Lectrosonics UH400 User Manual download pdf (Page 4)

UH400

NO PRE-EMPHASIS/DE-EMPHASIS

The signal to noise ratio of the 400 system is high enough to

preclude the need for conventional pre-emphasis (HF boost) in

the transmitter and de-emphasis (HF roll off) in the receiver. Pre-

emphasis and de-emphasis in an FM radio system usually

provides about a 10dB improvement in the signal to noise ratio of

the system, but the high frequency boost in the transmitter must

be removed in a purely complementary manner or else the

frequency response of the original audio signal will be altered.

Pre-emphasis can also cause distortion in the receiver. As this

signal is passed through the IF filters in the receiver, distortion

can be produced, most noticeably at full modulation. De-empha-

sis cannot be applied until the signal is converted into audio, so

there is no way around this problem short of eliminating pre-

emphasis altogether. Neither of these problems occur in the 400

system

PILOT TONE SQUELCH

The 400 system utilizes one of 256 different ultrasonic tones

between 25 and 32 kHz, that modulate the carrier to operate the

receiver squelch. The pilot tone frequency is chosen according

to which of the 256 channels has been selected by the frequency

switch setting. The basic benefit of the pilot tone squelch system

is that the receiver will remain muted until it receives the pilot

tone from the matching transmitter, even if a strong RF signal is

present on the carrier frequency of the system. The UH400

extends this concept even further by insuring that all transmitters

in a system have different pilot tone frequencies so that even

spurious RF from the wrong transmitters can’t open the receiver

squelch.

WIDE-BAND DEVIATION

±75kHz deviation improves the capture ratio, signal to noise ratio

and AM rejection of a wireless system dramatically, compared to

the more commonly used ±15kHz deviation.

LONG BATTERY LIFE

Switching power supplies throughout the design allow over 4.5

hours of operation using a single 9 Volt alkaline battery. (A 9V

lithium battery will provide over 12 hours of operation.) The

battery contacts are spring loaded to prevent “rattle” as the unit is

handled.

FREQUENCY AGILITY

The transmitter section uses a synthesized, frequency selectable

main oscillator. The frequency is extremely stable over a wide

temperature range and over time.

Two rotary switches, located on the side panel of the unit, provide

256 frequencies in 100kHz steps over a 25.5MHz range. This

alleviates carrier interference problems in mobile or traveling

applications.

CONTROLS AND FUNCTIONS

MODULATION LEDs

–10

–20

POWER

ON/OFF

LED

PWR OFF

LEVEL

P HTM

N O PHTM

1 5V

48 V

MIC LEVEL

PHANTOM POWER

VOLTAGE SELECT

POWER

SWITCH

FREQUENCY

1.6MHz 100kHz

FREQUENCY SWITCHES

(BEHIND DOOR)

INPUT

JACK

INPUT

JACK

Top View

Control Panel

Side View

This transmitter may be used with a wide variety of microphones.

The 3-pin XLR connector allows the transmitter to be used with

any dynamic microphone, as well as many two wire positive bias

lavaliere systems (such as those systems supplied by Lectroson-

ics).

POWER 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.

The PHTM (center) position of the power switch turns on the

phantom power while the NO PHTM (fully on) position disables

phantom power. Be careful to use the center position phantom

power only when necessary and keep the voltage selector switch

in the 5 Volt position for additional protection against accidents.

POWER ON/OFF LED

This LED glows green when the battery is good. When the lamp

glows red, there is about 30 minutes of operation left with the

recommended lithium battery, and about 20 minutes of life left

with an alkalline battery. The lamp will flash red when there are

only a few minutes of life remaining. A NiMh battery will give little

or no warning when it is depleted. If you wish to use NiMh

batteries in this unit, we recommend trying fully charged batteries

in the unit, noting the length of time that the batteries will run the

unit and in the future use somewhat less than that time to

determine when the battery needs to be replaced. A weak

battery will sometimes light the POWER LED to the “good” green

LECTROSONICS, INC.

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Lectrosonics UH400 User Manual Page 4

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