Sinusoidal Tone Versus Modulation Operation

The main synthesizer has two modes: low and high, corresponding to 10 and 200 kHz loop bandwidths, respectively. During single tone (sine) generation, the low loop bandwidth is selected for the best possible phase noise performance. The specified phase noise is based on low loop bandwidth. Override the loop bandwidth defaults if your application requires it.

Ideally, low loop bandwidth should be used when modulation is turned on; however, the modulation implemented on the NI 5650/5651/5652 requires that the high loop bandwidth must be used. Choosing high loop bandwidth increases phase noise from 20 kHz and greater; the phase noise close to the carrier does not change. Loop bandwidths do not affect far out noise density; that is, the far out noise of the system remains unchanged.