7700 MultiFrame Manual
7707IT Multi-Channel Intercom Fiber Transceiver
Page - 20
Revision 1.7
To cancel interfering audio signals, a null value is applied. Party-line nulling is digitally controlled but
implemented in the analog domain. This unique design allows the 7707IT to automatically self-calibrate
the nulling value. The self-calibration procedure is similar to manual methods commonly used in the
industry, but is performed automatically. Automatic null adjustment results in an accurate calibration in a
much shorter period of time than by manual means.
The self-calibration feature of the 7707IT requires that all other intercom devices be connected and
powered, but that none are actively being used to communicate audio. The 7707IT will apply an audio
test signal to the system, and automatically adjust its null value for accurate cancellation. Other intercom
devices will receive this test signal, but must not apply an output signal to the system. Automatic
calibration is completed in approximately 5 seconds. Interference from another intercom device will be
indicated on the card edge display, and will result in the factory default calibration value being selected.
CTRL
To initiate the self-calibration procedure, select the
CTRL
menu item in
menu level 1. The 7707IT accommodates independent configuration of
each channel. Use the toggle switch to choose the channel to which the
calibration will be applied and press the pushbutton to apply the displayed
selection.
CH01
to
CH08:
Range of Independent channels for the 7707IT-8.
CH01
to
CH03:
Range of Independent channels for the 7707IT-3.
Use the toggle switch to then select the
Null
menu item and press the
pushbutton to initiate the self-calibration procedure. Approximately 5
seconds after initiating the self-calibration procedure, one of the following
messages will be displayed:
DONE:
Calibration completed successfully.
FAIL:
Interference detected, or load impedance is beyond
calibration range. Check other devices. Default
calibration value applied.
Provided that the calibration is completed successfully, and the
DONE
indication is present on the display, the user may then press the pushbutton
to return to menu level 3. Selection of this automatic calibration value is the
normal case. While the
DONE
or
FAIL
messages are shown in the display,
the toggle switch can be used to manually adjust the calibration value up or
down. Press the pushbutton to apply the displayed value and return to
menu level 3.
0000
to
1024:
Range of manually adjustable calibration values.
Manual adjustment is intended as a tool for factory
test and debug.
The factory default applies a party-line null configuration value of
305
.
Changing the interface profile will restore the factory default threshold value
for the respective channel(s).
CH01 to CH03 or
CH08
NULL
DONE
FAIL
