They are useful for homing in on the source of emissions. IFF (if and only if) you know that the source you have isolated is the sole source of the emissions outage, then an X dB reduction measured with the probe could be expected to yield the same reduction at three or ten meters. But if the source of the emissions is distributed, I would not expect a linear extrapolation to work.
on 12/11/01 11:41 PM, KC CHAN [PDD] at [email protected] wrote: > > It just came to my mind that there are some near filed probes for EMC > debugging in the market. Are they useful? > >>>> Ken Javor <[email protected]> 11/27/01 01:15am >>> > > A much simpler answer is that as long as source (EUT) is small relative to > separation and separation is long relative to a wavelength then 1/r scaling > is fairly accurate, but if those conditions are not met scaling for another > distance cannot be performed. My earlier posting on this subject > incorrectly made the antenna short relative to a wavelength. That > requirement is only necessary in microwave bands with highly directional > antennas, not below a GHz where we use low gain antennas. > > on 11/26/01 5:01 AM, CE-TEST at [email protected] wrote: > >> >> Hi >> >> The transition from near to far field is very complex. >> It depends on the source of the radiation. >> If the source is electric field (voltage/air capacitor/small dipole) >> is has 3 vector components all at right angles of each other of which 2 are >> electric >> and one is magnetic. To make it more complex each of the 3 vectors >> have another relation ship with the distance : 1/r3 (E) 1/r2 (H) and 1/r >> (E). >> >> If the source is dominantly magnetic (small current loop or piece of wire >> carrying current) >> then the same reasoning as above exists but with magnetic and electric field >> terms exchanged. >> >> To discourage you completely: most sources are of a mixed character ! ;<)) >> >> Good information of this can be found in books such as >> Goedbloed 's that actually lists out the formula's in a >> easy form. >> >> For emc measurements we are mainly concerned with the 1/r terms >> because the others die out faster when the distance rises. >> >> >> Regards, >> >> Gert Gremmen >> >> -----Original Message----- >> From: [email protected] >> [mailto:[email protected]]On Behalf Of >> [email protected] >> Sent: maandag 26 november 2001 13:15 >> To: [email protected] >> Subject: Near field vs far field >> >> >> >> Hi all, >> >> CASE: >> We measure radiated emission on a 21" PC monitor inside a semi-anechoic >> chamber. >> >> In a 3m distance we measure 30dBuV/m at 30MHz >> >> What value could we expect at 1m distance ? >> >> I'm not asking for the correct dBuV/m value..., but what really happens when >> we go so far into the object near field ? >> >> Does it exist a kind of empiric equation which roughly can give us a number >> ? >> >> Please, if you have an links to the Web-articles about near-far fields >> effects, I would like to know. >> >> Best regards from >> Amund Westin in sunny Oslo/Norway >> >> >> >> ------------------------------------------- >> 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: >> [email protected] >> with the single line: >> unsubscribe emc-pstc >> >> For help, send mail to the list administrators: >> Michael Garretson: [email protected] >> Dave Heald [email protected] >> >> For policy questions, send mail to: >> Richard Nute: [email protected] >> Jim Bacher: [email protected] >> >> 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: >> [email protected] >> with the single line: >> unsubscribe emc-pstc >> >> For help, send mail to the list administrators: >> Michael Garretson: [email protected] >> Dave Heald [email protected] >> >> For policy questions, send mail to: >> Richard Nute: [email protected] >> Jim Bacher: [email protected] >> >> 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: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Michael Garretson: [email protected] > Dave Heald [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > Jim Bacher: [email protected] > > 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: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Michael Garretson: [email protected] > Dave Heald [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > Jim Bacher: [email protected] > > 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: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: [email protected] Dave Heald [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] 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.
