N9069C Noise Figure Measurement Guide 85
Measurement Related Tasks and Concepts
Calculating the Noise Power into Different Stages of the Noise Figure Measurement
System
Calculating the Noise Power into Different Stages of the Noise
Figure Measurement System
show the possible blocks in the signal path of the noise signal in the
noise figure measurement. The blocks with dotted lines indicate that you can
choose whether to use them or not. The non-linear components in the signal
path include the USB Preamplifier, the internal preamplifier and the input
mixer. The input noise power of these components should not exceed the
maximum value for the linear range.
Figure 3-8
Blocks in the Signal Path of the Noise Signal in the Noise Figure Measurement
To calculate the noise power in different stages,
Equation 3-2
in which,
— The unit of
is dBm.
— -174 dBm/Hz is the thermal noise per hertz calculated from
.
— BW is the bandwidth of the DUT, for most cases. The unit is Hz. If you are
going to calculate the noise power of the input mixer for frequency ranges
higher than 3.6 GHz, BW is the bandwidth of the preselector, which is
usually below 80 MHz.
—
is the excess noise ratio of the noise source. Normally, the ENR of a
noise source is given in dB.
— F is the noise figure in linear terms of a part of the test system, which is from
the DUT input to the input point of the noise power under calculation. For
example, if you are calculating the noise power of the input mixer for
frequency ranges below 3.6 GHz, the F includes the noise figure for the
combination of DUT, USB Preamp, internal attenuator, internal preamp.
—
is the gain of a part of the test system, which is exactly the same part
as that is used in F calculation. For example. if you are calculating the noise
power of the input mixer for frequency ranges below 3.6 GHz, use the
following equation.
1RLVH
6RXUFH
'87
86%
3HDPS
,QWHUQDO
$WWHQXDWRU
,QWHUQDO
3UHDPS
,QSXW
0L[HU
3UHVHOHFWRU
)RUIUHTX]
)RUIUHTXHQFLHV
!*+]
,QVLGHWKH6LJQDO$QDO\]HU
P
noise
174
–
10
log
10
×
BW
(
)
10
log
10
×
ENR
linear
F
+
(
)
Gain
dB
+
+
+
=
P
noise
kT
0
ENR
linear
ENR
linear
10
ENR
dB
10
⁄
(
)
=
Gain
dB
Summary of Contents for CXA N9000B
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