576 Chapter11
Synthesizer Section
Phase Noise Problems
Reference versus Reference PLL Phase Noise
If the problem seems to be in the frequency reference or reference PLL
circuitry, measure the noise with internal and external references. If
there is no difference, suspect the circuitry associated with the
100MHz VCXO
Fractional N versus Offset PLL or YTO PLL Phase
Noise
If the spectrum analyzer has excessive noise at >1 kHz offset, measure
the noise with center frequencies of 100 MHz and 2.5 GHz.
If the measurements are equal, suspect the fractional N circuitry and
the YTO loop circuitry on the A14 frequency control assembly.
If the measurements differ by 2 dB to 5 dB, with the 2.5 GHz
measurement at a higher noise level, suspect the offset lock loop
circuitry.
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