Ten-Tec 243 - Page 5

ats
80278 PTO
The
permeability
tuned
oscillator
is
exactly
the
same
as
the
one
used
in
the
OMNI.
It
is
housed
in
a
sealed
enclosure
on
top
of
the
main
chassis.
The
main
coil,
L3,
is
shunted
with
L2
and
has
Ll
in
series.
Adjustment
of
these
two
slug
tuned
coils,
which
are
on
the
same
coil
form,
determines
the
linearity
and
band
edge points.
L2 is the top slug.
Ll is the bottom
slug.
PTO ALIGNMENT
1.
Connect
frequency
counter
to
VFO
output
plug.
It
is
marked
with
a
red
band.
Counter
should
have
input
sensitivity
rating
of
at
least
100 mv.
2.
Set
tuning
shaft
25
kHz
up
from
full
counterclockwise
position
as
indi-
cated
on
dial
skirt.
Dial
skirt
should
be
zeroed
and
dial
pointer
should
indicate
close
to
left
index
scale
mark,
and
within
range
of
be-
ing
set
to index
with
serrated
zero-set
knob.
3.
Observe
counter
reading
and
if it
is
not
5.000
MHz,
slightly
touch
up
L2
slug.
Slug
position
in
the
coil
should
be
such
that
a
clockwise
rotation
of
the
slug
decreases
frequency.
4.
Run
tuning
knob
up
scale
and
note
counter
readings
at
each
100
kHz
of
increase.
If
readings
are
within
+
5
kHz,
linearity
is
within
specifi-
cations.
However,
in
most
cases,
linearity
may
be
improved,
especially
if
frequency
reading
at
5.500
MHz
is
not
exactly
aligned,
or
if
all
de-
viations
from
the
first
setting
are
in
the
same
direction.
5.
If
VFO
range
is
comporssed,
i.e.
reading
on
the
counter
at
what
should
be
5.5
MHz
is less than
this, reset tuning
to 5.0
position,
turn L2
slug
a
fraction
of
a
turn
clockwise
and
then
compensate
for
this
de-
crease
in
frequency
by
turning
Ll*
slug
also
clockwise
for
a
5.0
MHz
counter
reading.
Repeat
step
4
to
see
i-
correction
was
sufficient
or
too
much.
6.
TẾ
range
of
VFO
is
expanded
instead
of
compressed,
compensation
in
the
opposite
direction
is
indicated.
This
is
accomplished
by
turning
slugs
in opposite
direction.
*
NOTE:
To
reach
L1
slug
without
upsetting
position
of
L2
slug,
use
the
tuning
tool
with
reduced
shank
that
is
provided
with
ØMNI.
Also
note
that
L2
is
used
to
adjust
spread
of
VFO
range
and
L1
to
bring
frequency
to
cor-
rect value.
OFFSET
ADJUSTMENT
FOR
21.0
AND
28.0
MHz
BANDS
To
eliminate
band
edge
birdies
on
these
two
bands,
the
crystal
oscillator
frequencies
are
chosen
10
kHz
lower
that
what
normally
would
be
needed
compared
to
the
other
bands.
The
variable
PTO
oscillator
compensates
for
this
deviation
by
switching
in
varactor
diode,
D3,
by
means
of
the
OT
line
from
the
@MNI.
The
amount
of
varactor
capacitance
inserted
is
controlled
by
the
amount
of
dc
voltage
applied
through
potentiometer,
Rl.
To
set
this
adjustment,
proceed
as
follows:
1.
Set
@MNI
BAND
switch
to
14.0
and
frequency
on
dial
to
14.000.
2.
Set
MODE
switch
to
position
2
(EXT
BOTH).
3.
Using
the
calibrator
(@MNI-A)
or
frequency
counter
display
(GMNI-D),
set
tuning
to exactly
14.000 MHz.
4.
Set
BAND
switch
to
21.0
band
without
changing
either
main
tuning
knob
on
@MNI or Model
243, adjust
RI on XTAL/OSC
board
for
21.000 0
MHz,
or
zero
beat.
6L-b
£bL-p