4-16.
FM ACCURACY AND FLATNESS (Cont’d)
4. On the function generator, press AMPTD 4S0 mV (p-p). Then press the LEFT ARROW key until the
first digit on the left side of the decimal point is flashing.
S. Set the spectrum analyzer’s center frequency to that of the DUT. Choose a frequency span of 2
MHz. Observe the carrier on the display of the spectrum analyzer while performing step 6.
6. Press the function generator’s UP ARROW or DOWN ARROW keys until the carrier is nulled
(minimum amplitude). The function generator’s LEFT ARROW and RIGHT ARROW keys will
change the resolution of the UP ARROW and DOWN ARROW keys for a finer or coarser amplitude
adjustment.
7. Measure the ms amplitude of the FM input with the DVM. Note this value on the test record card
as
Vin.
Calculate the actual FM sensitivity and then the percent error. Actual deviation is equal to 2.404
times 100 kHz (since the modulation index is at the first Bessel Null). The actual FM sensitivity is
then:
Actual FM Sensitivity
(.2404)/(Vin x 1.414)
% Error
=
100 x (Actual FM Sensitivity
—
Range)/Range
Where “Range”
=
1 (for 1 MHz/V), or 10 (for 10 MHz/V).
8. Set the function generator’s amplitude to 4S mV p-p. Press the DUT’s the UP ARROW key to
select an FM sensitivity of 10 MHz/V. Repeat steps 6 and 7.
9. Repeat steps 4 through 8 at CW frequencies of 2.5, 6.9, 13.4,18 and 20 GHz (20 GHz applies to the
8340B only). After entering a new CW frequency, press the FM key twice to display the FM
sensitivity in the DUT’s ENTRY DISPLAY and then press the DUT’s DOWN ARROW key to select
an FM sensitivity of 1 MHz/V.
HP 8340B/41B
Performance Tests
4-77
