Heathkit GR-78 - Page 35

Page 08
as
‘The amplified IF sonal from C402 fe coupled through
apacitor CAIS tothe tie of second IF Amplifier 403.
‘at bas for OOS ie obtained by a yoltage diver
oniting of ebstre R19 and RADI, Transistor 403 is
aiiaed by slr rentor RAZ ies bypaed by
‘apeltor CA to ground, The amplified outout of 0403 it
fppledacromthe collector Toad risitor R426 nd it
‘ule rou eapacor C418 10 the following tage.
LOCAL OSCILLATOR
“Tw oc oslo, O00, sng lon ial eft
tnantor
(FET),
Th
oxlater
uned
ruit
corlst
of
coil
01,
trier
eapaclor
CDT
and!
unig
apitor
C801,
CbclarorInttion
voltage
I
eoupted
rough
canto
‘C308
to
ge
2
of
miner
Q201,
This
Harty
onary
‘gna 0 operate 485 kHe higher in franutney than the
Yecdved radio signal on Bande A, B,C, and D, A86 KH
Tower in fequoney on Band &; and ASK Me higr on
Band F.
AVG AMPLIFIER
‘A portion of the amplified sgl om tanutor 0403 i
upd throw epactor C421 10 the base of the AVC:
foutomatic volume con!) Ampitir CAO4, This sal
rected by the base-anittar portion of 404 an wpe
‘oltae drop is developed acon ha loud rstor RAT, This
‘oltage cause 8 colletorcurent to flow and resultant
‘opin cllcer voltae that corresponds tothe changes in
Algal strength, This varying OC vote I applied iso
IF Amplifier 0402, sheraby contig tg,
‘A portion ofthe amplified signal om IF Amplifior O40 ie
‘iso coupled through capacitor C410 to dodes D403 and
DADA, Thess two diode form a voltage doubler cult
heh provides AVC. voltage for AF amplifier QO},
Fests RAZ, ADA, aod RAD stall the correct
forward bia plot fr gat 2 of tad effet transistor 101
under 80 sgl condtns, Wher 8 gl rode, the
‘as chang fiom # postive voltage, ough zero, 10 a
roative voltage, This votoge varies, doperding upon the
sional
strevath.
Restor
AOS
ond
capacitor
C811
orm
an
AVG timing el
DETECTORS
‘A portion of the eutput a from IF anplifar 408i
‘ple
o
AM
detector
DAD
for
AM
oparation,
This
ott
flo! i ato applied through capacitor C429 to ge of
‘oduct detetor OHDS fr CW (Continuous wave, of S88
(ingle sidebar ection, 405 i 8 dus gute scan fd
affect ansitoc (FET) which exhibits exellent ioation
ecwaen gate} and gate 2; aliminating BEO oxilator
ing oF overloading on very strong sna. Gate 2 of
remit COS is bud by a vote divider costing ot
rositore RASS sa R34,
Injection
voltage
from
BEO
osistor
OA10
is
spied
to
(te
of
product
detector
O06
when
he
front
panel
‘ch
in
th
GW/SEB
poutlon.
Tha
IF
slg
and
he
DFO
‘gal
ae
combined
(rite
nthe
Wanitr,
The
esutant,
‘output
ie
au
sgl
that
is
devlopad
arom
itr
RAAT
and
coupled
Uvough
capeltor
CASS.
to.
the
AM
CW/SSB
switch
SWEOIB,
BFO
“Traitor QAO is Coots oxlatr which ie extramely
stable over wide ranger of temperature, Capacitors C426 ond
(425
provide
the
proper
feebok
fr
eacition
nd
orm
tunes ret with T40) 1 resorat at 458 KHz, Restore
"A37 ad 438 or voltae vider apply BC bing
tw the base of O80, Emit resistor RIE. provider
temperature stailzation for the trio, Injection wotge
1s coups (9 gate 2 of product detector C406, trou
‘capacitor
C424,
The
GFO
actuated
by
the
AM
CIES
frien in the CWSSB positon, This witch appli DC
perting
voltage
tha
eeu
rough
RC
408,