Hello, I quote MIL STD 462 # 4.2.6:
A: The EMI meter shall be tuned over a range of * 2 impulse band widths around the centre frequency of emission. A change in peak detector response of 3 dB or less indicates a broad band emission. A change of greater than 3dB indicates a narrow band emission. B: Measure the PRF of the emission. If the PRF is less than or equal to the impulse BW of EMI receiver it is a broad band emission, if greater it is a narrow band emission. Also practically, the easiest way to determine a NB emission is to drop down or increase the measuring BW 1 or 2 steps in a routine EMI receiver sweep around the emission in a broad span; if the emission remains constant, it is NB emission. Broad band emissions would drop approx 10 dB per step change in the bandwidth. Sweep time could also be varied, time domain BB emissions would change with sweep time; frequency domain NB emissions would more or less remain constant. You have to normalise BB emissions to a 1MHz BW, irrespective of actual measurement BW used. Otherwise, people could shonk a broad band CE03 or RE02 test pass. Computer clocks (and its harmonics) and intentional CW or modulated transmitters generally generate frequency domain NB emission. Commutator motors, thermostats, serial comms links generally generate time domain BB emissions. And finally yes, MIL STD 461D and most commercial standards have got around this NB/BB emission discrimination mess by specifying the measurement BW. Hope this helps. Regards Arun Kaore EMC Engineer ADI Limited Test & Evaluation Centre Forrester Road, St Marys NSW 2760 P O Box: 315, St Marys NSW 1790 Tel: 61 2 9673 8375 Fax: 61 2 9673 8321 Email: [email protected] <mailto:[email protected]> -----Original Message----- From: Price, Ed [mailto:[email protected]] <mailto:[mailto:[email protected]]> Sent: Friday, 08 October, 1999 4:21 To: 'Muriel Bittencourt de Liz'; Lista de EMC da IEEE Subject: RE: broadband & narrowband emissions > -----Original Message----- > From: Muriel Bittencourt de Liz [SMTP:[email protected]] <mailto:[SMTP:[email protected]]> > Sent: Thursday, October 07, 1999 5:43 AM > To: Lista de EMC da IEEE > Subject: broadband & narrowband emissions > > > Group, > > I'd like to have a clear definition of what are narrowband and broadband > emissions. This question may seem very plain for many members of > EMC-PSTC, but I always heard/saw this definition for emission and I > still couldn't make them clear to me.. > > Thanks in advance for your attention > > Regards > > Muriel > > -- > ====================================================================== > Muriel Bittencourt de Liz > GRUCAD - Group for Conception & Analysis of Electromagnetic Devices > Santa Catarina Federal University - UFSC > PO Box: 476 ZIP: 88040-900 - Florianópolis - SC - BRAZIL > Phone: +55.48.331.9649 - Fax: +55.48.234.3790 > e-mail: [email protected] <mailto:[email protected]> > ICQ#: 9089332 > Alternativa Adreso: [email protected] <mailto:[email protected]> > > --------- Muriel: Narrowband and Broadband are the two extremes of the spectral distribution of a signal's power. The classic NB emission has all of its power contained within a narrow range of the spectrum. Think of a perfect sine wave generator, with no sidebands or frequency instability. But how narrow is narrow? All of the power is within 100 Hz? Or 10 Hz? Or 1 Hz? Or...... Classifying a signal as NB depends a lot on your prejudices and experiences. At 10 GHz, a radar signal might occupy 10 MHz of spectrum. That's a lot of spectrum to an audio guy, even though it's only 0.1% wide! My particular experience says that a signal is NB if its occupied bandwidth is around 1% or less. The classic BB emission has its power distributed over a wide range of the spectrum. Think of the spectra from an infinitely fast transition. The power will exist no matter where you choose to sample it. Practically, there are no perfect NB or BB emissions. The problem lies in where (and how) we try to define the dividing line. Should we use percentage of occupied bandwidth? Or tuneability (with what detector bandwidth)? Or maybe modulation repetition rate? Is a NB signal which hops around quickly still NB? What about two NB signals real close together? Have you ever heard the story about the 4 blind men and an elephant? Regards, Ed :-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-) Ed Price [email protected] <mailto:[email protected]> Electromagnetic Compatibility Lab Cubic Defense Systems San Diego, CA. USA 619-505-2780 (Voice) 619-505-1502 (Fax) Military & Avionics EMC Services Is Our Specialty Shake-Bake-Shock - Metrology - Reliability Analysis :-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-) --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] <mailto:[email protected]> with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected] <mailto:[email protected]> , [email protected] <mailto:[email protected]> , [email protected] <mailto:[email protected]> , or [email protected] <mailto:[email protected]> (the list administrators). --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
