Mr. Mazzola's points are well taken but not the whole story. The modulation bandwidth defines the exclusion zone only to the extent that the modulation bandwidth is both necessary to convey the required information, and does not overlap another required channel.
For instance, if I decide to use a UHF-AM (225- 400 MHz) military band channel to transmit some digitized modem signal, I cannot unilaterally declare that my required bandwidth needs to facilitate 100 kB/s information transfer. I have to live in a world were uhf channels are spaced 25 kHz apart and cannot interfere with each other. This is basic stuff, but it bears mention given the previous post. -- Ken Javor Phone: (256) 650-5261 From: "Mazzola, Santo \(US SSA\)" <[email protected]> List-Post: [email protected] Date: Mon, 13 Aug 2007 10:24:26 -0400 To: "Price, Ed" <[email protected]>, "IEEE EMC Discussion Group" <[email protected]> Subject: RE: MIL-STD-461E Necessary Bandwidth Ed, We have a product that is a pulse transmitter. For Mil-STD-461E we use the following logic. The +/- 5 percent statement would not be adequate to cover all of the pulse energy. We use the -80 dBc as the necessary bandwidth criteria. We always state that the necessary bandwidth supersedes the +/- 5 percent statement for our product. It makes sense if you think about the fact that you are going to be making 80 dbc, CE106 spurious emissions measurements, the necessary bandwidth energy better be completed before you apply that criteria. It is actually a matter of the spectral mask ending and then the CE106 measurement beginning. The criteria for the spectral mask determines the necessary bandwidth and CE106 determines the spurious emissions. When the spectral mask ends, CE106 begins. Since CE106 requires 80 dBc for spurious I think that determines the end of the necessary bandwidth. The 99 % criteria would not work as I think that you would not be 80 dB down and that would be confusing. The MIL-STD-461E customers we have usually accept this logic. Although I must admit there is usually a lot of discussion concerning this. Sandy Mazzola BAE Systems _____ From: [email protected] [mailto:[email protected]] On Behalf Of Price, Ed Sent: Saturday, August 11, 2007 12:20 AM To: IEEE EMC Discussion Group Subject: MIL-STD-461E Necessary Bandwidth Over the past couple of weeks, I have been looking at how Japan defines their terms of "necessary" and "occupied" bandwidth for intentional emitters. When I went to compare this with how the US military uses 461E to define these same concepts, I was surprised that there doesn't seem to be a technical definition in MIL-STD-461E. Method CE106, Paragraph 5.6.1 states "The transmit mode portion of this requirement is not applicable within the EUT necessary bandwidth and within ±5 percent of the fundamental frequency.". (Method RE103, Paragraph 5.17.1 is similar.) OK, so what is the "necessary" bandwidth? Is this the 99% energy content spectrum? Is it the -80 dBc points? Looking around at possibly "higher" levels of authority, I notice that the NTIA May 2004 edition of Manual of Regulations and Procedures for Federal Radio Frequency Management contains a definition. Paragraph 6.3.2 almost defines "necessary" bandwidth, but then refers you to Annex J. Annex J, Paragraph 2.1 provides formulae for a number of specific modulations, but it also includes "best technical information from other sources" and a reference to ITU-R SM.328-8 (1994) and SM.853 (1994). OK, I'm still reading this Annex J (and it's Table A formulae), but do you think that I have made a reasonable assumption in using NTIA definitions for MIL-STD-461E? Ed Price [email protected] 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. 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