Data logger, oscilloscope, signal generator and more!

DrDAQ is a versatile instrument that connects to the USB port of any PC. Using the supplied PicoScope software it can be used as an oscilloscope, spectrum analyzer and signal generator.

From just £89.00


Speed of a pulse along a coaxial cable

IntroductionEducational data logger

Flick a switch in an electric circuit and the resulting effect (for example a light coming on) seems instantaneous. Electrons drift slowly in the circuit yet the electromagnetic wave travels through the circuit at unimagininably high speed.

This simple demonstration using a PC-based oscilloscope gives a clear picture of the time taken for a pulse to travel 200 m in a coaxial cable. It also provides graphic evidence of signal attenuation.

Equipment required

  • A PC with PicoScope installed
  • An ADC200/50 PC-based oscilloscope
  • A 200 kHz pulse generator (see below)
  • 200 m of coaxial cable

Experiment setup

In view of the limited number of applications for a pulse generator in the ‘A’ level syllabus and the relatively large requirement for signal generators, suitable pulses were produced by a signal generator giving a 100 kHz square wave through an R-C pulse-shaping network. (A note is included on pulse shaping- see below)

An ADC-200/50 PC–based oscilloscope (and PicoScope software), with its timebase set to 2 µs per div, was employed.

The coaxial cable was purchased from RS components (a considerable time ago). It is much easier to use if kept on its drum!

circuit diagram

Figure 1: circuit diagram

Carrying out the experiment

The 68 ohm resistors equal the characteristic impedance of the cable and prevent reflections.

The capacitor combines with the resistor and shapes the square wave into sharp pulses (see the note on pulse shaping).

Both ends of the outer sheath of the coax are connected to earth.

The signal generator is set at an amplitude of about 1 volt.

Channel A on the scope then shows the pulses before they enter the coax, channel B shows the corresponding pulses as they arrive after travelling 200 m in the cable a satisfying 1 µs later, equivalent to a speed of 2 x 10^8 m·s-1.


Figure 2: waveform as seen on PicoScope


  • 100 kHz square wave “differentiated” by RC network (see further note)
  • Positive peaks represent the leading edge of the square wave
  • Period (read from scope) is 10 µs (ie. 100 kHz frequency)
  • BLUE trace is pulse at start of coax cable
  • RED trace is pulse detected after 200 m of travel down cable
  • Time delay between red and blue is 1 µs
  • 200 m in 1 ms = 2 x 10^8 m·s-1.
  • The Y-gain for both channels is 500 mV so that attenuation of the red pulse is nicely shown another good discussion point.

Converting the 100 kHz squarewave to pulses (PicoScope view)

  • The 100 kHz square–wave (blue trace/channel A) is produced at the signal generator.
  • The pulses are produced by the 68 ohm resistance and capacitance, C.
  • A suitable values for C is 4700 pF a substitution box was used.
  • The R-C network effectively differentiates the square-wave, a good discussion point for mathematically-inclined students (and teachers).


  • I have been using my 4224 PicoScope for years. I travel abroad so this has been ideal due to its physical size. Storage of waveforms on my Laptop is very easy allowing me to quickly email waveforms to my Colleagues.

  • Not many USB scopes works on Win & Mac & Linux too, so that proves me that guys from Pico really cares about us, customers. This made my decision much easier when I was looking to buy an USB scope.

    Raul Trifan
  • We have been using Picoscope 6404D for quite some time, and are amazed by its accuracy and powerful emulations while working with numerous signal evaluations.

    J Mohanty
  • PicoLog TC-08: This is a very nice unit that works consistently and reliably.

    Jeff Hulett
  • It is a great scope. I had a weird problem - it did not work on one of my PC’s. Customer service gave me first class service. If I could give 6 stars for customer service - I would do so.

    Niels Larsen
  • Perfect Partner for Development of Encoder controlled Stepper Motor Actuators. Since the included software is really stable, this type of device is a great tool for great tasks!

    Helmut Schoettner
  • A superb piece of equipment worth its weight in gold

    Nigel Clinch
  • So simple to use & beats any other I have ever used hands down.

    John D Samsing
  • Great functionality in a compact size. I really like moving the mouse pointer to a position and having the Time and Voltage display the values at that point. Calibration equipment is a breeze with that feature.

    Don Horein

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