3-Meter Chamber for Emission Pre-Scanning
To all my distinguished colleagues. I wish to thank you for your responses to my call for help, and inform you of the finial outcome. Some of you I have contacted directly and some I have not (due to time constraints) but I want to thank all that have responded very much. I have read and considered each reply. In summary, I was required to substitute a 10x10x22 ferrite tile chamber for a 10 OATS for emission pre-scan testing and needed fairly good correlation. To make a long story short here is what I did: The chamber had a metal floor that was naturally the major contribution to reflections. I placed ferrite tile square assemblies 2x2 Ft. from under the Biconilog running 3 meters to under the EUT table. The tile squares fanned out in the middle to form something like an oval. Now I have minimum reflections and once plotted gives me a curve very close to theoretical using a Biconilog and a Biconical antenna. The horizontal and vertical plot points fall all most on top of each other on the curve. I now have a ferrite tile tunnel, with only one major reflection at 150 MHz. which is stable and about 4 dB P-P. I am starting to test equipment which has returned for commercial labs and show a correlation of about 2.6 to 3 dB. Now this is not bad if I do say so myself. I only need to recheck the Field Uniformity, which I do not think will be adversely affected. Al Patrick, Sr. EMC Engineer - Manager of EMC Lab Operations Scientific-Atlanta Inc. al.patr...@sciatl.com 770 236 5148
Re: 3-Meter Chamber for Emission Pre-Scanning
Patrick, In my company, we have a 10 meter semi-anechoic chamber (lined with cones). However, sometimes I also need to use an outside EMC test facility. I prefer a chamber instead of an OATS, because I do only pre-scans, and it is a lot faster in a chamber. For the first couple of years, I was using a 3 meter fully anechoic chamber lined with ferrite tiles. This lab uses a BiLog antenna at a fixed height (it is 1.5 or 2 meters), and applies a correction factor to account for the reflections that are present in an OATS or a semi-anechoic chamber. I always had problem co-relating the data between our 10 meter chamber and this 3 meter chamber. Now I use another EMC test facility with a 10 meter chamber, similar to the one at our company. The ferrite tiles generally work well to the frequencies of 500 MHz and then their absorption drops down. Also, keeping antenna at a fixed height does not provide accurate data for horizontal polarization, where one sees more emissions at higher antenna heights. Still, a chamber is great for pre-scans and trouble-shooting and saves you a lot of time. Only once in a while you need to verify your data at an OATS, or a 10 meter chamber. Regards, Ravinder PCB Development and Design Department Email: ajm...@us.ibm.com *** Always do right. This will gratify some people and astonish the rest. Mark Twain Patrick, Al al.patr...@sciatl.com on 08/19/99 12:28:38 PM Please respond to Patrick, Al al.patr...@sciatl.com To: emc-p...@ieee.org cc: Patrick, Al al.patr...@sciatl.com, 'alpatr...@op9.com' alpatr...@op9.com Subject: 3-Meter Chamber for Emission Pre-Scanning To all members of this distinguished group. I now come to you not to make commitment but to ask your for help. My situation is this; I had an OATS site to which I wanted to add a 3 Meter chamber (ETS Model 20) for Immunity test per the EU requirements. I started this quest in 1997 and have succeeded with the installation this month. Now my problem, along the way my company moved into a new campus (Great!), But now the CEO does not want an ugly OATS around his new campus. Now just before approving the new 3 Meter chamber, which took two years to get thirteen signatures, he says You can do your scanning in this chamber, Right! and looks at me just before he signs it. Now my eyes roll back in my head and I say (the only thing which will save this project) Yes Sir Assumptions: The chamber will only be used for pre-scans and diagnostics. I already know that you can't correlate a 3 Meter chamber to a 10 Meter OATS, but I have to try at least try until I can build a 10 OATS somewhere. I would like to hear from members who have used, or tried to use a 3 meter (10x10x22 FT. chamber lined with ferrite tile) for emission scans. I have already found that 1 Meter is about the best distant to scan with out to many reflections but it's easy to miss an emission too. I'm all ears as they say. Thank you, Al Patrick, EMC Lab Manager Scientific-Atlanta Inc. al.patr...@sciatl.com Title: 3-Meter Chamber for Emission Pre-Scanning To all members of this distinguished group. I now come to you not to make commitment but to ask your for help. My situation is this; I had an OATS site to which I wanted to add a 3 Meter chamber (ETS Model 20) for Immunity test per the EU requirements. I started this quest in 1997 and have succeeded with the installation this month. Now my problem, along the way my company moved into a new campus (Great!), But now the CEO does not want an ugly OATS around his new campus. Now just before approving the new 3 Meter chamber, which took two years to get thirteen signatures, he says You can do your scanning in this chamber, Right! and looks at me just before he signs it. Now my eyes roll back in my head and I say (the only thing which will save this project) Yes Sir Assumptions: The chamber will only be used for pre-scans and diagnostics. I already know that you can't correlate a 3 Meter chamber to a 10 Meter OATS, but I have to try at least try until I can build a 10 OATS somewhere. I would like to hear from members who have used, or tried to use a 3 meter (10x10x22 FT. chamber lined with ferrite tile) for emission scans. I have already found that 1 Meter is about the best distant to scan with out to many reflections but it's easy to miss an emission too. I'm all ears as they say. Thank you, Al Patrick, EMC Lab Manager Scientific-Atlanta Inc. al.patr...@sciatl.com
Re: 3-Meter Chamber for Emission Pre-Scanning
