Remove non-latin fonts from Ubuntu

Published on Wednesday, August 24, 2016 by One Transistor
The default Ubuntu installation comes with a lot of fonts. This is a good thing. Many of the latin have good support for Extended character sets. But no matter what locale and/or installation language you choose, Ubuntu will install by default some non-latin fonts for Japanese, Thai, Ethiopian, Myanmar, Lao, Tibetan, Korean, Punjabi, Sinhala, Arabic and Khmer languages.

I don't know whether these fonts are ever needed by the operating system (i.e. for the language choosing settings or for displaying some web pages) but as a latin alphabet user I don't need them and I didn't like the fact that they were cluttering my font selection dialog without being of any use to me. So I decided to uninstall them.

The list below is tested on Ubuntu 16.04. I managed to free about 100 MB by removing these fonts. And now, my font selection box (in LibreOffice, GIMP, Inkscape, etc.) is filled with latin only fonts that I can use. You can see in the screenshot below how it looks before and after removing the unneeded fonts.

Remove non-latin fonts from Ubuntu

Radio link analysis using SPLAT!

Published on Wednesday, July 20, 2016 by One Transistor
SPLAT! is a cross-platform, open-source software that can be used to analyze a radio link between two locations and to generate coverage maps of RF transmitters. Coverage maps are calculated using Longley-Rice Irregular Terrain Model (ITM) algorithm. SPLAT! can predict RF coverage for any frequencies between 20 MHz and 20 GHz. It is thus useful for ham radio, broadcast radio, terrestrial television and wireless networks.

To use SPLAT!, you need to know some parameters of the transmitter. These are the exact location (coordinates), antenna height, transmission frequency, polarization and effective radiated power (ERP). SPLAT! can then calculate both path loss and received signal strength.

The procedure of installing SPLAT! is described in a previous article. The point-to-point analysis calculates some useful parameters like: azimuth and elevation of receiving antenna, distance to transmitter, mode of propagation, received signal strength and density. You must also supply a receiver parameters file to SPLAT!. This will contain the location, antenna height and some other terrain parameters. SPLAT! will generate a report and a graph if you have Gnuplot installed.

SPLAT! height profile graph
SPLAT! height profile graph

Compile and setup RF coverage prediction software SPLAT!

Published on Tuesday, July 19, 2016 by One Transistor
SPLAT! is a cross-platform, open-source software that can be used to analyze a radio link between two locations and to generate coverage maps of RF transmitters. Coverage maps are calculated using Longley-Rice Irregular Terrain Model (ITM) algorithm. SPLAT! can predict RF coverage for any frequencies between 20 MHz and 20 GHz. It is thus useful for ham radio, broadcast radio, terrestrial television and wireless networks.

SPLAT! uses data from SRTM elevation files. Although it is cross-platform, up-to-date binaries for Windows are hard to find. On the other hand, for Linux users, it is available in the repositories of the major distributions. This post will show you how to compile SPLAT! on Windows and Linux, how to obtain and convert elevation data and at last how to generate point-to-point and coverage prediction analysis.

There are two variants of SPLAT! based on the type of elevation data they use. SRTM3 files are 90 meters resolution, 3 arc-sec files. These are the "standard definition" files suitable for SPLAT! And there are SRTM1, 30 meters resolution, 1 arc-sec files that are considered "high definition" and are suitable for SPLAT! HD. I recommend SRTM3 (SD) files because the results are very good and processing time is not too high.

SPLAT! line-of-sight coverage
SPLAT! line-of-sight coverage

A better way to power car audio in home

Published on Tuesday, June 21, 2016 by One Transistor
Usually, car audio systems like CD player or cassette player have good audio amplifiers, with four channels (front L/R and rear L/R) of enough power for in home use. The radio tuner is also of high quality, with automatic best frequency selection and RDS information. Not all car audio systems have audio auxiliary inputs, although with a little tweaking, you can add audio line level inputs to a cassette player so you can use it as audio amplifier with any audio source.

There are plenty of how-to's about this subject online. Yet I couldn't find one that handles the memory loss problem. Car audios are designed to be continuously powered by the battery. Therefore, most don't have a permanent storage memory for settings. Upon disconnecting the power, the device loses all audio settings and stored radio stations.

This article will deal with the memory loss problem. Unless you will never unplug the DC adapter from the mains, you will need something similar to what follows if you want to use a car audio device in home. Let's start with the basics.

The proper way to power car audio in home - with backup battery

DC Motor Controller for PCB Drill

Published on Thursday, June 09, 2016 by One Transistor
This is a simple circuit that can be use to vary the speed of a DC motor. It is very useful for controlling a PCB drill, but it can be used for whatever applications you want. The speed can vary from full to complete stop. The circuit is versatile and can be used with motors of different currents and voltages.

This circuit is widespread on the internet. Here is an example. The PWM signal is generated by a 555 chip. The chip drives a MOS-FET transistor that will switch the motor on and off. The 555 is powered from a 7805 regulator. Therefore, the motor DC voltage can be between 8 and 35 V (the circuit can be powered by AC 7...26 V). The maximum current is limited by MOS-FET.

The circuit shown here is designed to be AC powered by a mains transformer. But you can power it from a DC adapter, battery or even a computer power supply if you remove the diode bridge and connect the power lines straight to ground and positive pads, where the output pins of the bridge would otherwise fit.

DC Motor Controller for PCB Drill 555