Re: Antenna Calibration/Site Attenuation
Good comment, Ed. We all depend on our reputations as competent technical people that we can deliver the best product or service reasonable. Proper or deficient equipment can make or break (respectively) the quality of our well-intended work. Hence, knowledge of any weaknesses in a particular piece of equipment (in this case, an antenna) can at least allow us to investigate and compensate for the known weakness. A potential benefit of reporting anomalies with a particular piece of equipment is the bringing forth of comments from the (defending) manufacturer. The manufacturers normally will have performed exhaustive analysis and corroborative characterization on a given antenna during its development phase, but seldom will the users get access to that data unless the need to publish it arises. We may all learn how to identify more subtle anomalies, fix them, or compensate for them. I haven't noticed any antenna vendors jumping into the discussion on antenna characteristics, and we all know they read this forum daily. How about it, guys? Mike Conn Mikon Consulting
Re: Antenna Calibration/Site Attenuation
From: Cortland Richmond 72146@compuserve.com To: Grasso, Charles (Chaz) gra...@louisville.stortek.com; ieee pstc list emc-p...@ieee.org Subject: RE: Antenna Calibration/Site Attenuation Date: Monday, August 25, 1997 11:19 AM If it's mutual coupling... sure. But if it's a surface wave, that's real field strength. If the reason for 3 meters -- an approximation of distance to the victim receiver in a residential area -- is to be preserved, then perhaps this is a non-issue, as the error is all on the high side, and emissions will be reduced even lower than they would be on a ten meter site. (As an aside, can anyone here say if the COmmission has ever specifically ruled on how far away from residences Class A equipment must be kept? I remember a few years ago some chap got a NAL for operating a graphics work station in his home... but what about separate buildings out back, etc. ?) Cortland It would seem that businesses run in homes would tend to violate *any* distance requirement. I believe that the wording of the labeling specifically addresses may not cause harmful interference which could be at any distance.
RE: Antenna Calibration/Site Attenuation
Chris, The rule that supersedes the others is: Don't interfere. However... there's a general perception that Class A is cheaper to build than Class B and not to ask for stricter standards if aiming at a better deal. This can result in specifying Class A limits if there is any justification at all for claiming non-residential operation. We do know that even Class B isn't good enough all the time, and Class A would not be better, but worse than that, but what I am looking for is some evidence that there is a de-facto standard applied by the regulatory authorities (in my case the FCC) to the introduction into or near a residential neighborhood of equipment only verified to meet Class A. Cortland == Original Message Follows Date: 25-Aug-97 13:20:16 MsgID: 1054-3884 ToID: 72146,373 From: Chris Dupres chris_dupres Subj: RE: Antenna Calibration/Site Attenuation Chrg: $0.00 Imp: Norm Sens: StdReceipt: NoParts: 1 Hi Cortland. You asked: (As an aside, can anyone here say if the COmmission has ever specifically ruled on how far away from residences Class A equipment must be kept? In my meanderings around the Compliance Biosphere, I've spoken to many enforcement people, competent bodies, even Government administrators. The general opinion seems to be 'If you meet the general intention of the Directives via the Standards, then the world will be a better trading place'. Note the deliberate absence of the word 'distance' and 'field strength, and 'interference'. In general, the advice I live with, and give, is that you shouldn't expect a TV to work perfectly on top of a Microwave cooker, and you wouldn't expect an electric pencil sharpener to reverse if you use a portable phone nearby. I feel that in any one typical domestic situation, the RF signature of a location is so far removed from an OATS or screened room as to be almost meaningless in practical terms, but you gotta put some rules down somewhere. I akin it to judging how fast a car can go by the shape of the hub caps. (They only put Hot Hub Caps on fast cars?) I had a case of a TIG welder interfering with a VHF radio some 200 metres away, awful wide band hash whenever the TIG fired up. I've also had Quadrupole Mass Spectrometers (pico and femto amps) behaving perfectly when 600mA 2kV Argon Arcs are being started in the same vacuum chamber. In answer to your question, I'm not aware of any requirements for distances between emitters and receptors, notwithstanding that there may be local by-laws which prohibit people camping beside arc furnaces, or something. In the UK, if you regularly get nuisance interference from anything at all, one can approach British Telecom, the monopoly holder, who will investigate and find the source of the intereference, and politely suggest to the source that they do something about it, but I'm not sure what teeth they have. The point is, is that they don't seem to take distance into account. It's all to do with the Wireless Telegraphy act, I think. That should be as clear as mud... Chris Dupres Surrey, UK. **Primary Recipient: Cortland Richmond 72146,373 == End of Original Message =
