TEX1000-LCD
26 / 38
User Manual
Rev. 1.1 - 23/06/05
8.6.1 Audio input section
The audio input section contains the circuits that perform the following functions:
•
Input impedance selection
•
15 kHz filtering of the R and L channel
•
Stereo coder
•
Preemphasis
•
Mixing of the mono, MPX and SCA channels
•
Clipper (limits the level of the modulating signal so that the frequency deviation
does not go past the 75 kHz level)
•
Measurement of the modulating signal
8.6.2 PLL/VCO section
This section of the card generates the signal in modulated radiofrequency. It is
based on a PLL diagram that uses an MB15E06 type of integrated PLL.
8.7 Driver card
Before going to the final power amplifier, the RF signal is pre-amplified in this section
through a BFR 540 transistor. When the exciter is put in stand-by, the driver is inhibited.
8.8 Power amplifier
RF power amplifier section is made with four power amplifier modules combined
through a Wilkinson splitter and a Wilkinson combiner in strip-line technology.
The splitter is used to divide input power from driver card and to supply a quarter of
it to every RF module. The combiner is used to combine output power from every RF
module so as to have total power amplifier.
Splitter, amplifier and combiner are plans so that powers generated from the
amplifiers add its in phase, diminishing the loss of balance and therefore the
dissipation of useful power.
All RF section is placed on a fin that supplies to the cooling through forced ventilation.
Every RF module supplies 300W and is supplied from a switching supply.
The active device used in amplifier module is a Mosfet (BLF278).
8.9 LPF card
This card is a low-pass filter and its function is to suppress the harmonic components
generated by the amplifier below the levels required by regulations.
