User's Manual

HMa, HMa-941, HMa/EO1, HMa/E02, HMa/E06, HMA/E07-941, HMa/X
LECTROSONICS, INC.
4
The HMa transmitter uses a DSP controlled input limiter
featuring a wide range dual envelope design which
cleanly limits input signal peaks over 30 dB above full
modulation. Switching power supplies to provide con-
stant voltages to the transmitter circuits from the begin-
ning (3 Volts) to the end (1.7 Volts) of battery life, and an
ultra low noise input amplifier for quiet operation.
Digital Hybrid Wireless
®
Technology
All wireless links suffer from channel noise to some de-
gree, and all wireless microphone systems seek to mini-
mize the impact of that noise on the desired signal. Con-
ventional analog systems use compandors for enhanced
dynamic range, at the cost of subtle artifacts (known as
“pumping” and “breathing”). Wholly digital systems defeat
the noise by sending the audio information in digital form,
at the cost of some combination of power, bandwidth and
resistance to interference.
Lectrosonics Digital Hybrid Wireless
®
systems over-
come channel noise in a dramatically new way, digitally
encoding the audio in the transmitter and decoding it
in the receiver, yet still sending the encoded informa-
tion via an analog FM wireless link. This proprietary
algorithm is not a digital implementation of an analog
compandor but a technique that can be accomplished
only in the digital domain, even though the inputs and
outputs are analog.
General Technical Description
Channel noise still impacts received signal quality and
will eventually overwhelm a receiver. Digital Hybrid
Wireless
®
simply encodes the signal to use a noisy
channel as efficiently and robustly as possible, yield-
ing audio performance that rivals that of wholly digital
systems, without the power and bandwidth problems
inherent in digital transmission.
Because it uses an analog FM link, Digital Hybrid
Wireless
®
enjoys all the benefits of conventional FM
wireless systems, such as excellent range, efficient
use of RF spectrum, and resistance to interference.
However, unlike conventional FM systems, it does
away with the analog compandor and its artifacts.
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.
Bias Voltage
42V,15V, 5V
+4V
Input
Amp
Shunt
Limiter
AUDIO
FREQ
UP
DWN
Reference
Crystal
Reference
Crystal
3 V
Battery
Hi.Lo
Pass
Filter
Digital
Pot
Audio
Level
Phantom
Power
Audio
A-D
Converter
11001001
D-A
Converter
11001001
Control Panel
Microprocessor
Voltage
Controlled
Oscillator
Final
Amplifier
Filter
Amp
Encoded Audio
and Pilot Tone
Bicolor
Modulation
LEDs
Switching
Power
Supply
Digital Signal Processor
Phase Locked Loop
LCD
1.2V
4V
-3.3V
+3.3V