Service manual

OPERATION
3-11
April 2001
Part No. 001-9800-203
3.5.4 COMPANDING
The companding feature is optional with this
transceiver. It is a separate module that installs in
Option Slot 2 (or 1) on the audio/logic board.
Companding improves audio quality by decreasing the
amount of noise present in the audio signal. It does
this by providing a 2:1 compression of the audio signal
on the transmit end and a 1:2 expansion on the receive
end. Companding is especially recommended for 12.5
kHz bandwidth channels because audio quality
improvement is usually significant.
If this feature is used, it must be utilized in both
the transmitting and receiving mobile. The best results
are obtained if companding is also used in the
repeater; however, improvement also results if it is
only used in the mobile and handheld transceivers.
With telephone calls, companding must be utilized at
the repeater if it is used in the mobile. Viking VX
repeaters with the TIC module support companding,
but others may not.
Each LTR and conventional system can be indi-
vidually programmed for companding. Then whenever
a call is received or transmitted on one of these
systems, companding is automatically enabled.
Companding is not selectable by the user, and the
companding status is not indicated in the display. The
control line for this function (Output A or B) also must
be programmed for “Compand” and active high as
described in Section 4.9.
3.5.5 DATA SYSTEM/GROUPS
Digital equipment such as a mobile data terminal
or modem can be connected to this transceiver. An
optional data interface cable (see Table 1-3) connects
this equipment to J301 on the audio/logic board.
Installation of this cable is described in Section 2.7.
When data equipment is used, the transceiver can
be programmed so that data transmissions automati-
cally occur on data system/groups. Each LTR and
conventional group can be programmed for data trans-
missions. If the selected system/group is not
programmed for data transmissions, the first selectable
data group in the current system or the bank data
system/group is selected. Likewise, if the PTT switch
is pressed with a data system/group selected, the revert
or last selected voice group is selected. Refer to
Appendix A.4 for more information on operation with
a modem.
3.5.6 EMERGENCY SWITCH (HIGH TIER ONLY)
The Emergency option switch is available with
high tier models only, and it is used to set up a high
priority call. When the emergency switch is pressed,
the emergency mode is indicated by “EMERGNCY”
on the lower line of the display (this message can be
disabled by programming if desired). The transceiver
then looks at the emergency call information
programmed in the currently selected system (or revert
system if scanning). If there is no emergency informa-
tion programmed for that system, it looks at the default
emergency information programmed for that bank. It
then switches to the specified emergency system/
group.
No automatic transmissions occur with LTR
transceivers. However, the chance that the system will
be busy when a call is placed is minimized as much as
possible. The transceiver locks onto the emergency
system/group (other system/groups cannot be selected)
and scanning is disabled. The only calls received are
those occurring on the emergency system/group (calls
are not received on the selectable, fixed priority, or
block ID codes). To exit the emergency mode and
resume normal transceiver operation, transceiver
power must be cycled.
3.5.7 ENCRYPTION
Voice encryption is an optional feature that
prevents conversations from being monitored by
casual eavesdropping and analog scanners. This is
accomplished by encrypting the voice signal so that it
can be understood only by someone using a trans-
ceiver equipped with similar encryption device. To
have this feature, a separate encryption module is
installed in the Option Slot 1 on the audio/logic board.
The control line for this function is programmed as
described in Section 4.9.
Each LTR and conventional group can be individ-
ually programmed for encryption. Then when one of
these groups is selected, encryption is automatically
enabled or disabled. When encryption is enabled with
high tier models, is indicated in the display as