Estimating / Calculating Cnc Ratio; Estimating Cnc Ratio From Lst / Eirp - Comtech EF Data CDM-750 Installation And Operation Manual

CDM-750 High Speed Trunking Modem
DoubleTalk Carrier-in-Carrier Option

8.5.2 Estimating / Calculating CnC Ratio

CnC Ratio can be derived either from the downlink carrier levels or from the Carrier to Noise
Ratio (C/N).
8.5.2.1

Estimating CnC Ratio from LST / EIRP

The CnC Ratio is the difference in power of the interferer carrier to the desired carrier. For this
reason a positive value represents a stronger interfering carrier, and a negative value represents a
stronger desired carrier. The reason why the CnC ratio is an "estimate" when looking at BE EIRP
is because BE EIRP assumes that the actual BW used and the PEB are balanced, and therefore the
BE EIRP is an accurate proxy for the actual power of the carrier.
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 = Interferer BE EIRP – Desired BE EIRP
•
CnC Ratio at Site A = BE EIRP Link 1 – BE EIRP Link 2
•
CnC Ratio at Site B = BE EIRP Link 2 – BE EIRP Link 1
Notes:
•
From the standpoint of Site A:
CnC Ratio = 32.6 – 31.8 = +0.8
•
From the standpoint of Site B:
CnC Ratio = 31.8 – 32.6 = -0.8
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