ZETRON 748, Техническое руководство

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Installation
14 025-9368H
handheld, measure the Touch-Tone deviation before continuing. Measure the transmitter
audio with a service monitor and adjust R59 for unity gain (3 kHz in = 3 kHz out) through
the repeat path. This completes the adjustment of R59.
If using internal COR, it should now be re-adjusted as outlined in “Installation Procedure,”
step 7, earlier in this section.
Using a computer or terminal:
Press ENTER to leave the repeat audio adjust test.
Using a DTMF telephone:
Press “#” to leave the test mode.
6. TELEPHONE ADJUSTMENTS: The transmit and receive levels to and from the telco circuit
are factory set and should not be adjusted. Proper setup for unity gain through the repeat path
(steps 2, 4 and 5) will result in proper levels with the telco circuit.
The Model 748 Telco output levels for regenerated DTMF, modem tones and call progress tones
are fixed and cannot be adjusted. The audio from the receiver is factory set for proper levels into
the phone line and should not require adjustment. With R115 (PHONE TX) set at 12:00 (mid-
point), 60% deviation on the receive channel (375mVrms at TP4) should produce -10.5dBm
signal level into the telco circuit.
The Telco input level is also set at the factory so that a -20.0dBm receive signal level from the
telco circuit will produce 60% deviation on the transmit channel. The AGC circuit used by the
Model 748 for phone input will compensate for any low levels experienced on the phone lines.
7. DIAL TONE DETECTOR ADJUST: The dial tone detector is factory preset to 440 Hz and in
most systems should not need to be adjusted. R119 (DTONE) is used to adjust the frequency of
the detect circuit. The Dial Tone Detect LED DS1 will light upon detection of any dial tone and
can be used to adjust R119 if needed.
8. HYBRID BALANCE ADJUSTMENT: This purpose of this adjustment is to balance or match
the impedance of Model 748 to the phone circuit to which it will be connected. This is to adjust
for maximum return loss (minimize reflected signal) of the transmit and receive audio signals.
How well the modem works is directly dependent on this adjustment. This must be done at the
site on the phone circuit with which the Model 748 will be used.
To perform this test requires establishing a telephone connection through the local Central
Office. The Model 748 provides two ways of accomplishing this, answering an incoming call
and starting the test or taking in a phone number, dialing it and starting the test. The Model 748
then generates 400 Hz, 1000 Hz and 2225 Hz into the phone line, keys the transmitter and opens
the audio path from the telco to the transmitter. Caution the person at the other end to protect
their ears, this tone is loud!
Using a computer or terminal:
Select the “Hybrid balance adjust” by typing “8” followed by
ENTER
. The Model 748 will