The Mixer Circuit
The
1st
IF and the
2nd
Lo
are combined in the mixer circuit. The resulting
difference frequency (the 2nd IF) is a constant 4
kHz
in both bands, as
lhble
12-4 shows
Band
Super Low
LOW
High
‘able
12-4. Mixer Frequencies
1st
IF
2nd
L43
0.010
to
0.300
MHZ
0.014
to
0.304
MHZ
0.300tAJ
16.0
MHZ
0.304 to 16.004 MI-h
1.ooo
MHZ
0.996 MHz
2nd
IF
4.0
HI!4
4.0
HI2
4.0
kHz
A10
Digital IF
The three 4
kHz
2nd
IF
signaIs
from the sampler/mixer assemblies are input
to the A10 digital IF assembly. These signals are sampled at a 16
kHz
rate.
A
fourth input is the analog bus, which can monitor either an external input at
the rear panel AUX IN connector, or one of 31 internal nodes. A multiplexer
sequentially directs each of the signals to the ADC (analog-to-digital converter).
Here they are converted to digital form and sent to the A9 CPU assembly for
processing. Refer to “Digital Control Theory” for more information on signal
processing.
12-30
Theoryof
Operation
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