Low power VHF radios for water telemtry and industrial comtrol systems
April 2000
Fieldbus & Industrial Networking
Specific Technologies
A range of low power VHF transceivers of relatively uncluttered radio frequencies between 125 and 180 MHz has been introduced by Wood & Douglas. With a maximum transmitter output of just 10 mW and a range of up to 2 km, SX100 transceivers are intended for use in onsite telemetry and data exchange systems, particularly by water and sewerage utilities and in industrial control.
The SX100 can be specified to take advantage of the UK licence exempt frequency band at 173 MHz. This was the first band to be allocated to low power radio applications in the UK, but many early users have since migrated to newer licence exempt bands between 400 and 500 MHz. As a result, the latter bands have become overcrowded and prone to interference problems, while the former is significantly quieter.
Specifiable to any frequency between 125 and 180 MHz, the SX100 allows either serial or parallel channel selection of, respectively, up to 112 or up to eight serially programmed channels over a 2 MHz switching bandwidth. Frequency control is achieved using low-noise phase-locked loop synthesizer technology, with nonvolatile storage of frequency data.
Low power consumption of less than 40 mA from a 7,2 V d.c. supply when receiving and less than 65 mA when transmitting at 10 mW makes the device suitable for portable, battery-powered applications.
The transceiver is type approved to the European EN 300 220 telemetry specification as well as the MPT1328 UK standard. Besides data applications, this UK approval and frequency band also gives access to two channels allocated to short-range voice communications.
Physically and electrically compatible with the SX500 transceiver, which operates at 400–500 MHz, the SX100 has identical PCB mounting pins to allow direct substitution into target equipment.
The SX100 is packaged in a lightweight 60 x 38 x 17 mm screened enclosure that ensures compliance with EN 300 683 EMC regulations.
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