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## 1. Introduction**Measure phase response** under the **Tools** menu is for advanced MSK144users. Phase equalization is used to compensate for group-delayvariation across your receiver passband. Careful application of thisfacility can reduce intersymbol interference, resulting in improveddecoding sensitivity. If you use a software-defined receiver withlinear-phase filters there is no need to apply phase equalization.After a frame of received data has been decoded, **Measure phaseresponse** generates an undistorted audio waveform equal to the onegenerated by the transmitting station. Its Fourier transform is thenused as a frequency-dependent phase reference to compare with thephase of the received frame’s Fourier coefficients. Phase differencesbetween the reference spectrum and received spectrum includecontributions from the originating station’s transmit filter, thepropagation channel, and filters in the receiver. If the receivedframe originates from a station known to transmit signals havinglittle phase distortion (such as a station known to use a properlyadjusted software-defined transceiver), and if the received signal isrelatively free from multipath distortion so that the channel phase isclose to linear, the measured phase differences will be representativeof the local receiver’s phase response.Complete the following steps to generate a phase equalization curve:* Record a number of `wav` files that contain decodable signals fromyour chosen reference station. Best results are obtained when thesignal-to-noise ratio of the reference signals is 10 dB or greater.* Enter the callsign of the reference station in the DX Call box.* Select **Measure phase response** from the **Tools** menu, and open eachof the `wav` files in turn. The mode character on decoded text lineschanges from `&` to `^` while *WSJT-X* is measuring the phaseresponse, and it changes back to `&` after the measurement is