Re: EMC in the news: RFID Medical
Published in the Journal of the American Medical Association: http://jama.ama-assn.org/cgi/content/short/299/24/2884 $15 to download the article. From the summary, no real info on the test process: *Design and Setting * Without a patient being connected,^ EMI by 2 RFID systems (active 125 kHz and passive 868 MHz) was^ assessed under controlled conditions during May 2006, in the^ proximity of 41 medical devices (in 17 categories, 22 different^ manufacturers) at the Academic Medical Centre, University of^ Amsterdam, Amsterdam, the Netherlands. Assessment took place^ according to an international test protocol. Incidents of EMI^ were classified according to a critical care adverse events^ scale as hazardous, significant, or light. Regards --Robert E.Robert Bonsen Sr. Engineer Orion Scientific - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list.Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to emc-p...@ieee.org Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas emcp...@ptcnh.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald:emc-p...@daveheald.com All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
RE: Antenna factors to be used for NSA measurement
A well designed antenna will be balanced, i.e., it will be geometry independent. Looking at the factors for our 3110b, they look very nearly the same for horizontal and vertical polarization as well as at 3 meters and 10 meters. This suggests we should save the money for this model antenna and have 1 factor verified (10 meter horizontal) instead of having 4 factors verified. IMHO this is not completely accurate. There is not such thing as a geometry independent antenna factor, bad antenna balance/design only has an aggrevating influence on a physical inevitability. Check Zhong Chen's and Michael Foegelle's article in the 1998 IEEE EMC Conference proceedings, entitled A numerical investigation of ground plane effects on biconical antenna factor. In that paper they prove that even for an ideal antenna, with a perfect balance, the physics/geometry of the setup (due to the presence of the ground plane which alters the incident plane wave as well as coupling between the antenna and its image under the ground plane) inherently result in differences in antenna factors between polarizations, antenna heights and test distances. Actual antenna factor measurements as well as basic antenna physics back up this theory. By the way, Zhong and Michael work for ETS, manufacturer of the 3110B. Measured and predicted data on 3110Bs and other antennas (BiLog, other biconicals) show that for 2m transmit antenna height, which is pretty much the standard Tx antenna height cal labs test at, the vertical and horizontal factors are usually very close. However, once you lower the antenna transmit height to 1m (vertical and horizontal) and 1.5m (vertical only), substantial differences exist not only between antenna factors at different polarizations but also between the factors at different antenna heights for the same polarization. These differences can be several dBs, which is introduced as a measurement error in your NSA measurement if you use a factor which is not measured at the same height you're measuring your NSA at. This effect is more noticeable at shorter range length. Hence, 10m factors tend to be closer together than 3m factors. However, chamber and OATS performance at 10m range length is more critical than at 3m so this tends to even out. For chamber NSA measurements, the aforementioned variations in AF with height and polarization prove to be sufficient to bring a chamber out in a lot of cases, or make its performance look worse than it really is. This becomes a money issue when chamber manufacturers sign up for better-than-4-dB performance. For OATSes, there is a substantial performance margin so antenna factor error, although it has a negative effect on measurement accuracy, will not bring the OATS out of spec. I've been involved in OATS calibrations in which the performance margin was not sufficient to bring the OATS in, whereas when proper antenna cal factors were used the OATS passed well within spec. FYI, I used to work for ETS as a chamber design engineer before becoming an independent consultant. As such I've done quite a few antenna calibrations on 3110Bs and other bicons and combination bicon-logperiodic to be used for NSA calibrations, geometry specific for different test distances. Experience shows that at the low end, up to about 200 MHz, it can be almost mandatory to have geometry specific antenna factors because of the potential substantial measurement error introduced by using wrong antenna factors. Because of higher directivity, antenna factor variations are reduced at higher frequencies (where log-periodics are used), and a single antenna factor typically suffices. Unfortunately, not all organizations and experts were aware of this issue, or ignored it. That's why ANSI C63.5-1998 is written the way it is. The problem of antenna factor variations with different geometries is ignored because for EUT measurements it does not pose an immediate problem. However it is an issue with normalized site attenunation measurements. More work is currently being done in this area and the issues are being addressed. -Robert Robert Bonsen Principal Consultant Orion Scientific email: rbon...@orionscientific.com URL: http://www.orionscientific.com phone: (512) 347 7393; FAX: (512) 328 9240 --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
Re: Antenna factors to be used for NSA measurement
