David, Ideally an OATS should have no ambient signals within 6 dB of the lowest limit that you intend to use. Now, after everyone has had their laugh and picked themselves up off the floor, let's look at the practical aspects.
There are very few OATS facilities in the world that meet the requirement from DC to daylight (well, maybe we don't have to go that far, but you get the idea). I recall one that was built in an underground salt mine in England and there have been some in very remote locations in the US, but that's about it. Every other OATS that I know of has a few or more signals over the limit, some way over the limit. Factors to consider in making your decision would be - 1. How much of the spectrum of interest is occupied by ambient signals? In the past, we've been able to live with television transmitters as the only real serious signals were the video and audio carriers. The actual picture information was much lower in amplitude and the carriers seldom shared a frequency with an emission from a computer. This will (and is) change with the advent of digital TV. Spectrum utilization is much more efficient. Good for the spectrum planners. Bad for neighboring EMC labs. 2. How strong are the ambient signals? Are they strong enough to drive your pre-amplifier into gain compression or worse? You'll need filters to fix this. 3. Do ambient signals sit at frequencies you expect to measure on a routine basis? This should give you a general idea of things to worry about. Also, keep in mind that typically VHF/UHF ambient signals are stronger higher off the ground. Roof top OATS facilities will likely see higher ambient signal amplitudes than ground level facilities in the same area. Ambient signals in a metropolitan area are one of the strongest arguments for RF semi-anechoic chambers that I can think of. You might price out a chamber as part of the study. I've heard that the chamber vendors are hungry for business and have really sharpened their pencils as of late. Good luck with whatever you build and have fun. I've enjoyed the process of building labs each time I've been fortunate enough to do it. Ghery Pettit, NCE Intel -----Original Message----- From: Gelfand, David [mailto:[email protected]] Sent: Thursday, January 24, 2002 8:14 AM To: [email protected] Subject: Ambient noise limits for OATS? Hello all, We are being asked to evaluate ambient noise for a possible rooftop OATS. Are there any published limits to ambient noise for an OATS location? Thank you, David. David Gelfand Regulatory Approvals Kontron Canada ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: [email protected] Dave Heald [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server. ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: [email protected] Dave Heald [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
