Icom IC-R7O Maintenance Manual page 17

For the time-constants of AGC, the attack time is set by R106 and C160, and the release time is set by
R103, R105, C77 and C79.
In order to provide full break-in during transmission, AGC voltage is held by the switching circuit
consisting of Q22 and Q24.
When the AGC switch is set at FAST, the AGC voltage passes through R109 switched by 020 and is
quickly discharged.
(d) BFO circuit
Mode signals from J10 pass through the respective diode (one of D61 ~ D65) for each mode, and switch
2 crystals and shunt coils in series with a crystal, and the proper BFO frequency for each mode is
obtained.
Q13 is a crystal oscillator and Q14 is a buffer-amplifier.
(e) S-meter circuit and squelch circuit
AGC voltage is fed to IC4B, inverting the amplifier, giving a wide dynamic range and high linearity, and
causing the S-meter to move.
Part of S-meter voltage is fed to 1C4A, comparator, and this circuit provides a stable squelch function for
modes other than FM.
(f) Other circuits
IC7 is a voltage regulator supplying 8V to each part.
D52 and Q27 ~ Q29 are provided for use with a transmitter; the T8 signal which controls receiver
operation is obtained by the signal from the SEND terminal.