This is a discussion which starts up at least once every year. There are some issues with measuring NSA which are not very well understood including antenna factors. First of all, how you test and which factors to use should not be a matter of opinion. Unfortunately, the standards do not completely specify the requirements on the antenna factors which enhances confusion and introduces room for data manipulation. Having said that, there are some simple guidelines which are based on physics, literature and practical experience. 1. There is a difference between measuring EUTs and performing site attenuation measurements. NSA measurements are solely used for verifying the performance of the site. It uses a simple antenna substitution technique, in which the site under test is verified against the performance of the site on which the antenna factors are calibrated. Hence, the better the cal site on which the antennas are calibrated resembles a perfect OATS (i.e. an OATS with an infinitely large ground plane), the better quality the NSA measurement will be. As far as measurement method goes, a dual antenna factor calibration suffices if the same antennas will be used in the NSA measurement, there is no accuracy advantage when using a three-antenna method in this case. 2. Measurement distance. There are substantial difference in the antenna factors (and site attenuation) values at various range distances. In order to perform a correct NSA measurement, use the same range distance for the AF calibration as for the NSA measurement. The same goes for the EUT measurements, always use the same range distance. 3. Geometry. Although some OATSes and a few semi-anechoic chambers will pass NSA with using horizontal antenna factors only, this is not a correct measurement method. Since we're comparing the site-under-test to the AF measurement OATS, any change in the setup which results in a change in the physics of the AF or NSA measurement will introduce an artificial systematic error into the measurement. Both literature and experience has shown that AF measured at different geometries, with different polarizations and/or different source antenna heights), produce different antenna factors. Variations of up to 3 dB and sometimes more are to be expected for the low frequency regions. These variations will result in added errors in any site attenuation measurement in which the correct corresponding antenna factor is not used. In a lot of cases, this will bring a perfectly ok chamber or OATS out due to the artificial measurement error. 4. Accuracy. Antenna factors provided by the manufacturer or measured by a cal lab are typically not of sufficient accuracy (with a few exceptions). Accuracy in the AF measurement is extremely important since the NSA measurement does not provide for a lot of uncertainty margin for the AF. Typically, AFs are measured with a 2 dB uncertainty at best, even when higher accuracies are claimed. Cable layout, padding, equipment, etc. are extremely important. Also, AFs are typically only measured at one height at one polarization, which is not sufficient for accurate chamber cals. I recently was asked to calibrate a chamber using factors which were claimed to be better than +/- 1dB, but the frequency steps were so large that a small bump in the AF was completely missed, resulting in a more than +/-2dB uncertainty. Had the lab paid attention to setup and the peculiarities of this antenna, the AF measurement would have been fine, and we would have saved considerable time and money. Since most labs have a substantial margin for antenna factor error (up to 3 dB) in their uncertainty budget for EUT measurements, accuracy and geometry does not become much of an issue. However, in NSA measurements we're looking at substantially smaller margins and all of the aforementioned issues become important. On a final note, free-space factors are not an alternative. Simple physics dictates the presence of the ground plane (which is not present in free-space measured AF) adds a variable to the equation which in turn may add systematic errors to your measurement. And this has been demonstrated in literature. Free-space factors are for free-space measurement facilities (fully anechoic chambers). Using free-space factors (or single geometry factors) can only be allowed if the additional uncertainty is included in the error budget of the NSA measurements. And this is not the case with the current standards (ANSI C63.4-1992, CISPR22). Hope this helps. For a little more detail, check my web site. Regards, -Robert Robert Bonsen Principal Consultant Orion Scientific email: rbon...@orionscientific.com URL: http://www.orionscientific.com phone: (512) 347 7393; FAX: (512) 328 9240 --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line
Re: MIL-STD-285
At 11:08 03/09/2000 -0800, you wrote: There is a similar standard: IEEE Standard 299 Standard Method of Measuring the Effectiveness of the Electromagnetic Shielding Enclosures, Approved March 11, 1991 by IEEE Standard Board, Approved July 26, 1991 by American National Standards Institute (ANSI). The current version is IEEE299-1997. Please use this version since it differs substantially from the earlier 1991 version. This is the version that was evaluated by the military in favor of which MIL STD 285 was abolished. The 1997 version is a substantial improvement over IEEE299-1991, both technical and in flexibility. The old version mandates an extensive number of tests, making testing prohibitively expensive (or lucrative for the shield room testers). These mandatory requirements have been abandoned in favor of a more flexible suggested test procedure with frequencies and tests performed as needed for the application of the shielded room. Regards, -Robert Robert Bonsen Principal Consultant Orion Scientific email: rbon...@orionscientific.com URL: http://www.orionscientific.com phone: (512) 347 7393; FAX: (512) 328 9240 --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
