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@majordom Subject: 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, PE m...@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 Heald davehe...@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 Heald davehe...@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.
