PC Desktop Metal Case And Escaping RF ?

[BOBRR]

Hello,

Have a desktop pc.
Metal case.

Just wondering:

Does the metal case provide "good" rf shielding from all the rf
probably being generated inside it ? Much escape ?

I understand that the rf noise can, and probably is, being carried by the
wires entering and leaving the case, but was wondering how good a shield the case itself
is ? (lots of slots for the fan, etc.)

Thanks,
Bob

 

[56FB666]

I do not believe. I have a bluetooth usb module installed inside the pc case and a surprise surprise all bt devices work.

 

[majoco]

I get more RFI on my HF radios from the power supply inside my Canon printer than anything else - and the PSU runs all the time unless I pull the mains power plug, not just when printing.

 

[ratboy]

Cases are like a cake, no two designs are alike. I've had several that were good, and some that just stunk. You have to try it and see.

I used to have a monochrome monitor I used for HF RTTY back 20 years or so ago. It had a steel case and it threw out RFI like they were trying to make it do it. I had a ton of Ferrites on the power cord and I found a fully shielded cable to hook it up to my radio with, and another to the RTTY box, and only then did it quiet down to the point it was usuable. I found out by accident that replacing the power cable itself helped a lot. When I moved some stuff around, I needed a slightly longer cord to reach my surge protector and I dug one of my many power cords out and it was quieter than the original cord was with the ferrites on it. I spent like 6 years living with that buzz for nothing. I put the ferrite cores on the new cord and silence!

I'm kind of shocked with what happened a couple of days ago. I stuck my SDS200 on top of my PC with the side panel removed, and with just the supplied whip, I only have a few things that it has any trouble with so I needed to hit Avoid a few times. I got a pleasant surprise after I made a favorites list with the Michigan MPSCS system on it, and I guess I live far enough north that I was hearing all kinds of stuff from towers (According to the RR database map of towers) that I never thought I could possibly get! I was hearing stuff from the entire SE quarter of the lower peninsula and it was all copyable. The only thing I had to play with was one of the 911 dispatchers is on MPSCS is linked to 155.190 analog, and it's insanely loud. I adjusted it and all is well. A mile or so south at work tonight, and I get almost no MPSCS traffic at all. Just got Huron Township so it's not totally dead. I didn't see what tower it was. A lot of the tower locations are places I've never heard of. I've lived in this area for 55+ years and not heard of half the towns the towers are located in.

 

[jwt873]

Like ratboy indicates above.. No two designs are alike..

Theoretically, a grounded metal case will block RF generated by a computer's motherboard and inner workings. But, don't forget there are wires coming out of the case.. (Power, USB, speakers etc). They could potentially radiate RF.

Modern computers are pretty quiet.. I have two running here beside me and they have little to no effect on my ham radio or scanning operations... On the other hand, I have a security camera that I have to unplug in order to avoid interference on the 80 meter band.

 

[bharvey2]

Yes some metal cases are much better than others. However, The computer itself isn't the only potential culprit. External attachments such as keyboards and monitors can produce offending RF noise. I use a small, handheld shortwave radio made by CC Crane as a quick and dirty RF detector. I tune the radio to a particular band of interest in AM mode (say 14.300mhz for 20 meters), leave the telescoping antenna in its collapsed position and move it around potential noise sources like a metal detector. It works pretty well.

 

[kruser]

I bought an Cooler Master case years ago with extra RF shielding as one of its design points. Granted, the case did have excellent shielding built in. Tons of very flexible metal spring steel like contacts for odd surface shape (side access panels in this case) grounding like found in Motorola radios plus flexible strips that conducted electrically for filling wider gaps between things like the power supply chassis from the main chassis for example. Metal screened (fine screening) panels that need to pass airflow. The fine screen can be a pain though as it needs frequent cleaning to maintain the airflow.
I still use the case today as it is much larger than a full tower and was perfect for all the gadgets stuffed in it for the radio hobby.

The external cables can definitely be the next big source of RFI. I tamed most of that with nothing but shielded Cat5E cables and then ferrites for the various USB, Serial, Video and other cables feeding in or out from the case. It was not a cheap project but was worth it in my opinion.

 

[ratboy]

I just wish the HF RFI problems in my apartment could be solved so I could listen. I've never seen such a mess. It seems to be coming from everywhere, but the two main sources are the assisted living/Alzheimer's care place next door where my mom used to live, and on my floor anyway, the elevator area and a maintenance room right next to my apartment. From MW to CB band, about all I can get is one local AM station (I can hear others but they are totally washed out from the buzzing and hissing), and ch 19 truckers when they are really close from the nearby freeway. Other than that, it's hopeless. I guess I should have brought one of my HF portables and tossed a wire up and listened before I signed the lease. I just renewed for another two years so no HF for me, I should probably sell it all.

 

[R8000]

I do not believe. I have a bluetooth usb module installed inside the pc case and a surprise surprise all bt devices work.

Some cases will bring bluetooth and wi-fi antennas outside of the metal case, but underneath a peice of plastic trim such as the front cover.

 

[56FB666]

Some cases will bring bluetooth and wi-fi antennas outside of the metal case, but underneath a peice of plastic trim such as the front cover.

