Operation Model 8901B
Manual Tuning-Low-Noise
LO
The instrument tunes
to
the frequency keyed into it, via the keyboard, regardless
of
whether
a
signal
is
present. Once tuned, the
LO
is
locked
to
an
internal voltage-controlled, crystal oscillator for high
stability and low noise. Once locked, tuning does not change unless a new frequency
is
entered, Track
Mode
is
selected, the tuning
is
stepped up
or
down using the kHz
.h
or
kHz keys, Automatic Operation
or
Instrument Preset
is
selected. The manual
tune
mode
is
entered immediately when either MHz, kHz
fi,
or kHz
4
is
selected;
or
if
Range Hold
is
selected.
Manual Tuning-Track Mode
The Modulation Analyzer tunes
to
the keyed-in frequency in the same way
as
described in the previous
paragraph. However, the
LO
is
not locked
to
an
internal oscillator; instead the LO
is
locked
to
the input
signal itself and tracks
it
as
it
drifts.
This function
is
useful for measuring second
or
third harmonic
signals and for tracking spurious signals.
PROCEDURE
Select
FREQ,
then:
Tune Mode Selection
0
Select automatic tuning with AUTOMATIC OPERATION
or
AUTO TUNING (Blue Key,
0
Select manual tuning with either MHz
or
one of the
Wz
keys (with
or
without a preceding
0
Select track mode with TRACK MODE. (Return from the track mode
to
the low-noise mode, by
TRACK MODE).
numeric entry),
or
with RANGE HOLD.
selecting TRACK MODE again.)
Manual Tuning by Keyboard Entry
To manually tune
to
a
specific signal frequency, enter the frequency in MHz via the numeric keyboard,
then press the MHz key.
The MHz key can also be used alone
to
aid in tuning:
if
the Modulation Analyzer
is
tuned close but
not exactly
to
the input
signal,
select MHz
to
center the
signal
in the
IF'
passband.
If
in automatic
tuning mode, and no signal
is
present, select MHz alone
to
tune the Modulation Analyzer
to
the
last
frequency
at
which
a
signal
was
successfully tuned.
(If
no
previous successful tuning
has
been made,
the Modulation Analyzer tunes
to
100
MHz.)
RF Frequency Stepping
To step the tuning of the Modulation Analyzer, enter the desired frequency step size in kHz via the
numeric keyboard, then press either kHz
.h
or kHz
4.
Once the
step
size has been set, either
Wz
key
will change the tuning by
that
step size each time the key
is
pressed.
(At
power-up, the step size
is
set
to
0
kHz.)
3-116
RF
Frequency Tuning
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