Re: carbon-impregnated foam pyramids
Hi Lucian, I'm assuming you're talking about the wide-band pyramidal absorbers usually found in anechoic chambers. Their attenuation characteristics are typically measured one of three ways, depending on the frequency range of interest: a. coaxial waveguide: for very low frequencies, from DC to the cutoff frequency of the first TM mode (depends on dimensions, ~up to 200 MHz), in TEM mode b. square waveguide: for mid frequencies, around 300-500MHz, in TEM mode c. plane wave methods: two horns suspended on an arch positioned above the absorber at a height at least equal to the far-field distance, 1 GHz. All three methods try to emulate free-space far-field conditions in which a plane wave (E and H vectors perpendicular to the propagation vector) impinges upon the absorber, after which the backscattered reflection is measured. There are some other methods under development but those are not widely practised (yet). In all setups, a carefully calibrated vector network analyzer is used to measure the reflection coefficient of the system. Other instrumentation can be used as well but can be cumbersome to use, inaccurate and typically does not allow for the use of a gate to isolate the absorber response. The basic procedure is to measure the reflection of the test setup without the absorber as a reference (i.e. the response of the back of the coax or square waveguide, or a metal reference plate in the case of the plane wave method) and measuring the reflection levels with the absorber in place. The difference between the two is the absorption of the absorber. Although the basic principles are simple, obtaining valid measurements with these setups is very tricky. There are a lot of measurement and setup issues to consider. There is not an official standard for performance measurements of absorbers that I'm aware of. The de facto absorber test standard referenced by most absorber manufacturers is a university of Michigan report describing the arch method (plane wave). Hope this helps. -Robert Robert Bonsen Principal Consultant Orion Scientific email: rbon...@orionscientific.com URL: http://www.orionscientific.com phone: (512) 347 7393; FAX: (512) 328 9240 - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, jim_bac...@monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
RE: Precompliance Testing
Hi folks, The company mentioned, SARA, builds what they call a distributed RF analyzer named CASSPER. They have been working on it for a while now, demoed it at a couple of shows, and to the best of my knowledge the system started to ship recently. In the data sheets I analyzed, mention was made of background noise cancellation techniques by using two time and frequency synchronized receivers, one configured as the normal receiver and one as a reference receiver. The time and frequency sync between the two receivers allows for coherent simultaneous measurements of the reference signal and the measuring signal, hence allowing the system to dynamically reduce the noise level in the measurement. So far the data sheets... By the way, this noise cancellation technique will not work on ordinary receivers and spectrum analyzers because the time/frequency synchronization, which cannot be achieved with ordinary equipment, is essential. In theory this works great, but as with all noise/spurious signal cancellation techniques (common in the RCS and antenna measurement world) using a variety of mathematical principles, there will be practical limitations. Also, one of the drawbacks is that you are required to purchase another receiver for this technique to work. And of course this type of receiver with noise cancellation technique is not the kind of device the standards have made provisions for, so the question is if the data will ever be acceptable for compliance measurements per the standards. CASSPER is a very interesting device, very useful for a wide variety of RF applications. I would like to get my hands on one soon to tinker with it and find out exactly what its potential is. The company mentions as applications pre-compliance regulatory testing and EUT debugging, but as indicated it is not usable for compliance testing (yet?). Reference: http://www.sara.com/cassper Regards, -Robert Robert Bonsen Principal Consultant Orion Scientific email: rbon...@orionscientific.com URL: http://www.orionscientific.com phone: (512) 347 7393; FAX: (512) 328 9240 - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, jim_bac...@monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
Re: Characterizing a screen room
At 04:21 PM 4/27/99 GMT, you wrote: My company is planning to purchase a screen room for radiated emissions precompliance testing. I'm aware that reflections can cause resonances and drastically influence readings. What kind of testing could I do to characterize the room (aside from simple experience)? The simple answer would be this: don't even try. You're much better off using the company parking lot to do pre-compliance radiated emissions testing. For conducted emissions/immunity, and to a certain extent radiated immunity, a shielded room is great. But not for RE. The reason for this is the reflections/resonances you get from the walls and the ceiling. You can get higher than 20 dB ripples on your measurements in an untreated (no absorber materials on walls/ceiling) shielded room. And these ripples are not very repeatable, they will change considerably with position (eg, moving your antenna or EUT less than an inch may result in field variations of much more than 10 dB). Because of these huge variations, testing cannot help you characterize your room and take these reflections into account in your emissions measurements. If you absolutely need to use a shielded room, try lining it with absorber materials. Even a few absorbers are better than none at all. Or try using another type of pre-compliance device like a GTEM or something similar. Another alternative would be to turn the shielded room into a mode-stir chamber. By rotating the properly designed mode stirrer, you will even out the variations which will result in fairly usable, repeatable numbers. The size of the room determines the usable frequency range. Regards, -Robert Robert Bonsen Principal Consultant Orion Scientific email: rbon...