RAD SRM-5A SRM-5D Asynchronous Short Range Modems

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RAD SRM-5A SRM-5D Asynchronous Short Range Modems 


  • SRM-5A and SRM-5D are Miniature Asynchronous Short Range Modems for local data distribution, connecting full duplex asynchronous DTEs to computers.
  • SRM-5A and SRM-5D operate at distances up to 12 km (7.5 miles) and 27.5 km (17 miles), respectively, depending on the wire gauge and data rate
    (see Table 1). Both modems ensure integrity of data transmission, using unconditioned 4-wire dedicated lines at data rates up to 19.2 kbps. An internal filter overcomes both radiated and conducted noise, and provides surge protection.
  • Innovative circuitry allows the modems to operate without connection to the mains supply, by using ultra low power from the V.24/RS-232 data and control signals. The modems will operate even if only Transmit Data is connected, i.e. without any control signals. Both positive and negative signals are generated, irrespective of constantly high or constantly low Transmit Data.
  • The low transmit level minimizes crosstalk onto adjacent circuits within the same cable. Data is transmitted and received at a balanced interface, ensuring high immunity to circuit noise.
  • SRM-5A and 5D feature a switch-selectable DCE/DTE option. This allows the modems to operate as DTE for connection to a DCE (such as a multiplexer port) without the need for a cross cable.
  • The SRM-5A model is coupled to the dedicated line via isolation transformers rated at over 1,500 VRMS. The transformers, together with other circuitry, protect against AC or DC overvoltages. This makes SRM-5A suitable for connection to local circuits provided by most national telephone administrations (P.T.T.s).
  • Two connectors are provided for the line interface: a five-screw terminal block, and either an RJ-45 or RJ-12 connector
    (see Ordering).

    Note: RJ-12 is an RJ-11 connector with pins 1 and 6 grounded.


  • Asynchronous transmission rate up to 19.2 kbps
  • Transmission range:
    SRM-5A: up to 12 km (7.5 miles)
    SRM-5D: up to 27.5 km (17 miles)
  • No AC power required
  • Transformer isolated (SRM-5A only)
  • V.24/RS-232-C interface
  • Compact, lightweight, easy to install



Async Short Range Modem, transformer isolated


Async Short Range Modem

* Specify:
F for female 25-pin connector
M for male 25-pin connector
+ Specify line interface:
RJ-12 for RJ-12 and terminal block connectors
RJ-45 for RJ-45 and terminal block connectors
(Default is RJ-45 and terminal block connectors)





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