October 3, 2015, 3:51 pm
In my previous blog post, I discussed the basic TOF method for direct measurement of the speed of the light. In order to measure the time of flight accurately, we need to be able to both generate and detect very fast rising signals. One way to generate a fast rising, short duration laser beam is via an avalanche pulse generator as we discussed previously. In this blog post, we will take a look at the receiver end and conduct some experiments. A video of the experiment is included towards the end. Continue reading ‘Direct Measurement of the Speed of Light using a Cheap Laser Diode – II’ »
September 27, 2015, 8:50 am
Speed of light c in air can be measured either directly or indirectly. There are many ways to infer c with indirect measurements. For instance, we can measure the propagation delay of a signal through a coaxial cable (or an optical fiber) using the TDR analysis. With the length of the coax or optical fiber known, the speed of light can be calculated using the known velocity factor (or the refractive index of the fiber) and the measured propagation delay. Another example of indirect measurement is to measure the wavelength of a known frequency standing wave (e.g. a microwave signal) and derive the phase velocity of the electromagnetic wave in air. Continue reading ‘Direct Measurement of the Speed of Light using a Cheap Laser Diode – I’ »
July 11, 2015, 10:46 am
In this blog post, I compared the rise time of four oscilloscope probes of various bandwidths using an avalanche pulse generator and a Tektronix 2465 300 MHz oscilloscope. The bandwidth of an oscilloscope probe is typically characterized using a network analyzer. But using a sub-nanosecond rise time pulse generator and a reasonably high bandwidth scope, we can infer the approximate bandwidth of the probe under test using the following equation: Continue reading ‘Oscilloscope Probe Rise Time Testing’ »
May 18, 2013, 9:18 am
Avalanche transistors can be used to generate fast rise time pulses. Their usage in the hobby world was made popular following an application note (AN72) by Jim Williams and was further publicized via this EEVBlog video. Many people have built such avalanche pulse generators for oscilloscope bandwidth measurements. In this post, I will show you the one I built using a general purpose BJT as well as some rise time measurements. Continue reading ‘Avalanche Pulse Generator Build Using 2N3904’ »