6. Audio
FM/AM/WFM
The selection of receiving audio output signal between FM/WFM and AM is
performed at IC106. The volume of output audio signal is adjusted at the
electronic volume IC108 via the AF amplifier Q120. After converting the im-
pedance of the signal whose volume is adjusted at Q124, the signal is input to
pin 2 of audio power amplifier IC110 and output from pin 6 to drive a speaker,
etc.
7. VCO
The 1st Local
The VCO for the 1st local consists of the Colpitts oscillator. D106, D108 and
L105 determine the frequency, and they are oscillated at the transistor Q103.
The oscillated signal is added to pin 2 of PLL-IC101 through the butter ampli-
fiers Q105 and Q134.
The 2nd Local
The VCO for the 2nd local consists of the Colpitts oscillator. D110, D111 and
L113 determine the frequency, and they are oscillated at the transistor Q110.
The oscillated signal is added to pin 19 of PLL-IC101 through the butter am-
plifier Q135.
8. PLL
PLL-IC101 is used to control the oscillation frequency of VCO. The micro-
computer IC1 sends the signal with serial data to control IC101. The 12.8
MHz reference frequency of IC101 oscillates the crystal oscillator X101 at the
inside circuit.
The 1st Local
Using the control signal from IC1, IC101 compares the divided value of the
added signal to pin 2 of IC101 with the divided value of 12.8 MHz reference
frequency inside IC101. When the phase difference is occurred, IC101 out-
puts the pulse signal from pin 8 and converts into DC voltage at the active filter
Q107 and Q108. Then it is fed to the cathode of the VCO vari-cap diodes of
D106 and D108 to reduce the phase difference. This brings the stable oscilla-
tion at the desired frequency.
The 2nd Local
Using the control signal from IC1, IC101 compares the divided value of the
added signal to pin 19 of IC101 with the divided value of 12.8 MHz reference
frequency inside IC101. When the phase difference is occurred, IC101 out-
puts the pulse signal from the charge pump output pin 13 and converts into
DC voltage at the inside circuit for the active filter. Then it is fed to the cathode
of the VCO vari-cap diodes of D110 and D111 to reduce the phase difference.
This brings the stable oscillation at the desired frequency.
5 |
ACEC
ALINCO
