Nortel Networks 553-3001-211 manual Termination transmission characteristics

NT1R20 Off-Premise Station Analog Line card Page 179 of 894

The overall range achievable on an OPS line facility is limited by the signaling range (2300 ohms loop including telephone set resistance). The signaling range is unaffected by gain treatment; thus, gain treatment can be used to extend the voice range to the limit of the signaling range. For example, on 26 AWG wire, the signaling range of 2300 ohms corresponds to an untreated metallic loop loss of 15 dB. Gain treatment (such as a VFR) with

10.5dB of gain would maintain the OPS service loss objective of 4.5 dB while extending the voice range to the full limit of the signaling range.

	15.0 dB	(loss corresponding to the maximum signaling range)
–	4.5 dB	(OPS service loss objective)
=	10.5 dB	(required gain treatment)

The use of dial long line units to extend signaling range of OPS analog line cards beyond 15 dB is not recommended.

Termination transmission characteristics

The loss plan for OPS connections is designed so that a connection with an OPS termination provides satisfactory end-to-end listener volume when the OPS termination is a standard telephone. The listener volume at the distant end depends on the OPS termination transmit loudness characteristics; the volume at the OPS termination end depends on the OPS termination receive loudness characteristics.

A feature of many (though not all) standard telephones is that the loudness increases with decreased current. Thus, as the line (PBX to OPS termination) facility gets longer and loss increases, the increased loudness of the telephone somewhat compensates for the higher loss, assuming direct current feed from the PBX with constant voltage at the feeding bridge. However, this compensation is not available when:

•the termination is a non-compensating telephone

•the OPS port is served by a line card using a constant-current feeding bridge

•the OPS termination is to telephones behind a local switch providing local current feed, such as a fax machine or a key telephone system

Circuit Card Description and Installation