Patrick, I don't understandplease explain your statement: you can't correlate a 3 Meter chamber to a 10 Meter OATS. The only correlation necessary is having the required site attenuation and ground plane parameters. It is the same correlation that 10 meter sites are required to show. If your chamber falls within plus or minus 4 dB of the NSA tables using volumetric measurements, then you are deemed correlated. OATS have the same requirements except that linear measurements are made instead of volumetric measurements (volumetric measurements are harsher requirements). We use independent commercial testing organizations to do our site attenuation. Here is the process: 1. Site attenuation measurements are made on a 10 meter open area test site (OATS) that is known to fall within plus or minus 4 dB of the normalized site attenuation (NSA) tables. 2. If the OATS measures within 4 dB of NSA then the test equipment used to measure NSA is determined to be calibrated. 3. The same test equipment is then used to measure our chamber site attenuation using volumetric measurements. 4. If the site attenuation data falls within 4 dB of NSA then we are deemed correlated. Our site attenuation data has always been within plus or minus 4 dB of NSA. It is not an inexpensive process either because we have to fly people and equipment into our site and pay for two NSA measurements each time. But to answer your question.yes, professionally built chambers using state-of -the-art materials are quite good at measuring emissions. In some respects, they are superior to OATS. Bob == Patrick, Al al.patr...@sciatl.com on 08/19/99 02:28:38 PM Please respond to Patrick, Al al.patr...@sciatl.com To: emc-p...@ieee.org cc: Patrick, Al al.patr...@sciatl.com 'alpatr...@op9.com' alpatr...@op9.com (bcc: Robert E. Heller/US-Corporate/3M/US) Subject: 3-Meter Chamber for Emission Pre-Scanning To all members of this distinguished group. I now come to you not to make commitment but to ask your for help. My situation is this; I had an OATS site to which I wanted to add a 3 Meter chamber (ETS Model 20) for Immunity test per the EU requirements. I started this quest in 1997 and have succeeded with the installation this month. Now my problem, along the way my company moved into a new campus (Great!), But now the CEO does not want an ugly OATS around his new campus. Now just before approving the new 3 Meter chamber, which took two years to get thirteen signatures, he says You can do your scanning in this chamber, Right! and looks at me just before he signs it. Now my eyes roll back in my head and I say (the only thing which will save this project) Yes Sir Assumptions: The chamber will only be used for pre-scans and diagnostics. I already know that you can't correlate a 3 Meter chamber to a 10 Meter OATS, but I have to try at least try until I can build a 10 OATS somewhere. I would like to hear from members who have used, or tried to use a 3 meter (10x10x22 FT. chamber lined with ferrite tile) for emission scans. I have already found that 1 Meter is about the best distant to scan with out to many reflections but it's easy to miss an emission too. I'm all ears as they say. Thank you, Al Patrick, EMC Lab Manager Scientific-Atlanta Inc. al.patr...@sciatl.com Title: 3-Meter Chamber for Emission Pre-Scanning To all members of this distinguished group. I now come to you not to make commitment but to ask your for help. My situation is this; I had an OATS site to which I wanted to add a 3 Meter chamber (ETS Model 20) for Immunity test per the EU requirements. I started this quest in 1997 and have succeeded with the installation this month. Now my problem, along the way my company moved into a new campus (Great!), But now the CEO does not want an ugly OATS around his new campus. Now just before approving the new 3 Meter chamber, which took two years to get thirteen signatures, he says You can do your scanning in this chamber, Right! and looks at me just before he signs it. Now my eyes roll back in my head and I say (the only thing which will save this project) Yes Sir Assumptions: The chamber will only be used for pre-scans and diagnostics. I already know that you can't correlate a 3 Meter chamber to a 10 Meter OATS, but I have to try at least try until I can build a 10 OATS somewhere. I would like to hear from members who have used, or tried to use a 3 meter (10x10x22 FT. chamber lined with ferrite tile) for emission scans. I have already found that 1 Meter is about the best distant to scan with out to many reflections but it's easy to miss an emission too. I'm all ears as they say. Thank you, Al Patrick, EMC Lab Manager Scientific-Atlanta Inc. al.patr...@sciatl.com
3-Meter Chamber for Emission Pre-Scanning
To all members of this distinguished group. I now come to you not to make commitment but to ask your for help. My situation is this; I had an OATS site to which I wanted to add a 3 Meter chamber (ETS Model 20) for Immunity test per the EU requirements. I started this quest in 1997 and have succeeded with the installation this month. Now my problem, along the way my company moved into a new campus (Great!), But now the CEO does not want an ugly OATS around his new campus. Now just before approving the new 3 Meter chamber, which took two years to get thirteen signatures, he says You can do your scanning in this chamber, Right! and looks at me just before he signs it. Now my eyes roll back in my head and I say (the only thing which will save this project) Yes Sir Assumptions: The chamber will only be used for pre-scans and diagnostics. I already know that you can't correlate a 3 Meter chamber to a 10 Meter OATS, but I have to try at least try until I can build a 10 OATS somewhere. I would like to hear from members who have used, or tried to use a 3 meter (10x10x22 FT. chamber lined with ferrite tile) for emission scans. I have already found that 1 Meter is about the best distant to scan with out to many reflections but it's easy to miss an emission too. I'm all ears as they say. Thank you, Al Patrick, EMC Lab Manager Scientific-Atlanta Inc. al.patr...@sciatl.com
