RAD SRM-5SX SRM-6SX Sync 2-Wire Short Range Modems  

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RAD SRM-5SX SRM-6SX Sync 2-Wire Short Range Modems   


SRM-5SX and SRM-6SX, Synchronous 2-wire Short Range Modems, are used for local data distribution, connecting full duplex synchronous terminals to computers. A pair of modems ensures integrity of data transmission over 2-wire dedicated lines, for distances up to 1.3 km (0.8 miles), depending on wire gauge and data rate.
  • SRM-5SX and SRM-6SX are fully compatible and offer the same features. SRM-5SX is the ultraminiature version, only 61 mm (2.4 in) by 18 mm (0.7 in); SRM-6SX is 110 mm (4.3 in) by 22 mm (0.9 in).
  • Transmit timing can be provided by an internal, external or loopback clock derived from the receive signal.
  • Innovative circuitry allows SRM-5SX and SRM-6SX to operate without connection to the main supply, by using ultra low power from the data and control signals. For optimum operation, devices connected to SRM-5SX and SRM-6SX should provide RTS (Circuit 105) and DTR (Circuit 108.2) signals.
  • The low transmit level minimizes crosstalk on adjacent circuits within the same cable. Data is transmitted and received using a balanced signal, ensuring high immunity to circuit noise.
  • Coupling to the dedicated line is through isolation transformers which, in conjunction with other circuitry, protect against AC or DC overvoltages. The transformers are rated at over 1500V RMS, enabling the connection of the modems to local circuits provided by most national telephone administrations (P.T.T.s).
  • The line interface for SRM-5SX is a three-screw terminal block, and either an RJ-12 or an RJ-45 connector. The line interface for SRM-6SX is a three-screw terminal block, RJ-11 or RJ-45 connector. Optionally, SRM-6SX can be ordered with BNC female connector on a short cable (see Ordering).

Note: RJ-12 is a 6-pin RJ-11 connector with ground on pins 1 and 6.


  • Full duplex over single twisted pair or coax
  • Transmission data rate up to 19.2 kbps, synchronous
  • Transmission range up to 1.3 km (0.8 miles)
  • Internal, external, or loopback clock
  • Transformer isolated
  • LED indicator for carrier detection (SRM-5SX only)
  • No AC power required
  • Compact, lightweight, easy to install

Synchronous 2-wire Short Range Modem, Sub-miniature

Synchronous 2-wire Short Range Modem

* Specify DTE interface:
F for 25-pin, female connector
M for 25-pin, male connector
# Specify line interface for SRM-5SX:
RJ12 for integral RJ-12 jack and terminal block
RJ45 for integral RJ-45 jack and terminal block
+ Specify line interface for SRM-6SX:
RJ11 for integral RJ-11 jack
RJ45 for integral RJ-45 jack
(Default is terminal block)
& Specify
CX for female BNC coax connector on short cable in place of terminal block.





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