Channel Power Measurement: Spectrum Analyzer vs RF Power Meter?

How to make accurate channel power measurement (in my case using 8563E). I am seeing differences when using power meter. Using spectrum analyzer, the difference is also significant when CW is on and off from source (around 2dBm). Thanks guys.

http://cp.literature.agilent.com/lit...5965-6630E.pdf

A spectrum analyzer, if calibrated, offers you to measure a RF power AT SELECTED FREQUENCY. If there are other components like harmonics or spurs, you can separate their power from the power of your desired signal.
A power meter has a sensor responding to heat; so all signals, wanted or unwanted, do heat the sensor and you measure their combined effect. To be sure that you only measure a desired signal, you must use filters (and know their insertion loss ) . Such operation is done in spectrum analyzers, so if they are calibrated, they are better - they also cost much more for being better.

Sometimes average power measurement is needed in case of spread spectrum signals or WCDMA etc.Because power is spreaded in a bandwidth and it can be difficult to measure wit SA.(Modern SAs can handle this problem with expensive peronality options)
Power meter can be used with a proper filter for these kind of measurments with.