Randomness Explains Flat Tire Anecdotes Perfectly Well

Figure 2. First five simulated periods of 30 years.

Flat tires are random events. However, it seems that the human mind expects random events to be more regular than they actually are. This intuition on randomness might lead to the feeling that your own experience is somehow unexpected or strange, with anecdotes such as “my uncle seems to never have any flats, but my sister had three in the last year alone”. This is related…

Tom Sun, 01/22/2017 - 13:09

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How to Create a Configurable Filter Using a Kaiser Window

Figure 3. Frequency response of a low-pass filter with a Kaiser window; A=60.

This article explains how to create a windowed-sinc filter with a Kaiser (or Kaiser-Bessel) window. The windowed-sinc filters in previous articles typically had two parameters, the cutoff frequency and the transition bandwidth (or rolloff). With a Kaiser window, there is a third input parameter, the ripple. For the specific case of the Kaiser window, the same…

Submitted on 26 December 2016

The Transition Bandwidth of a Filter Depends on the Window Type

Figure 1. Low-pass filter with Blackman window, r=4.0 (filter has 41 taps).

This article contains more detailed information on setting the transition bandwidth (or roll-off) from How to Create a Simple Low-Pass Filter. That article suggest to use, as the filter length N, an odd number close to 4/b, where b is the required transition bandwidth. This is a good basic rule. However, in…

Submitted on 6 December 2016

The Radio Meteor Signal Path from Transmitter to Spectrogram, Part 3

Figure 3. Spectrogram of sampled signal.

This is part three of an article that describes the signal path of a radio meteor. The next step is sampling. At the point of sampling, there is a difference between a real-world BRAMS system and the simulation that produced the illustrations in this series of articles. In the real system…

Submitted on 5 September 2016

The Radio Meteor Signal Path from Transmitter to Spectrogram, Part 2

Figure 1. Combined reflected and directly received signal.

This is part two of an article that describes the signal path of a radio meteor. At the antenna of the receiver, the reflected signal is combined with a (much smaller) directly received signal. At first sight this might seem unimportant, since the amplitude of the direct component is typically much less than…

Submitted on 21 August 2016
Radio Meteor Zoo

If you’ve enjoyed, or simply read, my articles on the BRAMS network, you might be interested in the Radio Meteor Zoo. The Radio Meteor Zoo is a so-called citizen science project. In these kinds of projects, members of the public can help scientists with…

Tom Tue, 08/09/2016 - 19:57

The Radio Meteor Signal Path from Transmitter to Spectrogram, Part 1

Figure 1. Overview of the radio meteor signal path.

This is part one of a rather basic article that describes the complete signal path of a radio meteor, from the sinusoidal carrier wave that is initially transmitted, to the spectrogram that is typically used as the final result in the receiving chain. I have presented this material at…

Submitted on 1 August 2016
Why is Eb/N0 the Natural Figure of Merit in Digital Communications?

In digital communications, the measure of the signal to noise ratio of a signal is Eb/N0. Why is that? To figure it out, let’s start from the classical SNR, which is the ratio of the average signal power S to the average noise power N, given by…

Tom Wed, 06/29/2016 - 18:54