User Manual

VoiceXtender Modem Installer’s Guide
Installation and Setup
Rev. A - 8/97 3-5
center frequency assigned to each channel has been chosen to provide the
greatest flexibility of use. The VoiceXtender VX64 modem requires a segment of
bandwidth that is only one channel wide. Therefore, all nine channels are
available for voice applications.
Each modem used in a “logical” application (e.g., the master and slave units of
a single point-to-point link) must be configured with the same channel.
Transmit Output Power Switches (SW1-5 through SW1-7)
These switches set the power level for the VX modem. The transmit level you
select depends on local regulations and your application; however, the
minimum required power normally is recommended for most applications.
Depending upon the application, the setting selected as the transmit output
power is also used to determine the system gain. For more information, refer to
Path Analysis in Chapter 2, “System Planning.”
Burst Synchronization Timing Switch (SW1-8)
This switch sets the timing used to synchronize the communication between
modems - either Internal Burst Timing or External Burst Timing.
When an modem pair operates independently (point-to-point application), the
slave and master modems are configured for internal burst timing. (Slave units
are always configured for internal burst timing.)
In a hub configuration where there is more than one modem pair, it is critical
that all the modems transmit and receive at the same time to minimize inter-
channel interference. In this case, the synchronizing modem is configured for
internal burst timing and the synchronized modems are configured for external
burst timing. The burst synchronization signal is derived from the transmit
clock source of the synchronizing modem through the sync connection.
See the hub configuration is illustrated in Chapter 2, “System Planning.”
NOTE VoiceXtender modems can be burst synchronized with other VoiceXtender modems and
with model 64MP, 128 and 256 AirLink data modems. If VoiceXtender modems are burst
synchronized with AirLink data modems, one of the data modems must be configured as
the synchronizing unit.