TEX150-LCD/S
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User Manual
Rev. 1.0- 09/07/04
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Modulation
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RF amplification (Driver)
The board also features a stereophonic coder.
8.3.1 Audio input section
The audio input section contains the circuits that perform the following functions:
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Input impedance selection
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15 kHz filtering of the mono channel
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Mono channel preemphasis
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Mono, MPX and SCA channel mixing
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Clipper (limits the modulating signal level so that the frequency deviation does
not exceed 75 kHz)
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Modulating signal measurement
The board also features two 15 kHz filters for filtering both the L and R channels, and
a built-in stereophonic generator.
8.3.2 PLL/VCO section
This section of the board generates the modulated radiofrequency signal. It is based
on a PLL scheme that uses an integrated MB15E06 PLL.
8.3.3 Driver section
Before passing to the final power amplifier, the RF signal is preamplified in this section
by a BFR540 transistor. When the exciter is placed on stand-by, the driver is bypassed.
8.4 Power amplifier
The final power stage is enclosed in a fully shielded metal container fixed to the
central part of the device.
The RF signal coming from the main board reached the pilot, is amplified and then
sent to the final stage which takes care of final amplification up to 150W.
Amplification occurs in two stages, the first done with the BLF244, and the second
with a BLF147.
Besides actual RF amplification, this circuit performs other functions:
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Checks output power level depending on the setting
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Reduces delivered power in presence of high-level reflected power