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Radio receiver is one such gadget that people have been using for many generations. After the invention of radio communication by Guglielmo Marconi in 1895, the first radio receiver was also invented by Marconi. A radio receiver is an electronic device that can only receive radio signals and can convert the radio signals to audio and sound. A radio receiver can receive radio signals of various frequencies by tuning to a particular frequency. These frequencies are of two types – Amplitude Modulation (AM) and Frequency Modulation (FM). A radio receiver capable of receiving any analog audio on AM/FM frequency is called analog radio receiver and for many years people were using analog radio receivers.
Since the invention of analog radio by Marconi in 1895, many companies started manufacturing radio receivers. First came the De Forest RJ6 in 1916, and later many analog radio receivers like Sony TR-63 (1957), and H.H. Scott 350 (1961) came in the market, and they were the first analog radio receivers of that kind. After the emergence of digital electronics and digital radio transmission, digital radio receivers started to capture the market – receivers capable of receiving Digital Audio Broadcasting (DAB) – digital radio transmission. In 2003, Pure launched the PocketDAB 1000 and It was the world’s first pocket digital radio capable of playing DAB radio stations. However, radio receivers became diversifying when internet technology was implemented in them, which made it possible for the companies to introduce internet radio receivers. An internet radio receiver can be either an app of a computer or can be a standalone receiver, connected to the internet to receive internet radio stations. Kerbango internet radio receiver from 3com was the first standalone internet radio receiver of 21th century. This change in the technology of radio receivers even went beyond internet radio – after the arrival of Software Defined Radio (SDR). An SDR receiver is a radio receiver which can receive both analog and digital radio transmission but can be configured and controlled using software. This became possible after the introduction of System-on-a-Chip (SoC) fabrication technology, and the first SDR receiver was made with the BCM21551 processor by Broadcom in 2007. Such SDR radio receivers became popular among the ameture radio enthusiast and the USB dongle with the Realtek RTL2832U/R820T2 demodulator chip is often used by such enthusiasts as an SDR receiver. The technology of radio receivers has changed many times since the invention of the first radio receiver, and the radio receivers are becoming smarter with the advent of various new technologies.
Types of radio receivers
There are mainly two categories of radio receivers – analog and digital. Under the analog category, there comes either AM or FM receiver but can also be a combo receiver. Among the digital receivers, it can be either an AM/FM HD radio receiver or a DAB/DAB+ receiver. Internet radio receivers are also digital radio receivers but can only receive radio stations when connected to the internet.
AM radio receivers are capable of receiving only AM radio frequencies. AM radio stations broadcast radio signals using a technology called amplitude modulation and in short it’s called AM. It first started with a crystal radio 1904 and then came vacuum tube radios in 1906; after the invention of vacuum tubes by Lee De Forest. Carrying a radio receiver everywhere was not easy at that time because of their bulky design but soon after the invention of the transistor in 1947, radio receivers became portable and smaller in size. An AM radio receiver is capable of receiving AM radio broadcast, which can be of Long Wave (LW), Medium Wave (MW) and Short Wave (SW) frequencies. The Long Wave (LW) frequency range is 30–300 kHz and most of the old AM radio receivers were able to receive longwave radio broadcasts. The longwave signals can travel as far as 2,000 Km but reception at a distance of 17,000 Km was also experienced. Radio Algerie/Chaine 1 (198 Khz) of Algeria, RTL (234 Khz) of France, Médi 1 (171 Khz) of Morocco and Polskie Radio (216 Khz) of Poland are some AM radio stations broadcasting in long wave frequencies with high power antennas. Medium Wave (MW) frequency range is 525 kHz – 1710 kHz and most of the world’s local radio stations have still broadcast on medium wave frequencies since the 1920s. The medium wave stations can be received locally but at night the radio signals can travel as far as 2000 Km and stations can be heard from another city or country. Short Wave (SW) frequency range is 3–30 MHz and many international radio stations broadcast on shortwave frequencies because shortwave signals can be transmitted over a distance of several thousand kilometers, from one continent to another. The shortwave radio signals can travel to various parts of the world because they are reflected by the ionosphere, just like a mirror that reflects light. Among all the types of AM frequencies – only shortwave frequencies can be heard from various parts of the world using any ordinary AM radio receiver.
The first commercial AM radio was RJ6 manufactured by De Forest Radio Telephone And Telegraph Company in 1916. After the invention of Superheterodyne radio receivers by Edwin Armstrong, many companies like Zenith Electronics (USA), introduced AM radio receivers like model 12S-568 and the model 7G605 in 1942 – the first portable radio. Most of the vacuum tube radios were made to receive long wave and medium wave frequencies only because shortwave broadcast was not prevalent at that time. Philips was also one such company who started manufacturing vacuum tube radios in 1927 and became the world’s largest manufacturer of AM radios.
After the invention of the transistor (electronic component) in the early 1950s – many companies like Sony, Zenith, RCA, DeWald, and Crosley started manufacturing various types of AM radio receivers which were capable of receiving shortwave frequencies also. The Sony TR-63 released in 1957 was the first mass-produced transistor radio, leading to the mass-market penetration of transistor radios.
After the golden age of radio during the 1950s and due to the increase of international radio stations – many companies started manufacturing world band receivers. A world band receiver is capable of receiving any AM radio station, broadcasted in longwave, medium wave or shortwave frequencies. Many companies like Sony, Sangean, Grundig, and Philips, manufactured transistor based world band receivers.
