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User Manual
Rev. 1.0 - 29/11/16
BLUES30/50NV
ELETTRONICA
7.3 Main Board
The main board carries out the following functions:
• Audio and SCA input treatment
• Generation of carrier frequency
• Modulation
• R.F. amplification (Driver)
7.3.1 Audio input section
The audio input section contains the circuits that perform the following functions:
• 15 kHz filtering of the left and right channel
• Stereophonic Coding
• Preemphasis
• Mono, MPX and SCA channel mixing
• Clipper (limits the modulating signal level so that the frequency deviation does
not exceed 75 kHz)
• Modulating signal measurement
7.3.2 PLL/VCO section
This board section generates the modulated radiofrequency signal. It is based on
a PLL scheme that uses an integrated MB15E06 type.
The digital PLL section is composed of an high-stability oscillator controlled in
temperature and of a digital circuit that carries out the division and the comparison
of the working frequency. The oscillator generates a frequency of 10 Mhz that
comes divided in order to generate a fixed signal at 1 kHz.
This signal comes sended to the comparator/divisor digital circuit who confront it with
the signal generated from VCO, divided in base of exciter working frequency.
The AFC signal, in output of comparator, comes sended to the varicap diodes places
on VCO card and added to audio signal coming from from the Coder card.
The Voltage Controlled Oscillator (VCO) generates the signal on the exciter working
frequency, than in its turn it comes amplified to a level nearly 3/5mW (5/8dBm),
necessary for being able to pilot the R.F. Power Amplifier block.
