R.V.R. Elettronica PTX-LCD, User Manual

Page: 55 / 62

PTX-LCD
51 / 58 User Manual Rev. 2.3 - 18/07/07
R39 clipper symmetry adjustment
R40 38 kHz subcarrier suppression optimization
Mono/MPX board
LP1 Low pass filter 1
LP2 Low pass filter 2
RV1 Mono level
RV2 Board output level (modulation)
RV3 clipper circuit intervention threshold
D1 positive power supply voltage presence
D2 negative power supply voltage presence
D3 clipper intervention signalling
11.5 PLL/Driver card & VCO Card
The PLL/Driver board (Fig. 11-9) is placed on the left part of the PTX-LCD (Fig.
10-1 5) and is directly connected to the audio motherboard.
The digital PLL module is composed by a high stability temperature-controlled
oscillator and by the digital circuit doing the division and the comparison of the
working frequency. The oscillator generates a 10 MHz frequency divided by a
fixed 1 kHz signal.
This signal is routed to the digital comparator/divider circuit that compares it to the
signal generated by the VCO dived depending on the exciter’s working frequency.
The output of the comparator is the AFC signal that is applied to the varicap
diodes on the VCO board and added to the audio signal coming from the coder
card.
The Voltage Controlled Oscillator generates the RF signal that is aplified up to
around 300mW (25dBm), that is the level required to drive the R.F. Power Amplifier.
Nota: The VCO is cointained in a silvered brass box fixed on the PLL & Driver
board.