Super-Minature Belt Pack Transmitters
Rio Rancho, NM
5
Signal Encoding and Pilot Tone
In addition to controlling the limiter, the DSP also en
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adds an ultrasonic pilot tone to control the squelch
in the receiver. A pilot tone squelch system provides a
reliable method of keeping a receiver output muted
when the squelch is active, even in the presence of
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in the hybrid mode, a different pilot tone frequency
is generated for each carrier frequency to prevent
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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 select
ed Compatibility Mode and that the correct pilot tone
is added to the encoded signal.
Compatibility Modes
SMB 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, they can also
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Control Panel
The control panel includes four membrane switches and
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accurate gain adjustment and for battery status.
Battery Options and Operating Time
Switching power supplies convert regulated battery
voltages to operate various circuit stages with maxi
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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 or power is disconnected, so the trans
mitter will be turned on automatically when power is
restored and previous settings will be enabled.
Frequency Blocks
Lectrosonics established a “block” numbering system
years ago to organize the range of frequencies that
are available. Legacy transmitters and receivers used
two binary switches, each with 16 positions, to set the
operating frequency. 16 x 16 = 256, which defined the
standard number of frequencies in each block to be
256. Since the steps between frequencies is 100 kHz,
this results in a switching range of 25.6 MHz.
The lowest frequency in the switching range di
vided by 25.6 yields the block number. For example,
640.000 divided by 25.6 equals 25. In other words,
block 25 starts at 640.000 MHz.
To determine what block a particular frequency falls
into, divide the frequency and use the two significant
digits to the left of the decimal. For example, to cal
culate the block for 580.500 MHz, divide 580 by 25.6,
which equals 22.656, which indicates block 22.
Circulator/Isolator
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isolator using a magnetically polarized ferrite. This
device greatly reduces RF intermodulation produced
when multiple transmitters are used in close proximity
to one another (a meter or two, or less). The isolator
also protects the output amplifier against static shock.
