HP 8901B Operation And Calibration Manual page 227

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
W z
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 W z 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