Aeronetworks sro - Airborne Linux

I wanted to do some advanced RF antenna development work and needed an electromagnetic field solver that is a bit more up to date than NEC2 .  Commercial solvers from Matlab , Ansys and others are hideously expensive (in the order of $20,000 to $50,000) and do not fit in the wallet of a hobbyist or a small consulting company.  Recently, openEMS became available and it fills the niche with a capable free tool.  In general, openEMS is a solver - a Finite-Difference Time-Domain (FDTD) numerical engine.  You interact with it through Octave , which is almost identical to Matlab .  You can watch a good video by Thorsten Liebig here: https://www.youtube.com/watch?app=desktop&v=ThMLf0d5gaE   Getting it to work is a little painful, but it is free, so bear with it - then save a backup clone, or a zipped copy of the whole virtual machine directory and NEVER update it, to ensure that it keeps going and doesn't get broken by future updates, right when you are ...

Security Camera Management Programs There are two decent Linux programs for managing security cameras: Motion and ZoneMinder . For test purposes, I set a camera up inside my living room.  Once working, I'll install two outside, to watch the driveway and backyard.   Streaming Camera with Fish Eye Lens Motion is the simpler one of the two programs, but with almost 300 configurable options, it can do anything worth doing.  It works just as well as ZoneMinder , but it simply doesn't do things that are not needed.  For example, Motion supports a database, but Linux filesystem storage is usually good enough.  It doesn't have a fancy GUI, since it is intended to run on a server, stashed on a shelf in a dark corner.  There is a GUI which can be accessed with a web browser locally, or over the LAN, but I never used it.  One can also view real-time streams with a web browser.  Notifications can be sent and files uploaded to another machine with external p...

On a Mac, a simple thing such as copying an ISO file to a USB nurgle, is not necessarily simple, due to the helpful automounter.  Get a Linux ISO image over here:  https://ubuntu.com/download/flavours     Open a terminal, then do the following See which disks are on the machine: $ diskutil list Insert the USB nurgle, to see the disk node (Likely /dev/disk2 - NEVER disk1!!! ): $ diskutil list Unmount the nurgle: $ diskutil unmountDisk /dev/diskN Copy the ISO file to the USB nurgle: $ sudo dd if=/path-to.iso of=/dev/diskN bs=1m Once completed: $ diskutil eject /dev/diskN Caution Please note that writing to /dev/disk1 will very likely be extremely disappointing, so rather don't.  Eh? What is a nurgle ???  It is Aussie for a widget, a thingummabob, a whatchammacallit, a whassisname, or a hoosammawhatsit - a very versatile word to add to your technojargon vocabulary. La voila! Herman

Unlock Canada Revenue Agency PDF Forms It appears that there is a relatively new PDF feature to prevent casual copying and saving of a file and that some programs save PDF files with these foolish features active by default.  Many forms from the Canada Revenue Agency are locked in this way, which makes it difficult to do one's taxes, since one can fill the form, but cannot save it.  One can only print the form.  It should be possible to print to a file or export it to a new PDF file, but it is far better to reset the annoying anti-taxpayer flags, since the 'printed' form cannot be edited easily any more and I always manage to make a mistake or three that need to be corrected after review. If there is a Linux (virtual) machine handy, install qpdf and use it to reset the silly flags: $ su - password # dnf update # dnf install qpdf # exit $ qpdf --decrypt lockedfile.pdf unlockedfile.pdf One doesn't need a password to unlock these flags, so the fix is instant. La voila! He...

To backup or not to backup.  That is the question. Who likes to make backups? Anyone, Anyone? Hmm, I thought so... Versioned Backups I prefer to make backups with very simple tools, since when things go south, I don't want to have to install a complicated system just to get my data back. Most UNIX backup systems are based on rsync and by using a careful system of  hard links (multiple new names for the same old file), differential backups can save you oodles of disk space in the long run, while making it very easy to step through an archive and retrieve specific versions of old files: https://www.nongnu.org/rdiff-backup/ http://www.mikerubel.org/computers/rsync_snapshots/ https://popey.com/blog/2020/12/straightforward-linux-backups-with-rsnapshot/ Three for the Price of One The original article by Mike Rubel describes how to keep three backups for the price of one, using a combination of hard links and rsync . That idea then spawned the rsnapshot (pull) and r...

GNU Radio on Linux Software Defined Radio requires a reasonably fast computer and won't work properly on a virtual machine.  The heart of Free SDR is of course GNU Radio, from here https://www.gnuradio.org/ and here https://wiki.gnuradio.org/index.php/Main_Page. I like the GQRX program which I use with the RTL-SDR and Great Scott Gadgets HackRF One and these are all very well supported on Linux and Mac as described here http://gqrx.dk/tag/hackrf.   While I can make this work on my Mac, whenever Apple releases a large OS update, I have to re-install the whole house of cards all over again.  This gets very tiring after a while. So to get this lot working and keep it working, I bought a nice new Intel NUC https://www.intel.com/content/www/us/en/products/boards-kits/nuc.html and installed Ubuntu Linux Server 18.04 LTS on it. This is a long term support (10 year) Linux version which means that it will get security updates, but the essentials will remain mor...

The older free Numerical Electromagnetic Code version 2 (NEC2) from Lawrence Livermore Lab assumes an air dielectric.  This makes it hard (but not impossible) for a radio amateur to experiment with Printed Circuit Board Patch antennas and micro strip lines. Air Spaced Patch Antenna Radiation Pattern You could use the free ASAP simulation program , which handles thin dielectrics, you could shell out a few hundred Dollars for a copy of NEC4 , You could buy GEMACS if you live in the USA, or you could add distributed capacitors to a NEC2 model with LD cards (hook up one capacitor in the middle of each element.), but that is far too much money/trouble for most. More information on driving an array antenna can be found here: https://www.aeronetworks.ca/2019/03/driving-quad-patch-array-antenna.htm l Air Dielectric Patch   The obvious lazy solution is to accept the limitation and make an air dielectric patch antenna. An advantage of using air dielectric, is that t...

The eternal question : Which is better - EMACS or Vi? OK, this post is actually about the other eternal question! As I use Linux, Mac, Open and Free BSD (Yes, and that other ball of wax too...), I think I can answer objectively: Both OpenBSD and FreeBSD are reasonably easy to download, install and run on pretty much anything. At least, I have not found a server/desktop/laptop computer that it would not run on.  I even ran OpenBSD on a Sparc Station - remember those? OpenBSD Theo De Raadt has a ' cut the nonsense ' mentality so OpenBSD is simpler, with a smaller repository of programs, about 30,000 packages. However, with a little effort, you can install FreeBSD software on OpenBSD to get the rest. After a few days of use, you will know how. The best OpenBSD book is Absolute OpenBSD: UNIX for the Practical Paranoid. In general, OpenBSD feels a lot like Slackware Linux: Simple and very fast. FreeBSD FreeBSD can also with some effort, run Linux programs ...