2-Wire (Party-Line) Interface
In 2-Wire intercom systems, inefficiencies in the hybrid circuitry that combine or separate the send and receive audio signalsonto the same pair of wires inherently cause echo. Within analog systems the echo is not noticeable, but when connected to anextremely sensitive digital system, the echo becomes more problematic.
In order to minimize echo resulting from connection to an external 2-Wire system, it is necessary to optimize the hardware of thehybrid circuitry in the Tempest BaseStation. Tempest provides a user initiated AUTO-NULL feature that automatically optimizesthe 2-Wire interface. Nulling only impacts 2-Wire hardwired intercom connections.
2-Wire (Party-Line) Interface2-Wire party-line intercom systems carry one or two (depending on the system type) channels of full duplex intercom audio, plussystem power and other information on a single XLR-3M cable (2 wires and a ground). Each 2-Wire intercom type has a differentwiring scheme and unique line characteristics. It is imperative to have the rear panel connections and the front panel settingsadjusted correctly for audio to pass correctly between the systems.Steps to Configure a 2-Wire Intercom Connection• Adjust the Intercom Type Slide Switches to appropriate manufacturer compatible setting- RTS, Clear-Com, Bal.• Select 2-Wire connection for the appropriate channels.• Make the 3-pin XLR physical connections to the Tempest BaseStation and the 2-Wire system.• Null the system.• Adjust IN/OUT volume levels between the Tempest Wireless System and the 2-Wire system.Always confirm that the 2-Wire intercom system is functioning properly before connecting the Tempest Wireless system.Test each wired communication station before connecting the wireless system. Confirm operation of the wireless systembefore connecting to the wired system.After the slide switch is set correctly, the appropriate channels are set for 2-Wire operation, the XLR cable connections aremade, and power is provided by the 2-Wire system or Master Mode, then audio will pass between Tempest and the wiredsystem.
Audio may develop an echo that is heard in the wireless BeltStations until the system is nulled. The echo should not preventcommunication but is undesirable. The volume levels into or out from Tempest may need adjusting so that relative volumesare the same.
Echo Cancellation MenuIn the BaseStation’s Tech Menu is a selection for “Echo Cancellation” (ECAN). This refers to soft ware that assists in removing echofrom 2-Wire intercom connections. Hardware connections need to be optimized with the null procedure to minimize echo in thephysical link so that the soft ware can remove any residual echo.In the Tech menu, “Echo Cancellation” is “ON” by default, but is only enabled for channels that are selected for operation with a2-Wire intercom and have a physical connection to a 2-Wire system. See “Nulling” Section of this manual.If a 2-Wire intercom is never utilized in a system, ECAN can be turned “OFF” to ensure that it cannot create undesirable effects.This should not be necessary, though, and it is recommended that you keep ECAN “ON” at all times.ECAN is disabled while the BaseStation’s Auto-Null or Manual Null menu screens are active, to ensure that the hardware isoptimized for echo reduction. When ECAN is enabled, it requires up to 10 seconds of active audio to achieve maximum efficiency.Brief loud active audio can help accelerate efficiency.
Auto-Null Explained
Auto-Null sends a tone to each of the 2-Wire intercom channel connections. The Tempest Wireless BaseStation DSP monitors theecho and adjusts the line characteristics (Resistance and Capacitance) to optimize the interface to the external 2-Wire system.When Auto-Null is initiated, all of the functions of the BaseStation including communication are interrupted. The Auto-Nullprocess takes approximately 10 seconds. Intercom levels may need to be adjusted aft er the 2-Wire intercom lines have beennulled.
WARNING: Make sure all the wired belt packs are connected to the wired side and the mics are off. Have the crew remove their headsets. During Auto-Null, wired intercom users will hear the nulling tones and communication willbe interrupted. It is recommended that this feature should be used only during setup andnot during live events.
Auto-Null ProcedureTurn OFF all TALK buttons on both the wired and wireless systems. Since Tempest monitors a self generated tone to adjustthe null characteristics, any sounds entering through either the wired or wireless intercom systems will interfere with thenulling process. When the Auto-Null or Manual Null menu screens are accessed, Tempest sends a Mic Kill signal to allwireless BeltStations, but the wired communication stations will need to be turned OFF individually, or a hardwired MicKill signal will need to be initiated.

