Partyline: How do I set the null on the SB-440 main station?
SB-440 Channel Null Adjust
The screwdriver adjustable control beneath each TALK push button marked "NULL" allows nulling of the hybrid circuitry associated with each listen channel. The amount of null in the listen circuitry varies with the length of the intercom line. Adding or removing stations and intercom cable will change the null. For optimum performance the NULL control will need t be adjusted each time there is some change in the intercom line wiring.
If a panel microphone and speaker are being used the setting of the NULL control is critical to prevent feedback.
To adjust the NULL control on a given channel:
1. Turn the SIDETONE ADJUST control just below the Headset connector to minimum.
2. Set a TALK to the channel to be adjusted or send some program to the channel and adjust the NULL control for the channel for minimum level in the headphone.
If the headset microphone is being used hum or gently scratch it for a continuous signal source to null on. If a good null is not attainable, switch to the LONG / SHORT Line Length dip switch for the channel to its opposite setting. Use the setting that produces the best results.
3. Repeat the the adjustment for all four channels on the station.
4. Adjust the SIDETONE ADJUST control for the desired amount of sidetone in the headset.
The screwdriver adjustable control beneath each TALK push button marked "NULL" allows nulling of the hybrid circuitry associated with each listen channel. The amount of null in the listen circuitry varies with the length of the intercom line. Adding or removing stations and intercom cable will change the null. For optimum performance the NULL control will need t be adjusted each time there is some change in the intercom line wiring.
If a panel microphone and speaker are being used the setting of the NULL control is critical to prevent feedback.
To adjust the NULL control on a given channel:
1. Turn the SIDETONE ADJUST control just below the Headset connector to minimum.
2. Set a TALK to the channel to be adjusted or send some program to the channel and adjust the NULL control for the channel for minimum level in the headphone.
If the headset microphone is being used hum or gently scratch it for a continuous signal source to null on. If a good null is not attainable, switch to the LONG / SHORT Line Length dip switch for the channel to its opposite setting. Use the setting that produces the best results.
3. Repeat the the adjustment for all four channels on the station.
4. Adjust the SIDETONE ADJUST control for the desired amount of sidetone in the headset.
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