 

[bharvey2]

I just wish the HF RFI problems in my apartment could be solved so I could listen. I've never seen such a mess. It seems to be coming from everywhere, but the two main sources are the assisted living/Alzheimer's care place next door where my mom used to live, and on my floor anyway, the elevator area and a maintenance room right next to my apartment. From MW to CB band, about all I can get is one local AM station (I can hear others but they are totally washed out from the buzzing and hissing), and ch 19 truckers when they are really close from the nearby freeway. Other than that, it's hopeless. I guess I should have brought one of my HF portables and tossed a wire up and listened before I signed the lease. I just renewed for another two years so no HF for me, I should probably sell it all.

I feel ya. In my area, houses are packed pretty close together and doing anything on HF can be frustrating. Sometimes the noise floor on my particular band of interest at the time can be S9. I've been lucky in that it tends to fluctuate, presumably because offending sources get turned off and on. - Just need to look for times when the noise floor is lower.

 

[ratboy]

I feel ya. In my area, houses are packed pretty close together and doing anything on HF can be frustrating. Sometimes the noise floor on my particular band of interest at the time can be S9. I've been lucky in that it tends to fluctuate, presumably because offending sources get turned off and on. - Just need to look for times when the noise floor is lower.

I hate to say it, but an S9 level would be a HUGE improvement over the normal level here, which is +20 over on almost every freq, with +40 and higher spikes every 200 khz or so. I should make a recording of the only MW station I can really listen to and post it here. It's still horrible, with that signal still having noise in it, and it pegs my S-meter on almost any length of wire antenna. The noise is about 10db lower than the station is, so its horrible to listen to and it's Sean Hannity, etc, so I don't have any interest in it. if I want to wipe that station out so nothing is tolerable, all I need to do is turn on the insanely loud flourescent light over my kitchen sink. The RFI will jump a ton, and it buzzes very loudly too. Obviously, I never use it.

 

[kruser]

I hate to say it, but an S9 level would be a HUGE improvement over the normal level here, which is +20 over on almost every freq, with +40 and higher spikes every 200 khz or so. I should make a recording of the only MW station I can really listen to and post it here. It's still horrible, with that signal still having noise in it, and it pegs my S-meter on almost any length of wire antenna. The noise is about 10db lower than the station is, so its horrible to listen to and it's Sean Hannity, etc, so I don't have any interest in it. if I want to wipe that station out so nothing is tolerable, all I need to do is turn on the insanely loud flourescent light over my kitchen sink. The RFI will jump a ton, and it buzzes very loudly too. Obviously, I never use it.

Have you tried the simple test of running your radio on battery and turning off ALL electric inside your place including battery backup units etc??
You might get lucky and find something under your control is doing most of the noise generation.

I eventually solved most of my noise from the neighbors computers and devices with tons of switching type power supplies.
My noise levels were unbearable like yours. I eventually broke down and bought a nice Loop antenna like the Wellbrook type.
I just stuck it out on my balcony at first and was shocked at the fact the noise level was now almost totally gone!
I then started hooking up all my HF capable radios again as I was back in business.

I then gained permission to put some antennas on the roof which is right above my head as I'm on the top floor. The roof hatch is also just outside my door. They even gave me my own key for the roof hatch!
The loop was one of the antennas I moved to the roof mainly to gain much needed space back on my small balcony.
But... loops can be directional and offer decent and deep signal nulls depending on the aim of the loop. That brought the need to install a simple and cheap TV rotor on the loop. It works wonders and I can even almost completely null out the local clear channel 50KW KMOX station that's not far from me!
I later added yagi's also on rotors but with much better rotor's that gave true direction indication unlike the cheap ones they sell for TV antennas.

I don't know if putting a loop out on a balcony is an option in your case but if so, it very well may be your ultimate solution!

I'd still try killing ALL power in your place first though if you have not tried this. You'd be amazed at how noisy your own equipment can be.
I could not get DSL here back in the day as the RFI was killing its signal. It turned out the RFI generator was a very noisy lamp dimmer in one of my own lamps! Once I fixed that, they were able to install DSL and I had near perfect signal levels for being near 12,000 feet from the central office.
With the elevator equipment right next door and all the devices in use in other apartments out of your control, it may not help by killing all your power for a test but it's worth a try.
Don't forget battery powered devices as well as turning off any UPS backup units you may have running.
I also found very bad RFI coming in from our cable TV provided once. Simply unhooking the cable dropped the noise levels big time but I needed that signal back then! I made a common mode choke that helped wonders. Charter eventually fixed something outside and cured the noise problems at a later date when they switched to all digital signals and also upgraded their equipment to support Docsis 3.0 or better.

 

[ratboy]

Thanks for the suggestion, but sadly, the only thing that I can do that affects it is to make it worse by turning on that light over my kitchen sink. I have no balcony, and when I tried turning off the power, nothing at all changed as far as I could tell. I'm on the second of 3 floors, and I know several people who live here and I went up to one of the apartments on the 3rd floor with one of my receivers and it was the same. One of the big sources of the problems here is the place next door has some sort of equipment that generates a huge buzz across most of the HF spectrum. I'm thinking it's maybe the lights all over the outside, but it doesn't matter what it is at this point. It's just there. And I have a brand new loop antenna I got just before I moved and it does little except find peaks of buzzing about every 10 degrees of movement. The "nulls" are just a little lower than those peaks. It worked great when I put it together in my house and tried it out to make sure it worked.
Anyway, thanks for the suggestion, it looks like it's time for a sale...Might as well buy some other toys with that money than look at turned off HF receivers on my shelves.