Blonder tongue AMM-806, Reference Manual

Page: 122 / 285

115
Combining Two X-MOD or CTB Performance
Ratings (20 Log)
Using dB Subtraction Values
Example: Combine trunk and bridger
CNR to find the resultant CNR
at the Bridger output (no line extenders).
dB difference = 65-56.5 = 8.5 dB
dB subtraction figure = 0.6 dB
Bridger output CNR = 56.5-0.6 = 55.9 dB
So then, the resultant CNR measure is about 55.9 dB.
The 20 log & 10 log derate
charts are used to sum different
ratios. The following example demonstrates how:
Step 1 Sum Trunk and Bridger CTB
1.1 Find the dB difference between the
two ratios (65-60=5 dB)
1.2 Look up the derate (dB Subtraction) for 5.0
dB difference in the chart (3.88 dB)
1.3 Derate the poorer of the two CTB ratios
by this amount (60-3.9=56.1 dBc)
Step 2 Sum the Sum of Trunk and Bridger from
Step 1 with the line extenders
2.1 Find the dB difference between the
two ratios (58-56.12=1.88)
2.2 Look up the derate (dB Subtraction)
for 1.88 dB difference in the chart
(5.12) (round 1.88 up to 1.9).
2.3 Derate the poorer of the two CTB ratios
by this amount (56.12 - 5.12 = 51.0 dBc)
Using dB Subtraction Values
10 Trunk CTB = 65 dBc
1 Bridger CTB = 60 dBc
Line Extender CTB = 58 dBc
Combining Two CNR or SSO Performance Ratings
(10 Log)
10 Trunk CNR = 56.5 dB
1 Bridger CNR = 65 dB