Lectrosonics UM200b - Manual (Page 7)

Frequency Agile UHF Belt-Pack Transmitter
Since the internal circuits are all tightly regulated and the RF output stage has a separate discrete regulator, the
transmitter will continue to operate to a battery voltage of 6.5 Volts. From 6.5 Volts to 6 Volts, the transmitter will still
operate, but with degraded performance. Please note that a weak battery will sometimes light the POWER LED
immediately after turn on, but will soon discharge to the point where the LED will go out, just like a flashlight with
“dead” batteries.
The combination of an accurate battery condition indicator and regulation of all internal circuits provides much longer
battery life, as well as consistent performance over the life of the battery.
MODULATION LEDS
Indicate the proper setting of the MIC LEVEL control.
“-20” LED -- Flickers or glows when sufficient audio is present.
“0” LED -- Lights up when the input level is high enough to cause limiting. The input limiter has a very high
overload threshold (over 30 dB). Generally speaking, some limiting is desirable in normal operation to improve
the signal to noise ratio of the system. The limiting action is not audible and does not create distortion. A
highly trained ear would hear only the compression of the peaks in the audio signal, which is desirable with
most tape recorders and many sound reinforcement systems.
AUDIO LEVEL
Used to adjust the audio input level for the proper modulation.
ANTENNA
The flexible wire antenna supplied with the transmitter is cut to 1/4 wavelength of the center of the frequency block
(the frequency range) of the transmitter. It is removable via an SMA connector. The SMA connector is a 50 Ohm RF
port which can also be connected directly to test equipment. Replacement 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
A 18dB per octave low frequency roll-off is provided in the audio section, with the -3dB point adjustable from 35Hz to
150Hz. The actual roll-off frequency will vary somewhat according to the low frequency response of the mic capsule
being used.
The low frequency roll-off control is used to prevent undesirable subsonic (or very low frequency) audio, often produced
by air conditioning systems, automobile traffic and other sources from causing the compandor to mistrack. Excessive
low frequency content in the audio input can cause “pumping and breathing” of background noise or modulation of the
program audio in recording applications. In sound reinforcement systems, excessive low frequency content can cause
excessive power amplifier drain or even damage to loudspeaker systems. By rotating the control clockwise, the hinge
point of the roll-off is increased to reduce the level of low frequencies. In controlled situations, such as a motion
picture production set indoors where environmental noise is minimal, the control can be rotated counter-clockwise to
permit low frequency audio to be captured.
THE BELT CLIP
The belt clip may be removed for special applications by removing one screw.
USE ONLY THE SCREW THAT IS SUPPLIED
The circuitry is tightly packed into this unit. A longer screw will permanently damage the transmitter! Use only
Lectrosonics PN:28528 which is a Phillips head, 4-40 x 3/16", FL100 screw.
Rio Rancho, NM – USA 7