Radio Modem Module - LRM Series

The LRM module is a complete high performance radio modem built into a small screened can designed to mount directly onto a PCB for OEM applications. It is a simple to use, ready-made radio module for telemetry, alarm and data applications which requires no detailed knowledge of radio for its use. The LRM allows you to add wireless capability to your products with the minimum of effort.

A discrete component RF stage is used to give much better performance than would be possible using the simpler "single chip" solutions found in many other low cost designs.

Transmit power is settable between 10mW and 750mW and both UHF and 869MHz versions are available. The 869MHz version can be used from 863MHz to 870MHz, but is ideally suited for operation within the Pan-European 868MHz/869MHz band which which generally allows licence-exempt operation between 869.4MHz and 869.65MHz with an EIRP of 500mW or less. The UHF version is available in a number of sub-bands from 406MHz to 470MHz.

The modules can be supplied with either an industry standard 5V SPI Bus interface (Serial Peripheral Interface) for serial control of all the radio and modem parameters or with a hard-wired parallel interface where the transmit power and wanted channel frequency are selected from a number of pre-programmed configurations using 8 binary control lines.

The two versions of the LRM module are mechanically the same as each other and both have 16 pins on the lower face which are designed to plug into sockets on a mother-board.

SPI (Serial Control) Version

In the SPI version, you have full serial control of the radio and also have access to a highly configurable internal modem capable of over-air data rates up to 9600bps. This SPI version of the LRM module has similar capabilities to our full ZRT radio modem product in its "Transparent" mode, but is presented in a much smaller PCB mountable screened can with a 5V TTL traffic interface for OEM applications.

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. Access to the audio inputs and outputs is also available to allow optional use of external modem circuitry if preferred.

The receive signal level is accessible through the serial control bus in addition to being available as a dc voltage and it is possible to key-up of the transmitter using a serial command in addition to being able to use the hard-wired PTT control line.

Hardwired Parallel Control Version

In the parallel interface version, the serial data interface and the SPI serial control bus lines are replaced with eight digital inputs for binary coded control of channel frequency and/or transmit power.

This version does not have an internal modem. Instead, you have direct access to the audio interface for connection of external modem circuitry. Alternatively, for simple FSK operation at speeds up to 1200bps, you can apply a 5V TTL waveform directly to the modulation input.

Modules in the LRM range;

Model	Frequencies	Tx Power	Relevant Specifications & Notes
LRM470TR-1/SPI	406 - 470MHz	10mW - 750mW	ETSI EN300-220 & EN300-113
LRM470TR-1/Parallel	406 - 470MHz	10mW - 750mW	ETSI EN300-220 & EN300-113
LRM869TR-1/SPI	863 - 870MHz	10mW - 750mW	ETSI EN300-220
LRM869TR-1/Parallel	863 - 870MHz	10mW - 750mW	ETSI EN300-220

RF DataTech - European designers and manufacturers of radiomodem, data radio and specialist radio telemetry, paging and wireless data products