Model
8901B
Operation
1
n put/Outpu t Status
When the instrument
is
measuring frequency error, the output signal available at MODULATION
OUTPUT/AUDIO INPUT
is
the same
as
for the last modulation measurement
(as
indicated by the
MODULATION OUTPUT annunciator).
Relative Measurements
If
frequency error
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.)
Use Manual Tuning for Best Measurements
The frequency error function can be used with the automatic tuning low-noise LO tune mode, but
it
is
most valuable when used with
manual
tuning (normal or Track Mode).
It
is
not recommended
that
frequency error be used when in automatic tuning track mode, since an inherent tuning offset exists
in this mode.
Step Frequency Aids Multi-Channel Measurements
Check channel accuracy on multi-channel transmitters using the frequency error function in conjunc-
tion with the kHz
fi
and kHz
U
keys. Set the step frequency
to
the channel spacing
to
quickly determine
the accuracy of evenly-spaced channels.
LO
in Image Passband Distorts Measurements
When tuning manually,
it
is
possible
to
accidentally adjust the
LO
so
that
the input
falls
in the image
passband; for example, when using the kHz
fl.
and kHz keys. Frequency error measurements are
inaccurate when the input image enters the
IF
passband. Refer
to
RF
frequency
Zhing
on page
3-115
for an illustration of the image passbands.
Changing Resolution
Normally, the counter updates the display five times each second. For selection of other resolutions,
use Special Function
7.
(Refer
to
RF Requency Resolution
on page
3-131.)
Counter accuracy
is
the
reference accuracy
f3
counts.
Input/Output Status
When the Frequency Error function
is
selected, MODULATION OUTPUT/AUDIO INPUT continues
to
output the last-selected modulation
signal,
filtered and/or de-emphasized (except PRE DISPLAY)
as
previously selected. The calibration of this output depends on the input signal level and should be
assumed only when all errors are enabled (Special Function
8.8).
Parts Per Million Display
To display frequency error in parts per million (ppm), first display the frequency error, then enter
1/10
the reference frequency (in MHz)
as a
ratio reference, and select RATIO. The display shows the
frequency error in parts per million.
FW
Frequency Error
3-123
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