Lectrosonics HM Bedienungsanleitung PDF herunterladen (Seite 5)

Digital Hybrid

Plug-On Transmitter

Rio Rancho, NM

Input Limiter

A DSP-controlled analog audio limiter is employed before

the analog-to-digital (A-D) converter. The limiter has a range

of more than 30 dB 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, a fast attack and release limiter followed by

a slow attack and release limiter. The limiter recovers quickly

from brief transients, with no audible side effects, and also

recovers slowly from sustained high levels, to keep audio

distortion low and while preserving short term dynamics.

Signal Encoding and Pilot Tone

In addition to controlling the limiter, the DSP also en-

codes the digitized audio from the A-D converter and

adds an ultrasonic pilot tone to control the receiver’s

squelch. A pilot tone squelch system provides a reliable

method of keeping a receiver output muted (squelched)

even in the presence of signiﬁcant interference. When

the system is operating in the hybrid mode, a differ-

ent pilot tone frequency is generated for each carrier

frequency to prevent inadvertent squelch problems and

simplify multi-channel coordination.

Microprocessor and DSP

A microprocessor monitors user command inputs from

the control panel buttons and numerous other internal

signals. It works intimately with the DSP to ensure the

audioisencodedaccordingtotheselectedCompatibil-

ity Mode and that the correct pilot tone is added to the

encoded signal.

Compatibility Modes

The HM transmitter was designed to operate with

Lectrosonics Digital Hybrid receivers and will yield the

best performance when doing so. However, due to the

ﬂexibility of digital signal processing, the transmitters

can also operate in various compatibility modes for use

with Lectrosonics 200 Series, Lectrosonics 100 Series,

IFBandcertainnon-Lectrosonicsreceivers.Contact

the Lectrosonics sales department for a complete list of

compatible non-Lectrosonics receivers.

Control Panel

The control panel includes four membrane switches and

anLCDscreentoadjusttheoperationalsettings.Multi-

color LEDs are used to indicate audio signal levels for

accurate gain adjustment and for battery status.

Wide-Band Deviation

±75 kHz deviation improves the signal to noise ratio and

audio dynamic range of a wireless system dramatically,

compared to other designs that use ±30 kHz to 40 kHz

deviation. Wide deviation combined with a high powered

transmitters makes a signiﬁcant improvement in signal

to noise ratio and operating range.

Battery Options and Operating Time

Switching power supplies convert battery voltages to

operate various circuit stages with maximum efﬁciency.

With the variety of alkaline, lithium and rechargeable

NiMH batteries available today in the AA format, there

are many choices to maximize operating time or mini-

mize cost as needed for any application.

Frequency Blocks

Lectrosonics established a “block” numbering system

years ago to organize the range of frequencies avail-

able from the low 500 MHz band to the upper 700

MHz band. Each block includes 256 frequencies in 100

kHz increments. The block number is part of a simple

formula to derive the frequency. The block number is

multiplied by 25.6 to produce the lowest frequency in

the block. For example, block 27 x 25.6 = 691.200.

Circulator/Isolator

The RF output circuit includes a one way circulator/isolator

using a magnetically polarized ferrite. This device greatly

reduces the RF intermodulation produced when multiple

transmitters are used in close proximity to one another

(several feet apart). The isolator also provides additional

RF output stage protection.

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