Medias Mediatrix 1204, Справочное руководство

Страница: 338 / 390

Appendix D - Country-Specific Parameters Definitions
312 Mediatrix 1204
Input Impedance
Impedance of the Mediatrix 1204 at the Tip and Ring wires.
Terminal Balance Return Loss (TBRL) Impedance
Balance return loss attributable to transmission loss between two points. It is used to characterize an
impedance balancing property of the 2-wire analog equipment port.
Each country has its own definition of the TBRL value. For instance, in North America, TIA/EIA 464 (and TIA/
EIA 912) define two TBRL values:
600
Ω
for “on-premise” or short loop ports.
350
Ω
+ (1000
Ω
|| 21 nF) for “off-premise” or long loop ports.
A wire length above 2.5 km is considered long loop according to TIA/EIA 912 section 6.4 (7)(b)).
In Europe, ETSI 300 439 also mentions a TBRL value. However, most European countries have different
requirements regarding the TBRL Impedance. This is also true for other countries around the world. Each one
of them has different requirements.
Line Attenuation
Values are given in dBr (deciBel relative):
A “+” for input means that the digital side is attenuated by x decibels relative to the analog side.
A “+” for output means that the analog side is amplified by x decibels relative to the digital side.
A “-” for input means that the digital side is amplified by x decibels relative to the analog side.
A “-” for output means that the analog side is attenuated by x decibels relative to the digital side.
On-Off Sequences
Values in bold are “on” cycles, where tones are audible. Values in normal style are “off” cycles, where tones
are not audible. When not otherwise specified, sequences repeat forever. A “x” symbol means that the
sequences between parenthesis is repeated x times. The next cycle(s) repeat forever, unless otherwise
specified. Values are in seconds.
For instance:
3*( 0.1 – 0.1) then 0.6 – 1.0 - 0.2 – 0.2
means that the 0.1s on and 0.1s off sequence is repeated 3 times, afterwards the 0.6s on, 1.0s off, 0.2s on
and 0.2s off sequence repeats forever.