Clear-Com EF-701M - Manual (Page 30)

2 - 8 E F - 7 0 1 M I N T E R F A C E
Adjusting the Null
Normally, the following adjustment is made once during installation. (If the
configuration of the local party-line system changes substantially, it may be necessary to
re-null the system for optimum performance.)
1. Connect all the local party-line devices for that channel together and to the EF-701M.
2.Plug into the front-panel earphone jack labeled “test.” You will now hear a steady
200-Hz tone through the earphone.
3.Adjust the “R” control until the tone is at its minimum.
4.Adjust the “L” control until the tone is at its minimum.
5.Adjust the “C” control until the tone is at its minimum.
6.Because these controls interact with each other, you will need to repeat steps 3, 4, and 5
several times before fully minimizing the test tone.
7.Continue these adjustments until the test tone is virtually inaudible.
If a complete or almost complete null cannot be obtained, is likely that there is a prob-
lem with either the wiring of the external party line or with one of the other devices
attached to the external party line. The next section provides troubleshooting tips.
8.Unplug the earphone when the nulling operation is complete.