JK Audio RemoteMix 3 - Manual (Page 7)

7
Hybrid Null Adjustment (continued)
The amount of transmit/receive isolation will depend on the quality of
the telephone line. This circuit is factory set to give a good mix on an
average telephone line, and is therefore perfect for recording both
sides of a telephone interview.
To find the absolute null for any telephone line, follow this procedure:
1. Place a call to a quiet location.
2. Send a signal down the line at moderate levels, this can be a
prerecorded tape of music or speech, or preferably a test signal.
3. Connect the Receive line output to a meter or scope, or listen to
the receive signal over the headphones. Be sure to turn up the
From Phone or Headphones volume control depending on which
method you are using to monitor the receive signal.
4. On the back of RemoteMix 3 / 3.m, below the words Null Adj.,
there is a hole for a small flat blade screwdriver. This is a 10-turn
potentiometer to allow for very sensitive adjustments. Try to
remember the position of the blade, and the number of turns you
are making as you first adjust clockwise, and then back to the
original position, and then counterclockwise.
The goal is to adjust the null signal until the receive signal contains a
minimum amount of transmit audio. However, if you want a good mix
of transmit and receive signals, you must have someone on the far
end speak or send audio down the line as you adjust for the proper
balance.
To Reset Null to Factory Setting:
Disconnect from phone line, switch the Phone Line switch to On
Hook, and the set the null to minimum. This presets the null to an
average phone line impedance.