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For all 209 RXTE observations of the X-ray nova XTE J1550-564 during itsmajor outburst of 1998-1999, we have analyzed the X-ray power spectra, phaselags, and coherence functions. The phase lags and coherence measures are usedto distinguish three types of low-frequency QPOs (one more than those reportedby Wijnands, Homan, & van der Klis 1999). For the most common type, the phaselag is correlated with both the QPO frequency and the amplitude. The physicalsignificance of the QPO types is evident in the relationships between QPOproperties and the apparent temperature and flux from the accretion disk. Thereis also a clear pattern in how the QPO types relate to the presence ofhigh-frequency QPOs. In general, both the amplitude and the Q value(freq./FWHM) of low-frequency QPOs decrease as the high-frequency oscillationsincrease in frequency (100 to 284 Hz) and in Q value. We speculate that theantagonism between low-frequency and high-frequency QPOs arises from competingstructures in a perturbed accretion disk. However, we find that the frequenciesof slow (< 20 Hz) and fast (> 100 Hz) QPOs are not correlated. In addition, weencounter systematic problems in attempting to reliably compare the QPOfrequencies with broad features in the power continuum, since there are avariable number of such features in the power spectra. These results cast somedoubt on the reported global relationship between QPOs from neutrons stars andthose from black hole systems.Comment: 27 pages, including 2 tables and 7 figures. submitted to ApJ; rewrite  of astro-ph/000421

Characterizing the Quasi‐periodic Oscillation Behavior of the X‐Ray Nova XTE J1550−564