Nulling - Pliant Crewcom CCU-22 Operating Manual

Nulling

In order to minimize echo resulting from connection to an external 2-Wire system, it is necessary to optimize the
hardware of the hybrid circuitry in the Control Unit (CU) to match line impedance. CrewCom provides a user-initiated
Auto Null feature that automatically optimizes the 2-Wire interface. Nulling only impacts 2-Wire hard wired intercom
connections. Auto Null sends a series of tones to each of the 2-Wire intercom channel connections. Activate Auto Null
for new connections or whenever the 2-Wire system changes, such as when additional non-CrewCom wired Packs
are added or removed, or when cable lengths are changed.
During the nulling process, the CU DSP monitors the echo and adjusts the line characteristics (Resistance, Inductance,
and Capacitance) to optimize the interface to the external 2-Wire system. When Auto Null is initiated, all of the
functions, including communication, of the intercom channel being nulled are interrupted. The nulling process takes
approximately 10–15 seconds per channel. You may need to re-adjust the intercom levels to a proper level after the
2-Wire intercom lines have been nulled.
Optimize 2-Wire port hardware connections by nulling them in order to minimize echo in the physical link and to
enable the software to remove any residual echo. You may null from the Control Unit or from CrewWare.
Auto Null from the CU
During the Auto Null process, the CU LCD will display each 2-Wire port's resistance (R), inductance (L), capacitance
(C) and amplitude.
There are two options for auto nulling your CrewCom system – Null All and Null by Port . The following steps detail
how to initiate the Auto Null process from the CU:
1. Turn off all Talk buttons on wired equipment. Since CrewCom monitors a self-generated tone to adjust the null
characteristics, any sounds entering through the wired intercom system will interfere with the nulling process.
2. On the Control Unit, press Menu to open the main menu.
3. Scroll through the menu options to the Wired Settings and select Auto Null .
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