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Model 3320AjB
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Section IV
To Leveling Assembly
And
Modulotor Assembly
Switches
A,B,aC
Are Fet Switches
B20A/B-B- )!>02
Figure
4-14.
Simplified Amplitude Reference.
to correct the amplitude of the leveled 20 MHz. See
Paragraph
~3
for a detailed discussion of the thermopile
circuitry.
4-54. The leveled 20 MHz is applied to a mixer where it is
mixed with the 20 MHz to 32.99 MHz from the frequency
section. The difference frequency out of the mixer (0 Hz to
12.99 MHz) is amplified, filtered, and amplified again
before it is applied to a BCD controlled 10 dB/step
attenuata! assembly.
4-55. The 10 dB/step altenuator is capable of switching in
up to 90 dB of attenuation in 10 dB steps. The leveled
20 MHz is capable of applying 9.99 dB of attenuation in
0.01 dB, 0.1 dB, or I dB steps. These two altenuators work
in conjunction to cover the 3320B range of +26.99 to
-69.99 dBm. At +26.99 dBm, both attenuators are applying
o
dB of altenuation. When altenuation is added, the first
9.99 dB is from the leveled 20 MHz. Then at +16.99 dBm,
the 10 dB/step altenuator will supply 10 dB of attenuation
and the leveled 20 MHz is back to 0 dB of altenuation. This
operation continues through the attenuation range to
-69.99 dBm. The switching points of the 10 dB/step altenu-
ator below 0 dBm is -3.01 dBm, -13.01 dBm, -23.01 dBm,
etc.
4-56. Reference Section.
4-57. The reference section of the 3320AjB consists of two
voltage controlled crystal oscillators; a vernier oscillator,
which is switched in and out with the vernier .control, and a
EXTERNAL
RfFERENCE
INPUT
TO
20
MODULATOR IN
~
~------""'-------------"M:::H:",~·:~t-h~DE
TO
) .--<.
CO:~::;TOR
20Mttz
MIXER
~
;;' 8 :;.,.RANGE
VCXO
MHz
DIVIDERS
1
-
7
1 0
TO
1- --.
....,.~2
_-N IN
"H
AMPLITUDE
,..., .t
SECTION
Figure 4-15. Reference Section.
.
• 2
TO
REAR
~_,.!Ic...PANEl
MHz I MHz
OUT
TO
~_",I",.VERN
IER
MHz
~~~~JOL
4-9
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