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Parasitic Quadrifilar Helical Antenna

This article was reprinted in OSCAR News, March 2018: http://www.amsat-uk.org If you want to receive Satellite Weather Pictures , then you need a decent antenna, otherwise you will receive more noise than picture. For polar orbit satellites, one needs an antenna with a mushroom shaped radiation pattern . It needs to have strong gain towards the horizon where the satellites are distant, less gain upwards where they are close and as little as possible downwards, which would be wasted and a source of noise. Most satellites are spin stabilized and therefore the antenna also needs circular polarization, otherwise the received signal will flutter as the antennas rotate through nulls. The helical antenna, first proposed by Kraus in 1948, is the natural solution to circular polarized satellite communications. It is a simple twisted wire - there seems to be nothing to it. Various papers have been published on helix antennas, so the operation is pretty well ...

To C or not to C, That is the Question

As most would know, the Kernighan and Ritchie C Programming Language is an improved version of B, which is a simplified version of BCPL, which is derived from ALGOL, which is the Ur computer language that started the whole madness, when Adam needed an operating system for his Abacus, to count Eve's apples in the garden of Eden in Iraq. The result is that C is my favourite, most hated computer language , which I use for everything. At university, I learned FORTRAN with punch cards on a Sperry-Univac, in order to run SPICE, to simulate an operational amplifier. Computers rapidly lost their glamour after that era! Nobody taught me C. I bought the book and figured it out myself. Over time, I wrote a couple of assemblers, a linker-locator, various low level debuggers and schedulers and I even fixed a bug in a C compiler - not because I wanted to, but because I had to, to get the job done! Much of my software work was down in the weeds with DSP and radio modems...

Unlock CRA PDF Forms

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...

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