Icom IC-211 Instruction Manual page 32

and the BFO signal becomes the output. This signal is used for the carrier in CW
operation.
During CW operation, a key is connected to the base of Q62. The key turns 062 OFF
during key down, therefore turning ON Q63 and the carrier ON.
The output signal of 1С4 (DSB signal) is fed to the crystal filter FL1 through Q63 and
D7. FL1 cuts the unwanted side band of the DSB signal and the output is a Single Side
Band signal. (CW signals pass through FL1 as unchanged wave forms). From the filter,
the signal is sent to the transmit mixer circuit, through mode switch D57.
. 10.7MHz OSCILLATOR AND FM MODULATOR CIRCUITS
10.7MHz signals are oscillated by Q12 and amplified audio signals from the microphone
are supplied to varicap diode D11 connected in series with the crystal unit. Voltage of
these signals causes the capacitance of D11 to vary, and frequency modulation is ef-
fected. Since this transceiver is a heterodyne type, any frequency deviation that occurs
in this circuit appears unchanged as a frequency deviation in the 144MHz band, and so
use is made of a crystal unit with special characteristics to ensure suitable frequency
deviation and stability. Maximum frequency deviation is adjusted by R59.
These modulated signals are amplified by ІСб and fed to the transmit mixer circuit,
through mode switch D 10.
. TRANSMIT MIXER CIRCUIT |
These modulated signals, taken out from the blanced modulator or FM modulator by
L14, are applied to transmit mixer IC2.
133MHz band signals from the PLL unit, which is the same as the first local oscillator of
the receiver, are supplied through local oscillator transmit-receive switching diode D3 to
IC2 and mixed with the 10.7MHz modulated signals to give signals of 133MHz +10.7
MHz. As a balanced mixer is used for this mixing stage, 10.7MHz and 133MHz band
signals are canceled and do not appear in the output.
. PONER AMPLIFIER
The signals are further passed through
a concentrated
band-pass filter, to eliminate
signals outside the 144MHz band, and the then amplified by 028, 030, 031, and 032
to 10 watts or more.
ГА
The junction voltage of 016 апа 017 is applied to the bases of ОЗ1 апа 032, for the
bias voltage. The bias voltages are adjusted by R127 and R130.
D16 and 017 are connected to the cases of Q31 and 032 respectively, and compensate
the bias voltage by the temperature of O31 and 032.
. LOW-PASS FILTER AND SWR DETECTING CIRCUIT
Since the output includes harmonics, it is passed through 2 Chebyshev sections, and 1
contant-K section low-pass filter, to attenuate harmonics to —60dB or more. This
low-pass filter is set at about 180MHz cut-off frequency and minimum loss.
= Э са