Wavetek 3000 - Frequency Offset Circuit

4194
0
1718
/b98
/S93
AN .
/498
/398
1298
1198
MNz
MNz
MHz
/467
1449
270-
250 - -
210
170-
130
-90--
SO
280 -
2401
200 4
160
/20
90
~ I
40
O
O
3 .15 .1 PhaseDetector
?Oo
/70
/Zo
The frequency offset circuit converts
the frequency
of the VCO
to
a lower fre-
quency which retains the frequency error
information
for
use by the phase detec-
tor . In addition to the frequency off-
set circuit andthe phase detector,sev-
eral auxillarycircuits are included .
The phase detectorcompares the"offset"
VCO frequency to the reference

frequency
from theM31 .

(Refer to the description
of the M31 for a more detailed descrip-
tion of this 10 .000 - 9 .001 MHz refer-
ence .)
The
phase detector output voltage goes
positive or
negative to ultimately drive
the wide oscillator
higher
or
lower in
SO
/o
0
40
70
g12
Figure 3-21 . M34 - Signal Frequencies
THFnRY OF OPERATION
1212
BO 110 /60 ; 140
190 BZO 3(0
/00
200
300
OUTPUT
F - R10Ue/VC)
,
MNz
/so
.200
-~t~{- .~-_ -ma y
440 4,5 1 0 1 .00
400 500
3.15 .2 Frequency Offset Circuit
280
The VCO error information must be con-
verted to a frequency useable by the
phase detector . This conversion is
made
by mixer #1, a 270 MHz low pass filter,
mixer #2 and a 10
MHz
low pass
filter .
Refer to Figures
3-20, 3-21 and 3-22
for descriptions of signals .
Mixer
41
heterodynes
the VCO frequency
with the "MHz steps" reference
fre-
quency (1448
+
R) MHz .

The difference
frequency,

11448
+
R - VCOJ, is below
270 MHz .

This signal is sent to mixer
42 where
it is heterodynedwith the 40
MHz comb .

For any output frequency
graph
D in Figure 3-21
shows only
the comb
frequency which
will yield
the desired
output ( below
20 ?liz)
3-21
frequency until both inputs to the phase
of
m ;xPr # 2 .
Tf the
loop is
locked,
detector are the same frequency . The
mixer ,#
2 will
produce a 10 MHz
integratorserves as
a low pass filter
difference as Ghown
in Figure 3-21
for
the
phase detector . (assuming the "kHz" switches are set for