Open Source Hardware Engineering

Technical Articles

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This page links to a variety of technical articles, mostly or entirely about electrical engineering and mostly (or wholly) in PDF format. The amount of technical content is usually fairly high, and those without an engineering background may find them a bit, shall we say, uninteresting. That said, some of them may be of interest to the maker crowd.

In many cases there may not be much of an introduction to the technical topics in the articles and/or little discussion of scope. It's assumed that those who are looking for the content contained in an article will be able to readily identify it. If you find something that sounds interesting, but upon reading it makes no sense, then it's not for you.

Some of the articles here are only half-baked. We decided it was better to make them available than keeping them under wraps.

Click on the images next to the article descriptions below to see the corresponding PDF article.


It can be sometimes mildly annoying (or worse) when something is discovered on the internet you'd like to contact the author about, but there's no links provided for e-mail, or any way to post some comments. For example perhaps there are some errors in the articles here, or maybe you know a better way to do something.

We have set up a blog on WordPress where folks can post comments or feedback about this web site.

Photo of ferrite loop antenna

Inductance of Ferrite Rod Loop Antennas

This is the first article related to our research on electrically small loop antennas. This proposes a new method for the estimation of inductance of solenoids wound around ferrite rods, such as found in ferrite rod loop antennas. The PDF file linked (click on the photo to the left) also contains an attached zip file with data and example scripts in Matlab/Octave.

Also coming soon, we spent a good deal of time reading about and trying to understand the design and performance of electrically small loop antennas over the frequency range from a few 10's of kHz (LF) up through the AM broadcast band (MF). A new article will summarize what we think we learned.

Photo of chirping bird

Time Warping for Propagation Analysis

What with the coronavirus lockdown and all, we were looking at some old data on signal readability of NIST time broadcast station WWVB (60kHz). Changes in atmospheric propagation at sunrise and sunset are a big factor here. As a result, it's useful to view the data relative to sunrise and sunset, rather than normal 24-hour clock times. There were over 100 days worth of data and sunrise/sunset obviously don't occur at the same clock time every day. This article describes a method for warping 24-hour clock time so that sunrise and sunset always occur at the same warped time value. This makes correlations between signal quality and sun events easy to see. The PDF article includes an attached ZIP file containing scripts for Matlab/Octave which implement the proposed time warping algorithm.

Photo of chirping bird

Digitally Convenient Chirps

This concerns the world of digital RF signal generation by means of I-Q modulation. For testing purposes, it is often desirable to generate a signal with as many as hundreds or thousands of equal-amplitude subcarriers. This article describes a way to build the I and Q digital waveforms for such a signal. The result is unique in that it has a crest factor of one, both in the I and Q waveforms and in the up-converted RF signal, so it won't strain the capabilities of the hardware too much.

Photo of wireless temperature sensor

Wireless Weather Sensor Protocols

This PDF article describes the RF signals transmitted by many commercial wireless weather sensors manufactured or sold by Oregon Scientific, Ambient Weather and AcuRite. The descriptions are sufficient for those building maker projects to receive and decode these signals.

Photo of power transmission lines

Impedance of parallel wire lines with square conductors

So, the image at left is a bit misleading...but it caught your eye right?

Anyway, round wires are often used to build electromagnetic transmission lines -- like the old twin lead that was used with TV antennas (if you're old enough to remember that). There's a well known formula for the characteristic impedance of such lines, but what if you are making the line from square bars or wires? This article provides some emperically derived formulas for the impedance of such lines.

Photo of Albert Einstein

Einstein's paper on Special Relativity

Coming Soon...

A while back, we spent the time to read and understand this paper in it's entirety. It wasn't all easy going and notes were kept to help us through what we found to be the more difficult parts. Those notes, along with some observations have been added to the original text of the paper and it's available here in a PDF format. Those who have only have an undergraduate level background in calculus may find some of the notes helpful in working through the math.

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