Barnett Engineering B1474 Send/Receive, Transmit Level, Receive Gain, Equalization Mode

Adjust R12 so that the modem waits when the channel is busy, and transmits when the channel is free. When the BUSY light is ON, the modem is waiting for the channel.

To disable this feature, leave P1-9 unconnected and SW1.9 OFF.

If Option 002 trunking software is used, set SW1.9 according to the polarity of the RFCTS signal connected into P1-9. Set SW1.9 and R12 so that the data is only transmitted once the channel has been assigned.

Send/Receive

When using the Option 002 trunking software and data buffering, use SW1.10 to configure the modem for send or receive mode. Normally, all modems within a system should be set for send mode, meaning that they will key the trunking radio and wait for RFCTS when data transmission is required. Setting SW1.10 ON sets the modem into receive mode. In this mode, the modem will only hit PTT if the channel has already been established by another modem. Having one modem in send mode and another in receive mode will ensure that both modems do not try to acquire the channel at the same time.

Set SW1.10 to OFF if using hardware handshaking or conventional radios.

Transmit Level

To adjust the output level of the modem to between 0 and -20 dBm, set DIP switches SW2.1, SW2.2 and SW2.3 as specified Section 7 - Configuration.

The output levels given are referenced into 600 ohms. Should the output be driven into a high impedance, the level will be approximately 6 dB higher than expected.

If a high level is required into a single-ended input, connect P1-5 to ground, and use P1-4 to drive the input.

Receive Gain

DIP switch SW2.5 is used to boost the received signal. To insert 10 dB of gain, turn SW2.5 ON. This will amplify all incoming signals (including all valid data tones).

Equalization (Mode 1)

To enable the internal amplitude equalizer, set SW2.6 ON. To leave this feature disabled, set SW2.6 OFF. Use equalization when there is a large discrepancy in levels between the two tones.

Carrier Detect Delay (Mode 2)

When the receiving modem detects carrier, it mutes the RXD line for a short time to ensure that transients do not affect the received data. Set SW2.7 OFF to delay the received data for 5 msec, ON to delay the received data for 50 msec. Carrier detect delay should be less than the RTS/CTS delay at the sending end.

Full/Half Duplex (Mode 3)

B1474 BARNETT ENGINEERING LTD. PAGE 14