Product specifications

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Two-tone IMD measurements in Pulse Mode
The PNA-X employs clean internal sources with high output power, internal
combining network, and an optional IMD measurement application that makes
two-tone IMD measurements over the frequencies easier and faster. Unlike
traditional signal generators and a spectrum analyzer method, the IMD mea-
surements using PNA-X provides single point of setup dialog, guided calibra-
tion, and several-tens to one-hundred times improved measurement speed
in swept-frequency or swept-power IMD measurements. In this swept IMD
measurement, the PNA-X uses its unique narrowband filter path for better sig-
nal selectivity. In this section, we will discuss IMD measurements under pulse
condition with measurement setup considerations and techniques to overcome
measurement problems (narrowband pulse is not available in PNA-X applica-
tion measurement classes).
There is a fundamental setup conflict between typical IMD measurements
and wideband pulse measurements, when made together. The wideband pulse
measurements use relatively wide IF bandwidth (to narrow the data acquisi-
tion window), while IMD measurements in general use narrow IF bandwidth
to accurately measure low level distortion products. The following are some
considerations in IMD measurement setups under pulse operation.
Tone spacing versus IF bandwidth
The spacing between two main tones should be approximately more than 10
times wider than the IF bandwidth. If narrower tone spacing is required, the
IF bandwidth must be reduced to avoid signal interference (seen as ripples on
the traces) thus requires wider pulse width.
Use standard IF filter path
The IMD application automatically switches to the narrowband IF filter path,
where the IF signal is filtered with the high-Q crystal filter with 30 kHz band-
width. This filter prevents capturing the whole spectrum of pulsed-RF signal. It
must be switched to standard IF path when IF bandwidths greater than 30 kHz
are used.
Disable “Reduce IFBW at Low Frequencies”
The PNA-X uses narrow IF bandwidth to reduce trace noise at low frequencies
by default. The frequency and the IF bandwidth reduction ratio depend on the
frequency models. It is recommended that this capability is always turned off
when making IMD measurements under pulsed operation.
Use sweep averaging to reduce noise
IMD measurements become noisier with wide IF bandwidths, so sweep aver-
aging is recommended to reduce the noise.