Re: ??? RE: ??? RE: Near field H-field measurement.
A modern day antenna designer knows the complete current distribution over his radiating structure and thus, with enough computational horsepower, can predict electromagnetic fields emanating from his device. When the radiating device is an unintentional radiator where the current distribution is completely unknown, and we use a pickup device to sample one particular aspect of the field at one particular separation from the EUT, then we have no information on which to base any extrapolation. From: Cortland Richmond 72146@compuserve.com Date: Fri, 24 Jun 2005 03:20:06 -0400 To: ieee pstc list emc-p...@ieee.org Subject: Re: ??? RE: ??? RE: Near field H-field measurement. Ken Javor wrote The only practical solution is to use a probe that looks like the one the victim of rfi is going to be using, connected to a receiver of equal to or greater sensitivity than the victim, and similar bandwidth, and verify that the level of rfi at a particular separation is sufficiently low as to not interfere with a predetermined level of broadcast reception. And the measurement is made in such a way as to maximize emissions, in the traditional manner. And you cannot of course extrapolate the near field from the far field; not that anyone is trying. Yes, my rant does fall into the realm of significant oversimplification (grin). In _practice_, as you say, using a transducer similar to the expected victims', we end up with a useful number. It's not what the label says it is, but it'll do. (I eat no-fat cheese food, too.) Near field/far field extrapolation is useful when there's too little room to get into the far field of high-gain antennas; I've seen papers in the APS journal on this. Antenna designers do start knowing a lot about their radiating structures. Should we know more about our EUT's considered as antennas? Cortland Richmond KA5S 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/listserv/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 Cantwellmcantw...@ieee.org For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc 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/listserv/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 Cantwellmcantw...@ieee.org For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: ??? RE: ??? RE: Near field H-field measurement.
Every bit of the first three paragraphs is absolutely correct. That aspect of the rfi ought to be controlled which is most likely to cause a problem. In a band where a whip or loop are each possibilities, then both the electric and magnetic fields should be controlled, and separately measured. 61000-4-6 is the conducted immunity requirement that supports or supplants 61000-4-3 at frequencies below 80 MHz. Inherent in 61000-4-3 6 is the concept of intentionally transmitted rf from an antenna. The IEC decided a long time ago that 150 Ohms was a more representative transmission line impedance than 50 Ohms, and they are no doubt correct. Whatever the value chosen, once a signal has been coupled to a conductor, it is the source impedance of the conductor that is of interest. If it were desired at low frequencies to simulate a local source of very high or very low impedance fields, I would think an open-circuited parallel plate would work for electric fields, while a short-circuited plate or Helmholtz coil would work for low impedance fields. A comparison of the coupling from those types of fields compared to a plane wave is given in my 1997 IEEE EMC Symposium paper (Austin, TX). IMO, such test would only be for very special circumstances and do not warrant standardization as routine requirements. From: Bob Richards b...@toprudder.com Date: Fri, 24 Jun 2005 05:04:55 -0700 (PDT) To: emc-p...@ieee.org Subject: Re: ??? RE: ??? RE: Near field H-field measurement. Ken, I'm no expert, but as I understand it, making measurements at low frequencies, measured in the near field, it is possible to have a very high E-field and very low H-field if the radiating source is high impedance. The opposite is true if the radiating source is low impedance, ie: high H-field, low E-field. Also, if the coupling mechanism of the susceptible EUT is primarily inductive, (low impedance) then a high-impedance radiator will be less likely to cause interference than a low-impedance radiator. If my understanding is correct (tell me if I am wrong) then I can see the case for making low-frequency radiated emissions measurements with both E-field whips and H-field loops, with a limit specified for each, such as is done for GR1089 testing. There also needs to be some insurance that the immunity tests cover these two scenarios as well. I wonder just how well the conducted immunity tests relate. The 61000-4-3 test (with CDNs) is with a fixed source impedance of 150 ohms. Theoretically there can only be a 6dB increase in either current or voltage if the EUT port has a very low or very high impedance. Bob Richards, NCT. --- Ken Javor ken.ja...@emccompliance.com wrote: In my opinion... The right limit is the limit which protects reception of broadcast signals in licensed bands. At low frequencies where the antenna is either a loop or whip, the limit would be ascertained using a typical loop/whip connected to a typical receiver. The most accurate limit would be the rfi level at the receiver antenna port that allows a specified quality of reception in the presence of the rfi. The measurement would be made at a specified distance from the rfi source. The limit would then be so many dBuV or dBm in a certain bandwidth, using a particular loop/whip. The loop/whip construction and transducer factor would have to be specified. This is the only technically proper way of doing things until you are at a frequency/distance from rfi source such that a far field measurement is possible. A field intensity limit allowing the use of any suitable antenna is only appropriate if a far field measurement is possible. 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/listserv/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 Cantwellmcantw...@ieee.org For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc 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/listserv/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 Cantwellmcantw...@ieee.org For policy
RE: ??? RE: ??? RE: Near field H-field measurement.
Interesting thread; educational. There's the pure science of the issue and there's the regulatory expedient solution. Interestingly, the FCC mandates using a loop for frequency measurements below 30 MHz, but gives the limit in dBuV/m. The antenna factors of the loop antennas are typically given for both E and H field related by far field factor of 51 dB. As indicated before, 50 kHz is anything but far field, and one will not be able to measure the H field of a loop source of 50 kHz in the far field. So as Cortland pointed out, precise and inaccurate it is... Don Umbdenstock Manager Compliance Engineering Tyco Safety Products / Sensormatic 6600 Congress Avenue Boca Raton, FL 33487 USA 561.912.6440 djumbdenst...@tycoint.com From: Bob Richards [mailto:b...@toprudder.com] Sent: Friday, June 24, 2005 8:05 AM To: emc-p...@ieee.org Subject: Re: ??? RE: ??? RE: Near field H-field measurement. Ken, I'm no expert, but as I understand it, making measurements at low frequencies, measured in the near field, it is possible to have a very high E-field and very low H-field if the radiating source is high impedance. The opposite is true if the radiating source is low impedance, ie: high H-field, low E-field. Also, if the coupling mechanism of the susceptible EUT is primarily inductive, (low impedance) then a high-impedance radiator will be less likely to cause interference than a low-impedance radiator. If my understanding is correct (tell me if I am wrong) then I can see the case for making low-frequency radiated emissions measurements with both E-field whips and H-field loops, with a limit specified for each, such as is done for GR1089 testing. There also needs to be some insurance that the immunity tests cover these two scenarios as well. I wonder just how well the conducted immunity tests relate. The 61000-4-3 test (with CDNs) is with a fixed source impedance of 150 ohms. Theoretically there can only be a 6dB increase in either current or voltage if the EUT port has a very low or very high impedance. Bob Richards, NCT. --- Ken Javor ken.ja...@emccompliance.com wrote: In my opinion... The right limit is the limit which protects reception of broadcast signals in licensed bands. At low frequencies where the antenna is either a loop or whip, the limit would be ascertained using a typical loop/whip connected to a typical receiver. The most accurate limit would be the rfi level at the receiver antenna port that allows a specified quality of reception in the presence of the rfi. The measurement would be made at a specified distance from the rfi source. The limit would then be so many dBuV or dBm in a certain bandwidth, using a particular loop/whip. The loop/whip construction and transducer factor would have to be specified. This is the only technically proper way of doing things until you are at a frequency/distance from rfi source such that a far field measurement is possible. A field intensity limit allowing the use of any suitable antenna is only appropriate if a far field measurement is possible. 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/listserv/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 Cantwellmcantw...@ieee.org For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc 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/listserv/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 Cantwellmcantw...@ieee.org For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: ??? RE: ??? RE: Near field H-field measurement.
