Panasonic KX-FC379CX Service Manual page 104

(Causes and Countermeasures)
No. Countermeasure Side
1 Sending side 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.
2 Receiving side The
according to a CED signal frequency of
2100Hz (S1 and S2 are both ON), a DIS
Receiving side
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)
Sending side
3 Sending side Communication failure occurs in a long
distance communication on the telephone
line without an echo canceler.
4 Sending side
or
Receiving side
There are some cases (e.g. Mobil comms.)
5 Sending side
which cause the collision of TX / RX signals
Receiving side
due to the delay / echo and noise of the
network / terminal. (Refer to Fig. e)
Fig. a (Overlapping the Echo of the DIS signal and DCS signal)
Echo Communication Problem Example
echo canceler function
Countermeasure
Add a dummy signal to the beginning
of the training signal.
stops Change to a 1100Hz CED signal
frequency. (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
prevent the collision of the signals at
both end.
Fig. b (Countermeasure by Changing the CED Frequency)
103
KX-FC379CX
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)