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Tempest900 2-Channel Operating Manual
Manual Null
Generally, Auto-Null will adequately control the inherent echo caused by the 2-wire hybrid circuitry. However, “Manual Null” 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 because the
“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 cancellation software to
achieve maximum efciency.
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 to the next channel.
Repeat for all channels.
Other Causes of Echo
Please be aware that echo can be cause by several sources. A type of echo referred to as acoustic echo can be caused by another user’s headset,
but is inaudible to that user. Have other users turn OFF their TALK button and determine if the echo stops. Acoustic echo is minimized by
software resident in each BeltStation. Acoustic echo may be mitigated by decreasing the mic gain, sidetone or volume on the headset causing
the echo. Occasionally, it is necessary to replace headsets that continually 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.
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