Re: Active loop antenna overload
Dear all, The original poster (KC CHAN [PDD] kcc...@hkpc.org) have not mention about the frequency range of the intended measurements, nor even the ball-park figure about the dimension of the H-field loop 'sensor' or pick-up. So all this is just a lot of conjecture. :-) Note that the situation already exist if there is a electrostatic shield around the loop. i.e. I assume that the loop is fabricated from a solid copper-tube (type of shield) co-axial 'cable'. This would amount to multiple shielding the loop to selective frequencies using Lenz's Law. It works out to be a case of trying to make a pickup from the primary turn of a (loosely coupled?) air core-transformer with two or more 'single-turn secondary windings of different styles, all shorted'. I must say that would create some kind of challenge with any attempts to calibrate this combination especially with the cross sensitivity (axial and transversal) of the modified loop. I suppose all one gets from doing this is some idea of the presence of other frequencies but what kind of certainty about their amplitude or strength? Consider the secondary (scattering) effect of all those induced currents flowing in the 'shorted secondary' especially at resonance. Just another of my 2 cents worth :-) Tim Foo Cortland Richmond 72146.373@compuserve.cTo: KC CHAN [PDD] kcc...@hkpc.org, ieee pstc list emc-p...@ieee.org omcc: (bcc: Wan Juang Foo/ece/staff/npnet) Sent by: Subject: Re: Active loop antenna overload owner-emc-pstc@majordom o.ieee.org 09/26/01 01:09 PM Please respond to Cortland Richmond I think we may be assuming this overload is caused by the EUT. But this is just as likely to be caused by something else. Medium Wave and Long Wave broadcasting produces powerful fields at some distance from an antenna. This has a fix. If you place a narrowly resonant loop antenna, with feed point shorted, in close proximity to the wideband loop used for measurements, it will reduce pickup at the resonant frequency to a small fraction of the normal amount, and you will be able to at least SEE signals front-end overload may have prevented you from being able to notice. At frequencies far from the secondary loop's resonance, the measuring loop antenna factor will not be much affected, and you will even be able to get a useful idea of the fields you are seeing from the EUT. If you wish, you can have your loop recalibrated with the resonant loop permanently attached, which will restore the ability to make acceptable measurements. Cortland snip --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net 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: No longer online until our new server is brought online and the old messages are imported into the new server.
Re: Active loop antenna overload
I think we may be assuming this overload is caused by the EUT. But this is just as likely to be caused by something else. Medium Wave and Long Wave broadcasting produces powerful fields at some distance from an antenna. This has a fix. If you place a narrowly resonant loop antenna, with feed point shorted, in close proximity to the wideband loop used for measurements, it will reduce pickup at the resonant frequency to a small fraction of the normal amount, and you will be able to at least SEE signals front-end overload may have prevented you from being able to notice. At frequencies far from the secondary loop's resonance, the measuring loop antenna factor will not be much affected, and you will even be able to get a useful idea of the fields you are seeing from the EUT. If you wish, you can have your loop recalibrated with the resonant loop permanently attached, which will restore the ability to make acceptable measurements. Cortland --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net 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: No longer online until our new server is brought online and the old messages are imported into the new server.
Re: Active loop antenna overload
Assuming that moving the antenna away from the source is not a palatable solution, here is a more complex answer. The loop is electrostatically shielded, which means there is a small air gap somewhere around the loop shield, usually at the top or at the base. If you do a poor job of jumpering across that gap, you will decrease the loop sensitivity. You will have to recalibrate a new antenna factor of course. If you have or build a Helmholtz coil this is very easily done. -- From: Wan Juang Foo f...@np.edu.sg To: emc-p...@ieee.org Subject: Re: Active loop antenna overload Date: Tue, Sep 25, 2001, 8:39 PM Hi, I have some questions. What are the dimension of your loop? Are you measuring a static field? If so, I suggest you use a Hall-effect type sensor, I have had good results at powerline frequencies. If you are measuring the H-field component for anything in the 30 MHz or so region, I would be more careful about moving away from the source because of the extremely complex (nonlinear and usually unpredictable) field patterns in the near-field. Redesigning the input circuit would help but that would mean that the new setup have to be calibrated. :-) Just my 2 cents worth. Tim Foo, (or just call me 'Tim') E-mail: f...@np.edu.sg ECE, School of Engineering, http://www.np.edu.sg/ece/ Tel: + 65 460 6143 Ngee Ann Polytechnic, Fax: + 65 467 1730 535 Clementi Road, Singapore 599489 Robert Macy m...@california.com To: KC CHAN [PDD] kcc...