Measurement Modes With A Dsb System Downconverter - Keysight Technologies N9040B UXA Manual

Making Noise Figure Measurements
Making Frequency Converter Measurements

Measurement Modes with a DSB System Downconverter

The noise source generates broadband noise. In a DSB system downconverter
calibration setup, noise input from both the USB and LSB sidebands will be
converted to the same IF, as shown in
downconverter measurements have implicit linear averaging of the DUT
characteristics. The same ENR values are used for both the USB and LSB
frequencies, and are taken from the average frequencies of the USB and the
LSB. This corresponds to the LO frequency. Results returned are the average of
the two sideband powers.
The benefits of a DSB measurement are minimal filter requirements, and wide
frequency coverage. In the DSB measurement, the usual aim is to choose as
low an IF as possible, to minimize the separation between the sidebands, and
thus get the optimum resolution possible.
When making Double Sideband (DSB) measurements, it is important that
the IF is much lower in frequency than the LO frequency. This is because
the ENR values in the ENR table can only be applied to one frequency or, in
the case of a swept measurement, to one set of frequencies. The ENR
values can not be applied simultaneously to both the upper sideband and
to the lower sideband. The ENR values are therefore applied to the
midpoint between the upper sideband and the lower sideband, and this
equates to the LO frequency.
Consequently, the higher the IF frequency is in comparison to the LO
frequency, the further apart the upper and lower sidebands will be. The
further these upper and lower sidebands are from the LO frequency, the
less accurate the ENR value will be.
It is recommended for greatest accuracy that the IF frequency be no
greater than 1% of the LO frequency when making double sideband
measurements. When making a swept measurement, no frequency in the
swept frequency band should exceed 1% of the LO frequency.
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Figure 2-7. The DSB system
N9069C Noise Figure Measurement Guide