R.V.R. Elettronica TEX150, User Manual

Page: 37 / 110

TEX150
31 / 40 User Manual Rev. 4.0 - 27/07/01
9.10 PLL Card
The PLL card is situated internally, in the upper part of the unit.
The circuit includes a reference cristal oscillator (optional high stability), a logic
section that includes the frequncy dividers and comparator.
The reference cristal oscillator generates a 4MHz frequency that is divided to
generate a 1KHz fixed signal.
This signal is compared to the operating frequency generated by the VCO divided
opportunely on the ground of the frequency setted on the Contraves.
An indicator situated on the front panel signals the "unlocked" condition.
The comparator output (AFC signal) is sent to the varicap diodes situated on the
VCO Card.
9.11 VCO Card
The VCO card is situated internally, in the upper part of the unit.
This module includes an audio input stage at low frequency, a voltage controlled
oscillator at low noise (VCO) and a driver stage.
The audio signal supplied by the encoder mixer is amplified and then injected into
the VCO to provide class F3 modulation.
The voltage controlled oscillator (VCO) generates the signal on the frequency
setted on the Contraves.
This signal is amplified to 300 mW level (25dBm) to drive the final stage and to be
sent to PLL circuit situated on the PLL card.
The operating frequency genereted by the VCO is divided down before being
compared to a reference frequency, generated by a high stability oscillator (standard
5ppm). The error voltage is filtered and used to compensate the VCO frequency
and guarantee its stability.
A trimmer is present on this card for adjustment of deviation.