Data Carrier Detect
The DE1200 modem supports 3 methods of providing DCD to the Data Engine. These
are selected by using the MODEM command on your Data Engine.
MODEM 0
selects the DE1200 sine-wave carrier detect.
In
this mode, the DE1200
will
indicate carrier detect when a signal is received which
has
audio sine-wave
components (i.e. packet tones).
This
type of carrier detect
will
not prevent the Data
Engine from transmitting when only noise or voice is present on the frequency,
allowing the Data Engine to be used with un-squelched audio.
MODEM 1
selects the carrier detect from the 3105 modem chip.
In
this mode of
operation,
any
energy present on the frequency
will
cause the DE1200 to signal carrier
detect to the Data Engine, blocking transmission. This would be useful for a shared
voice/data channel when it
is
desirable to withhold packet transmission while voice is
being used.
This
carrier detect
cann
ot be used with un-squelched audio.
MODEM
2
selects the external carrier detect.
This
mode requires some external
device to supply a signal to pin 8 of the DB-15 connector (pin 12 on the DE1200
external modem header). You may choose to have your radio supply the squelch signal
(ground active),
or
you may have some external circuitry provide a carrier detect.
The DE1200 modem also
has
provisions for one additional Carrier Detect to be
connected to the modem at the pad marked PDl. This pad
is
located just back and
right of the crystal. A high ( +5 volts)
will
signal active carrier detect at this point,
and a ground
will
signal that the channel is clear. This input is selected with the
command MODEM 3.
The carrier detect threshold
is
set at the factory and should require no adjustment
under normal ci
rcum
stances.
If
you find it necessary to adjust the threshold, install a
lOK ohm potentiometer at R76.
This
potentiometer
will
then adjust the CD threshold.
V.23 Modification
The DE1200 modem supports V.23 operation.
In
order to select V.23, install a jumper
on the modem board at the pads marked V23. These pads are located just to the right
of U6.
Selecting V.23 operation
will
cause the modem to use 1300
Hz
for Mark and 2100 Hz
for Space instead of the standard Bell 202 tones.
8
DE1200 Modem
April
3, 1990
e
Copyright 1990, Kantronics Co.,
Inc.
All Rights Reserved.
Duplication of
this
manual without permission
of
Kantronics Co:,
Inc.
ia prohibited.
