1. 1 Chelmsford Amateur Radio Society Advanced Licence Course Anthony Martin M1FDE Slide Set 23: v1.0, 13-Oct-2004 (10) Measurements-3 - Oscilloscopes Chelmsford Amateur Radio Society Advanced Course (10) Measurements Part-3 - Oscilloscopes

2. 2 Chelmsford Amateur Radio Society Advanced Licence Course Anthony Martin M1FDE Slide Set 23: v1.0, 13-Oct-2004 (10) Measurements-3 - Oscilloscopes Oscilloscopes Oscilloscopes can be used for –Measuring DC voltages –Measuring amplitude –Measuring waveform period and frequency –Checking waveforms Oscilloscopes contain –A CRT or LCD display screen –A horizontal timebase –A vertical deflection input (or two) –A timebase trigger

3. 3 Chelmsford Amateur Radio Society Advanced Licence Course Anthony Martin M1FDE Slide Set 23: v1.0, 13-Oct-2004 (10) Measurements-3 - Oscilloscopes Focus Brightness Y input Vertical gain (V/div) Horizontal timebase (ms/div) Y-axis X-axis Oscilloscope Controls

4. 4 Chelmsford Amateur Radio Society Advanced Licence Course Anthony Martin M1FDE Slide Set 23: v1.0, 13-Oct-2004 (10) Measurements-3 - Oscilloscopes Measuring Amplitude Check variable controls are as “cal” Obtain a large trace Read the pk-pk amplitude in divisions. Read the vertical gain (volts/division) Calculate the pk-pk voltage The amplitude is half the pk-pk value The RMS voltage is amplitude x 0.707

5. 5 Chelmsford Amateur Radio Society Advanced Licence Course Anthony Martin M1FDE Slide Set 23: v1.0, 13-Oct-2004 (10) Measurements-3 - Oscilloscopes Measuring Frequency 1 2 3 4 5 Check variable controls are as “cal” Display a suitable number of cycles (say 5) Read the total divisions for the cycles Calculate divisions for 1 cycle Read timebase setting (ms/division) Calculate period in seconds Calculate: Frequency = 1 / Period

6. 6 Chelmsford Amateur Radio Society Advanced Licence Course Anthony Martin M1FDE Slide Set 23: v1.0, 13-Oct-2004 (10) Measurements-3 - Oscilloscopes Oscilloscope Probes Trimmer Scope probes reduce input capacitance and divide voltage, usually by 10. This means you must remember to multiply voltage readings by 10. All probes must be adjusted to match the ’scope by connecting to ‘probe cal’ point and tweaking for a level-topped square wave.