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Interconnection circuits between this modem and any other equipment should be such that the equipment
continues to comply with the requirements of clause 4.2 of EN41003 for TNV (Telephone Network Voltage)
circuits and clause 2.3 of EN60950 for SELV (Safety Extra Low Voltage) circuits after making connection
between circuits.
The power supply must be properly connected and switched on before the modem will work correctly.
Ringer Equivalence Number
The Ringer Equivalence Number (REN) is a customer guide indicating approximately the maximum number of
items of apparatus that should be connected simultaneously to the telephone line. The sum of the RENs should
not exceed 4. This value includes any BT provided instrument which may be assumed to have an REN of 1
unless marked otherwise. The REN of the 3900 Series modems is 3.
Connection to Leased Lines
This modem is suitable for connection to BT circuits with signalling at a nominal frequency of 2280 Hz and
may be connected to multipoint or point-to-point circuits. This apparatus does not require signalling or
otherwise use the frequency range 0 –200 Hz.
No d.c. interaction is intended between the modem and the B.T. network.
This apparatus may be directly connected to a speechband circuit or connected to relevant branch system for
speechband circuits.
Receive-to-Transmit Loss (RTL)
The RTL measurement provides an indication of the signal attenuation between the receive pair and transmit
pair of a four-wire circuit. The RTL number for the 3900 Series modems is 75.
The sum of the RTL numbers of terminal apparatus at opposite ends of a particular point-to-point circuit shall
be equal to or greater than 28; and in the case of apparatus permitted connection before 5 August 1984 it shall
be assumed for the purpose of this calculation to have an RTL number of 14 unless it has been tested and
specially allocated a number other than this.
Apparatus having an RTL number greater than 47 must be used to terminate the distant end of this circuit.
Failure to do so is a breach of the conditions of approval of this apparatus.
Connection Arrangements
If any other apparatus, including cable or wiring, is connected between this apparatus and the point of
connection to any speechband circuit, then all that other apparatus shall comply with the following:
1. The overall transmission characteristics of all that other apparatus shall be such as to introduce no
material effect upon the electrical conditions presented to one another by the apparatus and the
speechband circuit; and
2. All that other apparatus shall comprise only:
(i) apparatus approved for the purpose of connection between the apparatus and a speechband circuit;
and
(ii) cable or wiring complying with a code of practice for the installation of equipment covered by this
part of BS6328 or such other requirements as may be applicable.
