FAQs

Q: What is the difference between a radio telemetry module and a radio modem?

A: Radio telemetry modules such as the Wood & Douglas SX450G or SX500G have an analogue audio input and output interface. A radio module receiving this will demodulate the raw analogue audio. Audio waveforms with  frequency components up to 7kHz maximum can be sent over-air depending on the version of module ordered. An example of an analogue waveform is DTMF (Dual Tone Multi Frequency) telephone-type signalling.

Radio telemetry modules cannot work directly with digital RS232/422/485 type data. A radio modem is needed. A radio modem comprises of a radio module that has a daughter-board PCB which contains circuitry to handle ASCII RS232/422/485 data. It is able to convert this digital data into an analogue waveform that can be sent over the air. A radio modem receiving this signal is able to decode the analogue waveform and output an RS232/422/485 representation of the data received.

The radio modem circuitry ‘packetizes’ the incoming digital data into data frames with checksums and other forms of error prevention. These data frames are changed into complex audio waveforms optimised for radio transmission and reception. A receiving radio modem outputs the raw analogue audio down to its daughter-board modem circuit where the raw analogue audio is demodulated into 1s and 0s. The modem circuitry decodes the data from the frame, and if the checksum comparison works out, it outputs RS232/422/485 level data on a serial interface connector.  Radio modems can send and receive data, switching between TX and RX as necessary. This is called half-duplex operation.

A radio modem therefore is a robust reliable complete wireless solution for the bi-directional transfer of serial data messages, whereas a radio telemetry module is often bought by OEMs that integrate it into their own modem/signalling circuitry.

 

If you are looking for a complete radio modem solution, please consider our ORION radio modem. This is available in several versions covering VHF, UHF and the European 869MHz band. TX output power is 0.5Watts and gives you an over-air data rate of 9600bps in a 12.5kHz radio channel bandwidth. If you have access to 25kHz radio channels the over-air data rate jumps to 19200bps.

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