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We noticed an interesting phenomenon when using the amplifier paths in the Source 1/2 combiner that bears noting:

When an amplifier is switched in, its output match below 500 MHz is not very good. This is not a problem for match at the test port because the test port match is defined by the combiner and switches, not the amplifier. However, the bad output match can affect the performance of the combiner. When one input to the combiner sees a bad match, it causes ripple on the other input. What all this means is that, when you turn an amplifier on in one path, you can see ripple below 500 MHz in the other path.

The calibration compensates for this, but the calibration is only good for one set of conditions. The condition for calibration is both amps on which means, on a calibrated system, if you turn both amps on you do not see ripple. If you turn both amps off you do not see ripple. Only if you have one amp on and the other off will you see ripple in the non-amp path.

Please be aware of this when writing test plans. If you need to use an amp in a path, turn both amps on. This duplicates the calibration conditions and provides the most accurate source power.

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