Precision E-200-C Series - Television Receiver Alignment

If
a Sweep
Generator
and
Oscilloscope
are available,
the
re-checking
procedure is
less
time-consuming inas-
much
as
the result of
the alignment
procedure
becomes
instantly
evident on the
'scope
screen. Reference should
be
made
to
the Sweep Generator
Instruction
manual for
the
details of Visual
alignment and
check of
overall
response
curves.
Before
proceeding to
adjustment
of
the rest of
the
F.M.
receiver, it is
interesting
to
note that it
is not
always
neces-
sary to
attain
PERFECT
symmetry along
the
double-hump
portion of the I.F.
response
curve, due to
the
flattening
effect
of the
limiter stage or
stages.
In other
words the
humped
portion of
the I.F.
waveshape
becomes "clipped"
or
flattened
by
the
limiter action at
medium to high
input
levels. From
this
analysis it can
also
be
seen
that the dip
between
the two
humps in
the
overcoupled
I.F.
system should not be so
excessive as to
produce a
dip in the
center of the
curve even
AFTER
limiting.
The remaining
few adjustments are not
very critical
and
are much the
same as those
associated
with
the
alignment of
the first detector
and oscillator
of regular high frequency
bands. The Series E-200 or E-200-C is set
in accordance
with
the
receiver
manufacturers' service notes to, let us
say, 90
megacycles and the oscillator
trimmer and R.F. input trim-
mer
adjusted
for
maximum reading of the
resonance indi-
cator
which is still
a
V.T.V.M. or
20.000 ohms per volt multi-
tester at
the limiter grid
resistor return. The
receiver
dial is
tuned for
the
reception of
the same
frequency at which the
Signal
Generator is
set.
This
completes the adjustment of the
receiver,
however,
tuning of an F.M. set is
a
bit
different from the process
usually
associated with
the
tuning
of
receivers
designed for
amplitude modulated carriers.
When
tuning
for
and approaching an F.M. station carrier,
the speaker
output will slowly become louder and
louder,
and in the
event fnnt external noises are present, these
noises
will at
the
Same time
be
quite discernible. However, contin-
uing the tuning
process, a
point will
be reached, whereat the
station
signal,
will seem
to
grow
a
bit weaker,
but
simulta-
neously the
noise
level
will almost automatically and prac-
ticailjiJisaffjear.
At
this'
point the receiver is properly tuned
and
if the operator
continues
to turn the
dial, the signal
will
again appear
to
increase but with consequent increase
in
noise level. It is
therefore important that the
operator
or
owner of an F.M.
receiver be
instructed
in proper tuning
procedure if best
results
are to be
obtained.
If the F.M. receiver
incorporates
a
single
or multiple
shadow
tuning eye, the operator
should
then tune,
per the
set
manufacturer's instructions, for the required
eye pattern
instead of
tuning
by ear.
•
•
•
The foregoing information
was intentionally
limited, for the
sake
of
simplicity,
to just one
type of F.M. receiver circuit, namely those
incorporating a limiter-discriminator
following the
I.F.
section.
There are other means employed for demodulating an F.M. trans-
mission, such as the
ratio detector.
However,
once the
basic
concepts of
F.M.
receiver alignment
are understood and prac-
ticed, demodulator
type
variations present no special
complica-
tions. Always,
.follow
.the
receiver
.manufacturer's, instruction
for
the particular considerations he feels
will yield
the best
results
for the type
of circuit employed.
Inasmuch
as
the prime purpose
of this
book is to reveal
the
fundamental usage of the
A.M.
Signal Generator, we
purposefully
do
not burden the
reader with oscillographic alignment methods
which require the
additional ownership of
a
Sweep Signal Genera-
tor and a High Sensitivity Oscilloscope. However, suffice
it
to
say that the A.M. Signal
Generator is a
most valuable tool even
when
oscillographic alignment procedures are employed. Such
details are part of the
instructional
data
which accompanies
the
Sweep
Signal Generator.
* * *
At
such
time
as the
reader becomes actually engaged in
the
use of this
additional apparatus, he will become
aware
of the
ever increased
importance of a
good, stable
A.M.
Signal Genera-
tor such as the
E-200
and
E-200C.
* * *
TELEVISION
RECEIVERS
Although it
is
possible
to
align TV
receivers
via use
of
only A.M.
Signal
Generator
methods,
the
extended
time,
effort and
possible
complications
involved do
not
warrant
detailed
instructions to
such end.
The
nature of
TV
receiver circuits
are
such as
make it
advisable to
employ
oscillographic
means
of
alignment and
adjustment. With
this
in
mind, the
reader is
directed
to his
Sweep Signal
Generator instruction
manual for
TV applica-
tions.
In
addition, the
operator
should more
rigidly than
ever,
follow the set
manufacturer's
service notes.
When
so
doing,
you
will find that certain
TV set
adjust-
ment* permit
or
prescribe use of
A.M. signals.
Among
the
variow
points
involving use
of A.M.
signals are the
following.
1.
Alignment
of the
sound I.F.
section. Use
same
general
procedure
outlined for regular
F.M.
receivers.
2.
Adjustment
of sound
section
limiter-discrimina-
tor
circuits.
Use
same
general
procedure
outlined
for
regular F.M.
receivers.
3.
Adjustment
of trap
circuits. Resonate
traps in
accordance
with set
manufacturer's
details with
E-200-C
set
to
prescribed trap
frequency.
4.
Alignment of
stagger-tuned
video I.F.
stages.
Treat
each stage
individually. Set
generator to
fre-
quency
prescribed for that
stage.
Peak adjust the
I.F.
trimmers (or
slugs)
of
that stage, for
maximum re-
sponse in similar
manner
prescribed
for A.M. receivers.
5. TV
Response
Curve
Waveshape Analysis.
The
E-200-C,
when
connected for
use as a marker
generator
becomes
an
important TV
service
instrument. The
Marker or
"Pip" which
it superimposes on
Video
and
Sound
response curves,
permits
the operator to set
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