Ken, I'm no expert, but as I understand it, making measurements at low frequencies, measured in the near field, it is possible to have a very high E-field and very low H-field if the radiating source is high impedance. The opposite is true if the radiating source is low impedance, ie: high H-field, low E-field. Also, if the coupling mechanism of the susceptible EUT is primarily inductive, (low impedance) then a high-impedance radiator will be less likely to cause interference than a low-impedance radiator. If my understanding is correct (tell me if I am wrong) then I can see the case for making low-frequency radiated emissions measurements with both E-field whips and H-field loops, with a limit specified for each, such as is done for GR1089 testing. There also needs to be some insurance that the immunity tests cover these two scenarios as well. I wonder just how well the conducted immunity tests relate. The 61000-4-3 test (with CDNs) is with a fixed source impedance of 150 ohms. Theoretically there can only be a 6dB increase in either current or voltage if the EUT port has a very low or very high impedance. Bob Richards, NCT. --- Ken Javor ken.ja...@emccompliance.com wrote: In my opinion... The right limit is the limit which protects reception of broadcast signals in licensed bands. At low frequencies where the antenna is either a loop or whip, the limit would be ascertained using a typical loop/whip connected to a typical receiver. The most accurate limit would be the rfi level at the receiver antenna port that allows a specified quality of reception in the presence of the rfi. The measurement would be made at a specified distance from the rfi source. The limit would then be so many dBuV or dBm in a certain bandwidth, using a particular loop/whip. The loop/whip construction and transducer factor would have to be specified. This is the only technically proper way of doing things until you are at a frequency/distance from rfi source such that a far field measurement is possible. A field intensity limit allowing the use of any suitable antenna is only appropriate if a far field measurement is possible. 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/listserv/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 Cantwellmcantw...@ieee.org For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: ??? RE: ??? RE: Near field H-field measurement.
Ken Javor wrote The only practical solution is to use a probe that looks like the one the victim of rfi is going to be using, connected to a receiver of equal to or greater sensitivity than the victim, and similar bandwidth, and verify that the level of rfi at a particular separation is sufficiently low as to not interfere with a predetermined level of broadcast reception. And the measurement is made in such a way as to maximize emissions, in the traditional manner. And you cannot of course extrapolate the near field from the far field; not that anyone is trying. Yes, my rant does fall into the realm of significant oversimplification (grin). In _practice_, as you say, using a transducer similar to the expected victims', we end up with a useful number. It's not what the label says it is, but it'll do. (I eat no-fat cheese food, too.) Near field/far field extrapolation is useful when there's too little room to get into the far field of high-gain antennas; I've seen papers in the APS journal on this. Antenna designers do start knowing a lot about their radiating structures. Should we know more about our EUT's considered as antennas? Cortland Richmond KA5S 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/listserv/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 Cantwellmcantw...@ieee.org For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: ??? RE: ??? RE: Near field H-field measurement.
I disagree with this part: Near field or far field only matters when we want to know what one will be from the other, and this can be calculated. Theoretically you could map the entire wave-front surface at a given separation from the EUT and connected cables and using an electrical analog of the optical Huygens wave-front principle you could extrapolate the field at larger separations. But practically speaking you would have to separate out the radial and tangential electric fields, and you would have to accurately determine the vector nature (direction) of each portion of the wave-front as well as its magnitude, and this would have to be done in small enough patches that the magnitude and direction of the field vectors would be constant over the patch and it isn't going to happen. The only practical solution is to use a probe that looks like the one the victim of rfi is going to be using, connected to a receiver of equal to or greater sensitivity than the victim, and similar bandwidth, and verify that the level of rfi at a particular separation is sufficiently low as to not interfere with a predetermined level of broadcast reception. And the measurement is made in such a way as to maximize emissions, in the traditional manner. And you cannot of course extrapolate the near field from the far field; not that anyone is trying. From: Cortland Richmond 72146@compuserve.com Date: Thu, 23 Jun 2005 15:53:34 -0400 To: ieee pstc list emc-p...@ieee.org Subject: RE: ??? RE: ??? RE: Near field H-field measurement. Bob Heller asked: How would one go about accurately measuring low frequency fields say at 10 kHz where the far-field even at lambda/6 is 5000 meters? Accuracy and what regulatory authorities require are not always the same thing. It isn't hard to measure the magnetic field accurately, given a loop whose response is known (and which is either well balanced or shielded against E-field coupling) and an accurate receiver, analyzer, etc.. Near field or far field only matters when we want to know what one will be from the other, and this can be calculated. But do our regulatory agencies want to know the (accurate) result in dBpA/m? Usually not. They want dBuV/m -- and to simplify things, probably tell us to assume far-field conditions. Our measurements would then be reasonably precise -- and inaccurate. This is not necessarily a bad thing. It makes measurements faster and easier and *so long as limits are properly crafted* still protects victim devices. If everyone uses the same (inaccurate) method with reasonable precision, we'll get results that aren't wildly different from each others', so the tests we do will have a usable relationship to the real world even though the numbers are predistorted. (It still bugs me. If an accountant predistorted our corporate bosses' books this way someone would go to jail. But in this case, it is probably good enough. C'est la vie!) Cortland Richmond KA5S 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/listserv/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 Cantwellmcantw...@ieee.org For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc 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/listserv/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 Cantwellmcantw...@ieee.org For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: ??? RE: ??? RE: Near field H-field measurement.
In my opinion... The right limit is the limit which protects reception of broadcast signals in licensed bands. At low frequencies where the antenna is either a loop or whip, the limit would be ascertained using a typical loop/whip connected to a typical receiver. The most accurate limit would be the rfi level at the receiver antenna port that allows a specified quality of reception in the presence of the rfi. The measurement would be made at a specified distance from the rfi source. The limit would then be so many dBuV or dBm in a certain bandwidth, using a particular loop/whip. The loop/whip construction and transducer factor would have to be specified. This is the only technically proper way of doing things until you are at a frequency/distance from rfi source such that a far field measurement is possible. A field intensity limit allowing the use of any suitable antenna is only appropriate if a far field measurement is possible. From: Iain Summers iain.summ...@blueyonder.co.uk List-Post: emc-pstc@listserv.ieee.org Date: Thu, 23 Jun 2005 21:44:27 +0100 To: emc-p...@ieee.org Subject: Re: ??? RE: ??? RE: Near field H-field measurement. Ken very succinctly put. I believe it was me that you responded to in an earlier posting regarding Broadband over PowerLine (PowerLine Telecommunications in the UK and Europe). I have been trying to explain the point that you have made to those that write reports estimating the likely effects of BPL. The problem in the BPL world is both of accuracy and repeatability. Accuracy because authors are quoting figures to 2 decimal places of an E field that was derived from a loop in the near-field in an uncalibrated test site. Repeatability because there is no agreed way to measure emissions from BPL yet. As part of my research I am measuring both E and H and then conducting subjective mutual interference tests on a radio receiver to attempt to correlate the effects to a measured limit. The answer will not be an acceptable limit for BPL is ?dBuv/m. It may all be academic because politicians don't do EMC. Iain - Original Message - From: Ken Javor mailto:ken.ja...@emccompliance.com To: emc-p...@ieee.org Sent: Thursday, June 23, 2005 9:05 PM Subject: Re: ??? RE: ??? RE: Near field H-field measurement. There is a significant over-generalization here. An electrically small probe does not have to convert rf into heat and thereby measure total broadband pickup. There are any number of electrically short whips, dipoles and loops whose transducer factors as a function of frequency are well characterized. Thereof ere the electric or magnetic field intensity as a function of frequency can be accurately measured. What cannot be characterized is a single number that describes the field intensity anywhere except the point at which it is measured. To quote myself from a previous post on this very same subject. here there was interest in measuring rfi from broadband communications over power-lines: I don't know how BPL really works in detail but there are a few basic physical principles that apply regardless: 1) If the measurements of interest are really in the near field, especially in the induction field, then the only valid measurement is to use the same type antenna as the likely victim, and place it the same distance from the source as the victim will occupy. The idea of measuring a field intensity in the near field is worthless. What you are measuring is the noise potential delivered to a receiver connected to a representative victim antenna or more accurately, field probe. This is very close to the old idea of an antenna-induced limit, except that concept was based on open-circuiting the probe output, whereas here we are talking about power delivered into a 50 Ohm receiver front end. 2) The probe must look like the victim to be protected by the limit. If an electrically short whip is being used, you don't use a loop and try to correlate the two. And vice versa. And the whip or loop being used needs to be the same size as the likely victim - the probe delivers a potential that is proportional to the average field impinging over its physical aperture. Unless the field is close enough to a plane wave that over the physical dimension of the probe it is homogenous, you cannot correlate the output of two different size probes, even if they are both whips or both loops. Further, you cannot extrapolate the field intensity to another distance other than that measured unless you have a priori a complete understanding of the current distribution on the transmitting structure and are only using the probe to get an amplitude data point. From: neve...@comcast.net List-Post: emc-pstc@listserv.ieee.org Date: Thu, 23 Jun 2005 18:56:33 + To: emc-p...@ieee.org Subject: RE: ??? RE: ??? RE: Near field H-field measurement. By measuring the E and H components separately, using near-field probes, which are, in principle, electrically short
Re: ??? RE: ??? RE: Near field H-field measurement.
