Spirent DLS 6700, Operating Manual

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Appendix B "BACKGROUND NOISE MEASUREMENTS"
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Page B-1
Appendix B BACKGROUND NOISE MEASUREMENTS
Background noise measurements for the wireline simulator are performed with a
spectrum analyzer, in this case, an Agilent 4395A spectrum/network analyzer.
Input A is used in spectrum-noise mode and the results are displayed in power spec-
tral density units, i.e. dBm/Hz.
The noise floor of the Agilent 4395A with an input attenuator of 0 dB and resolution
BW=30 kHz (input A not connected) is illustrated in the graph below:
F
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7
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3
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Figure B.1 HP 4395A Noise Floor
Figure B.1 demonstrates the Agilent 4395A spectrum/network analyzer’s Noise Floor
over a Bandwidth of 0-30MHz. The graph shows that for frequencies up to 10 MHz,
the noise floor is about -144 dBm/Hz; for frequencies in the range 10-30 MHz, the
noise floor is about -151 dBm/Hz. Hence, when measuring noises with values close to
the noise floor of the analyzer itself, results are inaccurate in the sense that the ana-
lyzer’s noise adds to the noise of the device under test (DUT); the displayed result will
be worse than the real one.
In conclusion, the error introduced by the analyzer itself has to be taken into consid-
erations when measuring noises with values close to -140 dBm/Hz.