Panasonic KX-FG2452CX Service Manual page 119

(Causes and Countermeasures)
No. Countermeasure Side
1 Sending side
2 Receiving side
Receiving side
Sending side
3 Sending side
4 Sending side
Receiving side
5 Sending side
Receiving side
(Overlapping the Echo of the DIS signal and DCS signal)
Echo Communication Problem Example
Some time is needed to compare the level
of the receiving and sending signals for the
echo canceler. The header of the training
signal lacks due to a switching delay to
close S1.
The echo canceler function stops according
to a CED signal frequency of 2100Hz (S1
and S2 are both ON), a DIS signal is
returned as an echo, and a DCS signal
from the sending side overlaps the DIS
echo. Then the receiving side FAX cannot
retrieve the DCS signal.
(Refer to Fig. a)
Communication failure occurs in a long dis-
tance communication on the telephone line
without an echo canceler.
or
There are some cases (e.g. Mobil comms.)
which cause the collision of TX / RX signals
due to the delay / echo and noise of the
network / terminal. (Refer to Fig. e)
Fig. a
Countermeasure
Add a dummy signal to the beginning of
the training signal.
Change to a 1100Hz CED signal fre-
quency. (Refer to Fig. b)
Change the regular rime of 75 msec
between the CED signal and DIS signal
to 500 msec. This will give at least 250
msec to recover the echo canceler
operation. (Refer to Fig. c)
The sending side FAX sends a DCS
signal not after receiving the 1st DIS
signal but after receiving the 2nd DIS
signal. (Refer to Fig. d)
Decrease the transmission level from -
10 dBm to -15 dBm and the echo level
will decrease.
Decrease the receiving sensitivity from
-13 dBm to about -32 dBm so an echo
signal will not received.
Set additional Pause time (Service
mode: code No. 774) in between the
original and its repeated signals, to pre-
vent the collision of the signals at both
end.
(Countermeasure by Changing the CED Frequency)
119
KX-FG2452CX
Service Code
Service code (521)
(International mode select)
This countermeasure becomes
the default value.
Service code (520)
(CED frequency select)
Service code (593)
(Time between CED and 300
bps)
Service code (594)
(Overseas DIS detection
select)
Service code (596)
(Transmit level set)
Service code (598)
(Receiving sensitivity)
Service code (774)
(T4 timer)
Fig. b