It may not be possible to predict that emissions are NOT additive; it is rather easy to predict that they WILL be. A system of subassemblies all phase locked to the same clock will almost certainly prove additive in use. A system of subassemblies all individually clocked may well add, but if the tolerance on their clocking is loose enough, they may not.
Assuming subassemblies do add, when do you stop adding them? It turns out that if you add assemblies and get less than a 1 dB increase, you're done. This can be a surprisingly small number, too. 1 dB is only about a ten percent change. Of course, you still need enough in the rack to populate it in a typical manner, and so usually, I think, our racks will have MORE than the minimum number of each type of subassembly. But there remains the problem of knowing when to stop adding RACKS. An installation three meters wide and one rack deep is one thing; what about one five meters wide and two meters deep? What about one that essentially fills an entire 10 meter square? Such installations do exist. I don't know for sure, but I suspect that the 1 dB rule is applicable here as well, modified by another: The racks should be increased up to the point where the profile of emissions, as well as the amplitude, stops changing markedly from one increment to the next. Once we have dealt with number, size and shape, we can test with some confidence that things won't get worse. Whether we DO so, I don't want to argue! Cortland Richmond (Whose words here have nothing to do with his employer or his employer's opinions, procedures, or practices!) ====================== Original Message Follows ==================== >> Date: 28-Jul-00 14:40:20 MsgID: 1072-33047 ToID: 72146,373 From: "Grant, Tania (Tania)" >INTERNET:[email protected] Subj: RE: Return: Rack populating? Chrg: $0.00 Imp: Norm Sens: Std Receipt: No Parts: 1 From: "Grant, Tania (Tania)" <[email protected]> Subject: RE: Return: Rack populating? List-Post: [email protected] Date: Fri, 28 Jul 2000 14:39:42 -0700 Reply-To: "Grant, Tania (Tania)" <[email protected]> So, how do you know that "....emissions from identical modules are not additive", unless you test?. And, didn't the FCC say in the past (or still states in the present?) that there is no need to hang additional cables all of the same type as long as emissions are not raised by more than 2 dB! Again, how do you know unless you test. Tania Grant, [email protected] <mailto:[email protected]> Lucent Technologies, Intelligent Network Unit Messaging Solutions Group ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected]
