Lectrosonics UM700 User Manual download pdf (Page 7)

Digital Frequency Agile UHF Belt-Pack Transmitter

MODULATION LEDS

Indicate the proper setting of the MIC LEVEL control. There are two bicolor modulation LEDs that can light either red

or green.

“-20dB level” One modulation LED glows green and the transmitter is 20 dB below full modulation.

“-10 dB level” Both modulation LEDs glow green and the transmitter is close to full modulation.

“+0 dB level” The -20 LED glows red and the -10 LED glows green. The transmitter is in slight limiting and is

fully modulated. This is probably desirable. See the discussion below under Input Limiter.

“+10 dB level” Both LEDs are red. The transmitter is in limiting and you may want to reduce the transmitter audio

gain. See the discussion below under Input Limiter.

When the transmitter is first switched on, the modulation LEDs blink a code that indicates the current security level: 1

blink = level 1, 2 blinks = level 2 and 3 blinks = level 3.

Input Limiter

The 700 series transmitters employ a digitally-controlled analog audio limiter just before the analog-to-digital con-

verter. The limiter has a range of more than 30dB for excellent overload protection. A dual release envelope makes

the limiter acoustically transparent while maintaining low distortion. It can be thought of as two limiters in series,

connected as a fast attack and release limiter followed by a slow attack and release limiter. The limiter recovers

quickly from brief transients, so that its action is hidden from the listener, but recovers slowly from sustained high

levels, to both keep audio distortion low and preserve short term dynamic changes.

The audio level LEDs indicate limiter activity. The first red LED indicates that the limiter is active and that the trans-

mitter is fully modulated (audio level is between +0 and +10 dB). The second red LED indicates that the level is

10dB or more into limiting. Occasional forays into the red are desirable for most applications, since the distortion

introduced by the limiter is so minimal, and full modulation is thus assured. We strongly recommend setting the gain

of the transmitter high enough so that the first red LED occasionally lights.

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 compres-

sion of the peaks in the audio signal, which is desirable with most recorders and many sound reinforcement systems.

ANTENNA

The flexible bronze cable 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.

Replacement antenna is part AMM(xx) where “xx” indicates the frequency block, ie. AMM27 for block 27.

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 reduce the undesirable effects of very low frequency audio often pro-

duced by air conditioning systems, automobile traffic and other sources. Excessive low frequency content in the

audio input can cause overload 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 sys-

tems. A common example is wind blowing across a microphone, causing very high levels of low frequency audio

(“wind noise”). By rotating the roll-off control clockwise, the hinge point of the roll-off is increased to reduce the level

of low frequencies. In low noise situations, such as a motion picture production set indoors where environmental

noise is minimal, the control can be rotated counterclockwise 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

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Lectrosonics UM700 User Manual Page 7

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