Ken very succinctly put. I believe it was me that you responded to in an earlier posting regarding Broadband over PowerLine (PowerLine Telecommunications in the UK and Europe). I have been trying to explain the point that you have made to those that write reports estimating the likely effects of BPL. The problem in the BPL world is both of accuracy and repeatability. Accuracy because authors are quoting figures to 2 decimal places of an E field that was derived from a loop in the near-field in an uncalibrated test site. Repeatability because there is no agreed way to measure emissions from BPL yet. As part of my research I am measuring both E and H and then conducting subjective mutual interference tests on a radio receiver to attempt to correlate the effects to a measured limit. The answer will not be an acceptable limit for BPL is ?dBuv/m. It may all be academic because politicians don't do EMC. Iain - Original Message - From: Ken Javor mailto:ken.ja...@emccompliance.com To: emc-p...@ieee.org Sent: Thursday, June 23, 2005 9:05 PM Subject: Re: ??? RE: ??? RE: Near field H-field measurement. There is a significant over-generalization here. An electrically small probe does not have to convert rf into heat and thereby measure total broadband pickup. There are any number of electrically short whips, dipoles and loops whose transducer factors as a function of frequency are well characterized. Thereof ere the electric or magnetic field intensity as a function of frequency can be accurately measured. What cannot be characterized is a single number that describes the field intensity anywhere except the point at which it is measured. To quote myself from a previous post on this very same subject. here there was interest in measuring rfi from broadband communications over power-lines: I don't know how BPL really works in detail but there are a few basic physical principles that apply regardless: 1) If the measurements of interest are really in the near field, especially in the induction field, then the only valid measurement is to use the same type antenna as the likely victim, and place it the same distance from the source as the victim will occupy. The idea of measuring a field intensity in the near field is worthless. What you are measuring is the noise potential delivered to a receiver connected to a representative victim antenna or more accurately, field probe. This is very close to the old idea of an antenna-induced limit, except that concept was based on open-circuiting the probe output, whereas here we are talking about power delivered into a 50 Ohm receiver front end. 2) The probe must look like the victim to be protected by the limit. If an electrically short whip is being used, you don't use a loop and try to correlate the two. And vice versa. And the whip or loop being used needs to be the same size as the likely victim - the probe delivers a potential that is proportional to the average field impinging over its physical aperture. Unless the field is close enough to a plane wave that over the physical dimension of the probe it is homogenous, you cannot correlate the output of two different size probes, even if they are both whips or both loops. Further, you cannot extrapolate the field intensity to another distance other than that measured unless you have a priori a complete understanding of the current distribution on the transmitting structure and are only using the probe to get an amplitude data point. From: neve...@comcast.net List-Post: emc-pstc@listserv.ieee.org Date: Thu, 23 Jun 2005 18:56:33 + To: emc-p...@ieee.org Subject: RE: ??? RE: ??? RE: Near field H-field measurement. By measuring the E and H components separately, using near-field probes, which are, in principle, electrically short dipoles and loops. The biggist price to pay is the sensitivity, since they are electrically short. Also, they pick up the broadband field that gets detected in the detector circuit (DC output proportional to the field strength), so the frequency information is usually lost. Using isotropic probes can help, since it reduces the need for alignment of polarization. Unwanted pickup by the probe leads and the readout electronic, as well as the field perturbation by the probe and the operator sometimes cause considerable issues here. Neven -- Original message -- How would one go about accurately measuring low frequency fields say at 10 kHz where the far-field even at lambda/6 is 5000 meters? Bob Heller 3M EMC Laboratory, 76-1-01 St. Paul, MN 55107-1208 Tel: 651- 778-6336 Fax: 651-778-6252 = Price, Ed om To Sent by: emc-p...@ieee.org owner-emc-pstc@ie cc ee.org Subject RE: ??? RE: ??? RE: Near field 06/23/2005 11:24 H-field measurement. AM -Original Message- From: Bob Richards [mailto:b...@toprudder.com] ! t; Sent
Re: ??? RE: ??? RE: Near field H-field measurement.
There is a significant over-generalization here. An electrically small probe does not have to convert rf into heat and thereby measure total broadband pickup. There are any number of electrically short whips, dipoles and loops whose transducer factors as a function of frequency are well characterized. Thereof ere the electric or magnetic field intensity as a function of frequency can be accurately measured. What cannot be characterized is a single number that describes the field intensity anywhere except the point at which it is measured. To quote myself from a previous post on this very same subject. here there was interest in measuring rfi from broadband communications over power-lines: I don't know how BPL really works in detail but there are a few basic physical principles that apply regardless: 1) If the measurements of interest are really in the near field, especially in the induction field, then the only valid measurement is to use the same type antenna as the likely victim, and place it the same distance from the source as the victim will occupy. The idea of measuring a field intensity in the near field is worthless. What you are measuring is the noise potential delivered to a receiver connected to a representative victim antenna or more accurately, field probe. This is very close to the old idea of an antenna-induced limit, except that concept was based on open-circuiting the probe output, whereas here we are talking about power delivered into a 50 Ohm receiver front end. 2) The probe must look like the victim to be protected by the limit. If an electrically short whip is being used, you don't use a loop and try to correlate the two. And vice versa. And the whip or loop being used needs to be the same size as the likely victim - the probe delivers a potential that is proportional to the average field impinging over its physical aperture. Unless the field is close enough to a plane wave that over the physical dimension of the probe it is homogenous, you cannot correlate the output of two different size probes, even if they are both whips or both loops. Further, you cannot extrapolate the field intensity to another distance other than that measured unless you have a priori a complete understanding of the current distribution on the transmitting structure and are only using the probe to get an amplitude data point. From: neve...@comcast.net List-Post: emc-pstc@listserv.ieee.org Date: Thu, 23 Jun 2005 18:56:33 + To: emc-p...@ieee.org Subject: RE: ??? RE: ??? RE: Near field H-field measurement. By measuring the E and H components separately, using near-field probes, which are, in principle, electrically short dipoles and loops. The biggist price to pay is the sensitivity, since they are electrically short. Also, they pick up the broadband field that gets detected in the detector circuit (DC output proportional to the field strength), so the frequency information is usually lost. Using isotropic probes can help, since it reduces the need for alignment of polarization. Unwanted pickup by the probe leads and the readout electronic, as well as the field perturbation by the probe and the operator sometimes cause considerable issues here. Neven -- Original message -- How would one go about accurately measuring low frequency fields say at 10 kHz where the far-field even at lambda/6 is 5000 meters? Bob Heller 3M EMC Laboratory, 76-1-01 St. Paul, MN 55107-1208 Tel: 651- 778-6336 Fax: 651-778-6252 = Price, Ed om To Sent by: emc-p...@ieee.org owner-emc-pstc@ie cc ee.org Subject RE: ??? RE: ??? RE: Near field 06/23/2005 11:24 H-field measurement. AM -Original Message- From: Bob Richards [mailto:b...@toprudder.com] ! t; Sent: Thursday, June 23, 2005 7:06 AM To: emc-p...@ieee.org Subject: Re: ??? RE: ??? RE: Near field H-field measurement. Ken, I believe you are correct. There should be factors for this loop antenna from Emco that convert the raw reading (in dBuv) to a magnetic field level (like dBuA/m). The spectrum analyzer does NOT read in dBuv/m as he seems to suggest, it only reads in dBuv or dBm, but some analyzers do allow factors to be entered so the display will be in useful units. I prefer not having the analyzer apply factors. Less chance for errors that way, IMHO. Bob Richards, NCT. EMCO (ETS) shows generic correction factors for the 6502 at: http://www.ets-lindgren.c! om/product age.cfm/model/6502/producttype/Antennas They have a pair of charts for correcting the antenna output (in dBuV) to units of electric field (dBuV/m) or magnetic field (dBuA/m). I don't like the practice of a factor for converting loop output voltage directly to dBuV/m, because it is making the assumption of far-field conditions (377 ohms, and an H-field to E-field conversion
RE: ??? RE: ??? RE: Near field H-field measurement.
