Hi Erik,
Thanks for the excellent technical support.
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?After reducing the input level to below -15dBm, the discrepancy persists (image below).
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Hi John & Dave,
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Some high linearity applications really require input levels above -25 dBm. For example, measuring an LNA with 40 dBm OIP3 with the output tones limited to -25 dBm, then the intermod products will be 130 dB lower; i.e. buried in the noise floor.? Calculation: OIP3 = Po + ?/2. Rearranging ? = (OIP3 - Po)*2 = (40 dBm + 25 dBm)*2 = 130 dB.
Hence, there is a real need to test at higher input levels because it will substantially reduce the measured ?.
Close frequency spacing is required when there is either a channel filter or a pre-selector.
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73,
Chin-Leong Lim, 9W2LC.
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