Operation
RFI-148 250W VHF Paging Transmitter User Manual
Page 19 of 43
4.3.4 External Reference
The transmitter supports an external reference for channel frequency generation. To use the external
reference, a 10 MHz sine or square wave -10 dBm to 0 dBm signal must be applied to the “External
Frequency” input BNC connector on the back panel. The paging transmitter will attempt to use an external
reference by default.
AUTOMATIC REFERENCE SWITCHOVER
If the external reference is selected as the default reference, the transmitter will failover to the internal
reference in the event of the external reference failing.
The external reference is considered to have failed when there is no signal transition on the external
reference for at least two consecutive falling edges of the internal reference.
NOTE:
If the paging transmitter is transmitting when reference switchover occurs, there may be data loss.
4.3.5 Absolute Delay Adjustment
The paging transmitter can insert a small artificial delay on data presented on the LIU interface before it is
passed to the digital synthesiser. The delay adjustment can be set from 0 to 40 ms in 5 µs steps. The
additional net delay is accurate to
3 µs.
4.3.6 Carrier Offset
A carrier offset from the channel frequency can be specified from -5000 to +5000 Hz in increments of 1 Hz.
4.3.7 RF Diagnostics
The paging transmitter provides an RF diagnostics port output on the back panel. The RF diagnostics port
can be configured for two modes:
Transmission:
The sniffer port will output a signal identical to that of RF out, attenuated by
approximately 105 dB. This is the normal mode of operation.
Listening:
Attenuation from the antenna port to the sniffer port is reduced to less than 15 dB. This is
a special mode of operation used for network testing.
NOTE:
While the sniffer port is configured for
listening, transmission is disabled.
4.4 Data
The RFI-148 250 supports the following modulation formats:
POCSAG:
Baud rates of 512, 1200 and 2400 bps (2-level FSK) are supported.
FLEX:
Baud rates of 1600 (2-level FSK), 3200 (2-level or 4-level FSK) and 6400 bps (4-level FSK)
are supported.
