Icom IC-R7100 Service Manual page 14

3·1 ·19 AF AMPLIFIER CIRCUIT
(MAIN AND LOGIC UNITS)
The AF signaI output trom Ihe demodulator circuits is
amplified al Q49. The amplified signal passes through
a squetcn swilch (al) and is then applied la ICS (pin 2).
Pin 8 of
Ica
is connected with tne "AFUD " signal line
from Ihe LOG IC UNIT. The audio outpul level Is varied
by the [AF GAIN]
control
(Rl) on Ihe VR UNIT and is
Ihen applied la IC2 1 (pin 7) on tne LOGIC UNIT through
Ihe "AFG" signaI
une. The signaI is applied to IC8
(pin
8) on Ihe MAIN UNIT. The AF signa l is output trom
ICS (pin 3) and is theil power-amplified at an AF power
amplifier (IC9) 10 drive a speaker.
The amplified signal passes Ihrough a voltage limiter
circui t (Oa , 09, R49) and is Ihen applied 10 a comparator
(IC3b, pin 5). The noise squelch relerenee voltage is
applied la pin 6 ot IC3b and is varied by tne (SOUELCH]
control on Ihe VR UN IT. R5t adjusts tne input level of
IC3 b (pin 6).
The noise souelch is oulpul from IC3b (pin 7) and is then
applied la Ihe base ol 047 Ihrough 010. 051
snort-
c ircuits tne output Irom IC3b (pin 7) in SSB mode.
3·1·21 S·METER SaUELCH AND S·METER
CIRCUITS (MAIN UNIT)
The AF amplifier (011) amplilies Ihe " VOIC" signal Irom
Ihe optional UT·36 VOICE SYNTHESIZER UNIT on the
SPEECH UNIT.
The s -meter squelch runenons in any mode. The AGC
voltage is inverted and amplified at 1C4 a. The siçnal
output Irom lC4 a (pin 1) passes Ihrough 0 11 and is Ihen
applied la a comparator (lC4b, pin 6). The "ADSM"
voltage line Irom 011 is applied la IC15 (pin 5).
3·1·20 NOISE SaUELCH CIRCUIT
(MAIN UNIT)
The noise soueren functians in AM or FM N mode. Some
naise components in the AF signa! trom the ceramic
discriminator (X3) are applied to an active filter (IC17).
The active filter (lC17) amplifies naise camponen ts of
frequencies 20 kHz and above, and outpu ts the resulting
signals from pin 1. Output signals are rectified at tne
doubler circu il (059. 060) and are then converted la OC
voltage . The rect ified no tse voltage passes th rough a
differenlial ci rcuit (C179, R266) and is then applied to a
OC amplifie r (IC3a, pin 3).
When the scan is in operalion, the CPU (IC5. pin 91) on
Ihe LOGIC UNIT outputs a "HIGH " signal lor 35 msec. on
Ihe "IFBK" sig nal line. The "HIGH " signal lurns 036
a nd 037 ON to deactivate the squetch circuit. The
pu lse-type signaI Is applied to C179 through 055 tor rapid
charging .
• 5-METER
SQUELCH CIRCUIT
The s -rneter squelch reterence voltage passes thraugh a
OC ampli lier (07) and Is Ihen applled la Ihe comparator
(IC4b. pin 5) Ihrough 016 and is va ried by Ihe [SOUELCH]
co ntro l on the VR UN IT. R66 adjusts Ihe input level ot
lC4b (pin 5). This re ference vollage is added to the S-
meier vollage and is Ihen applled la the (S. METER] on
Ihe FRONT PANEL Ihrough 0 15 to indicate Ihe
s -merer
squelch th resho ld level.
The s-rneter squelch is outpui Irom lC4b (pin 7) and is
Ihen applied to the ba se of 047 Ihrough 017.
3-1 ·22 SaUELCH SWITCH CIRCUIT
(MAIN UNIT)
047 swi tc hes 02 ON or OFF depending on Ihe output
levell rom Ihe cornoa rators (IC3b. lC4 b). 03 controts
Ihe gate vollage of 0 1 by using Ihe collec lor voltage of 0 2.
Q1 c uts out the AF signaI whe n the squelch is closed.
02 outputs a " BUSY" signal la Ihe LOGIC UNIT and lig hlS
up the (BUSYI indical o r on Ihe FRONT PANEL when the
squelch is open.
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3 - 8