Back to top

Wireless Point to Point Control and Monitoring System

SRTU-121 wireless p2pSRTU-121 wireless point to point

This product has been discontinued. This web page is provided so current customers using the product can have a quick reference for specifications. Please contact Automation Electronics for current products that may meet your needs.

When you need to transfer a handful of digitals or a couple of analogs from one location to another, our wireless point to point controllers are ideal. Automation and Electronics SRTU-121 is designed to transfer control and monitoring signals from one point to another. It is a complete, off-the-shelf package, designed to operate with either 2.4 GHz or 902-928 MHz spread spectrum radios. Analog and digital signals can be transmitted up to 20 miles point-to-point without a license.

The SRTU-121 is designed with our "Simple RTU" board. The SRTU-121 transmits analog and digital data in both directions. In the event of a communication failure, it provides a communication failure output at each end of the loop. The SRTU-121 is expandable up to 16 digital inputs, 16 digital outputs, 4 analog inputs, and 4 analog outputs.


The basic unit transmits to its companion unit:

  • Six digital inputs and
  • Two 4-20 mA analog inputs

receiving in return:

  • Four digital outputs,
  • Two high current relay outputs, and
  • Two 4-20 mA isolated analog outputs


  • Low cost
  • Low power
  • Expandable
  • 12 bit A/D and D/A converters
  • 12 A relay outputs
  • Industrial temperature rating
  • Non licensed spread spectrum radio
  • MODBUS protocol


  • Wire line replacement
  • Water well monitoring/control
  • Lift station monitoring/control
  • Pressure reducing valve control
  • Point to multi-point SCADA systems
  • Pump control systems
  • Irrigation monitoring/control
  • Wireless 4-20 mA loops
  • Waste water plants


  • RPM: 110 VAC / 12 VDC battery backed power supply
  • DC24: 12 VDC /24 VDC @ 200 mA converter for 24 VDC analog loop supply
  • SRAO-2: Two 12-bit isolated analog out
  • EXP-164: 16 digital inputs, 16 digital outputs, 4 analog inputs, 4 analog outputs expansion module
  • DIF-16: 16 digital input field terminal board
  • PRO-8: 8 relay output board
  • SP1210: 12 V @ 10 AH per day solar supply with 5 days backup
  • SROAM 1200 bps, RS-232 radio modem for use with licensed analog radios
  • Radios: Spread spectrum 902-928 MHz 1 watt; range up to 20 miles with high gain antennas; UHF/VHF data radios quoted by application.
  • Antennas: Contact factory for available options.


Enclosure: 12" x 10" x 6" NEMA 4X, 13.3" x 11.29" x 5.58" actual
Operating temperature: -40 to +140 deg. F (-40 to +60 deg. C)
Power requirements
Typical: 30 VA @ 110 VAC, less than 5 W at 12 VDC
Digital Inputs: Six optically isolated (12 VDC @ 10 mA)
Digital Outputs: Four optically isolated 100 mA driver outputs
Relay Outputs: Two 12 A resistive @ 120 VAC form A
Analog Inputs: Two 12-bit 4-20 mA
Analog Outputs: Two 12-bit (isolated 4-20 mA) optional
Expansion I/O: 16 digital inputs, 16 digital relay outputs, 4 12-bit 4-20 mA A/Ds, 4 12-bit (isolated 4-20 mA) D/As
Ports: One RS-232/RS-485 port for communication
One RS-232 port for configuration
Protocol: MODBUS RTU
Type: Spread spectrum 2.4 GHz frequency hopping 10 to 600 mW standard
Range: Up to 1.5 miles with 4 dBi Omni; up to 10 miles with high gain antennas