Advanced Amateur Radio Exam

Understanding Oscilloscope Functionality and Applications

Introduction

Oscilloscopes are essential tools in electronics, offering a visual representation of electronic signals. Understanding how to use them effectively requires knowledge of their capabilities, limitations, and applications. This article explores various aspects of oscilloscope usage, from interpreting display patterns to improving their frequency response, with practical examples and calculations.

Limitations and Improvements

• Oscilloscope performance is limited by the accuracy of the time base and the linearity and bandwidth of the deflection amplifiers.

• The frequency response can be improved by increasing the horizontal sweep rate and enhancing the vertical amplifier frequency response.

Practical Uses of Oscilloscopes

• Using a dual trace oscilloscope allows for the simultaneous display of the input and output of a circuit, providing a comparative analysis of signal changes.

• An oscilloscope cannot directly determine FM carrier deviation, highlighting its limitations in certain measurement scenarios.

• The bandwidth of an oscilloscope defines its ability to display the highest frequency signal accurately.

• Oscilloscope probes must be compensated every time they are used with a different oscilloscope to ensure accuracy and reliability in measurements.

Lissajous Figures

Feeding a 100 Hz signal to the horizontal input and a 150 Hz signal to the vertical input results in a looping pattern with 3 horizontal loops and 2 vertical loops. This type of display, known as Lissajous figures, helps in analyzing the relationship between two signals.  When using Lissajous figures to determine phase differences, zero or 180 degrees phase shift is represented by a diagonal straight line on the screen.

Example Calculation

• Scenario: A 100-kHz signal is applied to the horizontal channel, and an unknown frequency is applied to the vertical channel. The waveform displays 5 vertical loops and 2 horizontal loops.

• Frequency Calculation: The unknown frequency is 40 kHz, determined by the ratio of loops (100 kHz / 2.5 = 40 kHz).

Oscilloscope in Transmitter Signal Quality Check

• The best instrument for checking the signal quality of a CW or single-sideband phone transmitter is an oscilloscope.

• For evaluating a transmitted signal's quality, the best signal source to connect to the oscilloscope's vertical input is the RF output of the transmitter through a sampling device.

Conclusion

Oscilloscopes are invaluable tools in the field of electronics, offering deep insights into the behavior of electronic signals. Understanding their functionality, how to interpret their displays, and their limitations and applications is crucial for anyone involved in electronics. Whether it's analyzing signal quality, measuring frequency, or comparing input and output signals, oscilloscopes provide a window into the dynamic world of electronic signals, making them indispensable in both troubleshooting and design processes.