How would one go about accurately measuring low frequency fields say at 10 kHz where the far-field even at lambda/6 is 5000 meters? Bob Heller 3M EMC Laboratory, 76-1-01 St. Paul, MN 55107-1208 Tel: 651- 778-6336 Fax: 651-778-6252 = Price, Ed ED.PRICE@cubic.c omTo Sent by: emc-p...@ieee.org owner-emc-pstc@ie cc ee.org Subject RE: ??? RE: ??? RE: Near field 06/23/2005 11:24 H-field measurement. AM -Original Message- From: Bob Richards [mailto:b...@toprudder.com] Sent: Thursday, June 23, 2005 7:06 AM To: emc-p...@ieee.org Subject: Re: ??? RE: ??? RE: Near field H-field measurement. Ken, I believe you are correct. There should be factors for this loop antenna from Emco that convert the raw reading (in dBuv) to a magnetic field level (like dBuA/m). The spectrum analyzer does NOT read in dBuv/m as he seems to suggest, it only reads in dBuv or dBm, but some analyzers do allow factors to be entered so the display will be in useful units. I prefer not having the analyzer apply factors. Less chance for errors that way, IMHO. Bob Richards, NCT. EMCO (ETS) shows generic correction factors for the 6502 at: http://www.ets-lindgren.com/productpage.cfm/model/6502/producttype/Antennas They have a pair of charts for correcting the antenna output (in dBuV) to units of electric field (dBuV/m) or magnetic field (dBuA/m). I don't like the practice of a factor for converting loop output voltage directly to dBuV/m, because it is making the assumption of far-field conditions (377 ohms, and an H-field to E-field conversion of +51.5 dB). The 6502 is a shielded loop, and responds to the H-field, no matter where you place it. You can accurately derive the E-field from the H-field only when you are confident of far-field conditions. Ed Price ed.pr...@cubic.com WB6WSN NARTE Certified EMC Engineer Technician Electromagnetic Compatibility Lab Cubic Defense Applications San Diego, CA USA 858-505-2780 (Voice) 858-505-1583 (Fax) Military Avionics EMC Is Our Specialty 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/listserv/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: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc 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/listserv/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 Cantwellmcantw...@ieee.org For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
RE: ??? RE: ??? RE: Near field H-field measurement.
-Original Message- From: Bob Richards [ mailto:b...@toprudder.com] Sent: Thursday, June 23, 2005 7:06 AM To: emc-p...@ieee.org Subject: Re: ??? RE: ??? RE: Near field H-field measurement. Ken, I believe you are correct. There should be factors for this loop antenna from Emco that convert the raw reading (in dBuv) to a magnetic field level (like dBuA/m). The spectrum analyzer does NOT read in dBuv/m as he seems to suggest, it only reads in dBuv or dBm, but some analyzers do allow factors to be entered so the display will be in useful units. I prefer not having the analyzer apply factors. Less chance for errors that way, IMHO. Bob Richards, NCT. EMCO (ETS) shows generic correction factors for the 6502 at: http://www.ets-lindgren.com/productpage.cfm/model/6502/producttype/Antennas They have a pair of charts for correcting the antenna output (in dBuV) to units of electric field (dBuV/m) or magnetic field (dBuA/m). I don't like the practice of a factor for converting loop output voltage directly to dBuV/m, because it is making the assumption of far-field conditions (377 ohms, and an H-field to E-field conversion of +51.5 dB). The 6502 is a shielded loop, and responds to the H-field, no matter where you place it. You can accurately derive the E-field from the H-field only when you are confident of far-field conditions. Ed Price ed.pr...@cubic.com WB6WSN NARTE Certified EMC Engineer Technician Electromagnetic Compatibility Lab Cubic Defense Applications San Diego, CA USA 858-505-2780 (Voice) 858-505-1583 (Fax) Military Avionics EMC Is Our Specialty 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/listserv/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: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
e: ??? RE: ??? RE: Near field H-field measurement.
Bob, You must be a crotchety old-timer like myself. Re the following from the appendix in MIL-STD-461E (it's there because I asked for it). The part I refer to is in italics. Placement of limits can be done in several ways. Data may be displayed with respect to actual limit dimensions (such as dBuV/m) with transducer, attenuation, and cable loss corrections made to the data. An alternative is to plot the raw data in dBuv (or dBm) and convert the limit to equivalent dBuv (or dBm) dimensions using the correction factors. This second technique has the advantage of displaying the proper use of the correction factors. Since both the emission level and the required limit are known, a second party can verify proper placement. Since the actual level of the raw data is not available for the first case, this verification is not possible. Ken Javor From: Bob Richards b...@toprudder.com Date: Thu, 23 Jun 2005 07:05:43 -0700 (PDT) To: emc-p...@ieee.org Subject: Re: ??? RE: ??? RE: Near field H-field measurement. Ken, I believe you are correct. There should be factors for this loop antenna from Emco that convert the raw reading (in dBuv) to a magnetic field level (like dBuA/m). The spectrum analyzer does NOT read in dBuv/m as he seems to suggest, it only reads in dBuv or dBm, but some anaylzers do allow factors to be entered so the display will be in useful units. I prefer not having the analyzer apply factors. Less chance for errors that way, IMHO. Bob Richards, NCT. --- Ken Javor ken.ja...@emccompliance.com wrote: I may be reading this post wrong, but the -51.5 dB factor is not an antenna factor at all. It is the ratio of magnetic to electric field intensity in a plane wave. It is -20*log (377). The use of that number is quite approximate in the near field of the transmitter. From: Y W Leung leungderek2...@yahoo.com.hk Date: Thu, 23 Jun 2005 11:41:41 +0800 (CST) To: fdev...@assaabloyitg.com Cc: emc-p...@ieee.org Subject: ??? RE: ??? RE: Near field H-field measurement. Dear Dave, Thanks for your information. Since the local regulatory body set both E-Field AND H-Field limit for frequency range under 195kHz. But as I know, for all radiated emission measurement under 30MHz should use loop antenna, so I use EMCO 6502 for E and H- fields measurement. The spectrum analyzer dispaly (dBuV/m) with transducer factors ( magnetic antenna factor -51.5dB). For H-field, I used extrapolation factor 3 to calculate the corresponding limit at 10m ( becasue the document states the limits at 300m!) I used the reading on the spectrum analyzer plus (-51.5dB) then I can get the H-field value then I compare it with the extrapolated limit at 10m (measuring distance). For the E-field, I use the reading on the spectrum analyzer and compare with the limit at 10m (use the same extrapolation factor 3 to determine from 300m). Since theoretically, when the Tx Rx antennas are both loop antenna, within the near field region, H field attenuate at the rate of 1/(r^3) and E-field attenuate at the rate of 1/ (r^2). My questions: I should use 2 or 3 for the calculation of E-field extrapolation? The mesurement methods is valid or not? I also thanks to all experts replied the message of this problem. Regards, Derek. 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/listserv/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 Cantwellmcantw...@ieee.org For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc 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/listserv/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: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: ??? RE: ??? RE: Near field H-field measurement.
