Icom IC-730 Instruction Manual page 22

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The 2 local oscillator is a VXO (Variable Crystal Oscillator),
and its frequency is varied 30.71901MHz ~ 30.72000 MHz
in 10Hz steps, and 30.7191MHz ~ 30.7200MHz in 100Hz
steps by the output signals of the CPU through the D/A
converter.
A part of incoming 39MHz signals is fed to the noise blanker
circuit. The noise blanker consists of noise amplifiers, a
noise detector and noise blanker gate control which blocks
the incoming IF signal when noise is present.
The AGC time constant of the noise blanker circuit can be
changed. It becomes effective for wider noise pulse such as
"woodpecker noise".
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The 9.0115MHz 2 IF signal passes through the AM crystal
filter, and is then fed to the MAIN unit. If the optional SSB
crystal filter, FL-30, and/or ON crystal filter, FL-45 is
installed, the suitable crystal filter is selected by the mode
switch.
During transmit, the 9.0115MHz transmitting signal from
MAIN unit passes through the crystal filter and is fed to the
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2 mixer to convert 39MHz signal. This output signal is fed
to the RF unit described above.
6 - 4 MAIN UNIT
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Composed of 2 IF Amplifiers, IF pass-band shift circuit, AF
amplifier, MIC amplifier, TX IF amplifier, VOX circuit, ANTl-
VOX circuit, CW monitor, ALC circuit, and meter control
circuit. During receive, the 9MHz 2
unit is amplified and then fed to the IF Pass-Band shift
circuit.
In this circuit, the 9.0115MHz signal is mixed with 9.4665
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IF signal from the 2 IF
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MHz local oscillator signal to convert the 9.0115MHz signal
into a 455K Hz signal.
This 455KHz signal is fed to a 455KHz ceramic filter in AM
mode, or to a mechanical filter in SSB and CW mode, then
again mixed with 9.4665MHz local oscillator to convert the
455KHz signal into the original 9.0115MHz signal.
The 9.4665MHz local oscillator frequency can be changed
±1.5KHz by sliding the IF SHIFT control to move the IF
Pass-Band center frequency. If installed the optional SSB
filter, FL-30, this circuit becomes Pass-Band Tuning circuit.
The 9.0115MHz IF signal is sent to the DET unit, and
demodulated AF signal is applied to this unit again, and
amplified by AF power amplifier to drive the speaker.
In VOX operation, a part of the AF output signals is applied
to the ANTl-VOX circuit, and its output voltage is fed to the
VOX circuit to prevent misfunction of the VOX by an audio
from the speaker.
In the ON mode, the side-tone oscillator is keyed according
to your keying, and its output signal is fed to the AF power
amplifier.
A voice signal from the microphone is applied to the MIC
amplifier, and speech processor circuit and fed to the
modulation circuit on the DET unit.
The 9.0115MHz DSB suppressed carrier from the DET unit
is applied the mixer to convert 455KHz signal, then it is fed
to 455KHz mechanical filter and removed unwanted side
band, and an SSB signal is produced. This signal is con-
verted to 9.0115MHz SSB signal and fed to the 2
through a buffer amplifier.
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IF unit