Introduction; Operating Characteristics; Frequency Resolution - HP 83522A Service Notes

Model 83522A
Operation
SECTION Ill
OPERATION
3-1. INTRODUCTION
3-2. This section is divided into four major
sections. Operating Characteristics explains the
frequency resolution characteristics in CW and
swept modes. Front and rear Panel Features are
shown with illustrated descriptions. Operating
Instructions provide a front panel frequency
calibration procedure, configuration switch
setting instructions, and crystal detector and
power meter leveling instructions. Operator's
Maintenance includes information on the plug-
in error codes, fuses, and service tags.
3-3. OPERATING CHARACTERISTICS
3-4. Frequency Resolution
3-5. Two areas relating to frequency resolution
must be considered; input resolution and
displayed resolution. lnpui resolution refers to
the number of bits (8 bits
=
256 points)
internally used in the digital to analog con-
verters (DACs) used to generate the tuning
voltage for a particular mode of operation. Table
3-1 cross references input resolution with each
DAC used. Displayed frequency resolution
refers to the number of digits shown on the
8350A FREQUENCY displays.
Table 3-1. Input Resolution
DAC outputs. With this DAC configuration the
STARTISTOP sweep mode is computed by the
microprocessor into a center frequency and a
AF sweep width. Therefore the operation of all
sweeps are set with a center frequency and
sweep width. The center frequency is specified
by the center frequency (CF) DAC and the
Vernier DAC, and the sweep width is deter-
mined by the AF DAC.
.
DAC Used
CF
Vernier
AF 1
-
118 o f band
AF 118
-
1/64 o f band
AF <1/64 of band
3-7. The C F DAC has 12 bits, hence 4096
points across the plug-in frequency band
(including overrange). The analog output ranges
from zero to ten volts, which is used to coarsely
specify the center frequency output of the plug-
in. These parameters give the C F DAC a
resolution of 0.024% (2.5mV) over the full band
(including overrange).
3-8. Resolution of Center Frequency is en-
hanced with a summed voltage input generated
by an 8-bit (256 points) Vernier DAC. Vernier
range is set to +0.05% of RF plug-in bandwidth
(including overrange). In multiband plug-ins,
total range of the vernier will vary with each
band sweep. Vernier resolution is determined by
dividing +0.05% bandwidth by 256 points (128
points either side of CF). The voltage range of
Voltage
Resolution
2.5 mV
40 pV
10 mV
1.25 mV
0.156 mV
the total 256 points on the Vernier DAC is equal
to four points on the 12-bit CF DAC (two points
on either side of CF). This increases C F
resolution from 0.024% (2.5mV) to 0.00038%
(.04mV), and improves the relative accuracy of
the C F by a similar factor.
Frequency
Resolution
I
0.606 MHz
9.45 kHz
2.43 MHz
0.303 MHz
38.0 kHz
NOTE
When adjusting the vernier through its
zero-point, the CF DAC is incremented or
decremented by the total value of the
vernier (2 points on the CF DAC). At this
3-6. Figure 3-1 is a simplified block diagram of
time the accuracy of the Center Frequency
the frequency tuning circuits. The net tuning
is again entirely dependent on the CF DAC
voltage results from the summation of the three
+0.005% of bandwidth.