Hello Bittware,
The maximum sample rate of the SA44B at the IF is ~486kS/s, which means a 5us pulse would only appear in ~3 samples. Generally in real-time modes, the energy of a signal needs to be present in 1.25 FFTs worth of data. In fact the Spike software even tells you the signal duration required for 100% probability of intercept (for the signal to be represented on display within 3dB). At the highest RBW, the 100% POI requirement of a signal is 592us. Once signals start becoming shorter than this, the energy level displayed will decrease.
In short, the SA44B is not the best tool to measure this type of signal using real-time mode.
What you can try, is using zero-span mode to capture the pulse in the time domain. A 5us signal can be captured in this mode. I have included a picture of this configuration with my SA44B. I used a 5us pulse with 80us period to demonstrate. The spectrum plot in the zero-span mode will still not be accurate, but you can get a good idea what the pulse looks like in the time domain.
The BB60C or SM200A would be better analyzers to measure this type of signal in real-time, the BB60C has a minimum 100% POI of 4.8us. As you have noticed though, the sweep time of our real-time mode is ~30ms and will also be that for the BB and SM. We accumulate ~30ms worth of spectrum before displaying the results in real-time which means you will see the accumulation of several pulses in your config in one sweep. At this point we are unable to have a finer resolution than this.
Regards,
Andrew
