HP 8753E manual Conversion Compression, Phase Measurements

Conversion Compression

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Input S i g n a l ( R F )	LL	I n p u t S i g n a l ( R F )
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Figure 6-97. Conversion Loss and Output Power as a Function of Input Power Level

Conversion compression is a measure of the maximm RF input signal level for which the mixer will provide linear operation. The conversion loss is the ratio of the IF output level to the RF input level, and this value remains constant over a specified input power range. When the input power level exceeds a certain maximum, the constant ratio between IF and RF power levels will begin to change. The point at which the ratio has decreased 1 dB is called the 1 dB compression point.

Notice in Figure 6-97 that the output power increases linearly with the increasing input signal level, until mixer compression begins and the mixer saturates.

You can measure conversion compression using the same basic test configurations that are used to measure the conversion loss

‘Ib set up for a conversion compression measurement, first measure the conversion loss of the mixer under test. Set up for a CW measurement at the frequency of interest. Sweeping the RF drive level over a 25 dB span soon shows the power level at which the conversion loss increases by 1 dB.

With power meter calibration controlling the RF drive level, and the receiver calibrated to measure output power, you can make accurate measurements of the output power at the 1 dB compression point.

Phase Measurements

When you are making linear measurements, provide a reference for determining phase by splitting the RF source power and send part of the signal into the reference channel. (This does not work for frequency offset measurements, since the source and receiver are functioning at different frequencies.)

lb provide a reference signal for the phase measurement, you need a second mixer. This mixer is driven by the same RF and LO sign& that are used to drive the mixer under test. The IF output from the reference mixer is applied to the reference (R) channel of the analyzer.

6-166 Application and Operation Concepts