Kenwood TK-701S Service Manual page 17

Squelch circuit
There are four inputs which activate the squelch gate:
noise squelch, signalling squelch, muting and monitor.
Noise squelch is supplied from the audio output of
U13: MC3359P to noise amp Q14: 2SC1815(Y) and
- then to the squelch control located on the PLL unit.
Noise from the squelch control is returned to the noise
amplifier section of U13: MC3359P pin 12.
Output from pin 13, it is then rectified and used to control
U13 pin 14. Pin 16, mute output is fed to squelch switch
Q24: 28C1815(BL).
TK-701
Signalling squelch from the PLL unit via the AC ter-
minal is achieved along with microphone hanger switch
logic by U200: TC4001BP, and is then supplied to
squelch switch Q24: 2SC1815(BL). Muting is directly
connected to squelch switch 024: 2SC1815(BL). These
three inputs are all squelched at logic low: that is, no
sound is output.
Muting is performed by squelch switch Q24:
2SC1815(BL) and is fed to squelch gate Q22 and Q23:
both 2SC1815(BL). The monitor is also coupled to the
inputs of Q22 and Q23. When the monitor is opened,
squelch is switched on.
Fig. 4-4 TC4001BP
Voo
U200 14( [3] 12) 11; 10; 9) 8|
TC4001BP En CE
t] 21 3] 4] 51 6. 7|
Vss
PLL unit
UI3
MC3359P NSO
I6 14 13
Dil
D202
To LED
drive
cilcuit
Fig. 4-5 Squelch Circuit
The priority order of each input over the squelch is
listed in the following table.
The input Jevel for squelch operation is listed in the
following table.
JU1 closed JU1 opened , an "H" Jevel
input L" ievel ened
1 Monitor 1 Noise squelch Monitor Sound output No suncd
(Squelch OFF) (Squich ON)
2 Noise Ich 2 Monit
se squelc onutor Noise squeich No sound Sou d ocstput
2 Signalling squelch 3 Signalling squelch {Cathode of D18) (Squelch ON) (Squich OFF)
2 Muting 3 Muting Signailing squelch No sound Soud ovstput
(Cathode of D202) (Squelch ON) (Squich OFF)
Muting No sound Sou d octput
(MUT terminal) (Squelch ON) (Squich OFF)
4-3