Blonder tongue AMM-806, Reference Manual

Page: 119 / 285

112
-65 -60 -58
20 20 20
-3.25 - 3.00 - 2.90
-4 -3 -3
-4 -4 -4
-4
System Calculations
Note:
Summing different ratios requires a grasp of the antilog concept.
For brevity, the example shown is for CTB only, but the approach is
identical for all system distortion and noise calculations.
Determine End Of Line CTB Given The Following:
10 Trunk CTB = 65 dBc
1 Bridger CTB = 60 dBc
3 Line Extender CTB = 58 dBc
Step 1. CTBs = 20 log (10 + 10 + 10 )
Step 2. CTBs = 20 log (10 +10 +10 )
CTBs 20 log (antilog -3.25 + antilog -3.00 + antilog -2.90)
Note: To perform the operations in step 2, use the “inverse” log or “antilog”
function on most calculators. Antilog (Inverse Log) is used to re-express
the different exponent values to voltage so the amounts may be easily
summed. Don’t forget the minus sign.
Step 3. CTBs = 20 log (5.62 x 10 + 1 x 10 + 1.26 x 10 )
Step 4. CTBs = 20 log (5.62 x 10 + 10 x 10 + 12.6 x 10 )
Step 5. CTBs = 20 log (28.12 x 10 )
CTB = 51 dBc
The 20 Log and 10 Log function derate charts & example on pages 86, 87
and 88 may also be used to sum different ratios if a scientific calculator is
not available.