Re: Antenna Calibration/Site Attenuation
Right. Harmful interference makes any classification meaningless. Cortland == Original Message Follows Date: 25-Aug-97 18:43:26 MsgID: 1054-4643 ToID: 72146,373 From: Doug McKean INTERNET:dmck...@paragon-networks.com Subj: Re: Antenna Calibration/Site Attenuation Chrg: $0.00 Imp: Norm Sens: StdReceipt: NoParts: 1 From: Cortland Richmond 72146@compuserve.com To: Grasso, Charles (Chaz) gra...@louisville.stortek.com; ieee pstc list emc-p...@ieee.org Subject: RE: Antenna Calibration/Site Attenuation Date: Monday, August 25, 1997 11:19 AM If it's mutual coupling... sure. But if it's a surface wave, that's real field strength. If the reason for 3 meters -- an approximation of distance to the victim receiver in a residential area -- is to be preserved, then perhaps this is a non-issue, as the error is all on the high side, and emissions will be reduced even lower than they would be on a ten meter site. (As an aside, can anyone here say if the COmmission has ever specifically ruled on how far away from residences Class A equipment must be kept? I remember a few years ago some chap got a NAL for operating a graphics work station in his home... but what about separate buildings out back, etc. ?) Cortland It would seem that businesses run in homes would tend to violate *any* distance requirement. I believe that the wording of the labeling specifically addresses may not cause harmful interference which could be at any distance. == End of Original Message =
Re: Antenna Calibration/Site Attenuation
Great dialog, just the path that I was hoping would develop. One thing I have learned since the question was first asked, all biconical antennas are not made equal. The original antenna calibrated at an outside test organization, exhibited a 5 dB difference between the vertical and horizontal polarizations at 3 meters in the frequency range of 30 - 50 MHz. Another antenna subsequently calibrated at the same organization had less than 1 dB difference between v and h, 1m and 10 m. This outcome was more in line with the expected outcome of the calibration per C63.5 which stated minor variations with polarizations and geometries where geometries is understood to mean test distances. Don Umbdenstock Sensormatic -- From: chasgra...@aol.com To: 72146@compuserve.com; chris_dup...@compuserve.com; emc-p...@ieee.org Subject: Re: Antenna Calibration/Site Attenuation List-Post: emc-pstc@listserv.ieee.org Date: Tuesday, August 26, 1997 5:20AM This has turned into an interesting discussion. 1. On the question of Class A vs Class B etc.. I vaguely remember that the genesis of the FCC limits for Class A Class B were indeed derived from the concerns of installation. As I recall, extensive research went into examination of the sensitivities of television receivers and apatment complexes and as a result the 3M test distance and Class B limits were born for residential applications. Of course this was back in the 70s when 300 ohm cabling for TVs was in vogue!!. Naturally the FCC recognized that not all EMI problems would be resolved by design/testing alone. Chris is correct in his statement that the emissions test bears little resemblelance to reality. The FCC ( others) insist on warning statements etc. (I believe the VDE has the honor of having the FIRST legal EMI requirements. In the original 0871 standards they were more concerned with conducted limits - hence their severity. The Class A radiated limits had relief in certain bands that allowed for very high emissions indeed.) 2. Mutual coupling (?) Reading the e-mails on enhanced emissions at 3M vertically polarized generated some thoughts. 2.1 I have discussed the issue of calibrating an antenna using ANSI C63.5 (horizontal only) and testing using ANSI C63.4 (vh) with one of the authors involved in BOTH standards. The answer I get consistently is that: a) we need to calibrate in free space ( or close to it) b) calibrating an antenna with V H makes the test look like the NSA and
Re: Antenna Calibration/Site Attenuation
