Barnett Engineering B1474 operation manual Introduction, Ptt

1 INTRODUCTION

The B1474 Radio Modem provides a reliable method of sending 1200 baud data signals over radio or cable facilities. Digital information is converted to tone format for transmission over the communication channel. Received tones are converted back to RS232 digital format.

Hardware handshaking using RTS and CTS signals allows the radio channel to be transparent to the connected equipment. Warm-up and power down delay times required by the radio do not affect the data signals. Alternatively, XON/XOFF or data buffering may be used where hardware handshaking is not available.

The communication channel can be a single pair cable, two pair cable or two-way radio. Conventional land mobile radio equipment can be used or, if specified at time of order, GE trunking radios may be used.

Power and audio signals are connected to compression terminals inside the modem; the digital interface is through a DB-25S connector. The B1474 requires 12 to 30 VDC, negative ground, and approximately 60 mA to operate.

Features available in the B1474 are:

Hardware or Software Handshaking

Either RTS and CTS hardware signals or software XON and XOFF characters can be used to pause the transmitting station while waiting for the radio system to respond. If short data streams are to be sent, full data buffering may be used to render the radio system transparent.

RTS/CTS Delay

This adjustable delay allows the radio to warm up before data is sent. The delay is active regardless of whether hardware handshaking or data buffering is used.

PTT

A low going push-to-talk signal is active whenever the modem is transmitting data.

Squelch Detect

If the radio channel is currently being used, the modem will not return the CTS signal until the channel is available. If XON/XOFF signaling is selected, XOFF will be returned to indicate a busy channel; then XON will be issued when the channel is free. (This feature may be disabled using a DIP switch.)

PTT Drop Delay

This adjustable delay prevents squelch tails from disturbing the received data at the other end of the system.

Level Selection

Transmit levels are adjustable from 0 to -20 dBm. The receive section has selectable gain of 10 dB, if required, to boost low incoming signal levels.

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