CIRCUIT DESCRIPTION
1) Receiver
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 mixer 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 mixer 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 mixer IC103 via the band switches D107 and D129.
223 ~ 367.995MHz
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 mixer IC103 via the band switches D107 and D129.
368 ~ 469.995MHz
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 mixer IC103 via the band switch D134.
470 ~ 999.995MHz
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 mixer IC103 via the band switch D120.
3. Mixer
The 1st Mixer
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 fre-
quencies in the mixer IC104. Then the signals are divided into the receiving
sides of FM/AM and WFM at D113 and D114.
3 |