Lectrosonics UM400a - Manual (Page 7)

Frequency Synthesized UHF Belt-Pack Transmitter
Rio Rancho, NM 7
Audio Level Control
The front panel AUDIO LEVEL Control is used to adjust
the input level (gain) for optimal modulation. The con-
trols provides continuously variable gain over a 43 dB
range for precise adjustment.
Modulation LEDs
The Modulation LEDs provide a visual indication of the
input audio signal level from the microphone. These two
bicolor LEDs can glow either red or green to indicate
modulation levels.
Signal Level -20 LED -10 LED
Less than -20 dB Off Off
-20 dB to -10 dB Green Off
-10 dB to +0 dB Green Green
+0 dB to +10 dB Red Green
Greater than +10 dB Red Red
The Modulation LEDs also indicate the Compatibility
Mode when the transmitter power switch is turned on.
The LEDs will blink simultaneously to indicate the mode
currently set:
• Once for 100 Series mode
• Two times for 200 Series mode
• Three times for mode 3
• Four times for Digital Hybrid Wireless (also called
the 400 Series mode)
• Five times for IFB mode (not available on very
early units)
• Six times for mode 6
Modes 3 and 6 provide compatibility with other manu-
facturer’s receivers - contact the factory for details.
Antenna
The flexible steel cable antenna supplied with the
transmitter is cut to 1/4 wavelength of the center of the
frequency block (the frequency range) of the transmit-
ter. The SMA connector is a 50 Ohm RF port which can
also be connected directly to test equipment. Replace-
ment antennas are available in pre-cut lengths for
specific frequency blocks, or as a kit with instructions to
cut the antenna for any frequency block.
Adjustable Low Frequency Roll-Off
The low frequency roll-off control is used to remove
subsonic (or very low frequency) audio, often produced
by air conditioning systems, automobile traffic and other
sources. Excessive low frequency content in the audio
input can cause a variety of audio problems including
driving the transmitter into limiting. In sound reinforce-
ment systems, as one instance, excessive low frequen-
cy content can cause excessive power amplifier drain or
even damage to loudspeaker systems.
30 100 1kHz 10k 20k
+6
+3
0dB
-3
-6
-9
-12
Line in
Mic in 150 Hz
Roll-off
Mic in 35 Hz
Roll-off
The side panel is marked to indicate the approximate
hinge point of the roll-off, but is normally adjusted while
listening to the audio. In controlled situations, such as
a motion picture production set indoors where envi-
ronmental noise is minimal, the control can be rotated
counter-clockwise to permit low frequency audio to be
captured.
Belt Clip Belt Clip
Retaining Screw
Location
Low Frequency
Roll-Off Control
Belt Clip
The belt clip may be removed for special applications by
removing one screw.
WARNING: Use ONLY the screw that is
supplied.
The circuitry is tightly fitted into this unit. A longer screw
will permanently damage the transmitter!