Every year a series of ARISS Slow Scan TV (SSTV) transmissions are scheduled from the International Space Station, the images are transmitting using the 145.800 MHz ham radio frequency. How can it be received and decoded? Let’s figure it out.

General Information

The images transfer from the ISS is carried out by the ARISS team, the quite noble goal of this project is to draw attention to space exploration and astronautics. These broadcasts are carried out several times a year, anyone in any place of the world can receive SSTV images at the 145.8 MHz frequency. The SSTV (Slow-scan television) format itself was created a long time ago, it was used even to transmit images of the far side of the Moon from the Russian “Luna-3” station. Much later, SSTV became popular among ham radio amateurs, because made it possible to transmit and receive images using a radio transceiver. With some changes, the SSTV format has survived to nowadays. …

Wireless technologies are now everywhere around us. But how does it really work? I will review different types of modulation and signal transmission modes, from the simplest to the most complicated.

Let’s try to figure out, without formulas and as simply as possible, how we can transfer data from point “A” to point “B”.

OOK (On-Off Keying)

The simplest form of digital coding. Just turn on / off the radio transmitter in accordance with the binary signal:

The reason for this article is, in fact, sad. The world-famous radio telescope of the Arecibo Observatory in Puerto Rico has collapsed and is beyond repair. For many years it was the largest radio telescope in the world (diameter 304 m, frequency range up to 10 GHz), with the help of which many discoveries were made. On this Wikipedia image it is still in working condition:

But the article is actually about another event. In 1974, a message to extraterrestrial civilizations was sent into space from this telescope. How it was encoded, let’s figure it out.

Encoding

First, it’s interesting to understand how the message was made. As we know, the message size was only 1679 bits (approximately 210 bytes), and it was transmitted at a 2380 MHz frequency with a power of 450 kW. Frequency modulation with 10 bit/s speed was used for transmission. The number 1679 was specially chosen — it is the product of two prime numbers 23 and 73, so there is only one way to draw the picture in the form of a rectangle. …

Now is the beginning of December — the best time to add a bit of light and warmth to the house. Nowadays almost all electrical equipment becoming ‘smart’ — let’s make the Christmas lights also smarter. I’ll show an easy way, how to control Christmas lights remotely and how to add voice control.

Lets’ get started.

Before we begin, just a quick note. This article is not sponsored by any of the manufacturers, everything was purchased by me at my own expense. There are also no ads or referral links in this article.

I will describe here using the Google Home service. Amazon Alexa or Apple Siri users can search for another tutorial. …

Modern smartphones are almost on par with desktop PCs in terms of RAM and CPU power. Can we replace a computer with a smartphone? Samsung is investing time and money for years in DeX technology. How usable is it? Let’s try to figure it out.

I recently wrote about my experience of using Raspberry Pi 4 as a desktop replacement. This was generally very positive, however, the effective usage of the Raspberry Pi requires some Linux knowledge. Samsung DeX, by contrast, is aimed at a wider audience. …

Since the introduction of the Raspberry Pi 4, a lot more people have been trying to use this microcomputer as their desktop PC. More recently, the Raspberry Pi 400 Personal Computer has been released, the name of which directly indicates its “main” purpose. I have long been interested in the possibility of using a portable and silent PC for simple tasks like creating this text, where the full-size desktop is redundant and the tablet is inconvenient. Finally, I bought a top-of-the-line Raspberry Pi 4 with 8GB of memory. It’s time to see how it works.

Readers who were born at the 70s or earlier, and had medium-, long- or shortwave receivers at home, probably remember that stations of different wavelengths propagate differently at different times of the day. But how does it really work?

I will show, how using an SDR receiver and 50 lines of Python code, it is possible to visualize radio stations signals with <0.01 Hertz accuracy and observe some interesting atmospheric effects.

General Idea

Most AM radio stations are broadcasting 24h per day, which allows us to analyse the radio signals they transmit. To do this, we will record the radio signal in WAV format and plot its spectrum using FFT (Fast Fourier Transform). FFT makes it possible to obtain an image in the frequency domain from a signal in the time domain, in other words, to get a spectrum of the signal. …

Once I came across a description of an Android application that measured the heart rate remotely by using the smartphone’s camera. The camera was not touching to the skin, also was not illuminated by LED. An interesting point was that the Google Play reviewers did not believe in the possibility of such a measurement, and the application was rejected. I don’t know the end of this story, but it became interesting to check whether this is possible. There is no need to make an Android application, it is much easier to test the idea in Python.

Let’s get started.

Getting the Camera Stream

First, we need to get a stream from the webcam, for which I will use OpenCV. The code is cross-platform and can run on both Windows and Linux/OSX. …