RAD SRM-5AC Asynchronous Multipoint Short Range Modems

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RAD SRM-5AC Asynchronous Multipoint Short Range Modems


The SRM-5AC, Asynchronous Short Range Modem, is used for local data distribution, connecting full or half duplex asynchronous DTEs to DTEs operating over unconditioned 4-wire lines (two twisted pairs). SRM-5AC ensures integrity of data transmission for distances up to 6.8 km (4.1 miles), depending on wire gauge.
  • SRM-5AC is equipped with an internal filter for high noise immunity. The internal filter overcomes both radiated and conducted interference, and is recommended for noisy environments, such as industrial locations.
  • SRM-5AC features a switch-selectable DTE/DCE interface, and a switch-selectable Printer Support Mode. It also features strap selection for carrier constantly on or controlled
    • When set to DCE, the modem carrier can be strapped to be constantly on, or controlled by the RTS signal (Circuit 105). Operation with controlled carrier enables connection of SRM-5AC in a multipoint configuration. Controlled carrier can also be used in applications requiring passing of a control signal end-to-end (RTS on one SRM-5AC is passed to DCD on the other unit). SRM-5AC also contains a LED to indicate carrier detection.
    • When set to DTE, SRM-5AC operates as a DTE for connection to DCE (such as a multiplexer port), without the use of a cross cable.
    • When set to Printer Support Mode, SRM-5AC supports printer flow control by transmitting DTR on the printer side (busy signal) to CTS on the other side. As a result, CTS at the computer side will drop when the printer becomes busy.
  • Innovative circuitry allows SRM-5AC to operate without connection to the mains supply by using ultra-low power from the data and control signals. The modem will operate even if only TD (Circuit 103), RD (Circuit 104) and RTS (Circuit 105) are connected.
  • The low transmit level minimizes cross talk onto adjacent circuits within the same cable. Data is transmitted and received using a balanced interface, ensuring high immunity to circuit noise.
  • SRM-5AC is coupled to the line through isolation transformers, which, in conjunction with additional circuitry, protect against AC or DC overvoltages. As the transformers are rated at over 1,500V RMS, the modem is suitable for connection to local circuits provided by most national telephone administrations.
  • Two connectors are available for connection to the line: a five-screw terminal block, and a modular socket for either RJ-12 or RJ-45 (see Ordering).
    Note: RJ-12 is an RJ-11 connector with Pins 1 and 6 grounded.
  • SRM-5AC is fully compatible with SRM-6AC and SRM-6ACU. Additionally, it is compatible with CMN-C6AC and CMN-C6ACU cards for mounting in the CMN-16 modem rack.



  • Asynchronous, full or half duplex
  • Data rates up to 19.2 kbps
  • Point-to-point or multipoint
  • Transmission range up to 6.8 km(4.1 miles)
  • DCE/DTE mode
  • Transformer isolated
  • No AC power required
  • Internal filter for high noise immunity and for surge protection
  • LED indicator for carrier detection

Asynchronous Short Range Modem

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





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