Heathkit SB-401 - LINEAR MASTER OSCILLATOR

Gea
reatrexit]
Page
131
v3
6AU6
ISOLATION AMP.
FROM DIODE |
BALANCED
MODULATOR 1
SUPPLY NETWORK
METER
Figure 6-7
SYMMETRICAL
CRYSTAL
BANDPASS
FILTER
(Figure
6-8)
BANOWIDTH
2.1 KHZ AT 6 DB MIN.
The
crystal
filter
is
a
2,1
kHz
lattice
type,
de-
signed
to
pass
the
usable
LSB
(3393.6
kHz)
and
As
Raa
ateamiy
USB
(3396.4
kHz)
modulated
signals,
and
a
carrier
(3395.4
kHz)
frequency,
The
carrier
fre-
quency
is
used
in
the
CW
and
Tune
Modes,
The
resulting
low
impedance
signal
is
coupled
through
capacitor
C118
to
the
grid
of
LMO
(linear
master
oscillator)
mixer
V4,
NOTE:
60
Resistance
measurements
on
the
crystal
filter
are
not
meaningful
due
to
differences
in
man-
ufacturers,
50
ATTENUATION DB
>
°o
3393
v 0 o
oe o
9 iv] “
m
3392
3397
3398
om i)
FREQUENCY KHZ
NOTE:
F
the
Fi
,
it
that
the
USB
CARRIER
FREQUENCY
L
1
NEA
R
MASTE
R
OSC
1
L
LA
TOR
would
pass
the
lower
sideband
frequencies,
Due
to
further
conver
sion,
the
signal
is
inverted
in
later
stages
and
the
output
frequencies
are
those
of
the
upper
sideband.
The
LMO,
consisting
of
tube
V6
with
its
asso-
ciated
circuit,
is
a
very
stable
linear
oscillator
iol
cus
that
operates
over
a
frequency
range
of
5
to
5,5
aren
IE
3.
395MHZ
megahertz,
The
tuning
capacitor
changes
the
:
aida
Be
LMO frequency and thus changes the operating
frequency of the Transmitter, The output signal
of
the
LMO
is
coupled
to
the
cathode
of
LMO
mixer tube V4,
In this instance (using 3,895 mHz as an oper-
ating
frequency),
it
can
be
seen
from
the
Fre-
—
quency
Chart
that
an
8,5
megahertz
signal
is
:
required
at
the
LMO
mixer,
Because
the
LMO
Figure
6-8
mixer
frequency
is
the
sum
of
the
carrier
generator and LMO signals, the LMO output
will be 5,105 megahertz,