Ken, I believe you are correct. There should be factors for this loop antenna from Emco that convert the raw reading (in dBuv) to a magnetic field level (like dBuA/m). The spectrum analyzer does NOT read in dBuv/m as he seems to suggest, it only reads in dBuv or dBm, but some anaylzers do allow factors to be entered so the display will be in useful units. I prefer not having the analyzer apply factors. Less chance for errors that way, IMHO. Bob Richards, NCT. --- Ken Javor ken.ja...@emccompliance.com wrote: I may be reading this post wrong, but the -51.5 dB factor is not an antenna factor at all. It is the ratio of magnetic to electric field intensity in a plane wave. It is -20*log (377). The use of that number is quite approximate in the near field of the transmitter. From: Y W Leung leungderek2...@yahoo.com.hk Date: Thu, 23 Jun 2005 11:41:41 +0800 (CST) To: fdev...@assaabloyitg.com Cc: emc-p...@ieee.org Subject: ??? RE: ??? RE: Near field H-field measurement. Dear Dave, Thanks for your information. Since the local regulatory body set both E-Field AND H-Field limit for frequency range under 195kHz. But as I know, for all radiated emission measurement under 30MHz should use loop antenna, so I use EMCO 6502 for E and H- fields measurement. The spectrum analyzer dispaly (dBuV/m) with transducer factors ( magnetic antenna factor -51.5dB). For H-field, I used extrapolation factor 3 to calculate the corresponding limit at 10m ( becasue the document states the limits at 300m!) I used the reading on the spectrum analyzer plus (-51.5dB) then I can get the H-field value then I compare it with the extrapolated limit at 10m (measuring distance). For the E-field, I use the reading on the spectrum analyzer and compare with the limit at 10m (use the same extrapolation factor 3 to determine from 300m). Since theoretically, when the Tx Rx antennas are both loop antenna, within the near field region, H field attenuate at the rate of 1/(r^3) and E-field attenuate at the rate of 1/ (r^2). My questions: I should use 2 or 3 for the calculation of E-field extrapolation? The mesurement methods is valid or not? I also thanks to all experts replied the message of this problem. Regards, Derek. 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/listserv/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 Cantwellmcantw...@ieee.org For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: ??? RE: ??? RE: Near field H-field measurement.
I may be reading this post wrong, but the -51.5 dB factor is not an antenna factor at all. It is the ratio of magnetic to electric field intensity in a plane wave. It is -20*log (377). The use of that number is quite approximate in the near field of the transmitter. From: Y W Leung leungderek2...@yahoo.com.hk List-Post: emc-pstc@listserv.ieee.org Date: Thu, 23 Jun 2005 11:41:41 +0800 (CST) To: fdev...@assaabloyitg.com Cc: emc-p...@ieee.org Subject: ??? RE: ??? RE: Near field H-field measurement. Dear Dave, Thanks for your information. Since the local regulatory body set both E-Field AND H-Field limit for frequency range under 195kHz. But as I know, for all radiated emission measurement under 30MHz should use loop antenna, so I use EMCO 6502 for E and H- fields measurement. The spectrum analyzer dispaly (dBuV/m) with transducer factors ( magnetic antenna factor -51.5dB). For H-field, I used extrapolation factor 3 to calculate the corresponding limit at 10m ( becasue the document states the limits at 300m!) I used the reading on the spectrum analyzer plus (-51.5dB) then I can get the H-field value then I compare it with the extrapolated limit at 10m (measuring distance). For the E-field, I use the reading on the spectrum analyzer and compare with the limit at 10m (use the same extrapolation factor 3 to determine from 300m). Since theoretically, when the Tx Rx antennas are both loop antenna, within the near field region, H field attenuate at the rate of 1/(r^3) and E-field attenuate at the rate of 1/ (r^2). My questions: I should use 2 or 3 for the calculation of E-field extrapolation? The mesurement methods is valid or not? I also thanks to all experts replied the message of this problem. Regards, Derek. fdev...@assaabloyitg.com ?? Dave, We have run the measurements at 300 m, 30 m, and 10 m and found the fall off of 1/R^3 apply because the magnetic field is being measured using a loop antenna. The far field E field rule does not apply for a magnetic field. Regards, Frank de Vall Sr. Engineering Manager - Compliance Assa Abloy ITG and HID Corporation drcuthbert@micron .com Sent by: To owner-emc-pstc@ie ee.org cc Subject 06/22/2005 08:29 RE: ?? 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/listserv/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: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
??: RE: ??: RE: Near field H-field measurement.
Dear Dave, Thanks for your information. Since the local regulatory body set both E-Field AND H-Field limit for frequency range under 195kHz. But as I know, for all radiated emission measurement under 30MHz should use loop antenna, so I use EMCO 6502 for E and H- fields measurement. The spectrum analyzer dispaly (dBuV/m) with transducer factors ( magnetic antenna factor -51.5dB). For H-field, I used extrapolation factor 3 to calculate the corresponding limit at 10m ( becasue the document states the limits at 300m!) I used the reading on the spectrum analyzer plus (-51.5dB) then I can get the H-field value then I compare it with the extrapolated limit at 10m (measuring distance). For the E-field, I use the reading on the spectrum analyzer and compare with the limit at 10m (use the same extrapolation factor 3 to determine from 300m). Since theoretically, when the Tx Rx antennas are both loop antenna, within the near field region, H field attenuate at the rate of 1/(r^3) and E-field attenuate at the rate of 1/ (r^2). My questions: I should use 2 or 3 for the calculation of E-field extrapolation? The mesurement methods is valid or not? I also thanks to all experts replied the message of this problem. Regards, Derek. fdev...@assaabloyitg.com 說： Dave, We have run the measurements at 300 m, 30 m, and 10 m and found the fall off of 1/R^3 apply because the magnetic field is being measured using a loop antenna. The far field E field rule does not apply for a magnetic field. Regards, Frank de Vall Sr. Engineering Manager - Compliance Assa Abloy ITG and HID Corporation drcuthbert@micron .com Sent by: To owner-emc-pstc@ie ee.org cc Subject 06/22/2005 08:29 RE: 璅?嚗?RE: Near field H-field AM measurement. Derek, in regards to the magnetic field measurement from 50 kHz to 1 GHz: You can figure that your measurement is in the far-field when the distance is 1/6 wavelength. At a distance of 10 meters this occurs above 5 MHz. So above 5 MHz the field will drop as 1/d and the difference between 300 meters and 10 meters is 30 dB. Below 5 MHz what is the difference between 300 meters and 10 meters? Let's run a?NEC-2 simulation?and see what we get. The antennas are 1 meter square loops in free space. I am comparing the current induced in the two receive loops placed 10 and 30 meters from the transmit loop. FREQ? ?0.25 MHz?? 82 dB ? 0.50? 69 ? 1.00? 57 ??2.00? 44 ? 4.00? 33 ? 8.00??30 I next placed the antennas 1 meter above perfect ground and obtained the same results. These results can be mathematically confirmed (I will leave that up to you) using the formulas I sent. It would be great if someone could run actual measurements at 10 and 300 meters. Once again we find that the FCC rules-of-thumb do not reflect reality. ?? Dave Cuthbert ?? Micron Technology 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/listserv/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: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc 有即時通知，收艂 -- - 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/listserv/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: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
RE: ??: RE: Near field H-field measurement.
