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*Subject*: [amsat-bb] SAREX QRM factors?*From*: Bob Bruninga <bruninga@xxxxxxxxxxxxx>*Date*: Wed, 16 Dec 1998 17:50:54 -0500 (EST)

Has anyone studied the analytical process necessary to characterize an FM channel performance in the presence of multiple interferring signals such as what SAREX experiences in orbit? We all understand the FM capture affect of one signal 10 dB stronger than another. But what if there are 10, 100, or 1000 equal (but less) powered interferring signals? How do the noise powers add so you can calculate a required Signal-to-average-QRM factor? Specifically, if there are 10 stations transmitting 50W EIRP packets simultaneously, how much power is needed by another desired station to achieve a 16 dB advantage? What if it were 20 or 50 or 100 50W stations? Assume all are using conventional 5 KHz FM. Further, clarify the difference betweent the 10 dB? Signal difference on FM to achieve "capture" versus the 16 dB? SNR needed for AFSK decoding. Here the 16 dB is relative to gausian noise, not interference...? The answer is somewhere between 0 (noise powers cancel in large numbers) or N where the power is N times larger (but this would require all signals to be in-phase)... Does anyone have the answer? I will post any good answers received. Bob ---- Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA. To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org

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