ZRT Radio Modem

ZRT Radio Modem

  • Low cost data radio
  • Up to 9k6 bps over-air in 12.5kHz channel (up to 4k8bps in 25kHz for 869MHz band)
  • VHF (Low-band and High-band) & UHF versions available
  • RS232, 5V TTL or combined RS232/RS485/RS422 data interface options
  • 12Vdc (10Vdc-15.5Vdc) supply
  • Low power consumption
  • Programmable power-save modes
  • Forward Error Correction (FEC) selectable at 9k6 bps
  • Supports “Store & Forward” operation
  • Explicitly supports MODBUS protocol in addition to Transparent (any protocol) operation
  • Highly sensitive receiver
  • Easy configuration using supplied software
  • Key parameters settable using AT Commands

The ZRT is a high specification, low cost data radio modem which is ideal for stand alone wireless data applications or for integration into OEM products. A discrete component RF stage is used to give better performance than would be possible using the simpler “single chip” solutions found in many other low cost designs.

Low-band VHF (66 to 88MHz), High-band VHF (138MHz - 225MHz), UHF (406MHz - 512MHz) and 869MHz (863MHz - 870MHz) versions of the ZRT are available for simplex or half-duplex operation.

Applications include security, command & control, data logging, metering, SCADA, radio telemetry, remote switching, differential GPS & NMEA data transmission, PTZ camera control or any similar applications where serial data needs to be transmitted reliably by wireless means.

Through the use of advanced DSP technology, the ZRT data radio has been optimised for reliability and low current consumption, making it particularly suitable for operation on remote sites without mains power.

The ZRT radiomodem can be supplied with an RS232-only, a combined RS232/RS485/RS422 or a 5V TTL serial interface. In each case, the speed of this serial interface can be set independently of the chosen over-air data rate. The RS485 version is ideal for use in radio based PTZ control links for remote operation of Pan/Tilt/Zoom surveillance cameras in situations where a serial cable is not practical.

The over-air data rate can be set to a range of values between 150bps and 9600bps and there is an internal buffer to cope with situations where the interface baud rate is higher than the selected over-air rate. For 150, 300, 600, 1200 & 2400bps, FSK/FFSK modulation is used with V.23, Bell202 and MPT1327 tone-sets all supported. At 4800bps GMSK is used, while at 9600bps the modulation is 4-level FSK (4FSK). If high speeds are not required, the modem can be programmed to a slower over-air rate to take advantage of the associated improvement in receiver threshold.

The ZRT is available in low power versions adjustable from 10mW to 750mW and higher power versions covering 100mW to 5W. The desired transmitter power can be set accurately within the relevant range under software control. The low power versions meet the ETSI EN 300 220 specification for use in licence-exempt channels throughout Europe while higher power 5W versions also meet the tougher European EN 300 113 requirements. The ZRT470TR-5 has been certified as meeting the necessary FCC and Industry Canada (IC) requirements to allow use in the USA and Canada.

The receiver is a very low current, double conversion superheterodyne with an active balanced mixer for very good intermodulation performance. Careful attention to spurious response, adjacent channel and blocking performance, makes the product ideal for crowded telemetry radio channels.

The RF and modem parameters of the ZRT are all PC programmable via the serial port. Transmit power, channel selection and a number of other key parameters can also be changed by simple serial commands through the RS232 port or by using AT commands embedded in the data string.

The ZRT radio data modem can operate transparently without packetising the data and without adding any other overheads, thereby maximising data throughput rates. Data is simply transmitted and received with minimal delay. Alternatively, a simple packetisation option can be enabled for use with old or non tolerant protocols, where the presence of a mute (squelch) tail may cause a problem at the end of a message.

Store and forward repeater operation is built-in and can support chains of repeaters up to 6 radios long in a tree and branch network configuration.

The RS232 and TTL versions support full RTS, CTS, DSR, DTR & DCD handshaking, although it is also possible to use just the transmit data, receive data and ground lines without handshaking. The combined RS232/RS485/RS422 version has it’s DSR line simply looped back from the DTL line and CTS looped back from RTS.