Judd had some questions about a shielded room, and I thought I would throw in my opinions.
-------------- snip ------------ >HELLO, >I'm planning on installing a screen room and I have a couple of questions >concerning layout and installation. The purpose of the room will be to >troubleshoot and prescans, repeatability is paramount. We will use a approved >lab for certifications and verifications. Comments: Don't expect to be able to measure the amplitude of the signals with much correlation with the amplitudes that the test house will measure on their open field site (unless your room is the size of a hangar for a blimp, like at Moffett Field California). The reason is that the emissions (waves) from the device under test will bounce around from the walls, ceiling and floor in a completely different manner than they will on the open field site, and will either reenforce the original signal or cancell it in ways that are unpredictable. That's one of the reason why the FCC specifies an open field test site with no reflecting objects/structures within a certain distance from the EUT and antenna. A shielded room is good for identifying frequencies coming from the EUT, but is worth squat for measuring their amplitudes. >1) With regard to construction, from the mfg. I have look at so far the sheet >material is basically the same thin gauge zinc steel over particle board >joined with a clamping mechanism. Will this joining system last or does it >need repeated tighting and testing? I had one for about 5-6 years and it was so well built (along the lilnes that you describe) that I never even thought about tightening the screws periodically. >2) I don't have ANSI C63.4- does any one know the distance I need to keep the >antennas away room? The answer to this question is the same as the first answer. C63.4 gives you the method of calibrating an open field test site. There is no way that you could use the same method to try and calibrate a shielded room (again, unless it is the size of the Goodyear blimp hangar). Think for a minute about the size of the dipole antenna (must use dipole per C63.4) that is needed for transmit and receive at 30 MHz and add at least 5 meters on each side. Then think about raising the receive antenna to 4 meters and having 5 meters of clearance to the ceiling (got to follow the C63.4 spec). That room gets so big that it is much cheaper to build an outdoor site. >3) With regard to the table for the UUT- What is the physical dimensions and >how far should it be from the enclosure.#005#? Same answer as above. >4) I'm considering a Anti-room- I can't afford a separate room so I'm >considering a partition in the big room. Just received some quotes and the >cost of the extra door is astounding! Is the anti-room worth the investment? I like this idea the best. If a shielded room is used to measure emisisons, then an Anti-room could be used to remove the emissions from the unit under test :>) On the serious side, all of the cabling is run through bulkhead connectors to whatever room you have available on the outside of the shielded room. The connections from the spectrum analyzer or receiver to the antenna go through BNC connectors typically, mounted on a sheet metal plate to maintain the integrity of the room. Same thing with F connectors, DB connectors, etc. >thanks >Judd Stewart 619.623.6639 You are welcome, Gabriel Roy Hughes Network Systems MD (57 days) Alas, the opinions expressed are mine alone as the company does not have an emc hotline.
