Lectrosonics Inc SMQL Manuale Utente
Super-Minature Belt Pack Transmitter
Rio Rancho, NM
5
actual roll-off frequency will vary somewhat according to
the low frequency response of the mic capsule being
used.
the low frequency response of the mic capsule being
used.
The low frequency roll-off is used to remove subsonic
(or very low frequency) audio, often produced by air
conditioning systems, automobile traffic and other
sources 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.
(or very low frequency) audio, often produced by air
conditioning systems, automobile traffic and other
sources 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.
Input Limiter
A DSP-controlled analog audio limiter is employed
before the analog-to-digital converter. The limiter has a
range of more than 30 dB for excellent overload protec-
tion. A dual release envelope makes the limiter acousti-
cally 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.
before the analog-to-digital converter. The limiter has a
range of more than 30 dB for excellent overload protec-
tion. A dual release envelope makes the limiter acousti-
cally 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
Operat-
ing 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,
IFB Compatibility Mode, and Mode 6 – see
Converter and adds an ultrasonic Pilot Tone to control
the receiver's squelch (only in 400 Series, 200 Series,
IFB Compatibility Mode, and Mode 6 – see
Pilot Tone
Squelch). It also controls the input limiter.
Microprocessor, PLL and VCO 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 encoded 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 encoded signal. (See
Pilot Tone Squelch.) It also
drives the LCD display and operates the PLL/VCO
circuits.
circuits.
Compatibility Modes
The SM transmitter was designed to operate 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 Lectroson-
ics Sales Department for a complete list of non-
Lectrosonics 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 Lectroson-
ics Sales Department for a complete list of non-
Lectrosonics compatible receivers.)
Pilot Tone Squelch
A fixed frequency pilot tone squelch system (such as
Lectrosonics 200 Series) ensures that a receiver
remains 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.
Lectrosonics 200 Series) ensures that a receiver
remains 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 400 Series (Digital Hybrid Wireless™) takes this a
step further by using one of 256 different ultrasonic
tones between 25 kHz and 32 kHz to modulate the
carrier and operate the receiver squelch. The pilot tone
frequency is chosen according to which of the 256
channels has been selected. (See
step further by using one of 256 different ultrasonic
tones between 25 kHz and 32 kHz to modulate the
carrier and operate the receiver squelch. The pilot tone
frequency is chosen according to which of the 256
channels has been selected. (See
SM Screen Selec-
tions.)
This ensures 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.
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 set and
adjust 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 set and
adjust 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.
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.
Battery Life
Switching power supplies throughout the design allow
about 4.5 hours of operation using a single AA lithium
battery (Two AA batteries for the SMD/Q). If shorter
operating times are acceptable, an alkaline or NiMH
battery can be used. In the SM, AA alkaline batteries
provide about 2 hours of operation, and a NiMH AA
battery provides about 3.5 hours of operation.
about 4.5 hours of operation using a single AA lithium
battery (Two AA batteries for the SMD/Q). If shorter
operating times are acceptable, an alkaline or NiMH
battery can be used. In the SM, AA alkaline batteries
provide about 2 hours of operation, and a NiMH AA
battery provides about 3.5 hours of operation.
Note: A NiMH battery will give little or no warning
when it is depleted. If you wish to use NiMH
batteries, we recommend trying fully charged
batteries in the unit, noting the length of time that
the batteries will run the unit and then using the
battery timer feature available on most 400 Series
receivers.
when it is depleted. If you wish to use NiMH
batteries, we recommend trying fully charged
batteries in the unit, noting the length of time that
the batteries will run the unit and then using the
battery timer feature available on most 400 Series
receivers.
The battery contact is designed to prevent “rattle” as
the unit is handled.
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.
256 frequencies in 100 kHz steps over a 25.5 MHz
range are available.
selectable main oscillator. The frequency is extremely
stable over a wide temperature range and over time.
256 frequencies in 100 kHz steps over a 25.5 MHz
range are available.
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.