Transmissionparameters Page167 of 544
Option11C and 11C Mini TechnicalReference 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 Table43).
Reference Source for ยต-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 Table42.
The values for the transhybrid (return) loss of a 2 wire interface when
terminated in its balance impedance is given in Table44.
Reference Level is 0 dBmO.
Table 4 3
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