingnition noise that is a whole other issue.

 

[N_Jay]

The power supply radiated 60hz Emf. Not a magnetic field.
No ground needed to shield. Don't need any formulas.

LOL,

Now, explain how you are so sure it was 60 Hz EMF?

If it was not magnetic, then you did not need to use the heavy piece of steel you ended up using.

If it was not magnetic, then you would have had to ground it to get any significant sheilding.

 

[John_M]

The power supply radiated 60hz Emf. Not a magnetic field.
No ground needed to shield. Don't need any formulas.

LOL,

Now, explain how you are so sure it was 60 Hz EMF?

If it was not magnetic, then you did not need to use the heavy piece of steel you ended up using.

If it was not magnetic, then you would have had to ground it to get any significant sheilding.

Read privious post.

 

[N_Jay]

The power supply radiated 60hz Emf. Not a magnetic field.
No ground needed to shield. Don't need any formulas.

LOL,

Now, explain how you are so sure it was 60 Hz EMF?

If it was not magnetic, then you did not need to use the heavy piece of steel you ended up using.

If it was not magnetic, then you would have had to ground it to get any significant sheilding.

Read privious post.

Well I have been reading this thread all along, and I went back and read the last few of your posts.

I still have the question:
Now, explain how you are so sure it was 60 Hz EMF?

If it was not magnetic, then you did not need to use the heavy piece of steel you ended up using.

If it was not magnetic, then you would have had to ground it to get any significant sheilding

 

[John_M]

Why am I so sure. First of all I witnessed it first hand. Now what would a piece of sheet metal glued on top of the power supply do if the issue was magnetism? Nothing. The power supply radiated 60hz EMF and the piece of sheet matel glued on top stopped it cold. If this post doesn't explain it I don't know what would. The power supply radiated 60hz EMF period.

 

[John_M]

I refuse to take part in this Childish conversation any further.
Have fun Guys!

 

[N_Jay]

Why am I so sure. First of all I witnessed it first hand. Now what would a piece of sheet metal glued on top of the power supply do if the issue was magnetism? Nothing. The power supply radiated 60hz EMF and the piece of sheet matel glued on top stopped it cold. If this post doesn't explain it I don't know what would. The power supply radiated 60hz EMF period.

You whitness a circuit that was sensitive to SOMETHING radiated from the power suppy. If you heard teh hum, or saw teh 60 Hz on a scope (maybe you did), THEN (and only then) could you say it was 60 Hx (and not some other frequency.

You have said absoilutly NOTHING that would tell me it was EMF!

As a matter of fact you have said SEVERAL thing that lead me to the conclusion it was MAGNETIC.

1) You talked about it only happening when they were VERY close.
EMF decreases at r-squared. Magnetic fields decrease at r-cubed. The are much more of a near field effect (matching your description).

2) You said,(or implied) that you had to try several types of material.
If it was EMF then almost any metal would have had the same results.
However, magnetis field would have only been sheilded by a ferrious metal (the steel you described).

3) You said the meteal sheild was not grounded. A nongrounded sheild is of minimum effectivness for an EMF, However, a magnetic sheild does not need to be grounded. (Again, reafirming my assumption, and contradicting your statement.)

4) the part you were sheilding was a powersupply transformer. A device, that by its very nature is a source of MAGNETIC fields, and typically not a source of EMF.

Could you entertain the thought that you could just posible be wrong?
Maybe open yourself to the idea that this could be a learning experiance for you?

 

[Al42]

4) the part you were sheilding was a powersupply transformer. A device, that by its very nature is a source of MAGNETIC fields, and typically not a source of EMF.

I'm trying to figure out how a transformer could radiate any EMF more than the wires connected to it. Maybe it's been too long since school, but I'm at a loss.