In that case there needs to be a spec. for the RMS phase error in a given bandwidth (presumably a very narrow bandwidth), as well as a residual FM spec. and a spec. for the phase noise at greater offsets.
These requirements should not be mutually exclusive - they just relate to the phase noise requirements at different offsets from the carrier, and the causes of the noise at different offsets will be different (reference oscillator, PLL IC, VCO etc).
Robert McGwier wrote:
Thank you all for this great conversation. I want to remind everyone that we need long term coherence in the receiver, which can only be accomplished by low phase noise, not for the purity of the tone needed to be heard by a human ear, but by the need to correlate for long known symbols to recover frequency and timing in the SMS text messaging system and to do COHERENT detection of the symbols transmitted. We want the analog transponder to support this. This is also contributes to the requirement for a much larger dynamic range in the system than we have had heretofore on our spacecraft.
This system needed was added to the requirements for the receiver after the initial requirements but not before the design was done and certainly not before it was built.
73's Bob N4HY