Radio skills seemed to be something of a lost art growing up, only thing i heard about radio was from the stories my grandfather used to tell me about CB radio. These days most devices that use radio are locked to a certain frequency range, this makes them useless for scanning radio frequencies other than the ones they are designed to receive and transmit, sometimes that might even be locked like with Wifi chips and monitor mode. But there is a workaround, not so long ago the FunCube dongle was released, initially made possible by AMSAT UK and the Radio Communications Foundation, around the same time it was discovered that the similar receiver functionality was possible with a cheap TV DVB-T dongle running a certain realtek chip (rtl2832U) which could be used with different drivers to enable it to receive everything from 20Mhz up to around 2GHz. With the rtl-sdr dongle people have a very inexpensive method of scanning radio frequencies, consequently there is a lot of projects relating to radio which have appeared over the last decade. There is now a large amount of functionality available for these dongles, from monitoring aircraft with ADS-B, Receiving satellite imagery from Meteor/NOAA Satellites and so much more.
There are many options for SDR programs depending on whether you use Linux, Mac or Windows, functionality and support for various hardware varies across the many different SDR programs. There are also programs for SDR which are designed to deal with particular standards rather than just being generic scanners, When it comes to SDR this is one of the fields Linux really excels at generally leading the way in a lot of areas, Windows 10 has security features such as automatic driver update and driver signing policies which makes it less practical but still capable option, Linux has been used on a large majority of the projects around SDR so you will find it a bit more capable. these are just some of the more widely used SDR packages, but there are more.
- SDR# Windows
- HDSDR Windows
- AngelSDR Linux/Windows
- gqrx Linux/Mac
- CubicSDR Linux/Mac/Windows
- SDR Touch Android
There are many different manufacturers of rtl2832U dongles, there are a few tuner options the three most capable are Rafael Micro R820T, R820T2 and Elonics E4000 which have the largest frequency range. There are several manufacturers which specialise in SDR hardware and RTL-SDR, one of the most notable is NooElec, but the RTL-SDR project also make some of their own versions of these devices and there are some schematics available on the RTL-SDR website so you can make your own if you are that way inclined. There are many other SDR devices which have been released in the last 5 years and are far superior supporting transmission in both full duplex and half duplex, however the cost of these devices are generally far higher than is acceptable for someone who might just be starting out experimenting with radio. The rtl2832u is a very cheap sollution for RX in comparison to more costly devices such as LimeSDR, PlutoSDR, HackRF and BladeRF.
Antenna design is an important part of radio, there are many different ways we can broadcast or receive radio signals, for instance your terrestrial TV signals are received from one direction most people use a yagi directional antenna which is orientated in a horizontal plane to get the best reception from the transmitter. radio dish are a similar concept only picking up radio signals from certain direction but with a wider range of angles for reception, by using a reflector they can focus more of the radiation at the LNB(Low-Noise Block downconverter), you will commonly see these used in satelite TV but this is also how radio telescopes work by collecting radiation over a larger area and focusing it on a receiver. These methods are all well and good when we only want to look at the radio signals coming from one direction, but if we want to receive or transmit signals in many directions like say for ADS-B or VHF radio then we might want an omni direction antenna like whip, discone or dipole antennas. There are many other types of antenna, whether you are receiving or especially for transmitting radio signals it is important to use an antenna best designed for the frequency. there are many applications out there which can help you with and antenna design and simulate near and far field radiation patterns such as 4nec2, OpenEMS and a few paid commercial apps
The rtl dongles can only receive radio signals in a very limited amount of the radio spectrum, many of the more expensive devices will receive signals up to 6GHz and beyond. To solve this it is possible to use a converter to step the frequency up or down exposing more of the radio spectrum to the rtl dongle. Many manufacturers sell up/down-converters to expand the frequency range of more expensive radio transceivers, but they are also a common component in satellite TV systems, this would also work to down convert high frequency radio signals for the rtl-sdr.