HP 8901B Operation And Calibration Manual page 237

Operation Model 8901B
COMMENTS
Input/Output Status.
When the instrument is measuring the LO frequency, the signal at MODULATION OUTPUT/AUDIO
INPUT remains unchanged.
Relative Measurements.
If
the LO frequency is to be displayed relative to a reference, enter the value as a ratio reference using
the RATIO key. (Refer to Ratio on page 3-215.)
Display Resolution.
Normally, the counter updates the display five times each second. For selection of other resolutions,
use Special Function 7. (Refer to RF
frequency
Resolution on page 3-131.) Counter accuracy
is
the
reference accuracy f 3 counts.
LO Does Not Phase Lock to INPUT.
In general,
LO
tuning is never exact but is close enough
to
give calibrated measurements. The
LO
does
not phase lock to the RF input signal.
LO Frequency for INPUT Less Than 2.5 MHz.
When the RF input signal is less than
2.5
MHz, the
LO
frequency is set to 101.5 MHz. This frequency
is arbitrary. The LO must remain on
to a l l o w
the RF input signal to pass through the input mixer.
Note that 101.5 MHz is the frequency the LO is set to for a 100
MHz RF
input signal with an IF
of 1.5
MHz.
3-128
LO
Frequency