Quonset Microwave
www.quonsetmicrowave.com
QM2010-10-20
USB RF Synthesizer Module
10 GHz
– 20 GHz output
For price, delivery, and to place orders, please contact Quonset Microwave, a subsidiary of Applied Radar:
315 Commerce Park Road, North Kingstown, RI 02852 Phone: 401-295-0062
-3-
Revised June 21, 2023
Integer and Fractional Modes of Operation
The QM2010 USB RF synthesizer Module is capable of operating in integer or fractional mode. In integer
mode, the frequency resolution of the QM2010-10-20 is dependent on the reference frequency and reference
divider as defined by this relationship
𝑓𝑟𝑒𝑠 =
𝑟𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒
𝑟𝑒𝑓 𝑑𝑖𝑣𝑖𝑑𝑒𝑟
∗ 4
. On first power-up, the QM2010-10-20 is set to
integer mode and uses the internal 50 MHz reference with a reference divider value of 1. This provides a
default frequency step size of 200 MHz. Operation in fractional mode allows for a frequency step size of 1
MHz. When operating in fractional mode, it is recommended to set the reference divider value to 1.
Table 1
–
Integer vs. Fractional Mode Comparison
Parameter
Integer Mode
Fractional Mode
Phase Noise
Comparable to fractional mode phase noise
at offset frequencies ≤ 100 kHz,
if
the
reference divider value is ≤ 2
Degrades as reference divider increases
Comparable to integer mode at offset
frequencies ≤ 100 kHz,
if
the reference
divider value = 1 (should always be 1 for
best performance).
Spurious Content
Better spurious performance
Additional spurs present at frequency offsets
≤ 5 MHz (see Figure 2)
Recommendation
Use
whenever
possible
for
best
performance
Use when fine frequency resolution is
required
Figures 1 and 2 illustrate the performance difference between integer and fractional mode when tuning to 15.9
GHz with a 50 MHz reference. In order to tune to 15.9 GHz with a 50 MHz reference, the user can either
operate in integer mode with a reference divider of 2, or in fractional mode with a reference divider of 1. Figure
1 depicts the phase noise differences between 15.9 GHz in fractional mode vs. integer mode with a reference
divider of 2, whereas Figure 2 shows the spurious content difference in a 10 MHz span between the two
modes of operation.
Figure 1 -
Fractional vs. Integer Mode Phase Noise
Figure 2
–
Fractional vs. Integer Mode Spectrum
10 MHz span, RBW = 10 kHz, VBW = 300 Hz