The problem I would anticipate from a substitution method would be knowing what part of the EUT was radiating and then simulating that structure for accurate correlation.
But more on to what has worked for our type of EUTs, narrow band signals typically cause our OATS grief. This is usually easy to remedy by using a narrow resolution bandwidth. For clock type signals that are essentially "CW", peak level = qp = average. So we will reduce the BW until we can see the signal in peak detection. Then we will reduce the BW further and establish that the signal level is still the same. That establishes that it is a narrow band signal and that the BW is not affecting the reporting level. As pk = qp level for a narrowband signal, we now have the "qp" level to report. I have the luxury of prescan semi-anechoic chamber to determine where the signals are located with reasonable correlation to the OATS measurements. So far, I have not had to contend with broadband emissions from an EUT on an ambient. Don Umbdenstock Sensormatic From: Brent DeWitt [mailto:[email protected]] Sent: Wednesday, January 28, 2004 2:50 PM To: [email protected] Subject: RE: OATS Measurement The method Dave Cuthbert mentions can work it some cases. I have tried a variation on his method which is to use a combiner for the two signals rather than re-radiating the ambient. The problem is that it doesn't give you a very deep null if the ambient has significant multi-path components, which was the case at my site in the mountains. While it is possible that the radio station could be exactly on the EUT emission frequency, it very rarely is. Most of the time I've seen this problem, it can be solved by simply reducing the measurement bandwidth to sort the two signals out. Of course this only works on narrow band signals and you get a peak reading rather than quasi-peak, but there is a work around. I have successfully argued on occasion that the reading can be adjusted by the same ratio of peak (at the same RBW) to quasi-peak levels of a similar emission from the EUT measured in the clear. Brent DeWitt From: [email protected] [mailto:[email protected]]On Behalf Of Ken Javor Sent: Wednesday, January 28, 2004 10:50 AM To: Grasso, Charles; 'Tsang Steven'; '[email protected]' Subject: Re: OATS Measurement Mr. Grasso and I disagree. He comes from a point of strength (his knowledge and expertise in modeling), and I, from a position of weakness (little knowledge and less interest in predictive techniques). If I were concerned whether the EUT were emitting at a particular frequency, and if I had a screened or anechoic chamber, I would do the following very quick test (realizing this doesn't answer the original post's question, except in a basic operational sense): I would put the EUT and a radio tuned to the offending ambient station in the chamber. I would pull the door to until radio reception was just marginal. Then I would energize the EUT and monitor effect on radio reception. I would move the radio as close to the EUT as I could to see if there was any response, but I would use the response at roughly three meters as a gauge of whether there would be a real problem. > From: "Grasso, Charles" <[email protected]> > Date: Wed, 28 Jan 2004 10:28:18 -0700 > To: "'Ken Javor'" <[email protected]>, "'Tsang > Steven'"<[email protected]>, > "'[email protected]'"<[email protected]> > Subject: RE: OATS Measurement > > I must disagree. I would cite Mr Leferinks paper from the Boston EMC > Symposium. In it he concluded that > a) correlation was possible for tuned dipoles to +/- 4db - an 8dB swing.and > b) for test objects the variation in field strength can be as high as 40dB > for "actual EUTs" and therefore correlation between different radiated > emissions test methods is impossible. > > I think its time we use predictive techniques rather than correlation > techniques between test facilities. There will be a paper in the Santa > Clara Symposium this year addressing just this issue. > Best Regards > Charles Grasso > Senior Compliance Engineer > Echostar Communications Corp. > Tel: 303-706-5467 > Fax: 303-799-6222 > Cell: 303-204-2974 > Email: [email protected]; > Email Alternate: [email protected] > > > -----Original Message----- > From: Ken Javor [mailto:[email protected]] > Sent: Wednesday, January 28, 2004 7:25 AM > To: Tsang Steven; [email protected] > Subject: Re: OATS Measurement > > > Is the (semi?) anechoic measurement a 3 meter measurement? If it is and it > meets the NSA curve, you ought to be able to correlate your anechoic and > OATS measurements reasonably well. If they correlate where you don't have > ambients, you ought to be able to use the anechoic measurement in lieu of > the OATS measurement where the ambient intervenes. > >> From: "Tsang Steven" <[email protected]> >> Reply-To: "Tsang Steven" <[email protected]> >> Date: Wed, 28 Jan 2004 12:41:22 +0800 >> To: [email protected] >> Subject: OATS Measurement >> >> >> Dear all, >> I have a question regarding on OATS measurement (3m site, 30MHz to > 1000MHz), I >> hope someone could help me on this issue. >> Currently my company is undergoing a accreditation porcess and the > accreditor >> is asking on the method of testing to overcome the issue of the noise > floor >> covering the signal generate from the EUT (i.e. Radio station signal ). >> We have propose to measure the signal from EUT in an aechoic chamber and > use a >> signal generator to simulate the signal with a change of frequency (i.e. >> 10kHz) to avoid the signal being block by the noise floor and re-measure > the >> signal on OATS. >> This method is rejected by the assessor and asking to provide an > alternative >> method. Could someone provide the solution, thanks!!! >> >> Best Regards, >> >> emc_st >> >> _________________________________________________________________ >> ??? : ???, ????? http://go.msnserver.com/HK/34698.asp >> >> >> ------------------------------------------- >> This message is from the IEEE EMC Society Product Safety >> Technical Committee emc-pstc discussion list. >> >> Visit our web site at: http://www.ieee-pses.org/ >> >> To cancel your subscription, send mail to: >> [email protected] >> with the single line: >> unsubscribe emc-pstc >> >> For help, send mail to the list administrators: >> Ron Pickard: [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: >> http://www.ieeecommunities.org/emc-pstc >> > > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: http://www.ieee-pses.org/ > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Ron Pickard: [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: > http://www.ieeecommunities.org/emc-pstc > This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ieee-pses.org/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [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: http://www.ieeecommunities.org/emc-pstc This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ieee-pses.org/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [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: http://www.ieeecommunities.org/emc-pstc This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ieee-pses.org/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [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: http://www.ieeecommunities.org/emc-pstc
