HP 8901B Operation And Calibration Manual page 309

Model 8901B Operation
HP-IB PROGRAM CODES
LOG display = LG
LIN display
=
LN
PREVIOUS RATIO
=
R2
RATIO off
=
R O
RATIO on = R1
SPCL
=
SP
MEASUREMENT TECHNIQUE
In the Ratio mode, measurements are made in the same way as when not in the Ratio mode; however,
before the result is displayed, the internal controller converts it
to
ratio. The following equations are
used for computing ratio:
(M/R) (100%) =
% ratio for all measurements,
(20) log (M@) =
dB
ratio for the following measurements:' AM FM, @M, AUDIO DISTN,
IF
LEVEL, SINAD (29.0 SPCL), Ext Audio RMS Level, and (10) log (M/R) =
dB
ratio for the
following measurements2 FREQ, AUDIO FREQ, FREQ ERROR,
LO
Frequency (33.0 SPCL),
IF
Frequency (34.0 SPCL),
where M is the (undisplayed) measurement result and R is the ratio reference.
COMMENTS
Input/Output Status
The output signal at MODULATION OUTPUT/AUDIO INPUT is unaffected by the Ratio function.
Displaying the Reference
When using a currently-displayed measurement result as the ratio reference, that result actually becomes
the reference. The only way to read this reference then is to display it via Special E'unction 11.2.
Display Flicker
Since displayed measurement results are computed from the actual physical measurements, least-
significant digit flicker in the physical measurement can often lead to larger apparent flicker in the
displayed result. For example, an AM measurement varying between 50.0% and 50.1% will vary between
100.0% and 100.2% REL with a ratio reference of 50 (or between 0.00 and 0.02
dB
after switching to
logarithmic units).
dB Ratio
When using
dB
ratio; any ratio reference or measurement result that causes ratio M/R (refer to previous
equations) to equal 0, results in a display of Error
11
since the log of 0 is undefined.
When uV, mV, or V units are used, this equation provides the ratio result for RF POWER, TUNED RF LEVEL, and RF
LEVEL
(35.0 SPCL) measurements.
When watts units are used, this equation provides the ratio result for RF POWER, TUNED RF LEVEL, and R F LEVEL
(35.0 SPCL)
measurements.
Ratio and Log/Lin
3-217