@orionscientific.com URL: http://www.orionscientific.com phone: (512) 347 7393; FAX: (512) 328 9240 - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, jim_bac...@monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
RFC: feasibility of online test equipment exchange
Request For Comment: Feasibility of on-line RF and EMC test instrument marketplace As a small RD firm, we sometimes run into a situation in which we have RF and/or EMC test equipment laying around that we have no use for anymore. And on occassion we need a specialized test instrument for just a single long-term project so renting is not an option. After talking with some collegues, I came up with the idea of developing an on-line equipment exchange for the EMC and RF testing community. This equipment exchange would allow EMC, RF and coms engineers to sell, trade or buy surplus and used test equipment. It is not intended to be just another auction site. The basic services I am thinking of are as follows: For sale or wanted (for trade?): the following types of equipment: EMC test equipment: from spectrum analyzers to anechoic chambers or GTEMs, from cables to antennas, debugging equipment, software, old copies of test standards, etc. RF test equipment: network analyzers, RF sources, communication analyzers, meters, measurement software, positioning hardware, anechoic materials, antennas, etc. Various: oscilloscopes, power supplies, books on electromagnetics, anything else potentially useful to a test lab. My goal is to primarily list high-quality laboratory grade equipment, for labs needing better used/refurbished test equipment than is available at the local HAM fests. Submissions will be screened to eliminate noise and inappropriate entries. A quick-and-dirty demo is set up at: http://www.orionscientific.com/market/index.htm with some examples of what I have in mind. With this RFC, I would like to get the list members' input regarding the following issues: a. the basic question: is there a need or want for such a service? how many of you gentlefolk would use a service like this, to buy or to sell? I imagine it would be interesting for smaller labs, how about the bigger ones? Any ideas on how to go about reaching the people potentially interested in it? Advertising in eg. ITEM? Word of mouth? b. any suggestions for modifications to the initial setup? Additional categories perhaps, like employment offers, full-time, contract or consulting? c. in order to cover the costs incurred with providing a professional service like this, we will have to charge a small fee. I think I would prefer to be asked a small flat-rate percentage after (and only then) the item gets sold, with enforcement through the honor system. Any thoughts on this? Also, would there be a need for a rating system to keep people honest, like for example eBay has? d. have I missed any obvious issues? Thanks for your time. Please respond directly to: excha...@orionscientific.com I will post a summary of the responses. Regards, -Robert Robert Bonsen Principal Consultant Orion Scientific email: rbon...@orionscientific.com URL: http://www.orionscientific.com phone: (512) 347 7393; FAX: (512) 328 9240 - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, j...@gwmail.monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
RE: Conductive Paint
FYI: An article regarding the use of conductive coatings in plastic enclosures appears in this year's (1999) edition of ITEM (http://www.rbitem.com): Performance characteristics of conductive coatings for EMI control, Brian Jackson and Thomas Bleeks, p. 125, 137-146. Emphasis is on EMI application, but they do go into mechanical and durability issues. Just thought I'd mention it. -Robert Robert Bonsen Principal Consultant Orion Scientific email: rbon...@orionscientific.com URL: http://www.orionscientific.com phone: (512) 347 7393; FAX: (512) 328 9240 - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, j...@gwmail.monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
vehicle EMC and safety regs in EU
Hi all, I was wondering if the collective could help me with the following: What are the regulations in the EU regarding vehicle EMC (and safety) issues? Any requirements for whole-vehicle testing? What about an add-on device like a GPS receiver/navigational device. I am aware of the various SAE and CISPR standards, but I'm wondering which ones are mandated by the EU. Any directives on that? I would also like to hear from test houses who can do the kind of testing (EMC and safety) as described in the standards on vehicle testing. Happy holidays to all. Regards, -Robert Robert Bonsen Principal Consultant Orion Scientific email: rbon...@orionscientific.com URL: http://www.orionscientific.com phone: (512) 347 7393; FAX: (512) 328 9240 - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, j...@gwmail.monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
Re: 10m Indoor OATS Facelift
