Lectrosonics UM250c User Manual download pdf (Page 7)

UHF Belt-Pack Transmitter

OFF Switch

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 produc-

tion 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.

Caution

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.

Belt Clip Retaining Screw

(Under Clip)

BATTERY INSTALLATION

The transmitter is powered by a standard alkaline or

lithium 9 VDC battery. It is important that you use ONLY

a LITHIUM battery for longest life. Standard zinc-carbon

batteries marked “heavy-duty” or “long-lasting” are not

adequate. Ni-cad rechargeable batteries will only provide

a few minutes of operation, or less, and will run down

quite abruptly. Alkaline batteries provide 2 hours of

operation. Lithium batteries will provide up to 7 hours of

operation. Care should be taken not to leave a fully

discharged lithium battery in the transmitter, as swelling

of the battery can make it difficult to remove from the

compartment. The battery status circuitry is designed for

the voltage drop over the life of lithium batteries.

Batter y Compartment

To open the battery compartment, press outward on the

cover door in the direction of the arrow as shown in the

drawing. Only firm, sliding pressure is needed to open

and close the battery door. Swing the door open and take

note of the polarity marked inside showing the location of

the positive (+) and negative (-) terminals. You can see

the large and small contact holes inside the battery

compartment with the door open.

Insert the battery correctly and close the cover by

pressing the door closed and across, reversing

the opening procedure illustrated above. If the

battery is inserted incorrectly, the door will

not close. Do

Swing the

not force the

door open

Press outward on the

battery door in this

direction

door

closed.

Rio Rancho, NM – USA

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Lectrosonics UM250c User Manual Page 7

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