Icom IC-230 Instruction Manual page 14

6.5
6. 6.
6.7
Receiver RF Amplifier and First Mixer Module
The input signal is amplified by the field effect cascade amplifier, Q1 (3SK40), and passed
into the RF filter: This filter is a high Q helicalized resonators with excellent bandpass
characteristics and shockproof construction. From the output of the helicalized
resonators the signal is fed to the gate of the first mixer, Q2 (2SK19) where it is mixed
with the output from VCO, which is fed into the source of Q2 to obtain the 10.7 MHz
of IF signal. The output of the mixer is fed through the first caramic filter FL 1 (SFC
10.7 MA) to the IF amplifier. All the transistors in the receiver RF unit are field effect
transistors, which have the highest possible sensitivity and signal to noise ratio and the
lowest possible cross modulation.
Receiver 1st IF amplifier, 2nd IF amplifier, Limiter and Discriminator Module
The 10.7 MHz signal from the first ceramic filter in the RF unit is amplified by Q1
(28C372) and fed to the gate of the 2nd Mixer Q2 (2SK19) through the 2nd ceramic
filter FL 1 (SFC 10.7 MA). The variable resistor in the emmiter circuit of the First IF
transistor Q1 adjusts the IF gain and S-meter sensitivity. The 2nd Oscillator Q9 (28C372)
is crystal controlled and operates on 10.245 MHz. The output is taken from the emitter
of Q9 and fed into the gate of the 2nd Mixer Q2 (2SK19) to obtain the 455 KHz.
IF signal, which is passed through the 3rd ceramic filter FL 2 (CFP 455E) and amplified
by Q3, Q4, Q5, Q6, Q7 and Q8 (28C372s). The output of Q8 is then demodulated in
the discriminator circuit, consisting of L4 (15-14), L5 (15-15), and D7 and D8 (1N60s).
Receiver Audio Amplifier, Squelch Amplifier Module
The output of the discriminator drives two circuits the audio amplifier and the squelch.
The audio signal, after being adjusted by the volume control R-1, is then fed to IC 1
(TH9004AP), followed by the audio power amplifier stage Q8 and Q9 (2SD235s),
which gives an audio output of 1.5 watts.
The squelch circuit is made up of Q5, Q6 (25C372s), Diodes D3, D4 (IN60s), and Q7
(25С373). In the absence of a signal, the noise component at the output of the
discriminator is amplified by Q5 and Об. Diodes D3 and D4 rectify this amplifier
component, Q7 couples it through the 10 K ohm R-2 squelch control to the DC amplifier
and Q7's output is coupled directly to the base circuit of IC 1. When the squelch control
is adjusted, the amount of DC required to cut off IC 1 is found, thus establishing the
squelch threshold, When a signal is incoming via the discriminator, this bias is overcome,
permtting the audio amplifier and driver to perform normally.