--- On Tue, 26 Aug 1997 08:12:00 -0400 UMBDENSTOCK, DON umbdenst...@sensormatic.com wrote: Great dialog, just the path that I was hoping would develop. One thing I have learned since the question was first asked, all biconical antennas are not made equal. The original antenna calibrated at an outside test organization, exhibited a 5 dB difference between the vertical and horizontal polarizations at 3 meters in the frequency range of 30 - 50 MHz. Another antenna subsequently calibrated at the same organization had less than 1 dB difference between v and h, 1m and 10 m. This outcome was more in line with the expected outcome of the calibration per C63.5 which stated minor variations with polarizations and geometries where geometries is understood to mean test distances. Don Umbdenstock Sensormatic ---End of Original Message- Don: Not meaning to single you out, but your post tweaked a concern of mine. Are we all operating in a sense of fear in this forum? Do we really have to obfuscate the facts by referring to an original antenna and another antenna? Or am I the only one who would like to know exactly which antenna and test lab that you're talking about? Ed -- Ed Price ed.pr...@cubic.com Electromagnetic Compatibility Lab Cubic Defense Systems San Diego, CA. USA 619-505-2780 List-Post: emc-pstc@listserv.ieee.org Date: 08/26/97 Time: 08:32:35 --
RE: Antenna Calibration/Site Attenuation
Ed brings up a good point. This forum is designed to allow communications between EMC and Product Safety professionals who are looking to help each other in the interest of the advancement of the compliance industry. If there is a certain test house or equipment manufacturer that provides inadequite services or products, why shouldn't that be disclosed on this forum? Why would anyone want me to find out on my own that a certain manufacturer has probelms with Biconical Antennas? It seems to me that an open channel of communication would help convince the manufacturers or service providers in the industry who are lacking to shape up. Is it simply an issue of fear of litigation? Regards, Randy Flinders EMC Test Engineer Emulex Network Systems Corporation Phone: (714) 513-8012 Fax: (714) 513-8265 E-Mail: r_flind...@emulex.com WebSite: www.emulex.com * opinions expressed herein are personal, and in no way reflect the position of Emulex Corporation. -- From: ed.price[SMTP:ed.pr...@cubic.com] Sent: Tuesday, August 26, 1997 8:32 AM To: UMBDENSTOCK, DON Cc: 'EMC-PSTC Discussion Group' Subject: Re: Antenna Calibration/Site Attenuation --- On Tue, 26 Aug 1997 08:12:00 -0400 UMBDENSTOCK, DON umbdenst...@sensormatic.com wrote: Great dialog, just the path that I was hoping would develop. One thing I have learned since the question was first asked, all biconical antennas are not made equal. The original antenna calibrated at an outside test organization, exhibited a 5 dB difference between the vertical and horizontal polarizations at 3 meters in the frequency range of 30 - 50 MHz. Another antenna subsequently calibrated at the same organization had less than 1 dB difference between v and h, 1m and 10 m. This outcome was more in line with the expected outcome of the calibration per C63.5 which stated minor variations with polarizations and geometries where geometries is understood to mean test distances. Don Umbdenstock Sensormatic ---End of Original Message- Don: Not meaning to single you out, but your post tweaked a concern of mine. Are we all operating in a sense of fear in this forum? Do we really have to obfuscate the facts by referring to an original antenna and another antenna? Or am I the only one who would like to know exactly which antenna and test lab that you're talking about? Ed -- Ed Price ed.pr...@cubic.com Electromagnetic Compatibility Lab Cubic Defense Systems San Diego, CA. USA 619-505-2780 List-Post: emc-pstc@listserv.ieee.org Date: 08/26/97 Time: 08:32:35 --
Re: Antenna Calibration/Site Attenuation #2
***MESSAGE #2*** Ignore first message!! *** This has turned into an interesting discussion. 1. On the question of Class A vs Class B etc.. I vaguely remember that the genesis of the FCC limits for Class A Class B were indeed derived from the concerns of installation. As I recall, extensive research went into examination of the sensitivities of television receivers and apatment complexes and as a result the 3M test distance and Class B limits were born for residential applications. Of course this was back in the 70s when 300 ohm cabling for TVs was in vogue!!. Naturally the FCC recognized that not all EMI problems would be resolved by design/testing alone. Chris is correct in his statement that the emissions test bears little resemblelance to reality. The FCC ( others) insist on warning statements etc. (I believe the VDE has the honor of having the FIRST legal EMI requirements. In the original 0871 standards they were more concerned with conducted limits - hence their severity. The Class A radiated limits had relief in certain bands that allowed for very high emissions indeed.) 