Lectrosonics UM250c - Manual (Page 8)

UM250C
OPERATING INSTRUCTIONS
1) Install a fresh battery according to the
instructions above.
2) Insert the microphone plug into the input jack,
aligning the pins; be sure that the connector
locks in.
3) Attach the antenna to the SMA connector on
the top of the transmitter.
4) Mute the sound system.
5) Turn the transmitter power switch to the “ON”
position.
6) Position the microphone in the location you will
use in actual operation.
7) While speaking or singing at the same voice
level that will actually be used, observe the
MODULATION LEDs. Adjust the AUDIO
LEVEL control knob until the LEDs begin to
light. Start at a low setting where neither LED
lights as you speak. Gradually, turn the gain
up until one LED lights, then the other.
The -20 LED lights when the audio level is
about 12dB below full modulation. The “0” LED
lights when the limiter begins to operate. There
is 30dB of limiting range without overload
above the “0” LED, so it is desirable that it
lights up occasionally during use.
8) Once the gain has been adjusted, the audio
system audio can be turned on to make level
adjustments. Set the Power switch to the ON
position and adjust the receiver and/or sound
system level as required. Please note, there
will be a delay between the moment the switch
is thrown and the time when audio will actually
appear at the receiver output. This intentional
delay eliminates turn on thumps, and is
controlled by the pilot tone squelch control.
OPERATING NOTES
The AUDIO LEVEL control knob should not be used to
control the volume of your sound system or recorder
levels. This gain adjustment matches the transmitter gain
with the user’s voice level and microphone positioning.
If the audio level is too high — both LEDs will light
frequently or stay lit. This condition may reduce the
dynamic range of the audio signal.
If the audio level is too low — neither LED will light, or the
-20 LED will light dimly. This condition may cause hiss
and noise in the audio, or pumping and breating in the
background noise.
The first LED turns on 12dB below full deviation. The “0”
LED turns on at full deviation and indicates that the input
shunt compressor is operating. The input limiter will
handle peaks over 30dB above full modulation, regardless
of the gain control setting. The limiter uses a true abso­
lute value circuit to detect both positive and negative
peaks. The attack time is 5 milliseconds and the release
time is 200 milliseconds. Occasional limiting is desirable,
indicating that the gain is correctly set and the transmitter
is fully modulated for optimum signal to noise ratio.
Different voices will usually require different settings of
the AUDIO LEVEL control, so check this adjustment as
each new person uses the system. If several different
people will be using the transmitter and there is not time
to make the adjustment for each individual, adjust it for
the loudest voice.
ADJUSTING THE TRANSMITTER FREQUENCY
If you are experiencing interference from another signal
on your frequency, you may want to change the operating
frequency of your system. The left switch changes the
operating frequency by 1.6 MHz per step and the right
switch changes it 100 kHz per step. If you are experienc­
ing interference, change the operating frequency in 100
kHz steps to find a clear channel. If it is not possible to
find a clear channel using the 100 kHz switch, return it to
its original position and change the 1.6 MHz switch by
one click then try the 100 kHz switch again.
To gain access to these switches, slide the access door
sideways with a fingernail.
Note
With the UDR200A receiver, these switches also appear on the front
panel of the receiver. Normally, you should set the transmitter
switches to match the receiver switch settings.
With the UDR200B receiver, the front panel LED character
display will indicate the correct transmitter switch set­
0 1
2
3
4
5
6
7 8 9
A
B
C
D
E
F 0 1
2
3
4
5
6
7 8 9
A
B
C
D
E
F
1.6 MHz 100 kHz
tings.
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