I would like to be able to measure the instantaneous frequency of my FM modulated signal.

Question:

I would like to be able to measure the instantaneous frequency of my FM modulated signal.

Answer:

Essentially, this graph is called a time trend of frequency. Essentially it is a graph of the demodulated signal. This is something that can be done with the help of TDSJIT3.

This can be demonstrated using a signal from an AFG3000 to generate an FM sine wave. The modulation profile can be anything, but in this example has been chosen to be a sine profile. I then used JIT3 to measure the frequency, and then created a time trend plot to plot frequency for the entire record.

The modulated sine wave is 1MHz, and deviates 0.5MHz, at a 10kHz modulation frequency. This means that acquiring the signal at 100usec/div, there will be 10 cycles of the demodulated sine captured by the oscilloscope. JIT3 will measure a MAX of about 1.5MHz, and a MIN of about 500kHz. See Figure 1 for the measurements and the time signal.

Figure 1

Figure 1: Modulated FM sine wave and JIT3 Measurements

Notice in Figure 2 that 10 full cycles of the demodulated signal have been captured, just as we wished.

Figure 2

Figure 2: Time Trend plot of the demodulated signal

Download File (1.33 KB)

This FAQ Applies to:

Applications: Jitter Measurement and Timing Analysis

Product: TDS7054, TDS7254, TDS7404, TDS5052, TDS5054, TDS5104, TDS7104, TDS6604, CSA7154, CSA7404, TDS6404, CSA7404B, TDS7154B, TDS7254B, TDS7404B, TDS7704B, TDS5034, TDS5032, TDS5054B, TDS5104B, TDS5032B, TDS5052B, TDS5054BE, TDS5034B, TDS6804B, TDS6604B, TDS6154C, TDS6124C, DPO7054, DPO7104, DPO7254, DPO70404, DPO70604, DPO70804, DSA70404, DSA70604, DSA70804, DPO7354, DPO71254, DPO71604, DPO72004, DSA71254, DSA71604, DSA72004

FAQ ID : 52871

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