RAD SRM-8H High Speed Short Range Modem  

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RAD SRM-8H High Speed Short Range Modem    


The SRM-8H, High Speed Short Range Modem, is used for local data distribution, connecting full duplex Sync or Async DTEs, computers or controllers over unconditioned 4-wire dedicated lines. SRM-8H operates at data rates of 56 or 64 kbps, at distances up to 10 km (6 miles), according to the wire gauge and data rate.
  • Four models are available:
    • SRM-8H/V.24, with V.24/RS-232 interface
    • SRM-8H/V.35, with V.35 interface
    • SRM-8H/X.21, with X.21 interface
    • SRM-8H/530, with RS-530 interface.

    Each model has a 25-pin D-type connector for the DTE interface. V.35 interface: a 45 cm (17.7") cable is supplied, with a 25-pin, female connector on one side and a 34-pin, male or female connector on the other side.X.21 interface: a 45 cm (17.7") cable is supplied, with a 25-pin male connector on one side, and a 15-pin X.21, male or female connector on the other side.

  • Four LED indicators are available to facilitate diagnostics: Power, Test, Data Carrier Detect and Transmit Data.
  • Transmit timing is provided via three sources: an internal oscillator, an external clock or a loopback clock derived from the receive signal. For the X.21 interface, transmit timing can be either via internal clock or recovered from the line.
  • The modem's carrier is strap-selectable for either continuous operation, or switched operation for passing control signals end-to-end. Switched operation is controlled by the RTS signal.
  • SRM-8H performs diagnostic loops in compliance with the ITU V.54 standard. Two V.54 loops are available: local analog loop (V.54, loop 3) and remote digital loop (V.54, loop 2). The loops are activated by a 3-position switch in all models, or by the DTE interface Circuit 141 (Pin 18) and Circuit 140 (Pin 21) in all models except SRM-8H/X.21. The Test LED lights when any diagnostic loop is active.
  • The low transmit level minimizes crosstalk onto adjacent circuits within the same cable. Data is transmitted and received using a balanced interface, ensuring high immunity to circuit noise. Additionally, SRM-8H is coupled to the dedicated line through isolation transformers which, in conjunction with other circuitry, protect against AC or DC overvoltages.
  • The line interface consists of two independent connectors: a 5-screw terminal block, and a selectable RJ-11 or RJ-45 connector (see Ordering).
  • Power is supplied from a standard, wall-mounted power supply, 300 mA (center - positive; sleeve - negative).
  • SRM-8H is also available as a card for mounting in a 19" modem rack (see CMN-16 card, CMN-C8H data sheet


  • Synchronous or Asynchronous
  • Data rates of 56 or 64 kbps, selectable
  • V.54 diagnostics, including local and remote test
  • Internal, external or receive clock
  • Transmission range up to 10 km (6 miles)
  • Controlled or continuous carrier
  • Isolation transformers
  • V.35, V.24/RS-232, X.21 or RS-530 interfaces
  • LED indicators
  • Miniature, lightweight, easy to install
  • Operates with an external, wall-mounted power supply


High Speed Short Range Modem

* Specify:
V24 for V.24 interface
V35M for V.35 interface, male connector
V35F for V.35 interface, female connector
X21M for X.21 interface, male connector
X21F for X.21 interface, female connector
530 for RS-530 interface
# Specify line connector:
RJ11 for RJ-11 jack
RJ45 for RJ-45 jack
(Terminal block provided with all models)

Wall-mounted 9 VDC / 230 VAC power supply

Wall-mounted 9 VDC / 115 VAC power supply

For ordering information on the card version for the CMN-16 rack, see the CMN-C8H.




RAD Products

For discount pricing on RAD Data Communications
email us at sales@data-connect.com
or call 301-924-7400