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Transmission parameters Page 167 of 544
Option 11C and 11C Mini Technical Reference Guide
The line or trunk undergoing testing is connected to a 4 wire E&M trunk,
which is terminated with 600 OHMS. The return loss is measured against its
characteristic input impedance (see Table 43).
Reference Source for µ-Law or A-Law is 0 dBmO.
Transhybrid Loss
The source impedance of a two wire interface must match the terminating
impedance (line plus telephone set or line plus far end trunk). If the source
impedance does not match, there will be a problem with stability and listener
echo.
The match of the output source impedance to the line or trunk impedance is
measured by connecting the interface to a 4 wire trunk. The reflected signal
from the hybrid is then measured when the 2 wire interface is terminated with
the balance impedance given in Table 42.
The values for the transhybrid (return) loss of a 2 wire interface when
terminated in its balance impedance is given in Table 44.
Reference Level is 0 dBmO.
Table 43
Return Loss
Interface Echo Return Loss (dB)
Single Frequency
Return Loss (dB)
4 Wire Trunk >28 >22
2 Wire Line >18 >12
2 Wire Trunk >22 >17