Derek, in regards to the magnetic field measurement from 50 kHz to 1 GHz: You can figure that your measurement is in the far-field when the distance is 1/6 wavelength. At a distance of 10 meters this occurs above 5 MHz. So above 5 MHz the field will drop as 1/d and the difference between 300 meters and 10 meters is 30 dB. Below 5 MHz what is the difference between 300 meters and 10 meters? Let's run a NEC-2 simulation and see what we get. The antennas are 1 meter square loops in free space. I am comparing the current induced in the two receive loops placed 10 and 30 meters from the transmit loop. FREQ 0.25 MHz 82 dB 0.50 69 1.00 57 2.00 44 4.00 33 8.00 30 I next placed the antennas 1 meter above perfect ground and obtained the same results. These results can be mathematically confirmed (I will leave that up to you) using the formulas I sent. It would be great if someone could run actual measurements at 10 and 300 meters. Once again we find that the FCC rules-of-thumb do not reflect reality. Dave Cuthbert Micron Technology 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/listserv/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: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: Near field H-field measurement.
Derek, The FCC specifies using a loop antenna for measuring field strength below 30 MHz. Extrapolation can be used if the field strength is measured at two distances and the factor calculated (it will be close to 1/R^3), otherwise the default of 40 dB/decade (1/R^2) must be used. We normally use 30 m and 10 m for the two distances. We have taken measurements at 300 m, 30 m, and 10 m and found the extrapolation factor to be consistent. At these frequencies, there is negligible difference with or without a ground plane. Regards, Frank de Vall Sr. Engineering Manager - Compliance Assa Abloy ITG and HID Corporation Y W Leung leungderek2000@y ahoo.com.hk To Sent by: emc-p...@ieee.org owner-emc-pstc@ie cc ee.org Subject Near field H-field measurement. 06/20/2005 11:56 PM Dear experts, I am measuring the fundamental and spurious emissions from an EUT ( with interanl loop antenna) of fundamental frequencies of about 50kHz to 200kHz. The measuring range of spurious emission is up to 1GHz. The limits are according to a local standard from a local regulatory body. The emission limits for both fundamental and spurious emissions are quoted in electric field ( dBuV/m) and magnetic field (dBuA/m), means the emissions from the EUT must not exceed the limits of both E field AND H-field. The spectrum analyzer display (dBuV/m) because it already included the transducer factor ( magnetic field antenna factor:-55dB/m and the cable loss). I am using EMCO 6502 loop antenna for the radiated emission measurement at 10 measuring distance. Since the limits are quoted by the regulatory body are at 30 and 300 meters distance, so I use extrapolation factor (value of 3) i.e. 20 log (300/10)^3 to determine the corresponding limit at 10 meters from a 300 meters limit which equals to 88.3dB mark up for the H-field. My questions are : 1. From theory, if both Tx and Rx antennas are loops antenna, under near field conditions, H-fields is predominant, so the H-field is inversely proportional to D^3, so I use the extrapolation factor 3. For H-field measurement , I just use the reading from the spectrum analyzer plus the cable loss and magnetic antenna factor (-5dB), and use this calculated value to compare with the extrapolation value. please correct me if I am wrong. ( I know there is another approach of extrapolate the measured value and compare with the limits). Please correct me the method and extrapolation factor if I am wrong. 2. Since the requirement of the limits are in both H-field and E-field. Which extrapolation factor (2 or 3) should be used to determine the limit from i.e. 300 meters to 10 meters? The reason of supporting if use 2 is because under near field coditions, the E-field is inversely proportional to D^2. But now both Tx and Rx antennas are loop antennas, so finally I use 3 to extrapolate the limit of E-field ( i.e. from 300 to 10 meters) and compare with the spectrum analyzer reading, please comment and/or correct me if I am wrong. Thanks advance for your any comment or opinion. Regards, Derek Leung. 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/listserv/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: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc 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
RE: Near field H-field measurement.
Derek and Robert, The fields from an electric dipole drop off as: Magnetic: 1/r^2 and 1/r Electric: 1/E^3, 1/E^2, and 1/E For a magnetic dipole (loop): Magnetic: 1/r^3, 1/r^2 and 1/r Electric: 1/E^2, and 1/E This link provides the formulas that will allow to to calculate the field strength versus distance. http://www.conformity.com/0102reflections.html I have correlated these formulas to NEC-2 to confirm that NEC-2 can be used to find the H or E field strength at various distances. Dave Cuthbert Micron Technology From: owner-emc-p...@ieee.org [mailto:owner-emc-p...@ieee.org] On Behalf Of Robert A. Macy Sent: Tuesday, June 21, 2005 8:58 AM To: Y W Leung Cc: emc-p...@ieee.org Subject: Re: Near field H-field measurement. Near field?! You're way inside near field below 200KHz. At those fundamental frequencies, you are correct. Magnetic fields drop at the rate of inverse cube from a dipole. You didn't say the size of the EUT. However, if it is smaller than 1/5 the distance to the antenna, you can correctly assume the nonradiating magnetic field is dropping at inverse cube. I'm reluctant to rely on any accuracy using a loop to measure E-Field at that low a frequency. Should use a field probe. The E Field should drop off as the inverse square function. In the range of 50-200KHz, measure E-Field and H-Field at two distances and you should see those ratios. - Robert - On Tue, 21 Jun 2005 13:56:25 +0800 (CST) Y W Leung leungderek2...@yahoo.com.hk wrote: Dear experts, I am measuring the fundamental and spurious emissions from an EUT ( with interanl loop antenna) of fundamental frequencies of about 50kHz to 200kHz. The measuring range of spurious emission is up to 1GHz. The limits are according to a local standard from a local regulatory body. The emission limits for both fundamental and spurious emissions are quoted in electric field ( dBuV/m) and magnetic field (dBuA/m), means the emissions from the EUT must not exceed the limits of both E field AND H-field. The spectrum analyzer display (dBuV/m) because it already included the transducer factor ( magnetic field antenna factor:-55dB/m and the cable loss). I am using EMCO 6502 loop antenna for the radiated emission measurement at 10 measuring distance. Since the limits are quoted by the regulatory body are at 30 and 300 meters distance, so I use extrapolation factor (value of 3) i.e. 20 log (300/10)^3 to determine the corresponding limit at 10 meters from a 300 meters limit which equals to 88.3dB mark up for the H-field. My questions are : 1. From theory, if both Tx and Rx antennas are loops antenna, under near field conditions, H-fields is predominant, so the H-field is inversely proportional to D^3, so I use the extrapolation factor 3. For H-field measurement , I just use the reading from the spectrum analyzer plus the cable loss and magnetic antenna factor (-5dB), and use this calculated value to compare with the extrapolation value. please correct me if I am wrong. ( I know there is another approach of extrapolate the measured value and compare with the limits). Please correct me the method and extrapolation factor if I am wrong. 2. Since the requirement of the limits are in both H-field and E-field. Which extrapolation factor (2 or 3) should be used to determine the limit from i.e. 300 meters to 10 meters? The reason of supporting if use 2 is because under near field coditions, the E-field is inversely proportional to D^2. But now both Tx and Rx antennas are loop antennas, so finally I use 3 to extrapolate the limit of E-field ( i.e. from 300 to 10 meters) and compare with the spectrum analyzer reading, please comment and/or correct me if I am wrong. Thanks advance for your any comment or opinion. Regards, Derek Leung. 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/listserv/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 Cantwellmcantw...@ieee.org For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc 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/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail
Re: Near field H-field measurement.
