Comtech EF Data CDM-760 - Calculating Cnc Ratio from Carrier to Noise Ratio (C;N) on a Spectrum Analyzer

Appendix J Revision 4
CDM-760 Advanced High-Speed Trunking Modem MN-CDM760
J–17
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)
CnC Ratio from C/N
C/N (dB)
Symbol Rate (Msps)
CnC Ratio (by Carrier Direction)*
Link 1 Link 2
SR
Link 1
SR
Link 2
CnC A
(Site A  Site B)
CnC B
(Site B  Site A)
9.5
7.5
5.0
6.5
+0.86 dB
-0.86 dB
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