Lectrosonics SMQV - Signal Encoding and Pilot Tone; Compatibility Modes

Super-Minature Belt Pack Transmitter
Rio Rancho, NM
5
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 squelch in
the receiver. A pilot tone squelch system provides a reli-
able method of keeping a receiver output muted (audio
mute) even in the presence of significant interference.
Whenthesystemisoperatinginthehybridmode,adif-
ferent pilot tone frequency is generated for each carrier
frequency to prevent inadvertent squelch problems in
multi-channelsytems.
Microprocessor Control
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
SM transmitters are designed to operate with Lec-
trosonics Digital Hybrid receivers and will yield the
best performance when doing so, however, due to the
flexibility of digital signal processing, the transmitter
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 more information
about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.
Variable Power Output
Thisadvancedfeatureallowstheoperatortooptimize
the transmitter for maximum battery life, or for maximum
operating range. Power output is selected using the
LCD in a setup mode while the RF output of the trans-
mitter is turned off.
Battery Options and Operating Time
Switching power supplies convert regulated battery
voltages to operate various circuit stages with maxi-
mumefciency.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minimizecostasneededforanyapplication.
The firmware “remembers” the power status when a
battery fails, so the transmitter will be turned on auto-
matically when the battery is replaced and the previous
settings will be enabled.
Frequency Blocks
Lectrosonics established a “block” numbering system
yearsagotoorganizetherangeoffrequenciesavail-
ablefromthelowendat470MHzbandtotheupper
endat952MHz.Eachblock(except944)includes256
frequenciesin100kHzsteps,whichisthemaximum
switching range of the transmitters. Block 944 is a spe-
cialbandbetween944and952MHz.
Circulator/Isolator
TheRFoutputcircuitincludesaonewaycirculator/iso-
latorusingamagneticallypolarizedferrite.Thisdevice
greatly reduces 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 against static
shock.