Lectrosonics Inc SMV ユーザーズマニュアル
5
Frequency Agile UHF Ultra-Miniature Belt-Pack Transmitter
Rio Rancho, NM – USA
from the audio signal. Excessive low frequency content
in the audio input can cause a variety of audio problems
including driving the transmitter into limiting.
in the audio input can cause a variety of audio problems
including driving the transmitter into limiting.
INPUT LIMITER
A digitally-controlled analog audio limiter is employed
just before the analog-to-digital 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, 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.
just before the analog-to-digital 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, 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.
Two bicolor LEDs indicate limiter activity. (See
Operating
Instructions, Adjusting Audio Levels.)
DIGITAL SIGNAL PROCESSOR
The DSP encodes the digitized audio from the A-D
Converter and adds an ultrasonic Pilot Tone to control
the receiver's squelch (only in 400 Series, 200 Series
and IFB Compatibility Modes with the Pilot Tone enabled
– see
Converter and adds an ultrasonic Pilot Tone to control
the receiver's squelch (only in 400 Series, 200 Series
and IFB Compatibility Modes with the Pilot Tone enabled
– see
Pilot Tone Squelch).
MICROPROCESSOR, PLL AND VCO
CIRCUITS
CIRCUITS
An 8-bit 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
Compatibility Mode and the correct pilot tone is added to
the endocded signal. (See
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
Compatibility Mode and the correct pilot tone is added to
the endocded signal. (See
Pilot Tone Squelch.) It also
drives the LCD display, controls the Pilot Tone, operates
the PLL/VCO circuits.
the PLL/VCO circuits.
COMPATIBILITY MODES
The SM transmitter was designed to be compatible with
Lectrosonics 400 Series receivers and will yield the best
performance when doing so. However, due to the
flexibility of digital signal processing, the SM is also able
to operate with Lectrosonics 200 Series, Lectrosonics
100 Series, IFB and certain non-Lectrosonics receivers
in special compatibility modes. (Contact the
Lectrosonics Sales Department for a complete list of
compatible receivers.)
Lectrosonics 400 Series receivers and will yield the best
performance when doing so. However, due to the
flexibility of digital signal processing, the SM is also able
to operate with Lectrosonics 200 Series, Lectrosonics
100 Series, IFB and certain non-Lectrosonics receivers
in special compatibility modes. (Contact the
Lectrosonics Sales Department for a complete list of
compatible receivers.)
PILOT TONE SQUELCH
The Digital Hybrid Wireless™ system uses one of 256
different ultrasonic tones between 25 and 32 kHz, that
modulate the carrier to operate the receiver squelch.
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 via the Control
Panel mounted FREQ switch. (See
the 256 channels has been selected via the Control
Panel mounted FREQ switch. (See
SM Screen Selec-
tions.) The pilot tone squelch system ensures 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. 400
Series Compatibility Mode 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.
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. 400
Series Compatibility Mode 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.
CONTROL PANEL
A waterproof control panel which includes four mem-
brane switches and an LCD screen is used to change
and control the operational settings, and also provide a
visual feedback of overall system operation. (See
Controls and Functions.)
brane switches and an LCD screen is used to change
and control the operational settings, and also provide a
visual feedback of overall system operation. (See
Controls and Functions.)
WIDE-BAND DEVIATION
A ±75 kHz deviation improves the capture ratio, signal to
noise ratio and AM rejection of a wireless system
dramatically, compared to other designs that use 30 kHz
to 40 kHz deviation. This combined with a full 100 mW
of power output makes a significant improvement in
signal to noise ratio and maximum operating range.
noise ratio and AM rejection of a wireless system
dramatically, compared to other designs that use 30 kHz
to 40 kHz deviation. This combined with a full 100 mW
of power output makes a significant improvement in
signal to noise ratio and maximum operating range.
BATTERY LIFE
Switching power supplies throughout the design allow
about 4.5 hours of operation using a single AA lithium
battery. An alkaline AA battery provides about 2 hours,
and a NiMH AA battery provides about 3.5 hours of
operation. The battery contacts are spring loaded to
prevent “rattle” as the unit is handled.
about 4.5 hours of operation using a single AA lithium
battery. An alkaline AA battery provides about 2 hours,
and a NiMH AA battery provides about 3.5 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 membrane switches, located on the Control Panel,
provide 256 frequencies in 100 kHz steps over a 25.5
MHz range.
selectable main oscillator. The frequency is extremely
stable over a wide temperature range and over time.
Two membrane switches, located on the Control Panel,
provide 256 frequencies in 100 kHz steps over a 25.5
MHz range.
CIRCULATOR/ISOLATOR
The RF output circuit includes a one way circulator/
isolator using a magnetically polarized ferrite. This
device greatly reduces RF intermodulation produced
when multiple transmitters are used at separations of
less than five feet. It also provides additional RF output
stage protection but is rarely seen in a wireless micro-
phone transmitter due to its high cost.
isolator using a magnetically polarized ferrite. This
device greatly reduces RF intermodulation produced
when multiple transmitters are used at separations of
less than five feet. It also provides additional RF output
stage protection but is rarely seen in a wireless micro-
phone transmitter due to its high cost.