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Appendix J
CDM-760 Advanced High-Speed Trunking Modem
J.5.2.2
Calculating CnC R atio from Ca rrier t o Noise Rati o (C/ N) on a
Spectrum Analyzer
For this example, assume Site A is running a link to Site
B (referred to as Link 1), and Site B is running a link to
Site A (referred to as Link 2):
CnC Ratio = C/N Interferer – C/N Desired + 10log(SR Interferer /
•
SR_Desired)
CnC Ratio at Site A = C/N Link 1 – C/N Link 2 + 10log(SR Link 1 / SR
•
Link 2)
CnC Ratio at Site B = C/N Link 2 – C/N Link 1 + 10log(SR Link 2 / SR
•
Link 1)
C/N (dB)
Link 1
9.5
Notes:
•
From the standpoint of Site A:
CnC Ratio = 9.5 – 7.5 + 10log(5.0 / 6.5) = +0.86
•
From the standpoint of Site B:
CnC Ratio = 7.5 – 9.5 + 10log(6.5 / 5.0) = -0.86
CnC Ratio from C/N
Symbol Rate (Msps)
SR
Link 2
Link 1
7.5
5.0
J–17
CnC Ratio (by Carrier Direction)*
SR
CnC A
Link 2
(Site A Site B)
6.5
+0.86 dB
Revision 4
MN-CDM760
CnC B
(Site B Site A)
-0.86 dB
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