Simple screened room integrity test

Quick test: there should be no reception of cellular and FM/AM/TV broadcast inside the room if the door is closed. Any reception indicates a leak.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

Yes, Vladimir gave the right hint. Take an AM/FM radio, see which stations are strongest (on AM that's usually Rush Limbaugh...), go inside. Then walk around the perimeter of that room. Since you bought a screen room I assume you have a spectrum analyzer. Put it in the middle in a shielded box. Seriously, I had a Agilent analyzer spew so much junk from its LCD that it almost made me sick. Now connect a coax long enough to reach the corners. Plug in the mid-size EMCO near-field H-probe and sniff along the seams and especially the door.

Oh, and do _not_ leave the key in the outside of the door lock. There are usually no phones inside and your cell phone won't do you any good after you hear the thud of that big door.

--
Regards, Joerg

http://www.analogconsultants.com/

Indeed. The electromagnetic noise generated by the measurement equipment itself is very annoying. It is good to have all analysers outside of the room.

BTW, I have seen some smart people who installed the fluorescent lighting with the active ballasts inside of the EMC chamber.

:) It is warm and quiet. When doing the EMC measurements, I am always thinking about taking a nap in the chamber. It is difficult to resist the temptation during the long wideband sweeps...

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

Really? Our screen rooms have a phone (going through a filtered jack) and Ethernet (going through a fiber-optic converter); I figured this was quite commonplace...

Use the old stuff that was designed by guys who really knew what they were doing.

Medieval folks had their version of water boarding for those guys: Put them in a cage, dunk them into the moat around the fortress a couple of times, then ask them whether they'd do it again. If they say yes, dunk again ...

Can't do that. Finding a consultant snoring away would not be a great motivator. But I did once funnel a piece of wire through one of the ports and plugged the coax inside into my EMC receiver so it wasn't so eerily quite in there. Picked up the Don Cossack Choir on shortwave, when even Radio Moscow would stop their dreaded propaganda. Some of the best a capella pieces ever.

--
Regards, Joerg

http://www.analogconsultants.com/

Oh, then you must be very young. In the olden days we even had to make our own electricity :-)))

But really, the screen rooms at most of my clients are rather spartan. A bare plywood floor is considered luxurious.

--
Regards, Joerg

http://www.analogconsultants.com/

Go into the room and try to use a TX or RX in the frequency range you expect to use it.

I've never seen a perfect screened room; there was always some leakage. The best I ever saw was at an airbase with Search Radar and a variety of HF through VHF radios.... Zinc wall, Ceiling and door panels. Double finger stock on door, and no windows. All antenna coaxes entered via a well shielded box that had separate containments for the filters for each antenna. It was very good, but....

The best I ever used was in the microwave lab at Teledyne Ryan Aero in San Diego. DOUBLE solid zinc walls & doors, brass finger stock coming AND going on the doors, air filtered in through double tightly woven brass wool, ... DAMN but I lust for that room.

THen again, we were building stuff in there that we would later be throwing at the moon, so it had to be absolutely perfect.

Jim

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Ours isn't nearly that good. It has what looks like copper window screen all around, so you can breathe and talk through the walls no problem. The door is solid metal with copper finger stock all around and the power passes through filter modules. I haven't got inside yet to do any testing - the area is roped off while cubicles are being assembled in the surrounding open area. Once I get in, I intend to do the cell phone test described in theis thread and haul in a scope to look at the noise of the lights.

It takes a lot of effort to drop all leakages at all bands to the noise floor of the analyser. There are the test chambers like that at the big companies I worked for; I can only imagine how much did it cost.

However what is really required that the leakages should be at least

10dB below the EMC limits that you are after. This implies no reception of cellular or AM/FM/TV.

Best I ever saw was the 25 x 15 x 100 meters hall for the indoor experiments on the radar antennas. It was a perfectly shielded building inside the other building. That was back in the USSR. In our days, they couldn't find better use for this chamber then giving it for rent as a warehouse.

How could be any windows in the schreened room?

Fixing all leaks requires the special equipment and a lot of work. It is very costly, too.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

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We were selling some displays to a company making USN shipboard radars. They had huge screened rooms. They also had a different attitude about some other things. At the first engineering meeting there, they asked us hom much cooling water we would need.

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you don't want to operate a transmiter inside a screen room..

think about where the power goes.

Mark

[snip]

Where DOES it go ?:-)

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |

| 1962 | America: Land of the Free, Because of the Brave

Sure you do, if you hook up an appropriate dummy load with a reasonably low VSWR. We've got some 500W dummy loads around that make nice little space heaters...

Into the DUMMY load hopefully. But, if you have an antenna hooked up, guess who/whats the dummy!

--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"©

"Treason doth never prosper: what\'s the reason?
For if it prosper, none dare call it treason."

"Follow The Money"  ;-P

Years ago I helped with the commissioning of a couple of Belling-Lee rooms. These were used to stop emitters getting out, so only about 3 freqs were of interest. The usual tests were to use a Spec An outside to see the ambient environment, then take them inside to verify the atttenuation. This was an HP141 type, some of the newer one generate significant internal noise that can screw up your results.

Then we fired up the emitters inside to verify that they were sufficently attenuated outside.

The Belling-Lee engineer also mentioned that one of his clients (UK MOD ?) used a high-power sweep oscillator inside the room, while monitoring outside.

The biggest problems were torquing down the panels evenly and the door fingerstock being adjusted correctly.This took about 2 days to get it near-perfect. Unfortunately, these items require periodic checking throughout the room's life, as they do shift with time and use.

Barry

I used a kW transmitter in the room I described before. The power went out the coax to the antenna of choice.

Where else would it go?

A colleague was involved in installing a Faraday cage for emc testing. When they'd finished, the boss came to look at it. Just after they shut the door, his mobile phone rang...