7
UHF Belt-Pack Transmitter
Rio Rancho, NM – USA
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 pro-
duced 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 #28528 which is a Phillips head, 4-40 x 3/16", FL100 screw.