• On the Tempest BaseStation press MENU to open the Main Menu. 
  
• Rotate the Volume Control to scroll through the menu options to the “Wired Intercom Settings”
• Select “Auto-Null.” 
• Select “Null Now” to start the Auto-Null process. 

Normal functions will be interrupted for about 10 seconds during the Auto-Null process. Progress of the null process can beobserved on the BaseStation LCD display.The BaseStation display will indicate “Auto-Null Complete” once the Auto-Null process is completed. Press MENU to escapeto the Operational screen.
Activate Auto-Null for new connections or whenever the 2-Wire system changes significantly, such as when additionalwired belt packs are added or removed, or when cable lengths are changed significantly.
Test for EchoTalk into the wireless system for at least 10 seconds to test for echo (SHOUT A LOUD 10 COUNT!) Echo Cancellation (ECAN) software is disabled in the Auto-Null and Manual Null screens to ensure the best hardware null. Press MENU to exit the nulling menu screen, and toenable ECAN. When ECAN is first enabled, it requires up to 10 seconds for it to achieve convergence. There will usually besome noticeable echo during the first few seconds of testing, but it will diminish over time as the ECAN software convergesto an inaudible level. Brief louder active audio can help accelerate efficiency.
HEADS UP: If multiple BaseStations are connected by 2-Wire intercom connections, each BaseStationmust be nulled separately. Null one BaseStation at a time.
Manual NullGenerally, Auto-Null will adequately control the inherent echo caused by the 2-wire hybrid circuitry. However, “ManualNull” is available if there is residual echo.If echo persists after testing for at least 30 seconds:1. Turn OFF all TALK buttons on wireless and wired equipment. Since Tempest analyzes a tone to adjust the Null characteristics,any sounds entering through the wired or wireless systems will interfere with the nulling process.2. Press MENU and advance to the “Manual Null” screen.3. Press CHAN SEL to advance to the desired channel.4. Rotate the “IN” knob to adjust the “RBAL” null value until the “Amplitude” is minimized.5. Rotate the “OUT” knob to adjust the “CBAL” value until the “Amplitude” is minimized.6. Repeat the “RBAL” and “CBAL” adjustment. The repeat process and order of adjustment of the process is important becausethe “CBAL” adjustment is most effective when the “RBAL” is close to its absolute minimum.7. Once the best null is achieved, turn the “IN” knob clockwise to add six to the “RBAL” value. For example, if the minimum“RBAL” value is 123, adjust to 133.8. Exit the Manual Null screen. Test for echo for at least 10 seconds. It will take up to 10 seconds for echo cancellati on softwareto achieve maximum efficiency.
If the echo is not acceptable, use the IN knob to adjust the “RBAL” null value up one and test again. If necessary, turn the“RBAL” value down two and test again. Continue with this trial and error method until the echo is minimized.Manual Null requires each channel to be nulled individually. Return to the Null Screen and press CHAN SEL to advance tothe next channel. Repeat for all channels.
Other Causes of EchoPlease be aware that echo can be cause by several sources. A type of echo referred to as acoustic echo can be caused byanother user’s headset, but is inaudible to that user. Have other users turn OFF their TALK butt on and determine if the echostops. Acoustic echo is minimized by software resident in each BeltStation. Acoustic echo may be miti gated by decreasingthe mic gain, sidetone or volume on the headset causing the echo. Occasionally, it is necessary to replace headsets thatcontinually cause unacceptable echo.
If a user removes his headset, the Mic may detect and repeat the sound from the earpiece. Whenever a headset is removed,always turn OFF the Talk function.