If Level - HP 8901B Operation And Calibration Manual

Model 8901B
HHRRREBRHH
Operation
IF Level
FUNCTIONS
IF LEVEL
DESCR I PTl ON
The signal level in the Modulation Analyzer's IF can be measured and displayed as a percent of the
optimum level. An
IF
level display of 100% indicates sufficient signal strength to guarantee accurate
modulation measurements. AM accuracy is directly affected by the IF level. FM and
@M
accuracy is
affected only if the IF level is very low.
PROCEDURE
To display the IF level as a percent of optimum, select IF LEVEL (Shift, @M).
HP-IB PROGRAM CODE
IF LEVEL
=
S3
MEASUREMENT TECHNIQUE
Once the instrument is tuned and the IF Level function
is
selected, the automatic level control (ALC)
loop of the AM Demodulator detects the average level of the IF. If the ALC loop is closed and there is
sufficient IF signal available, the ALC loop automatically adjusts the IF gain within the loop to force
the detected IF to equal the ALC reference. When the instrument is running in automatic operation,
the input attenuation is adjusted to keep the
IF
level within range of the ALC loop.
In the IF Level measurement mode, the detected
IF
level is compared to the ALC reference and the
ratio of the two levels is expressed as a ratio in
%.
If the ALC loop is closed and if there is sufficient IF
level, the display will read 100%. If the ALC loop is open (Special Function 6.2) or if there is insufficient
IF level, the display will not read 100%. If the IF level is too high the display w i l l read greater than
100%. If the IF level is too low, the display will read less than 100%.
BLOCK DIAGRAM
LOCAL
p
OSCILL,
>
I
IF Level Measurement Block Diagram
IF Level 3-93