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5. The difference between these two frequencies
is the actual peak-to-peak frequency deviation.
It should be between 190 MHz and 210 MHz.
Record the difference on the Test Record.
Unlocked Narrow FM Mode
1. Set up the 682XXB/683XXB as follows:
a.
Reset the instrument by pressing SYSTEM ,
then Reset . Upon reset, the CW Menu is dis
-
played.
b. Press Edit F1 to open the current frequency
parameter for editing.
c. Set F1 to 5.0 GHz.
2. Set up the Spectrum Analyzer as follows:
a. CF: 5.0 GHz
b. Span/Div: 100 kHz (1 MHz across the display)
3. On the 682XXB/683XXB, make the following set-
tings:
a.
Press MODULATION , then FM . At the result-
ing FM Status menu, press More to go to the
additional FM Status menu.
b. At the additional FM Status menu, press
Unlocked Narrow , then press Previous Menu
to return to the main FM Status menu.
c. At the FM Status menu, press Edit Dev. and
set the deviation to 0.240 MHz.
d.
Press Edit Rate and set the rate to 99.8 kHz.
e.
Press On/Off to FM on.
4. Since the 682XXB/683XXB is now in Unlocked
Narrow FM mode, it is necessary to retune the
Spectrum Analyzer to center the display.
5. On the 682XXB/683XXB, use the cursor control
key to place the cursor under the last 0 in the de
-
viation setting (0.240
MHz). While observing the
first Bessel null (Figure 3-9), increase/decrease
the deviation frequency with the cursor control
key to reduce the carrier as low as possible.
6. Record the FM deviation frequency, displayed on
the 682XXB/683XXB, on the Test Record.
682XXB/683XXB MM 3-35
PERFORMANCE FREQUENCY
VERIFICATION MODULATION TESTS
CENTER FREQUENCY
BESSEL
NULL
Figure 3-9. Typical Spectrum Analyzer Display of
Bessel Null on FM Waveform
NOTE
You may need to adjust the RBW
setting on the Spectrum Analyzer in
order to see the >–48 dBc null.