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Radio Modems

Radio modem 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.


Judd Telemetry can supply the ZRT modem detailed on this page and continue to support RDT’s RM96xx range.

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.


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 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 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 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.




RM96xx datasheet ZRT datasheet