Forgot! E Fields from a true dipole do drop off at the inverse cube rate also, It's just that the fields almost always get referenced to a ground or ground plane which makes them drop off for all practical purposes at the rate of the inverse square. - Robert - From: Y W Leung leungderek2...@yahoo.com.hk Date: Tue, 21 Jun 2005 13:56:25 +0800 (CST) To: emc-p...@ieee.org Subject: Near field H-field measurement. Dear experts, I am measuring the fundamental and spurious emissions from an EUT ( with interanl loop antenna) of fundamental frequencies of about 50kHz to 200kHz. The measuring range of spurious emission is up to 1GHz. The limits are according to a local standard from a local regulatory body. The emission limits for both fundamental and spurious emissions are quoted in electric field ( dBuV/m) and magnetic field (dBuA/m), means the emissions from the EUT must not exceed the limits of both E field AND H-field. The spectrum analyzer display (dBuV/m) because it already included the transducer factor ( magnetic field antenna factor:-55dB/m and the cable loss). I am using EMCO 6502 loop antenna for the radiated emission measurement at 10 measuring distance. Since the limits are quoted by the regulatory body are at 30 and 300 meters distance, so I use extrapolation factor (value of 3) i.e. 20 log (300/10)^3 to determine the corresponding limit at 10 meters from a 300 meters limit which equals to 88.3dB mark up for the H-field. My questions are : 1. From theory, if both Tx and Rx antennas are loops antenna, under near field conditions, H-fields is predominant, so the H-field is inversely proportional to D^3, so I use the extrapolation factor 3. For H-field measurement , I just use the reading from the spectrum analyzer plus the cable loss and magnetic antenna factor (-5dB), and use this calculated value to compare with the extrapolation value. please correct me if I am wrong. ( I know there is another approach of extrapolate the measured value and compare with the limits). Please correct me the method and extrapolation factor if I am wrong. 2. Since the requirement of the limits are in both H-field and E-field. Which extrapolation factor (2 or 3) should be used to determine the limit from i.e. 300 meters to 10 meters? The reason of supporting if use 2 is because under near field coditions, the E-field is inversely proportional to D^2. But now both Tx and Rx antennas are loop antennas, so finally I use 3 to extrapolate the limit of E-field ( i.e. from 300 to 10 meters) and compare with the spectrum analyzer reading, please comment and/or correct me if I am wrong. Thanks advance for your any comment or opinion. Regards, Derek Leung. 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/listserv/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 Cantwellmcantw...@ieee.org For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
RE: Near field H-field measurement.
Derek, are your magnetic field measurements only in the range of 50 to 200 kHz? Or, do you intend to measure to 1 GHz? If the former, you may need to modify your 300 to 10 meter scaling for specific frequencies between 50 and 200 kHz. I can find you the formula for this. If the latter, you definitely need to modify the scaling formula. Dave Cuthbert Micron Technology _ From: owner-emc-p...@ieee.org [mailto:owner-emc-p...@ieee.org] On Behalf Of Y W Leung Sent: Monday, June 20, 2005 11:56 PM To: emc-p...@ieee.org Subject: Near field H-field measurement. Dear experts, I am measuring the fundamental and spurious emissions from an EUT ( with interanl loop antenna) of fundamental frequencies of about 50kHz to 200kHz. The measuring range of spurious emission is up to 1GHz. The limits are according to a local standard from a local regulatory body. The emission limits for both fundamental and spurious emissions are quoted in electric field ( dBuV/m) and magnetic field (dBuA/m), means the emissions from the EUT must not exceed the limits of both E field AND H-field. The spectrum analyzer display (dBuV/m) because it already included the transducer factor ( magnetic field antenna factor:-55dB/m and the cable loss). I am using EMCO 6502 loop antenna for the radiated emission measurement at 10 measuring distance. Since the limits are quoted by the regulatory body are at 30 and 300 meters distance, so I use extrapolation factor (value of 3) i.e. 20 log (300/10)^3 to determine the corresponding limit at 10 meters from a 300 meters limit which equals to 88.3dB mark up for the H-field. My questions are : 1. From theory, if both Tx and Rx antennas are loops antenna, under near field conditions, H-fields is predominant, so the H-field is inversely proportional to D^3, so I use the extrapolation factor 3. For H-field measurement , I just use the reading from the spectrum analyzer plus the cable loss and magnetic antenna factor (-5dB), and use this calculated value to compare with the extrapolation value. please correct me if I am wrong. ( I know there is another approach of extrapolate the measured value and compare with the limits). Please correct me the method and extrapolation factor if I am wrong. 2. Since the requirement of the limits are in both H-field and E-field. Which extrapolation factor (2 or 3) should be used to determine the limit from i.e. 300 meters to 10 meters? The reason of supporting if use 2 is because under near field coditions, the E-field is inversely proportional to D^2. But now both Tx and Rx antennas are loop antennas, so finally I use 3 to extrapolate the limit of E-field ( i.e. from 300 to 10 meters) and compare with the spectrum analyzer reading, please comment and/or correct me if I am wrong. Thanks advance for your any comment or opinion. Regards, Derek Leung. 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/listserv/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: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc 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/listserv/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: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
RE: Near field H-field measurement.
Mr.. Leung, At low frequencies, you may have undesirable effects from underground pipes / etc... Or your EUT may be significantly large compared to the antenna to influence the measurement. This makes the assumption of 3rd order rolloff uncertain. The FCC guidance is to measure at 2 distances to establish the extrapolation factor that you do have [due to external effects / size of EUT vs measuring distance / etc.] or to use a 40 dB / decade [or inverse square] extrapolation factor. If you are measuring at 10 meters, take another measurement of the fundamental frequencies at 20 meters. If you truly have a 3rd order rolloff of the field then the difference of the H-field readings at 10 meters and 20 meters will be 18 dB different. This corresponds to 20 * [ rolloff factor] dB/ decade. For a factor of 3, you have a 60 dB / decade rolloff of the field. If you do not have a difference of 18 dB, you can calculate what the correct extrapolation factor is. Hope this helps. Best regards, Mac Elliott From: Y W Leung leungderek2...@yahoo.com.hk List-Post: emc-pstc@listserv.ieee.org Date: Tue, 21 Jun 2005 13:56:25 +0800 (CST) To: emc-p...@ieee.org Subject: Near field H-field measurement. Dear experts, I am measuring the fundamental and spurious emissions from an EUT ( with interanl loop antenna) of fundamental frequencies of about 50kHz to 200kHz. The measuring range of spurious emission is up to 1GHz. The limits are according to a local standard from a local regulatory body. The emission limits for both fundamental and spurious emissions are quoted in electric field ( dBuV/m) and magnetic field (dBuA/m), means the emissions from the EUT must not exceed the limits of both E field AND H-field. The spectrum analyzer display (dBuV/m) because it already included the transducer factor ( magnetic field antenna factor:-55dB/m and the cable loss). I am using EMCO 6502 loop antenna for the radiated emission measurement at 10 measuring distance. Since the limits are quoted by the regulatory body are at 30 and 300 meters distance, so I use extrapolation factor (value of 3) i.e. 20 log (300/10)^3 to determine the corresponding limit at 10 meters from a 300 meters limit which equals to 88.3dB mark up for the H-field. My questions are : 1. From theory, if both Tx and Rx antennas are loops antenna, under near field conditions, H-fields is predominant, so the H-field is inversely proportional to D^3, so I use the extrapolation factor 3. For H-field measurement , I just use the reading from the spectrum analyzer plus the cable loss and magnetic antenna factor (-5dB), and use this calculated value to compare with the extrapolation value. please correct me if I am wrong. ( I know there is another approach of extrapolate the measured value and compare with the limits). Please correct me the method and extrapolation factor if I am wrong. 2. Since the requirement of the limits are in both H-field and E-field. Which extrapolation factor (2 or 3) should be used to determine the limit from i.e. 300 meters to 10 meters? The reason of supporting if use 2 is because under near field coditions, the E-field is inversely proportional to D^2. But now both Tx and Rx antennas are loop antennas, so finally I use 3 to extrapolate the limit of E-field ( i.e. from 300 to 10 meters) and compare with the spectrum analyzer reading, please comment and/or correct me if I am wrong. Thanks advance for your any comment or opinion. Regards, Derek Leung. 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/listserv/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: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc 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/listserv/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: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at:
RE: Near field H-field measurement.
