|Figure 1: Demodulation is one method|
of determining the envelope of an RF burst
Let's take a look at how some common, yet critical, measurements can be made for these types of signals. One often-required measurement is to determine the envelope of an RF burst; we'll look at four approaches to this task.
The first example concerns an RF burst with a mean frequency of 9.75 GHz (Figure 1). We can determine the envelope of the bursts by setting up a demodulate math operator on the RF pulse and setting the carrier frequency to 9.75 GHz to measure amplitude modulation. The red trace, F6, is the demodulated carrier.
|Figure 2: Various measurements|
may be made on demodulated RF pulses
However, when we measure the frequency of the demodulated waveform (P6), we find a 500-kHz modulation, which tells us the pulse-repetition frequency (PRI), a common RF-burst measurement. We can also measure the PRI using the period parameter (P2), with which we find a PRI value of 1.999 μs. This also can be measured directly with an automatic parameter by first demodulating the RF carrier and using standard oscilloscope measurement parameters.
|Figure 3: A Hilbert transform in Matlab|
reveals an RF burst envelope
The actual code for the Hilbert transform is derived by performing the transform on the input waveform, extract the absolute value, and output that value back as a waveform for display on the oscilloscope. It can be done in four separate lines or in a single line of Matlab code (Figure 3). The Hilbert transform waveform updates live and in real time
|Figure 4: Determining an RF burst|
envelope with three chained math
|Figure 5: The Parameter Track operator|
shows how a measurement changes
|Figure 6: A Track plot of an RF bursts's|
In upcoming posts, we'll look at some other measurements involving electronic-warfare applications, including RADAR analysis, frequency-domain measurements, and more. Stay tuned (yes, pun intended)!