A13/14
FRACTIONAL-N
1ST LO
A12
REFERENCE
@-
vcxo
40MHz
-=
$
REFERENCE
HARMONIC
FREQ (MHz)
1
1.000
:
0.500
0.333
1
1ST IF
Ad
SOURCE
3.0 to
6.8GHz
YIG OSC
3GHz TO
sg6232d
Figure 12-6. Harmonic Analysis
External Source Mode
In external source mode, the analyzer phase locks its receiver to an external
signal source. This source must be CW (not swept), but it does not need to be
synthesized. The user must enter the source frequency into the analyzer. (The
analyzer’s internal source output is not used.)
To accomplish this, the phase lock loop is reconnected so that the tuning voltage
from the A11 phase lock assembly controls the VCO of the
Al4
fractional-N
assembly and not the
A3
source. See Figure 12-7. The
VCO’s
output still drives
the
1st
LO of the samplers and down-converts the RF signal supplied by the
external source. The resulting
1st
IF is fed back to the A11 phase lock assembly,
Theory of Operation 12-23
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