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The beatnote frequency is set by the relative frequency
difference between the two sources. If you have two very
accurate sources set at the same frequency, the resulting
beatnote will be very close to 0 Hz. You may have to look
carefully at the HP 3561A's display to see a beatnote close
to 0 Hz.
On the other hand, less accurate sources may create a
beatnote greater than 100 kHz. Searching for the beatnote
will require that you adjust the center frequency of the
HP 8640B above and below the frequency of the DUT until
the beatnote appears on the analyzer's display. If the
beatnote signal does not appear, you will need to verify the
presence of an output signal from each source before
proceeding.
Once you have identified the beatnote, tune the HP 8640B
until the beatnote frequency is < 100 kHz.
SPAN
100 000 Hz
A: MAG
- 7
dBV
I
10
dB
/ D I V
- 8 7
START:
RANGE: - 7 dBV
STATUS: PAUSED
^Frequency
Domain
..Time
Domain
. 1 1
0 Hz
BW: 9 5 4 . 8 5 Hz
STOP:
100 000 Hz
0-100kHz
DEFINE
START
DEFINE
CENTER
DEFINE
SPAN
DEFINE
TIME LEN
FRO AXIS
L I N LOG
Figure 3-12. The Beatnote is Displayed in Both the
Frequency and Time Domain by the HP 3561 A.
3-36
Signal Source Applications
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