Patent ID: 7170704

Claim:
A method for characterizing a read channel of a disk drive, the method comprising: storing a pseudorandom number (PN) sequence at a first location on a recording surface of the disk drive; storing the PN sequence at a second location or at the same location but at a different time on the recording surface, wherein the PN sequence is stored at the first location with a polarity opposite of that of the PN sequence stored at the second location or the same location but different time; reading the PN sequence at the first location to generate a first playback signal; determining a first dibit response from the first playback signal; reading the PN sequence at the second location to generate a second playback signal; determining a second dibit response from the second playback signal; and arithmetically combining the first and second dibit responses to generate a combined dibit response in which at least some non-linear echoes are isolated.