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DETAILED
PROCEDURES
Adjusting VF
Signal Levels
This section contains information to allow you to adjust the voice levels
of the circuit. If the terms which are used in this section are unfamiliar,
refer to the detailed explanations of these terms which are provided
earlier in this appendix.
PBXs or Telephones
When the TLP is unknown, it must be determined. If the TLP levels
from/to the PBX are known, set the CELP accordingly (see Section 3).
If a 4-wire PBX is being used, and it delivers –16 dBm transmit power,
then the transmit interface is –16 dBm. Set the CELP transmit to expect
–16 dBm accordingly. Note that selecting a –16 dBm transmit level into
the CELP puts a 16 dB amplifier into the transmit path. Consequently,
carelessly selecting the –16 dB setting creates the danger of overloading
the transmit CODEC in the CELP.
•
If a test tone (usually 1004 KHz) is available from the PBX then use
the tone to set up the levels.
•
Always set up levels starting at the talker end and work your way to-
ward the listener end.
•
Set up the CELP to accept whatever level is coming in from the PBX.
•
When measuring the level, always use the CELP as the load and use
the meter in "Bridged'' mode.
•
Make measurements from the DMARC block or DB25 on multiplexer.
•
It is always preferable to set the CELP to 0 dBm rather than to any
other value.
If TLP information is not available or the test tone cannot be passed by
the termination equipment for some reason, then the levels must be ad-
justed using a "voice'' method (again starting at the talker end). When
using the voice method, it should be noted that short term peak power in a
normal VF signal measured approximately 15 dB greater than the peak
power as measured with a moving coil dBm meter (such as the Electro-
data VF Monitor). With the CELP expecting 0 dBm input the actual short
term peak power into TIP and RING should not exceed 0 dBm.
When a loud talker is speaking on the phone, then you should measure
no more than –15 dBm peak voice power going into the CELP transmit in-
put.
When using tones or the voice method, you should measure the VF signal
power on TIP and RING going into the CELP using a meter in BRIDGED
or HIGH IMPEDANCE mode.
If the receiving phone is a 4-wire phone, you should be able to adjust the
receive level for a comfortable listening level.
If the receiving phone is a regular 2-wire phone with hybrid arrange-
ment, then you should be able to adjust the hybrid for zero insertion loss
in each direction. If the hybrid is passive (with no gain sections) then you
APPENDIX D
D-11
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