Yes indeed. Another Old member of the Fraternal Association of Radio Technicians!
Unless an ambient is _exactly_ on the emission's frequency, you CAN narrow bandwidth down to find it. This is no help at all if you want to QP it -- and many times you need that for the margin -- when it is "modulated," but it does allow zeroing in on a weak narrow band emission in the presence of strong broadband ones. But we can do that before we go to the OATS. Once we get there, we want to measure it. And then we have to be careful all that broadband stuff isn't pushing the SA front-end into compression. Anyone here every USE that 3 dB button on the preselector? (grin) I really like cancelling a strong ambient before it gets to the SA. Cortland ====================== Original Message Follows ==================== >> Date: 12-May-99 21:45:03 MsgID: 1068-19969 ToID: 72146,373 From: "Brent DeWitt" >INTERNET:[email protected] Subj: bandwidth reduction (was: Phase cancellation) Chrg: $0.00 Imp: Norm Sens: Std Receipt: No Parts: 1 Ed is correct and brings up another aspect of the measurement issue (without knowing he's done it ;} ) The issue is resolution bandwidth reduction to resolve EUT and adjacent ambient signals. Having spent a bunch of years (old fartz alert!) looking at 141T and 8568/66 displays, I've come to the conclusion that it is almost always possible to _find_ an EUT emission. The problem is making an acceptable (to authorities) measurement of it. If the emission is narrow band, as a simple clock harmonic, I've had no problem reducing the measurement bandwidth to as small as 100 Hz to get an accurate and reasonable reading. The problem is with "modulated" emissions. What I have argued (successfully), is that if I can measure the _ratio_ of peak to Quasi-peak emissions at another harmonic of the same fundamental source in a narrow band vs 120 kHz bandwidth, that the same "correction factor" can be applied in narrow band peak measurement in the presence of an ambient. The folks I know at the FCC are pretty reasonable when your argument makes sense, and for the EU, you just need to be _prepared_ to stand on well justified engineering principles in case you are asked. One opinion............ Brent DeWitt > The difficulty with this method is when you get an EUT emission > that lands right on an ambient emission. (Or close enough to > include both signals in the analyzer/receiver passband.) You may > know that there's an EUT emission at that frequency, but the > ambient may exceed or even mask the EUT emission. And your > amplitude measurement is then corrupted. > > Ed --------- 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). ====================== End of Original Message ===================== --------- 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).
