Скачать или смотреть #159

This short video shows a quick way to get a good estimate of the frequency deviation of a FM transmitter using a spectrum analyzer. This method isn't as accurate as the Bessel Null method shown in this video:
   • #101: How to measure FM Frequency Deviatio...  
But is is faster and easier to setup, and doesn't require a single, adjustable modulation tone. The RBW is set wide enough to "swallow up" the sidebands, and then a min hold and max hold trace are used to capture the excursion. The frequency difference between the skirts of these two traces represents the peak-peak deviation. Note that the wattmeter is included for two reasons - to monitor the output power, and to provide a low-level RF sample of the transmitter output to send to the spectrum analyzer. This could also be done with any other form of RF sampler or tap, such as a directional coupler, etc. Just be sure to keep the power injected into the spectrum analyzer at a safe level.