Nulling

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 CU, press Menu to open the main menu.
3. Scroll through the menu options to the Wired Settings and select Auto Null.
4. Select Null All to start the Auto Null process for all 2-Wire ports of the selected device. Normal functions will be interrupted for about 60 seconds during the Auto Null process (about 15 seconds per channel). An alert will display, asking you to confirm that you want to proceed.
   1. Auto Null with CrewCom will send a mic kill signal to connected AudioCom and RTS wired systems, but not to Clear-Com wired systems. Auto Null operation will mute the audio from CrewCom RPs as it connects to connected wired systems; however, those wireless RPs will still communicate with one another while the null is in progress.

   

   Auto Null in Process

   2. After you confirm to proceed, progress of the null process can be observed on the LCD Display. The display will indicate “Auto Null Complete” once the Auto Null process is completed.
5. If nulling “by port,” you will be prompted to select which ports after confirming your Null by Port selection.
6. Press the Home button to escape to the Home screen or press the Menu button to return to the previous screen.

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 – Auto Null all 2-Wire ports on the Control Unit and Null Port. The following steps detail how to initiate the Auto Null process from CrewWare:

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. In CrewWare, open the CU's Device Management detail view. (See Devices Tab - Control Units for more information.)
3. Click on the Auto Null button at the top of the window to initiate nulling for all 2-Wire ports on the selected Control Unit. Normal functions will be interrupted for about 60 seconds during the Auto Null process (about 15 seconds per channel). An alert will display, asking you to confirm that you want to proceed.
   1. Auto Null with CrewCom will send a mic kill signal to connected AudioCom and RTS wired systems, but not to Clear-Com wired systems. Auto Null operation will mute the audio from CrewCom Radio Packs as it connects to connected wired systems; however, those wireless Radio Packs will still communicate with one another while the null is in progress.
   2. After you confirm that you want to proceed, progress of the null process can be observed on the CU's LCD Display and in CrewWare's "Nulling" panel at the bottom of the CU's detail view. The CU's display will indicate “Auto Null Complete” once the Auto Null process is completed.

      

      CU Screen: Auto Null in Process

      

      CrewWare: Auto Null in Process

4. If nulling “by port,” click the Null Port button under the 2-Wire port you wish to null.

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.