Mr. Leung, Here is an excerpt from the FCC Rules pertaining to measurements below 30 MHz using a loop antenna. At frequencies below 30 MHz, measurements may be performed at a distance closer than that specified in the regulations; however, an attempt should be made to avoid making measurements in the near field. Pending the development of an appropriate measurement procedure for measurements performed below 30 MHz, when performing measurements at a closer distance than specified, the results shall be extrapolated to the specified distance by either making measurements at a minimum of two distances on at least one radial to determine the proper extrapolation factor or by using the square of an inverse linear distance extrapolation factor (40 dB/decade). Bill Stumpf D.L.S. Electronics 166 South Carter Street Genoa City WI 53128 bstu...@dlsemc.com phone: 262.279.0210 _ From: owner-emc-p...@ieee.org [mailto:owner-emc-p...@ieee.org] On Behalf Of Ken Javor Sent: Tuesday, June 21, 2005 9:19 AM To: emc-p...@ieee.org Subject: Re: Near field H-field measurement. A limit specified at 300 meters is outside my experience. I have seen limits at 1 m (military ), and 3, 10, and 30 meters (commercial). I'm not sure how to extrapolate below 30 MHz where you are using the EMCO loop. But above 30 MHz where you are only measuring electric field, the extrapolation is 1/r, that is, electric field rolls off linearly with increasing distance. It does not matter that the sources are magnetic loops - at 30 MHz and up you are so far above the intentional emissions that the radiating source doesn't look like a magnetic loop anymore, it is a fortuitous conductor, and you are in its far field so the impedance of the field is that of free space. From: Y W Leung leungderek2...@yahoo.com.hk List-Post: emc-pstc@listserv.ieee.org Date: Tue, 21 Jun 2005 13:56:25 +0800 (CST) To: emc-p...@ieee.org Subject: Near field H-field measurement. Dear experts, I am measuring the fundamental and spurious emissions from an EUT ( with interanl loop antenna) of fundamental frequencies of about 50kHz to 200kHz. The measuring range of spurious emission is up to 1GHz. The limits are according to a local standard from a local regulatory body. The emission limits for both fundamental and spurious emissions are quoted in electric field ( dBuV/m) and magnetic field (dBuA/m), means the emissions from the EUT must not exceed the limits of both E field AND H-field. The spectrum analyzer display (dBuV/m) because it already included the transducer factor ( magnetic field antenna factor:-55dB/m and the cable loss). I am using EMCO 6502 loop antenna for the radiated emission measurement at 10 measuring distance. Since the limits are quoted by the regulatory body are at 30 and 300 meters distance, so I use extrapolation factor (value of 3) i.e. 20 log (300/10)^3 to determine the corresponding limit at 10 meters from a 300 meters limit which equals to 88.3dB mark up for the H-field. My questions are : 1. From theory, if both Tx and Rx antennas are loops antenna, under near field conditions, H-fields is predominant, so the H-field is inversely proportional to D^3, so I use the extrapolation factor 3. For H-field measurement , I just use the reading from the spectrum analyzer plus the cable loss and magnetic antenna factor (-5dB), and use this calculated value to compare with the extrapolation value. please correct me if I am wrong. ( I know there is another approach of extrapolate the measured value and compare with the limits). Please correct me the method and extrapolation factor if I am wrong. 2. Since the requirement of the limits are in both H-field and E-field. Which extrapolation factor (2 or 3) should be used to determine the limit from i.e. 300 meters to 10 meters? The reason of supporting if use 2 is because under near field coditions, the E-field is inversely proportional to D^2. But now both Tx and Rx antennas are loop antennas, so finally I use 3 to extrapolate the limit of E-field ( i.e. from 300 to 10 meters) and compare with the spectrum analyzer reading, please comment and/or correct me if I am wrong. Thanks advance for your any comment or opinion. Regards, Derek Leung. 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/listserv/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: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http
Re: Near field H-field measurement.
A limit specified at 300 meters is outside my experience. I have seen limits at 1 m (military ), and 3, 10, and 30 meters (commercial). I'm not sure how to extrapolate below 30 MHz where you are using the EMCO loop. But above 30 MHz where you are only measuring electric field, the extrapolation is 1/r, that is, electric field rolls off linearly with increasing distance. It does not matter that the sources are magnetic loops - at 30 MHz and up you are so far above the intentional emissions that the radiating source doesn't look like a magnetic loop anymore, it is a fortuitous conductor, and you are in its far field so the impedance of the field is that of free space. From: Y W Leung leungderek2...@yahoo.com.hk List-Post: emc-pstc@listserv.ieee.org Date: Tue, 21 Jun 2005 13:56:25 +0800 (CST) To: emc-p...@ieee.org Subject: Near field H-field measurement. Dear experts, I am measuring the fundamental and spurious emissions from an EUT ( with interanl loop antenna) of fundamental frequencies of about 50kHz to 200kHz. The measuring range of spurious emission is up to 1GHz. The limits are according to a local standard from a local regulatory body. The emission limits for both fundamental and spurious emissions are quoted in electric field ( dBuV/m) and magnetic field (dBuA/m), means the emissions from the EUT must not exceed the limits of both E field AND H-field. The spectrum analyzer display (dBuV/m) because it already included the transducer factor ( magnetic field antenna factor:-55dB/m and the cable loss). I am using EMCO 6502 loop antenna for the radiated emission measurement at 10 measuring distance. Since the limits are quoted by the regulatory body are at 30 and 300 meters distance, so I use extrapolation factor (value of 3) i.e. 20 log (300/10)^3 to determine the corresponding limit at 10 meters from a 300 meters limit which equals to 88.3dB mark up for the H-field. My questions are : 1. From theory, if both Tx and Rx antennas are loops antenna, under near field conditions, H-fields is predominant, so the H-field is inversely proportional to D^3, so I use the extrapolation factor 3. For H-field measurement , I just use the reading from the spectrum analyzer plus the cable loss and magnetic antenna factor (-5dB), and use this calculated value to compare with the extrapolation value. please correct me if I am wrong. ( I know there is another approach of extrapolate the measured value and compare with the limits). Please correct me the method and extrapolation factor if I am wrong. 2. Since the requirement of the limits are in both H-field and E-field. Which extrapolation factor (2 or 3) should be used to determine the limit from i.e. 300 meters to 10 meters? The reason of supporting if use 2 is because under near field coditions, the E-field is inversely proportional to D^2. But now both Tx and Rx antennas are loop antennas, so finally I use 3 to extrapolate the limit of E-field ( i.e. from 300 to 10 meters) and compare with the spectrum analyzer reading, please comment and/or correct me if I am wrong. Thanks advance for your any comment or opinion. Regards, Derek Leung. 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/listserv/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: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc 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/listserv/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: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
