Short Range Devices (SRD),
Restricted Radiation Devices (RRD),
Low Interference Potential Devices (LIPD)
These are terms used for Low RF Power (<500mW) Licence-exempt Radio Communication Devices in the Industrial Scientific Medical (ISM) band. There are various ISM band radio modules using different modulation technologies and protocols.
Radiometrix specialise in low current consumption, direct FM/FSK radio modules without any protocol overhead, which allows Embedded Systems Engineers to use efficient proprietary protocols and manipulate data at bit level using even 8-bit microcontroller, and precisely control power saving duty cycle for battery operated devices which need to last several years in the field.
In addition to ISM radios, Radiometrix provides custom development of high power 12.5kHz or 25kHz Narrow Band FM multi-channel radios for high-end security and defence industry customers.
FM Radio Modules
Very High Frequency (VHF) radio modules provide the best operating range for Fixed wireless Telemetry or Telecommand networks due to lower RF attenuation at VHF and Narrow Band operation when used with a half-wavelength dipole base station antenna. E.g. Automatic Wireless Irrigation Control, Automatic Meter Reading (AMR), Fire Alarms.
Ultra High Frequency (UHF) radio modules provide the best operating range for portable wireless Telemetry or Telecommand applications where shorter helical or monopole antenna are used. E.g. handheld terminals, industrial remote controls for cranes or pumps.
Single Frequency modules are lower cost, smaller modules consuming less current. They are available as Narrow Band VHF, Narrow Band UHF and Wide Band UHF.
Single Frequency modules are suitable for most of the applications where there is no need for all the transmitter-receiver pairs to be all working simultaneously or applications in which data loss due to a collision is not critical. For example in a temperature monitoring system in a food warehouse where each transmitter on the same frequency can transmit temperature sensor reading every 10 minutes with predetermined sequence without causing interference to each other.
Operating frequency for a single frequency module is determined by crystal frequency. Radiometrix can supply custom VHF and UHF frequency modules, for example, single channel VHF modules can be supplied between 120-174MHz subject to an MOQ and lead-time.
Wide Band FM (WBFM)
These are the more widely used lower cost smaller modules with wider bandwidth for higher data rates up to 64 or even 160kbps. Due to wider receiver bandwidth, sensitivity will be lower, reducing their typical operating range to about 200-300m line of sight with 10mW RF transmit power.
Narrow Band FM (NBFM)
12.5kHz or 25kHz channel spacing Narrow Band FM modules provide better operating range due to higher receiver sensitivity down to -118dBm for 12dB SINAD.
However, due to lower bandwidth, data rate is restricted to 5-10kbps.
Key data sheet parameters to identify a genuine Narrow Band FM transmitter:
1. Adjacent Channel TX power <200nW (< -37dBm) for 20kHz or 25kHz NBFM
<10uW (< -20dBm) for 12.5kHz NBFM
2. Peak FM Deviation: ±3kHz (typical) for 25kHz NBFM
±1.5kHz (typical) for 12.5kHz NBFM
20kHz - 40kHz for Quasi Narrow Band or Wide Band FM
3. Occupied Band Width 16kHz for 25kHz NBFM
8.5kHz for 12.5kHz NBFM
Key data sheet parameters to identify a genuine high performance Narrow Band FM receiver from a cheaper RF IC based narrow band module:
1. Blocking >84dB at +/- 2MHz for Class 1
2. Adjacent Channel Selectivity >54dB for Class 1 for 12.5, 20, 25kHz NBFM
3. Adjacent Band Selectivity higher dB value
4. Image rejection higher dB value
5. Spurious Response rejection higher dB value
6. Inter-modulation rejection higher dB value
Certain countries like Japan and South Korea permit only 12.5kHz NBFM to be used for certain ISM band applications. From 1 January 2008, FCC requires 12.5kHz NBFM VHF/UHF radio for FCC Part 90 licensed usage. E.g. QPT1 type 2W transmitter can be used for long range telemetry under Part 90.
Synthesiser based Multi-channel modules allow a multi-user application to share the same ISM band in the same area, with minimum interference to each other. The 433.05-434.79MHz European band can be divided into 320kHz wide channels for a Wide Band FM Multi-channel operation (e.g. RDL2, TDL2) or 25kHz channels for a Narrow Band FM Multi-channel operation (e.g. LMT2/LMR2, SMX2).
For example, in an industrial control system where there is no coordination between operators and the likelihood of two or more operators trying to transmit at the same time can cause interference or potentially dangerous operation, it is better to use a multi-channel module set to operate on a different frequency channel for each machine operator and respective machine he/she is going to control.
Factory tuneable front-end filters on some multichannel modules (e.g.TR1M / TR2M) enable Radiometrix to provide multichannel narrow band radio modules to operate on a customer’s own licensed VHF / UHF sub-band at shorter lead-times.