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IMD Measurement using 8753C?
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on May 31, 2008
on May 31, 2008 by Dr_joel
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Regarding IMD measurement, is there any difference between 8753B and C versions? In two tone measurement, is there a way to use just one external source?
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May 31, 2008 8:57 AM
While it is possible to do IMD measurements with an 8753, it's really a challenge and you must take great care in setup.
The 8753 uses a sampling receiver, so there are lots and lots of images. Further, the phase noise of the source is only moderate, so your tone spacings must be pretty wide. Also, the IF is at 1 MHz, so is quite susceptible to spurious signals if your tone spacing is also 1 MHz. There's no facility to use an external source and the internal source at the same time in external source mode, so you must use the internal source, locked to the R channel, then combine with an external synthesiser. The IF has many, many images as the IF filter has a Sinx/x response, so many sidelobes down only 13 dB for the nearest. The harmonics of the source are only about 25 dBc at max power so you must watch out that they do not cause IM in the DUT, and the source ALC might respond to the signal from the other source combined in, so you might need isolators to avoid creating source IMD. The samplers will also generate their own IMD so you will need to attenuate the signal into the receiver to avoid creating IMD in the receiver.
Fortunately, we fixed all these issues in the PNA-X, so it wil do about -85 dBc IMD measurements.
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