RAD SRM-5TX SRM-5SX Async/Sync 2-Wire Short Range Modems   

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RAD SRM-5TX SRM-5SX Async/Sync 2-Wire Short Range Modems    


  • SRM-5TX and SRM-6TX, Asynchronous 2-wire Short Range Modems, are used for local data distribution, connecting asynchronous V.24 digital equipment. The modems operate full duplex over existing 2-wire single twisted pairs or coax cables at data rates up to 19.2 kbps, over a range of 1 km (0.6 miles).
  • SRM-5TX and SRM-6TX are fully compatible with each other and offer the same features. SRM-5TX is smaller, only 69 mm (2.7 in) by 18 mm (0.7 in); SRM-6TX is 110 mm (4.3 in) by 22 mm (0.9 in).
  • SRM-5TX and SRM-6TX are also available as cards for mounting in a 19'' modem rack (see the CMN-16 and CMN-C6TX data sheets).
  • The transmit carrier is strap-selectable for either continuous operation or switched operation. The switched carrier operation enables transfer of one control signal end-to-end, making the modem suitable for connection to printers and statistical multiplexers. When in switched carrier operation, the carrier is controlled by the DTR signal (Circuit 108/2) and transferred to the DSR signal (Circuit 107) in the opposite modem. The DCD signal (Circuit 109) remains ON, regardless of the transmit carrier strapping. A LED indicator lights on SRM-5TX, whenever DSR is present.
  • Innovative circuitry allows SRM-5TX and SRM-6TX to operate without connection to the mains supply, by using ultra-low power from the data and control signals.
  • Coupling to the twisted pair line is done via isolation transformers which, in conjunction with other circuitry, protect against AC or DC overvoltages.
  • The low transmit level of the modems minimizes crosstalk onto adjacent circuits within the same cable.
  • The modems are available with a male or female integral 25-pin connector for the DTE interface, and a 3-screw (2-wire and ground) terminal block for the line. SRM-6TX is available with an RJ-11 connector, an RJ-45 connector or a female BNC on a pig-tail.SRM-5TX comes with a choice of RJ-12 or RJ-45 connector (see Ordering), in addition to the terminal block.

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


  • Transmission data rates up to 19.2 kbps, asynchronous
  • Transmission range up to 1 km (0.6 miles) over 19 AWG
  • Full duplex operation over single twisted pair or coax cable
  • One control signal transferred end-to-end
  • Transformer isolated
  • V.24/RS-232 interface
  • LED indicator (SRM-5TX only)
  • Available as a card for 19" modem rack
  • No AC power required
  • Compact, lightweight, easy to install

Asynchronous 2-wire Short Range Modem,Sub-miniature

Asynchronous 2-wire Short Range Modem

* Specify DTE interface:
F for female connector
M for male connector
+ Specify line interface for SRM-5TX:
RJ-12 for integral RJ-12 jack and terminal block
RJ-45 for integral RJ-45 jack and terminal block
(Default is terminal block and RJ-45 connector.)
# Specify line interface for SRM-6TX:
RJ-11 for integral RJ-11 jack
RJ-45 for integral RJ-45 jack
CX for female BNC connector on short cable
(Default is terminal block.)





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