At 09:25 AM 11/23/98 -0500, CTL c...@prodigy.net wrote: Check out Panashield, Inc. Panashield is a chamber vendor, one of the many. As all chamber vendors, they're in the business of selling their shielding and absorber materials. Their efforts to help a customer solve his/her testing problem are motivated by the opportunity to sell products (granted, some will go pretty far to sell their stuff--your mileage will vary). Other vendors include Lindgren RF Enclosures, Braden Shielding, EMC Test Systems and a number of smaller shielding companies. Consultants are in the business of selling their time and expertise to help customers decide on the best solution for the customer's testing requirements. Independent consultants do not gain from selling anything. There is a difference. Just an FYI. original message deleted Regards, -Robert Robert Bonsen Principal Consultant Orion Scientific email: rbon...@orionscientific.com URL: http://www.orionscientific.com phone: (512) 347 7393; FAX: (512) 328 9240 - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, j...@gwmail.monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
Re: where we do it
Hi Ed, Cool list. For a next list you may want to add the OATS at NIST in Boulder, CO. They had the biggest meanest bull snake living underneath their ground screen. On occasion he would feel like defending his territory and scare us all when we were doing antenna calibrations. I wonder if it's still there after the latest site upgrade. Just to let you know, what Hans described is not really a novel idea. The concept of other-than-rectangular semi-anechoic chambers has been used many many times, e.g. the boat-shaped chambers and AEMI's doubly horn design. Typically, these concepts have been proven to be fairly impractical and expensive. The performance gain is small and the layout is usually designed through raytracing such that the direct reflection from chamber walls misses the critical points on the quiet zone. Howevever, this does not mean that the overall quiet zone performance is better (usually isn't), it just means that the chamber is optimally designed to comply with the ANSI standard measurement method at five points. These techniques are typically used to mask the use of inferior performing absorbers, absorbers which can't perform up to the level required for them to be used in a compliant EMC chamber. Chamber building cost is also an important parameter of superior chamber design and non-rectangular chambers usually turn out to be a LOT more expensive, due to labor and material cost. Improvements in chamber performance are gained by numerically optimized absorber design and improved bulk material measurements. The latest ferrite/foam hybrids outperform older designs by up to 10 dB in the low-frequency range. Other than the geometry issue (ALL modern chambers are built rectangular due to improvements in absorber performance and material costs), the larger chambers are being built with multi-scan capabilities. For the Xerox chamber (built by ETS, where I designed and verified it) the range has been qualified for 5(!) different positions, for quiet zones from 3m to 10m diameter, all with +/- 3dB max. deviation from theoretical NSA. They have two antenna masts in place for multiscan (polarization, frequency bands) capability. Other high-performance chambers (ETS's HP (FtCollins) and Sony (San Diego), and TDK/Lindgren's UL (Melville) ) have multi-range capabilities as well. So chamber builders have already made great strides in making Hans's dreams come true. The superior performance chambers are already out there, more are still to come whenever the larger corporations are willing to shell out the big dollars. Although those chambers use more expensive absorber material than standard 10m chambers and are somewhat larger in size, the designs are close to the practical limits on footprint (dictated by measurement range and quiet zone size) and performance. Regards, -Robert Robert Bonsen Principal Consultant Orion Scientific email: rbon...@orionscientific.com URL: http://www.orionscientific.com phone: (512) 347 7393; FAX: (512) 328 9240 - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, j...@gwmail.monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
RE: ANSI C63.4 -- ferrites
In my experience when doing testing of semi-anechoic chambers for NSA performance using ferrites is a must to avoid measurements being influenced by the vertical drop portion on both the transmit and receive end. Using a spacing of about half a foot inbetween individual ferrite beads has worked best for me. Especially in the lower frequencies, up to about 150MHz, the effect of the cable drop on vertical pol measurements is considerable (sometimes more than 1.5 dB). Thus, in all the NSA test specifications I write, I insist on the use of ferrites. Of course, not using ferrites on the vertical cable drop allows a chamber tester to tweak the cables such that at a specific problem frequency the vertical cable drop portion acts as a reflector to reduce or increase the transmitted/received signal levels somewhat. This may bring a chamber/OATS in spec which really isn't. Or bring it out if the tester is not aware of the problem. For better repeatability and better NSA measurements, ferrites are required. They do not make the cable totally RF-invisible but do considerably reduce the influence of the cable on the measurements. Regards, -Robert Robert Bonsen Principal Consultant Orion Scientific email: rbon...@orionscientific.com URL: http://www.orionscientific.com phone: (512) 347 7393; FAX: (512) 328 9240 - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, j...@gwmail.monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
