Specifications

Figures 2-11 and 2-12 show pulsed residual phase

noise measurements where the PRF is 20 kHz and

the duty cycle is 10 percent, but different low-pass

filters are used to demonstrate the effects of the

PRF—even though measurement results are valid

only out to PRF/2 in offset frequency. Figure 2-11

shows a broad offset range pulsed carrier measure-

ment using only the default 100-MHz low-pass fil-

ter and allowing the system to autorange the LNA.

Note the 20 kHz PRF spurious signal and integer

multiples of the PRF. The break in the graph at

10 MHz is due to the fact that the PRF lines are too

close together to be resolved by the spectrum ana-

lyzer (the resolution bandwidth and video band-

width of the spectrum analyzer can be adjusted to

resolve these spurs). There is also a break in the

curve at a 1 kHz offset. This is caused by the LNA

gain being automatically set to a lower gain than

required. (The presence of large phase transients

or large PRF lines causes the autoranging of the

LNA to select a gain lower than the maximum

available.)

Figure 2-12 shows a pulsed carrier noise floor

measurement using the internal 200 kHz low-pass

filter. The low-pass filter reduces the transients

within the baseband signal to a level that allows

the proper autoranging of the LNA (to select the

maximum available gain). The measured results to

PRF/2 of offset frequency are virtually identical to

the measurement using the 20 kHz LPF.

Figure 2-11. Pulsed carrier measurement using

100 MHz LPF

Figure 2-12. Pulsed carrier measurement using

200 kHz LPF