Lectrosonics UM250b - Manual (Page 6)

LF ROLL-OFF
ADJUST
FREQUENCY
1.6M 100K
FREQUENCY
ADJUST
ANTENNA
OFF ON
–20
0
LECTROSONICS
UM250B
LEVEL
AUDIO
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
LF ROLL OFF
35 150
75 Hz
CONTROLS AND FUNCTIONS
INPUT JACK
The input on the UM250B accommodates virtually every lavalier, hand-held or shotgun microphone available. Line level
signals can also be accommodated. Use a Switchcraft TA5F connector on the cord. See the separate sheet titled
“Transmitter 5-Pin Input Jack Wiring” regarding the correct connections for various microphones, and other sources.
ON/OFF SWITCH
Turns the battery power on and off. Even when the switch is turned off or on abruptly, the pilot tone muting system
prevents “thumps” or transients from occurring.
“ON” LAMP
Glows brightly when the battery is good and the ON/OFF switch is ON. A weak or dim lamp means that the battery is
weak. When the light goes out there is about 15 to 30 minutes of operation left with alkaline batteries and about 2
hours left with lithium. If the lamp fails to light, the battery should be replaced.
The “ON” lamp is connected to a precision battery test circuit that continuously monitors battery voltage. The LED is
at full brightness with a new 9 Volt alkaline or lithium battery. As the battery voltage drops during use, the LED
brightness will also decrease. After about 7 hours of operation (with a lithium battery) the battery voltage will be
about 7 Volts and the LED will be nearly out.
FREQUENCY ADJUST
These two rotary switches adjust the center frequency of the carrier. The 1.6M is a coarse adjustment and the 100K
is the fine adjustment. Each transmitter is factory aligned at the center of its operating range. The default position of
the frequency select switches is in the center of the transmitter’s range.
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 7 Volts. From 7 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.
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