Keysight Technologies CXA N9000B, Manual

Page: 42 / 88

42 N9069C Noise Figure Measurement Guide
Making Noise Figure Measurements
Using the U7227-Series USB Preamplifiers in Noise Figure Measurements
Rough Guide for the Noise Figure Test System Configuration
To configure the test system for accurate noise figure measurements, the first
priority is to make the instrument noise figure (USB preamp signal
analyzer) as low as possible. To reduce the instrument noise figure, the USB
preamplifier and internal preamplifier should be used whenever possible. If an
overload or compression exists in the test system, removing or turning off the
preamplifier (USB preamplifier or internal preamplifier) or adding internal
attenuation can eliminate the problem. On the signal analyzer,
— To turn on/off the internal preamplifier, press AMPTD , Signal Path tab,
Internal Preamp , On / Off .
— To set the internal attenuator, press AMPTD , Attenuation tab, and set the
attenuation.
Figure 2-16 and Figure 2-17 show the supported DUT characteristics (noise
figure and gain) of different system configurations for different frequency
ranges up to 26.5 GHz. The X-axis is for the DUT noise figure, the Y-axis is for
DUT gain. This rough guide is based on the noise power calculation before the
non-linear components. For more details about noise power calculation in
different stages of the test system, refer to “Calculating the Noise Power into
Different Stages of the Noise Figure Measurement System” on page 85 .
Before using Figure 2-16 and Figure 2-17 to find a proper test system
configuration, you need to pay attenuation to the following points:
— The DUT reference bandwidth used to calculate the noise power is 3.59
GHz, which is the worst case for the lower band (10 MHz to 3.6 GHz). To
maintain consistency between the lower band and higher band, the same
DUT reference bandwidth is used in the calculation for frequency ranges
above 3.6 GHz. Then the reference bandwidths (Ref BW) for both below 3.6
GHz and above 3.6 GHz are both 3.59 GHz.
If the DUT has a narrower bandwidth, the DUT characteristics can be
increased accordingly. For example, if the DUT has a bandwidth of 100
MHz, the supported DUT gain can be increased by a factor of
, that is by 15.6 dB.
— The noise figure and gain for the U7227C USB Preamplifier are used in the
calculation. If you are using the U7227A or U7227F, the supported DUT
characteristics should be different.
— A 6 dB ENR noise source is used in the calculation. If you are using a noise
source with higher ENR, the supported DUT gain will be lower.
— For different instruments and for a wide frequency range, the data for the
USB preamplifier and the X-Series signal analyzer differs considerably, the
most precise data is used in most cases.
10 3.59 10
9
×
100 10
6
× ⁄ ( )
log
×