Plug-on UHF Transmitter
Rio Rancho, NM
5
No Pre-Emphasis/De-Emphasis
The Digital Hybrid Wireless
®
design results in a signal-to-
noise ratio high enough to preclude the need for con-
ventional pre-emphasis (HF boost) in the transmitter and
de-emphasis (HF roll-off) in the receiver. This eliminates
the potential for distortion on signals with abundant
high-frequency information.
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 distor-
tion. 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 recov-
ers slowly from sustained high levels, to keep audio dis-
tortion 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 in 100 kHz increments to prevent inadvertent
squelch problems and simplify frequency 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 transmitter was designed to operate with Lectroson-
ics Digital Hybrid Wireless
®
receivers and will yield the
best performance when doing so. However, due to the
flexibility of digital signal processing, the transmitter can
also operate with Lectrosonics IFB receivers that may
be available in the future.
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.
Summary of Contents for HMA-941 Series
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