Canon FACSIMILE BASIC 2000 Service Manual page 338

7.3.3 Echo countermeasures
The following describes the main countermeasures against echo that are
adopted on Canon facsimiles.
(1) Countermeasure on Receiver
Add a tonal signal (1080 Hz, 0.5 sec) before the CED tone (selected by the
SSSW).
By adding a tone other than 2100±21 Hz before CED, disabling of the
echo suppressor can be prevented.
A tone of 1080 Hz is added on Canon facsimiles.
A–32
Long distance
transmission line
TX RX
CED
Preamble
NSF
CSI
Fig. A-33 Echo Countermeasure on Receiver
Tonal signal
(1080 Hz, 0.5 sec)
DIS