Good afternoon. Prompt please Hackrf still actual or not? Hype was on it in 2015, now there are no new articles, and no tutorials. Advise who owns this iron, is it worth taking it or are there newer things?
What's on the radio
If the word “radio” brings to mind only the old grandfather “Grundig” or “Ocean”, then this is a very narrow view of things. We live in a time of wireless devices, the Internet of things, 5G and other interesting things. More and more information is transmitted "over the air", so a good specialist must understand radio protocols. I will tell you how to receive a signal, where to look for it and how to analyze it.
First you need to understand what and where you can find on the radio. The list is extensive: from images from weather satellites to commands for nuclear submarines.
As far back as World War I, it was known that transmitted radio signals could be received by anyone. So everything really important is transmitted encrypted, and you should not hope to turn on the radio and find out the secrets of the Pentagon. But you can still find something interesting.
Let's walk on the frequencies.
Extra low frequencies up to 30 kHz: communication with submarines. Radio waves of such a low frequency are able to penetrate even into the depths of the ocean, which, of course, is used by the military. The Zeus system operates at a frequency of 82 Hz, the similar American Seafarer system operates at a frequency of 76 Hz. The wavelength of such a transmission is comparable to the radius of the Earth, and the efficiency of the antenna is thousandths of a percent. Almost a megawatt must be fed into it in order to get one watt at the output. Slightly higher in frequency, at about 14 kHz, you can find the signals of the Alpha navigation system . Everyone can receive these signals if you put the antenna on the roof or drive away from the city, where there is no interference. On YouTube you can find videos of enthusiasts.
At a frequency of 77 kHz, accurate time signals are transmitted from Germany. The DCF77 system , the most popular in Europe, allows desktop and even some wristwatches to synchronize. If your watch has the Atomic Clock or Radio Controller logo, it can receive this signal.
Long waves - 400 kHz - are occupied by the signals of the so-called PFP - driving radio beacons (in the English literature NDB - non directional beacon). Each aircraft has a radio compass that shows the direction to the selected airport.
On medium and short waves (from 2 to 20 MHz) weather forecasts for ships and meteofaxes, telemetry of various devices are transmitted; STANAG military modems, over-the-horizon radars and much more work. Much of this can be received on a good shortwave receiver.
Taxi drivers and truckers work on the so-called Citizen Band 27 MHz.
At frequencies from 30 to 40 MHz, home radiotelephones used to work, now they are practically gone. A big tube with a long antenna from old movies is it. The owners usually did not suspect that anyone could hear their conversation, there was no encryption in these phones.
At frequencies from 88 to 108 MHz, the well-known FM radio sounds. Radio engineers call it WFM (Wide FM, as opposed to narrowband FM portable radios). A little lower, the so-called Soviet VHF was transmitted, now these stations are also almost everywhere closed.
Aviators operate at frequencies from 118 to 137 MHz. Pilots' conversations with controllers and between aircraft, for example, at an air parade, are transmitted in an open and unencrypted form.
NOAA weather satellites operate at a frequency of 137 MHz. You can receive their signal and decode a picture of Earth from space, you just need to know the time when the satellite flies over your head. Enthusiasts succeeded here and posted it on YouTube .
At frequencies in the range of 140-200 MHz and 400-500 MHz - different services and services: traffic police, firefighters, ambulance, elevator operators, guest workers. The 433 MHz band is reserved for portable radios that you may have seen for sale. Portable radio devices also operate nearby in frequency, to which we will return.
Previously, pagers, devices for receiving text messages, worked at a frequency of 165 MHz, and all their messages were transmitted to subscribers in clear text, available for decoding. Now there seem to be no pagers left in Russia, but in Europe and the USA they are still alive, they are used by firefighters, doctors and other services.
American communications satellites SATCOM operate at a frequency of 255 MHz . They are interesting in that the satellites are old and analog and, in principle, anyone can communicate through them, no passwords and authentication. What is still used by some Brazilian and Mexican farmers who have adapted such satellites instead of a free radiotelephone. All you need is a radio station for this range and a directional antenna. Anyone can do this, but in Russia the signal is weak.
At frequencies of 865 MHz and 2.4 GHz is the ISM band (Industrial, Scientific, Medical). Radio modems, IoT devices and various devices work there. If you want to transfer data from your Arduino wirelessly, take the module for this range.
Cellular communications operate at frequencies of 900 and 1800 MHz.
At a frequency of 1090 MHz, ADS-B operates - aircraft transponders, thanks to which you can see flying aircraft on the Flighradar24 website . And these signals can also be received and decoded independently.
At a frequency of 1575 MHz, GPS signals are transmitted, thanks to which navigation works in your smartphone or car.
Even higher in frequency (10 GHz or more) satellites and radio relay communication lines operate.
The excursion was not very short, but it was necessary. Now it's time to talk about what we need to receive and transmit radio signals.
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