SystemTriple-conversion superheterodyne
First I.F.248.45MHz
Second I.F.38.85MHz
Third I.F.450kHz
SensitivityAM/FM -6dB/12kHz or over, -60dB/30kHz or less
WFM-6dB/150kHz or over
SelectivityFM/WFM 12dB SINAD, AM 10dB S/N
typ.FM: 30 ~ 1080.63uV(-4dBu)
1. Receiver system : Triple Superheterodyne Conversion
1st IF.:248.45MHz
2nd IF.:38.85MHz
3rd IF.:450KHz
2. Front End
0.5 ~ 29.995MHz
The signal from the antenna is switched by the band switch (D109), passed
through the low-pass filter and amplified by RF amplifier Q109. Then the
signal is fed to the 1st mix er IC103 via the band switch D115.
30 ~ 136.995MHz
The signal from the antenna is switched by the band switch (D128), passed
through the low-pass filter and amplified by RF amplifier Q111. Then the
signal is fed to the 1st mix er IC103 via the band switch D112.
137 ~ 222.995MHz
The signal from the antenna is switched by the band switch (D116), passed
through the low-pass filter and amplified by RF amplifier Q116. Then the
signal is fed to the 1st mix er IC103 via the band switches D107 and D129.
223 ~ 367.995MHz
368 ~ 469.995MHz
470 ~ 999.995MHz
3. Mixer
The 1st Mixer
The signal from the antenna is switched by the band switch (D132), passed
through the low-pass filter and amplified by RF amplifier Q118. Then the
signal is fed to the 1st mix er IC103 via the band switches D107 and D129.
The signal from the antenna is switched by the band switch (D122), passed
through the low-pass filter and amplified by RF amplifiers Q123 and Q138.
Then the signal is fed to the 1st mix er IC103 via the band switch D134.
The signal from the antenna is switched by the band switch (D133), passed
through the low-pass filter and amplified by RF amplifier Q126. Then the
signal is fed to the 1st mix er IC103 via the band switch D120.
The input signal and 1st local signal generate sum and difference frequencies
in the mixer IC103. SAW filter FL101 selects the signal of 248.45MHz and
eliminates the adjacent channel signals.
The 2nd Mixer
The input signal and the 2nd local signal generate sum and difference frequencies in the mixer IC104. Then the signals are divided into the receiving
sides of FM/AM and WFM at D113 and D114.
3
FM/AM
WFM
4. IF
FM/AM
FM
In the receiving side of FM/AM the signal of 38.85MHz is selected by crystal
filter XF101. Then the signal is amplified at the 1st IF amplifier Q112 after
eliminating the adjacent channel signal.
In the receiving side of WFM the signal of 38.85MHz is selected b y band-pass
filter . Then the signal is amplified at the 1st IF amplifier Q112 after eliminating
the adjacent channel signal.
The amplified signal at the 1st IF amplifier Q112 is led to the demodulator pin
24 of IC105. The signal of 12.8MHz from the ref erence b uff er output of IC101
is multiplied by 3 in Q133. Then the signal is mixed with the signal of pin 1 of
IC105 in the mixer circuit inside of IC105 and conv erted into the 2nd IF signal
of 450kHz. The con verted 2nd IF signal is output from pin 3 of IC105.
The output signal from pin 3 of IC105 is led to pin 7 of IC105 after eliminating
the adjacent channel signal at the ceramic filter FL103. The input 2nd IF
signal to pin 7 of IC105 is demodulated at the limiter amplifier and quadrature
detector circuits inside of IC105, then output from pin 12 of IC105 as an AF
signal.
AM
WFM
5. Squelch
The output signal from pin 3 of IC105 is led to the pin 5 of IC105 after eliminating the adjacent channel signal at the ceramic filter FL103. The 2nd IF signal
input to pin 5 of IC105 is AM-demodulated inside of IC and output from pin 13
of IC105 as an AF signal. The 1st IF amplifier Q112 is controlled by reverse
AGC at A GC amplifier Q117 to get better audio output even though the input
is changed, and the gain is controlled.
The output signal from pin 3 of IC105 is led to pin 7 of IC105. The input 2nd IF
signal to pin 7 of IC105 is demodulated at the limiter amplifier and quadrature
detector circuits inside of IC, then output from pin 12 of IC105 as an AF signal.
The AF signal got from pin 12 of IC105 is fed to pin 19 of IC105. The input
signal is output from pin 21 of IC105 passing through the noise filter amplifier
and rectifier circuits inside of IC. The rectified signal is added to the A/D port
of the microcomputer IC1. Judging the signal, the microcomputer controls
ON/OFF of the audio output.
4
6. Audio
FM/AM/WFM
7. VCO
The 1st Local
The 2nd Local
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 impedance 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.
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 amplifiers Q105 and Q134.
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 amplifier Q135.
8. PLL
The 1st Local
The 2nd Local
PLL-IC101 is used to control the oscillation frequency of VCO. The microcomputer 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.
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 outputs the pulse signal from pin 8 and conv erts 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 oscillation at the desired frequency.
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 outputs the pulse signal from the charge pump output pin 13 and converts into
DC voltage at the inside circuit for the activ e filter . Then it is f ed 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.