Correlation between upper and lower noise sidebands

Experimental measurements, supported by a simple model, are used to show that the upper and lower phase modulation (PM) noise sidebands are always equal and 100% correlated, independent of whether the noise power originates from multiplicative or additive processes. Similarly we show that the upper and lower amplitude modulation (AM) noise sidebands are also equal and 100% correlated, independent of whether the noise power originates from multiplicative or additive processes. Moreover the single sideband AM (PM) noise is always equal to ½ the total AM (PM) noise. Although the upper and lower PM (AM) noise sidebands are equal and correlated for broadband additive noise, the phase between the AM and the PM sidebands varies randomly with time. These conclusions still hold even when the RF noise sidebands are not symmetric about the carrier