Owner`s manual

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MB-R-OM-03/11
OPERATION
The Model MB-R is turned on and off by the rocker switch near the lower left rear
corner on the base. The volume control knob (marked VOL) adjusts speaker loudness
to the level preferred by the operator. The volume control may have a built-in, on-
off switch. THE VOLUME CONTROL SWITCH SHOULD BE LEFT ON AT ALL TIMES.
Turn the unit on and off using the switch in the rear of the unit. The volume control
does not affect transmitter operation.
The squelch control (marked SQ) allows the operator to eliminate undesirable
receiver background noise when no signal is being received. Turning the knob
(marked SQ) fully counterclockwise “unsquelches” the receiver, allowing background
noise and very weak signals to be heard. Some operators may prefer to leave the
receiver unsquelched at all times. For those who prefer to use the squelch, periodic
unsquelching can serve as a receiver test, since a large reduction in background noise
might indicate receiver malfunction. To squelch the background noise, rotate the SQ
control clockwise only as far as necessary to just stop the noise.
Further rotation may result in not hearing more distant aircraft. There may be some
circumstances in which an operator does not wish to hear more distant aircraft, such
as, when such aircraft are communicating with a different ground station. In this
situation, the control may be rotated fully clockwise. The squelch control does not
affect transmitter operation.
If the Model MB-R has more than one channel, use the rotary channel switch on the
front panel to select the desired channel. Transmit and receive frequencies are
switched simultaneously. Changing the switch position connects a different pair of
crystals (one each for receiving and transmitting) and re-adjusts all tuned circuits for
the new channel. There may be small channel-to-channel variations in the receiver
sensitivity (as may be indicated by the speaker noise level) but this will not affect
communications significantly. In case of a communications problem, check that the
channel frequency selector switch has not been inadvertently changed to a different
channel.
An aviation type, noise-canceling microphone is recommended. To transmit, press
the push-to-talk (PTT) switch on the microphone. Hold the microphone close (1/4
inch or 1/2 cm) to your mouth and speak directly into the center of the microphone’s
acoustical opening, at a moderate voice level.
While the MB-R’s audio leveling circuits compensate for variations in microphone
output, “microphone technique” is extremely important for good clear transmissions.
Aviation microphones are purposely designed to be highly directive and are very
sensitive to the distance from the speaker’s mouth primarily to reduce pick-up of
background noise. It is impossible to overemphasize the importance of holding these
microphones close to the mouth and speaking clearly.