@hkpc.org, Sent by: cc: (bcc: Wan Juang Foo/ece/staff/npnet) owner-emc-pstc@majordomSubject: Re: Active loop antenna overload o.ieee.org 09/24/01 03:45 PM Please respond to Robert Macy Move the antenna further away. then use correction factors to calculate what it would have been at the original distance. Magnetic fields decrease as the inverse cube of the distance. So just apply a correction factor to boost the amplitude back up. For example, twice the distance away means the signal will look 1/8 as much or around 18dB smaller. Of course, that assumes the source is a magnetic dipole AND your original measurement distance is at least 3 diameters (diameters of the sensing loop AND diameters of the source loop) away to begin with. [ Also, conductive surfaces and magnetic materials need to be out of the field of interest. Make certain the minimum distance to such interference is at least 3 times the distance between what you're measuring and your sensing loop. ] If the above assumptions don't hold, come back at me. - Robert - Robert A. Macy, PEm...@california.com 408 286 3985 fx 408 297 9121 AJM International Electronics Consultants 619 North First St, San Jose, CA 95112 -Original Message- From: KC CHAN [PDD] kcc...@hkpc.org To: emc-p...@ieee.org Date: Monday, September 24, 2001 12:19 AM Subject: Active loop antenna overload Dear All When doing the magnetic field measurement by a active loop antenna, what we can do if we find the loop antenna is saturated/overloaded? Is there any ways that we can do to overcome this? Best Regards KC Chan snip --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net 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: No longer online until our new server is brought online and the old messages are imported into the new server. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings
Re: Active loop antenna overload
Hi, I have some questions. What are the dimension of your loop? Are you measuring a static field? If so, I suggest you use a Hall-effect type sensor, I have had good results at powerline frequencies. If you are measuring the H-field component for anything in the 30 MHz or so region, I would be more careful about moving away from the source because of the extremely complex (nonlinear and usually unpredictable) field patterns in the near-field. Redesigning the input circuit would help but that would mean that the new setup have to be calibrated. :-) Just my 2 cents worth. Tim Foo, (or just call me 'Tim') E-mail: f...@np.edu.sg ECE, School of Engineering, http://www.np.edu.sg/ece/ Tel: + 65 460 6143 Ngee Ann Polytechnic, Fax: + 65 467 1730 535 Clementi Road, Singapore 599489 Robert Macy m...@california.com To: KC CHAN [PDD] kcc...@hkpc.org, Sent by: cc: (bcc: Wan Juang Foo/ece/staff/npnet) owner-emc-pstc@majordomSubject: Re: Active loop antenna overload o.ieee.org 09/24/01 03:45 PM Please respond to Robert Macy Move the antenna further away. then use correction factors to calculate what it would have been at the original distance. Magnetic fields decrease as the inverse cube of the distance. So just apply a correction factor to boost the amplitude back up. For example, twice the distance away means the signal will look 1/8 as much or around 18dB smaller. Of course, that assumes the source is a magnetic dipole AND your original measurement distance is at least 3 diameters (diameters of the sensing loop AND diameters of the source loop) away to begin with. [ Also, conductive surfaces and magnetic materials need to be out of the field of interest. Make certain the minimum distance to such interference is at least 3 times the distance between what you're measuring and your sensing loop. ] If the above assumptions don't hold, come back at me. - Robert - Robert A. Macy, PEm...@california.com 408 286 3985 fx 408 297 9121 AJM International Electronics Consultants 619 North First St, San Jose, CA 95112 -Original Message- From: KC CHAN [PDD] kcc...@hkpc.org To: emc-p...@ieee.org List-Post: emc-pstc@listserv.ieee.org Date: Monday, September 24, 2001 12:19 AM Subject: Active loop antenna overload Dear All When doing the magnetic field measurement by a active loop antenna, what we can do if we find the loop antenna is saturated/overloaded? Is there any ways that we can do to overcome this? Best Regards KC Chan snip --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net 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: No longer online until our new server is brought online and the old messages are imported into the new server.
Re: Active loop antenna overload
Move the antenna further away. then use correction factors to calculate what it would have been at the original distance. Magnetic fields decrease as the inverse cube of the distance. So just apply a correction factor to boost the amplitude back up. For example, twice the distance away means the signal will look 1/8 as much or around 18dB smaller. Of course, that assumes the source is a magnetic dipole AND your original measurement distance is at least 3 diameters (diameters of the sensing loop AND diameters of the source loop) away to begin with. [ Also, conductive surfaces and magnetic materials need to be out of the field of interest. Make certain the minimum distance to such interference is at least 3 times the distance between what you're measuring and your sensing loop. ] If the above assumptions don't hold, come back at me. - Robert - Robert A. Macy, PEm...@california.com 408 286 3985 fx 408 297 9121 AJM International Electronics Consultants 619 North First St, San Jose, CA 95112 -Original Message- From: KC CHAN [PDD] kcc...@hkpc.org To: emc-p...@ieee.org List-Post: emc-pstc@listserv.ieee.org Date: Monday, September 24, 2001 12:19 AM Subject: Active loop antenna overload Dear All When doing the magnetic field measurement by a active loop antenna, what we can do if we find the loop antenna is saturated/overloaded? Is there any ways that we can do to overcome this? Best Regards KC Chan --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net 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: No longer online until our new server is brought online and the old messages are imported into the new server.
