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  • Extends RS-232/485 links over radio network
  • Transfer rates over VHF/UHF FM radio channel up to 16000 bps
  • Can be connected to external radio
  • HDLC frames featuring addressing and routing
  • Fieldbus protocols support
  • AT command set



PRM III is series of packet radio modems intended for data transfer over VHF or UHF FM radio channels utilizing external or internal radio transceiver, still enabling voice transfer option. Data transfer through radio channel uses HDLC frames and effective error detection and correction algorithm, and line coding as well. These features make radio channel reliable, secure and transparent digital link for transferring asynchronous data of any format. Transfer rates in channel are: 1200, 2400 bps with FFSK modulation, 4800, 9600, 8000, 16000 bps with GMSK modulation. Built-in network protocol enables addressing of up to 127 modem units in the network, while routing technique enables digipeating over 8 units in a chain, thus significantly extending effectual cover range. Hayes AT command set provides standard command interface for mode configuration and control via RS-232 serial interface. Fieldbus oriented operating modes supports transparent transfer for number of industrial protocols: Modbus, IEC-60870-5, DirectNET, etc.


Packet radio modem is optimal communication solution for:

  • Interconnecting distant sites without cable infrastructure;
  • Stable communication insensitive on congestions and interuptions;
  • Reliable transfer of small amount of measuring-control data;
  • Low exploations costs;
  • Simple system extension. It is used:
  • In telemetry (hydrology, meteorology, ecology, etc.)
  • For remote monitoring and control (power utilities, water supplying systems, etc.)
  • In alarm systems
  • File transfer between remote terminals (reports, daily logs, etc.)

Best conditions of delivery and payment, as well as dealer discounts, can be obtained from our Sales Department. E-mail contact: This e-mail address is being protected from spambots. You need JavaScript enabled to view it

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Serial Interface
Connector DB9F (female), RS-232C, DCE
Data rates 1200, 2400, 4800, 9600, 19200, 38400 bps
Format 8N1, 8E1, 8O1
Flow control Hardware, RTS/CTS
Command interface Hayes AT command set
Radio Network Interface
Speed & Modulation 1200, 2400 bps (FFSK);4800, 9600 bps (GMSK 0.5); 8000,16000 bps (GMSK 0.3)
Medium access CSMA/CA
Packet format HDLC
Line coding NRZI
Error detection CRC16 CCITT
Error correction ARQ (acks & retransmissions), window size 1
Addressing 127 addresses in network, with routing feature
Digipeating "Store & Forward" over up to 8 digipiters
Packet send criteria
Character number Fixed: 255 (CO), 495 (FO & FO/R)
Specific character Adjustable: 0-255 (ASCII character code)
Time Adjustable: (0-255) x 20ms
Operating modes
Connection Oriented CO: dial-up connection; packet acknowledgement; error detection and correction (ARQ); automatic connection over predefined route option.
Fieldbus Oriented FO: transparent packet broadcast to predefined route; error detection and bad packet rejection.
Fieldbus Oriented with Routing FO/R: fieldbus packet routing according to fieldbus address and routing table; error detection and bad packet rejection.
Supported protocols IEC-60870-5, Modbus, DirectNET, K-Sequence (Koyo), HostLink (Omron), and other industrial protocols.
External radio
Connector DB9M (male)
Consumption ≤50mA
Audio output level 420mVpp (internally adjustable 30mVpp-3Vpp) at 600Ω
Audio input sensitivity 2.8Vpp (internally adjustable 90mVpp-5Vpp) at 10KΩ
Transmission activation output Transistor collector, max. 20V and 30mA.
Input level for busy channel indication ≥2V at 10KΩ
Internal radio
Frequency range 403-434 MHz or 450-480 MHz
Channel bandwidth 12.5 or 25 kHz
Channel step 6.25 or 10 kHz
Frequency control Syntetisator
Frequency stability 1.5 ppm
Receive/Transmit transition ≤10msec
Output transmission power 2W (+33dBm)
"Spurious" and "Harmonic FM" ≤ -20dBm
Transmitter stability Preserved up to 10:1 VSWR
Receiver sensitivity @ 10-5 BER -116dBm
Selectivity ≤60dBm
Antenna connector Female TNC
Antenna impendence 50Ω
Consumption Reception ≤100mA, transmission ≤1.6A
Power Supply 10-16 VDC
Power Supply connector 2-pol jack
Connector for external microphone (optional) RJ-45
Operating temperature -30°C to +60°C
Storage temperature -40°C to +85°C
Humidity 95% maximum RH at 40°C, non-condensating
Case Aluminum profile
Dimensions 112 x 30 x 165 mm