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5.3 The frequency generated by the DDS IC is
determined by the 32-bit frequency word loaded into
the frequency register on the 409B. The output fre-
quency is given by:
F
= F
out
setting
Where:
F
= 28,633,115.306666667 Hz (int.)
clock
F
= Binary value in DDS IC.
setting
(F
ranges from 0 to 2
setting
Kp = PLL Multiplier (1 or 4 to 20)
This reduces to:
F
= F
out
for the internal (default) clock and the default PLL
Multiplier (Kp=15) settings.
5.4 Since the DDS IC is a sampled data system, the
output frequency is limited to a maximum of 1/2 the
master clock frequency (F
is possible to generate an output near 50% of the
clock, the distortion may be unacceptable. There-
fore, the output is limited to approximately 40% of
the system clock and steep output filters are pro-
vided on board: in this case 7th-order elliptical low
pass filters.
5.5 If you are using an external clock and a Kp
which give a clock substantially lower than the
429.497 MHz default internal clock, you may need
to filter the Outputs to obtain acceptable distortion
for your application. For best performance, set the
corner frequency at 40% or less of your external
clock frequency times Kp. The lower your filter as a
percentage of your clock frequency, the lower the
distortion.
5.6 For example, if you are using a 10 MHz external
clock, with the default reference multiplier (Kp) of
15, then the internal clock is 150 MHz. An optimal
filter for this frequency would then be approxi-
mately 60 MHz (40% of 150 MHz).
NOVATECH INSTRUMENTS
32
*Kp*F
/2
Hz
clock
31
-1)
MHz
setting
31
<= 2
-1). While it
setting
6.0
PERFORMANCE TEST
6.1 Install the 409B as directed in the Serial Opera-
tion part of Section 3. Connect your host controller
and operate the 409B per Section 4. The test limits
assume a stable environment of 18-28
Allow the 409B to warm up for at least 15 minutes
before performing any measurements. For best
results, the 409B should be verified in its installed
6.2 See Table 3 for a list of recommended test
equipment to perform the following measurements.
Table 3: Recommended Test Equipment
Item
Oscilloscope
50Ω Termination
Frequency
Counter
Counter Time
Base
External Clock
6.3 Verify Frequency Accuracy. To verify the fre-
quency of the 409B, set the output sequentially to
each value in Table 4. Connect the recommended
frequency counter set to 50Ω termination and 1Hz
resolution. Verify the limits show in Table 4. Test all
channels to verify functionality of all outputs. If you
do not use an external reference for the frequency
counter, be sure to add the error of your counter to
the tolerance. (LSD = Least Significant Digit on
counter).
Table 4: Frequency Test Points
Frequency
100 kHz
1 MHz
10 MHz
8
o
C.
NOTE:
environment.
Minimum
Specification
Recommended
300 MHz,
Tektronix
50Ω
TDS3032B
50Ω,
1%
Tektronix
±
011-0049-01
180 MHz
HP53132A
10 MHz,
Novatech
<
0.1ppm
Instruments
±
Model 2960AR
400 MHz
Novatech
Instruments
Model 440A
Tolerance
0.15 Hz
±
1.5 Hz
±
15 Hz
±
409B Manual, 17-Apr-2015
1 LSD
±
1 LSD
±
1 LSD
±
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