2. Mutual coupling (?) Reading the e-mails on enhanced emissions at 3M vertically polarized generated some thoughts. 2.1 I have discussed the issue of calibrating an antenna using ANSI C63.5 (horizontal only) and testing using ANSI C63.4 (vh) with one of the authors involved in BOTH standards. The answer I get consistently is that: a) we need to calibrate in free space ( or close to it) b) calibrating an antenna with V H makes the test look like the NSA and hence site anomilies dominate the vertical readings. 2.2 For my type of products (floor standing), Vert 1M seems to be worst case. This has more to do with the install than mutual coupling - I test at 10M. My humble opinion only. Charles Grasso EMC Engineer
RE: Antenna Calibration/Site Attenuation
Hi, Yes I attended that presentation. In ANSI C63.4 Methods for SA there is a fudge factor for taking out the mutual coupling between antennas for 3M SA measurements. Doesn't this take care of the problem? Charles Grasso EMC Engineer StorageTek gra...@louisville.stortek.com Tel:(303)673-2908 Fax(303)661-7115 -- From: Cortland Richmond[SMTP:72146@compuserve.com] Sent: Saturday, August 23, 1997 1:53 PM To:Thomas Donnelly; ieee pstc list Subject: Re: Antenna Calibration/Site Attenuation Tom, Did you get to the presentation about getting the most out of a biconical antenna? Some thoughts contained there on antenna calibration, too. I found some time ago that using antennas does lead to the kind of mutual coupling Martin talked about, and also -- and this is not mentioned much -- even with small sources, there is a definite surface wave near the ground plane at 30-35 or 40 MHz. This skews reading upwards, but as it is part of the site propagation, I think it has to be factored out by doing that vertical antenna factor measurement. A couple more meters, and the surface wave is no longer a problem. I say surface wave, because I don't think this is a mutual coupling problem. Even small sources seem to generate it. I am presently working on an antenna calibration for a semi-anechoic chamber in which I shall be able to investigate this more closely. Regards, Cortland
RE: Antenna Calibration/Site Attenuation
If it's mutual coupling... sure. But if it's a surface wave, that's real field strength. If the reason for 3 meters -- an approximation of distance to the victim receiver in a residential area -- is to be preserved, then perhaps this is a non-issue, as the error is all on the high side, and emissions will be reduced even lower than they would be on a ten meter site. (As an aside, can anyone here say if the COmmission has ever specifically ruled on how far away from residences Class A equipment must be kept? I remember a few years ago some chap got a NAL for operating a graphics work station in his home... but what about separate buildings out back, etc. ?) Cortland == Original Message Follows Date: 25-Aug-97 07:21:19 MsgID: 1054-2813 ToID: 72146,373 From: Grasso, Charles (Chaz) INTERNET:gra...@louisville.stortek.com Subj: RE: Antenna Calibration/Site Attenuation Chrg: $0.00 Imp: Norm Sens: StdReceipt: NoParts: 1 Hi, Yes I attended that presentation. In ANSI C63.4 Methods for SA there is a fudge factor for taking out the mutual coupling between antennas for 3M SA measurements. Doesn't this take care of the problem? Charles Grasso EMC Engineer StorageTek gra...@louisville.stortek.com Tel:(303)673-2908 Fax(303)661-7115 -- From: Cortland Richmond[SMTP:72146@compuserve.com] Sent: Saturday, August 23, 1997 1:53 PM To:Thomas Donnelly; ieee pstc list Subject: Re: Antenna Calibration/Site Attenuation Tom, Did you get to the presentation about getting the most out of a biconical antenna? Some thoughts contained there on antenna calibration, too. I found some time ago that using antennas does lead to the kind of mutual coupling Martin talked about, and also -- and this is not mentioned much -- even with small sources, there is a definite surface wave near the ground plane at 30-35 or 40 MHz. This skews reading upwards, but as it is part of the site propagation, I think it has to be factored out by doing that vertical antenna factor measurement. A couple more meters, and the surface wave is no longer a problem. I say surface wave, because I don't think this is a mutual coupling problem. Even small sources seem to generate it. I am presently working on an antenna calibration for a semi-anechoic chamber in which I shall be able to investigate this more closely. Regards, Cortland == End of Original Message =
