Specifications

15
If the actual local ambient temperature is not entered
into the analyzer, it will make its calculations with the
wrong temperature assumption. An extra error term in
the over-all uncertainty margin will be present. This can
be a significant value if the true noise figure of the DUT is
low. Figure 10-2 shows typical differences between the
displayed and actual noise figures for different ambient
temperatures.
Figure 10-2
● HINT 10:
Account for the temperature of
the measurement components
Y-Factor noise figure analyzers assume that the surface
temperatures of all components in the measurement
(noise source, DUT, connectors, cables, etc.) are the
default value for Tcold, 290K (16.8°C, 62.2°F). If this is
not the case, enter the correct temperature of each
component into the analyzer and monitor them
regularly. Full featured noise figure analyzers allow the
entry of the temperatures of any components added before
and after the device.
Figure 10-1 shows the measurement response curve
where the noise powers N
1
and N
2
are due to input noise
temperatures Tcold and Thot, respectively. The solid
line on this graph represents the response when T
0
is
considered as the reference ambient temperature of 290K.
If the T
cold
of the noise source (for a solid state noise
source, its surface temperature) is not equal to T
0
, then the
dotted line may become the response curve. The noise
power added by the DUT would then be N
a
´ and not N
a
.
Figure 10-1
+1K
T
amb
= 296.5K (=74 F)
T
amb
= 305K (=89 F)
0.24
0.20
0.16
0.12
0.08
0.04
0 0.4 0.8 1.2 1.4 1.8
NF(dB)
NF(dB) = F mea - Factual
P
out
N
2
N
1
N
a
´
N
a
T
o
T
c
T
h
T
s