Nortel Networks Circuit Card - Manual (Page 181)

NT1R20 Off-Premise Station Analog Line card Page 181 of 906
Circuit Card Description and Installation
The overall range achievable on an OPS line facility is limited by the
signaling range (2300 ohms loop including telephone 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
10.5 dB 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.
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
15.0 dB (loss corresponding to the maximum signaling range)
– 4.5 dB (OPS service loss objective)
= 10.5 dB (required gain treatment)