Electronic – Measurements using spectrum analyzer

measurementspectrum analyzer

I need to measure the following characteristics of a frequency synthesizer using a spectrum analyzer:

  • Frequency range: 2.286 GHz to 2.346 GHz

  • Output power: -2.5 dBm to 2.5 dBm

  • SSB phase noise: typical: -122 dBc/Hz, maximum: -116 dBc/Hz, at 100 kHz offset

  • Integrated SSB phase noise: -45 dBc, at 100 Hz to 1MHz

  • Reference spurious suppression: typical: -106 dBc, maximum: -80 dBc, with reference frequency = 15 MHz

  • Non-harmonic spurious suppression: -90 dBc

  • Harmonic suppression: typical: -30 dBc, maximum: -20 dBc

Am I able to measure all those specifications using a Rohde and Schwarz FSC6 model .06: datasheet ?

I can choose any spectrum snalyzer in the world, but I was told that Rohde and Schwarz is the one of the best brands, and that's the one I found more useful for the specifications I need to measure, because of its frequency range and phase noise (I don't know if I'm reading it correctly). What do you think?

Best Answer

The phase noise of the spectrum analyser is -100 dBc worst case, -110 dBc typical. This is (hopefully) worse than the synthesiser you are trying to measure. So no, you won't have much luck seeing your synth phase noise above that of the S/A local oscillator. This is not unusual. Spectrum analysers often have worse phase noise than synthesisers. I haven't needed to do this test for a while so I'm not up to date with the test equipment available. One technique I have used is to phase-lock a low phase noise signal generator to the synth output. A ring mixer is used as a phase comparator, which results in the signal generator and synth being in quadrature. The phase noise sidebands then appear at the mixer output at baseband. That is, phase noise at 100 kHz offset appears at 100 kHz at the mixer output, both sidebands superimposed. Your signal generator needs to have FM modulation capability down to DC in order to lock. You may also be able to infer phase noise performance in your final system by measuring reciprocal mixing performance. You may have trouble seeing -106 dBc ref spurs in the noise.