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Model 8902A
Operation
Input/Output 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 toRatio on page
3-245.)
Use Manual Tuning for Best Measurements.
The frequency error fiinction 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 fiinction in
conjunction with the kHz
t
and kHz 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
. h
and kHz
4
keys. Frequency error measurements are
inaccurate when the input image enters the IF passband. Refer to R F Freqirmcy Tuning on page
3-141
for an illustration of the image passbands.
Changing Resolution.
Nwmally, the counter updates the display five times each second. For selection of other resolutions,
use Special Function
7.
(Refer to Rt;' Frqi/cncy Rcsohtion on page
3-157.)
Counter accuracy is the
reference accuracy
*3
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.
3-149
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