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I IV{'IEL
4OO TRANSCEIVER
A .
C i . c u i t T h e o r y ( C o n t )
The single sideband,
suppressed
carrier
At the sarne tirne,
one d€flection
plate of
signal Jrom the First
IF Amplilier
is fed
the balanced rnodulator
is grounded,
un-
to the Transmitter
Mixer,
V2, u'here
balancing the modulator
and allowing
full
signals Irom
the VFO Amplifier
are
carrier
input for tuning puiposes,
A
mixed,
and the resultant
signal at the
similar
procedure
is followed in the CW
final transmitted
frequency
is alnplified
position of the Phone -CW switch,
to allow
through the Transrnitter
Mixer,
the
full carrier
output duiing
CW operation.
D r i v e r ,
V 3 , a n d t h e P o w e r A m p l i f i e r s ,
D u r i n g C W o p e r a t i o n t h e c a t h o d e o f V 1 6 8
V4 and V5.
The signal from the VFO
i6 opened from grotrnd,
cuttrng ofI the
Amplifier
iE initiated
in the particular
tube.
This allows CW operation
with no
Frequency
Control Unit being used.
The
danger of pickup of audio through an open
signal frorn the Frequency
Control
Unit
microphone,
Attempts
to operate on CW
is routed to the VfO
Amplilier,
and on
by keying the lnicrophone
jack,
and insert-
4 0 a n d 8 0 r n e t e i s ,
i s s u b t r a c t i v e l y
i n g c a r r i e r ,
a r e n o t r e c o m m e n d e d .
mixed with the single sideband signal
f r o m t h e I F A m p l i I i e r .
O n 2 0 , 1 5 , a n d
R E C E M
l 0 m e t e r s ,
t h e f r e q u e n c i e s a r e a d d i t i v e l y
m i x e d ,
r e s u l t i n g i n o u t p u t o n t h e o p p o s i t e
I n R E C E I V E
p o s i t i o n , o r a t a n y t i m e w h e n
sideband,
the transrnitter
is not in TRANSMIT
or
S T A N D B Y ,
a l l c i r c u i t s u s e d i n t r a n s m i t t i n g
When in TRANSMIT,
thc gain oI the First
are disabled throrgh
the relay controlled
I I
A m p l i f i e r
i s c o n t r o l l e d t h r o u g h t h e
c i r c u i t s ,
t h c r e l a y s b e i n g e n e r g i z e d I o r
A u t o m a t i c L i m i t i n g
C o n t r o l n e t w o r k
t r a n s m i t t i n g ,
a n d d e - e n e r g r z c d f o r r e c e i v -
D 4 0 l - 4 0 2 ,
e t c . ,
t o c o n t r o l t h e g a i n o f
i n g .
R c l a y K 2 , w h e n d e - e n e r g i z e d ,
a l l o w s
t h e s t a g e i n r e s p o n s e t o t h e a v e r a g e i n -
s i g n a l s f r o r n t h e t r a n s r n i t t i n g t a n k c i r c u i t
put power to the power amplifiers.
This
and antenna to be ted to the Receiver
RF
A L C s y s t e m w i l l c o r n p e n s a t € { o r a n y
A m p l i f i e r ,
V 6 , w h e r e t h c y a r e a m p l i l i e d ,
extremely
strong input signaLs, but does
and then {ed to the control
giid oI the
n o t c o m p l e t e l y e l i m i n a t e t h e n e c e s s i t y o f
R e c e i v e r M i x e r ,
V ? .
T h e l o c a l o s c i l l a t o r
proper
adjustrnent ol the Mic.
Gain
signal from
the VFO Amplifier
is now
Control.
Although this feature wil]
used to heterodyne the received
frequency
prevent the transmitter
Jroln flat-topping
to the IF frequency,
either upper or lower
a n d s p u r i o u s e r n i s s i o n s , c o n s i d e r a b l e
s i d e b a n d .
A 1 1 I F a r n p l i f i c a t i o n i s
distortion
may occur if the Mic.
Gain
accomplished
at this Jrequency,
nominally
c o n t r o l i s n o t p r o p e r l y a d j u s t e d .
R e f e i
5 l ? 4 . 5 k c , a n d i n t h e P r o d u c t D e t e c t o r
to Operating
Instructions.
Vl0A,
the IF lrequency
is heterodyned
w i t h c a r r i e r
f r e q u e n c y g e n e r a t e d b y
T U N E A N D C W O P E R A T I O N
C a r r i e r
O s c i l l a t o r ,
V I 5 ,
t o r e s $ l t i n
detection of the sarne sideband used to
Normally,
the Jrequency oJ the carrier
generate the transmitted
signal.
It i6
o s c i l l a t o r i s a p p r o x i m a t e l y 3 0 0 c p s o u t -
t h u s n o t p o s s i b l e { o r t h e t r a n s c e i v e r
t o
side the passband of the crystal
lattice
receive
a 6ignal on any frequency
other
filter.
In TUNE position,
to enable the
than that to which the trarlsrnitter
is tuned,
transmitter
to be tun€d to the maximum
nor to detect the wrong sideband.
This
power output condition,
the frequency
of
simple
single conversion
de6ign results
the carrier
oscillator
is moved approxi-
in an extrelnely
stable signal,
and an
mately
500 cps to place it well within
image response down more than 80 db.
the passband ofthe
cry6tal
lattice
filter,
Since the VFO frequency
from the
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