Frequency Section; Amplitude Section 4-2; Reference Section - HP 3320A Operating And Service Manual

Model 3320AjB
Section IV
4-41. Frequency Section.
442. The frequency section of the 3320AjB is composed
of a BCD controlled voltage tuned oscillator (VTO), phase
locked to a 10 kHz reference signal, and six range dividers,
including Option 006 (see Figure 4-2).
4-43. The output frequency of the frequency section is
variable from 20 MHz to 32.99 MHz with the vernier in/out
control in the vernier out position. With the vernier in/out
control in the vernier in position, two more additional
digits are variable via the vernier oscillator making the
output frequenc)' of the frequency section 20 MHz
to
32.9999 MHz. In the following discussion. the frequencies
given are considered to be with the vernier in/out in the
vernier out position. Refer to Paragraph 4-60 for a
discussion of the vernier oscillator.
4·44. VTO, Phase-Lock Circuitry. The BCD signal, from
the controller section. for the ovcrrange digit and the two
most significant digits of 3320AjB output frequency, is
applied to a
0/
A converter on the VTO assembly (sec
Figure 4-10). The D/A converter converts the BCD signal
to
a de voltage which is applied to the VTO as a pretunc
voltage. This sets the VTO close to the desired frequency.
4-45. Precise frequency control is achieved by phase-
locking the output of the VTO to a 10kHz reference signal
from the reference oscillator. This is accomplished by
applying the output of the VTO to a
-0-
N counter. The
-0-
N
number is controlled by the same BCD signal which
pretuned the VTO plus the BCD signal for the remainder of
the frequency digits. This signal sets the -:- N coumer in
such a manner that the counter will divide the output of
the VTO to 10 kHz (refer to Paragraph 4-70 for a detailed
discussion on the
-0-
N counter). The 10 kHz output from
the -:- N counter is applied to a phase comparator where it
is compared
to
<l
10kHz
signal from the reference
oscillator. Any difference in phase between the two signals
will be developed as a de voltage. This de voltage is applied
to the VTa to correct its frequency.
4-46. Range Dividers. The output signal of the VTO is
applied either
to
the amplitude section or to a series of
range dividers, depending on the position of the range
control. Seven ranges are available on the 3320AjB,
including Option 006. Table 4-1 lists the range positions,
the number of range dividers used for each position, and
the output frequency of each range divider.
4-47. With the range control in the 10 MHz position, the
output of the VTO (20 MHz to 32.99 MHz) is applied
directly to the amplitude section. In the amplitude section,
the Signal is mixed with 20 MHz and the difference
frequency (0 Hz to 12.99 MHz) is available at the 3320A/B
output jack.
448. With the range switch in any position other than the
MHz position, the output of the VTO is applied to one or
more of the range dividers. Each divider uses a divide and
mjx technique to increase the resolution of the Output
signal by one decade while decreasing the maximum
frequency by one decade (see Figure 4-1 I). For example, if
the range control is placed in the 1000 kHz position. the
VTO output (20 MHz to 32.99 MHz) is divided by 10
(2 MHz to 3.299 MHz) and mixed with 18 MHz from the
reference section. The sum of these two signals (20 MHz to
21.299 MHz) is applied to the amplitude section. This
signal is mixed with 20 MHz in the amplitude section, and
the difference frequency (0 Hz to 1299 kHz) is available at
the 3320A/B Output jack.
4-49. Amplitude Section.
4-50. 3320A Amplitude. The 3320A output signal is
variable from 0 dBm to 13 dBm, into SO ohms, by a front
panel potentiometer.
The
potentiometer applies a de
voltage to a modulator to amplitude modulate a 20
MHz
signal from the reference section (sec Figure 4-12). The
leveled (amplitude modulated) 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 HI to 12.99 MHz) is amplified, filtered, and
amplified again before it is applied
to
the 3320A output.
20 TO 21.299MHz
leMHz
3320AJ9· B-!!)l!)
SIGNAL TO
AMPLITUDE
SECTION
100kHz
RANGE
POSITION
~-c,.....,tr--
SIGNAL TO
NEXT RANGE
DIVIDER
leMHz
1000 kHz
RANGE
POSITION
2 TO 3.299MHz
10MHz
RANGE
POSITION
SIGNAL
FROM
_-",,-1\_-1
VTO
Figure 4-11. Range Dividers.
4-7