SRM3A from RAD
The SRM-3A ( SRM3A/F SRM3A/M ) from RAD, ultra-miniature async, transformer isolated Short Range Modem, is used for local data distribution, connecting full duplex asynchronous DTEs to computers. SRM-3A
( SRM3A/F SRM3A/M ) ensures integrity of data transmission, using unconditioned 4-wire dedicated lines at data rates up to 19.2 kbps. It operates over distances up to 13 km (8 miles) depending on wire gauge and data rate (see Table 1).
SRM-3A ( SRM3A/F SRM3A/M ) connector is 9-pin D-type. This connector, as well as the ultra-miniature size of SRM-3A, make it an excellent choice for computers such as Unisys U6000/50 and U7000/52 or IBM PC/AT.
SRM-3A is compatible with SRM-5A and SRM-6A, thus enabling connection of equipment using a 9-pin connector to equipment using a 25-pin connector (see Figures 1 and 2).
The low transmit level minimizes crosstalk onto adjacent circuits within the same cable. Data is transmitted and received at a balanced impedance, ensuring excellent immunity to circuit noise.
The modem incorporates innovative circuitry design, which enables the unit to operate without connection to the mains supply, by using ultra low power from the standard EIA RS-232-C/ITU V.24 data and control signal voltages. The modem operates fully even if only Transmit Data is connected (i.e. without the DTE sending Request to Send or Data Terminal Ready signals). Both positive and negative signals are generated in compliance with EIA RS-232-C/ITU V.24 standards, regardless of constantly high or constantly low Transmit Data.
SRM-3A ( SRM3A/F SRM3A/M ) is coupled to the dedicated line through isolation transformers which, in conjunction with electronic circuitry, protect against AC or DC overvoltages. As the transformers are rated at over 1,500 VRMS, SRM-3A modems are suitable for connection to local circuits provided by most national telephone administrations (P.T.T.s).
The line side of the SRM-3A ( SRM3A/F SRM3A/M ) offers connection to ground of the RS-232-C plug. This may be connected to the shield of the STP wiring to provide end-to-end ground continuity.
SRM-3A ( SRM3A/F SRM3A/M) data sheet and installation information
(pdf 491)