Later companies started manufacturing radio receivers with both AM and FM modes, and today most of the radio receivers can receiver AM and FM frequencies. AM/FM receivers became so popular that many products like alarm clocks, CD/MP3 players, walkmans, portable speakers, etc were manufactured with integrated AM/FM radio. Sony Walkman was one such popular product that came with an AM/FM receiver. However, many radio receivers, manufactured today, also come without AM mode. Due to the decline of AM listeners, many companies now-a-days don’t integrate AM receivers with FM radio receivers. Today, only selected radio models have both AM/FM modes and world band receivers manufactured by companies like Degen and Tecsun have such features. However, due to the rise of smartphone users and the integration of FM receivers in smartphones, the number of AM listeners have reduced overtime.
Analog receivers receive the analog radio signals using a telescopic or loop antenna. The received radio signals are then amplified by the Radio Frequency (RF) amplifier and are mixed with oscillator waves. Then the Intermediate Frequency (IF) amplifier sends the amplified signals to the detector, which detects the audio and feeds it to the audio amplifier. The audio amplifier finally amplifies the audio and makes it audible with the help of a speaker.
The radio broadcasting frequencies and the radio receiver manufacturing standards are regulated by the Federal Communications Commission (FCC) of the USA and companies must follow the standards regulated by FCC. Because of this reason almost all radio receivers manufactured by branded companies can only receive frequencies of commercial radio stations but can’t receive any other kind of communication frequencies like Air or Police band frequencies.
2. Digital radio receivers: Digital radio receivers work only with digital radio transmission or internet broadcast, and a digital radio receiver converts the digital audio signals received from the digital radio signals to analog audio. This analog audio is then converted to sound using an analog audio amplifier. The digital radio signals can be either compressed or uncompressed but are usually compressed in MP2 format. Various types of digital radio receivers include: Digital Audio Broadcasting (DAB), HD Radio and Internet Radio receivers. First came the Digital Audio Broadcasting (DAB) receivers during the 90s and The Norwegian Broadcasting Corporation (NRK) launched the first DAB channel in the world on 1 June 1995 (NRK Klassisk). Many DAB receivers came in the market, and PocketDAB 1000 was the world’s first pocket DAB receiver launched by Pure International in 2003. Few years after the rise of DAB receivers, the HD radio receivers were introduced in the market by many companies like Sangean, Sony, TEAC, Yamaha, JVC, Kenwood and Pioneer. Such an HD radio receiver was capable of receiving digital AM/FM radio signals. As the HD radio broadcasting stations were running only in some countries like the USA and Canada, such HD radio receivers couldn’t hit the international market abundantly. Later in the aughts, internet radio receivers became popular among the internet users, and such a radio receiver requires internet connection to play any internet radio station. It was either an app used on a computer or a standalone receiver connected to the internet. Kerbango internet radio receiver from 3com was the first standalone internet radio receiver, but the standalone receivers couldn’t dominate the market because of the easy availability of internet radio apps which were able to play internet radio stations when used on a computer (connected to the internet). But the story doesn’t end here – after the rise of System-on-a-Chip (SoC) processors, the working of a Software Defined Radio (SDR) receiver became possible. An SDR receiver is a radio receiver that can be used to receive radio signals with the help of a computer, and it’s controlled using software. The BCM21551 processor from Broadcom was first SoC used in an SDR receiver in 2007. Since then many companies have launched many types of SDR receivers in the market and the USB dongle with the Realtek RTL2832U/R820T2 demodulator chip can also be used as a SDR receiver, and it’s very popular among the ameture radio enthusiasts. Now-a-days many companies like Yaesu (USA) manufactures radio transceivers with inbuilt SDR functionality.
Many other companies like Pioneer, Tecsun, Revo, Tivoli, Geneva, etc manufacture DAB radio receivers. A newer version of DAB broadcast called the DAB+ has started in many countries and many new DAB receivers are manufactured to work with DAB+ but the older ones can’t. However the newer DAB+ receivers are backward compatible and can receive DAB broadcast also. Because of many good features of DAB technology, many AM/FM radio stations have switched to DAB completely, but this isn’t the case for the USA, because in North America most of the radio stations are using HD radio technology instead of DAB for digital radio broadcasting.
DAB radio receivers use technology for decoding digital radio signals to play the radio station. The tuner digitally tunes the radio frequency and Orthogonal Frequency Division Multiplexing (OFDM) signals are demodulated by the OFDM demodulator. The demodulated signals are used by the channel detector and the digital signals of the tuned station are used by the packet demux and decoder to make use of the digital signals by different services and audio playback. Each of these components of the receiver are controlled by the controller through a control bus, and user inputs are also used by the controller through the user interface.
It’s also possible to listen to any online radio station using any internet radio station using any mobile app or PC software. PC software like Scream Radio from Steamcore (https://www.screamer-radio.com/) is an internet radio software that can be used on Windows PC for listening to online radio stations. In order to listen to any online radio station using the internet radio receiver, one must get the streaming URL link. Many websites like https://www.internet-radio.com/ hosts online radio stations but to get the streaming link, you have to download the M3U playlist file and open it using a text editor like notepad. After opening the playlist file in notepad you will see the streaming URL as a web address with a port number (example: http://us4.internet-radio.com:8266/). You need to copy that URL link and use it with your internet radio receiver to play that radio station.
This seems a very easy way of listening to online radio stations but there are many radio stations that don’t use a static URL link for streaming their radio stations and it’s always encrypted. Such radio stations can only be played on their official website or using their mobile app. Many international radio stations like Voice of America and China Radio International use encrypted radio streams.
Internet radio receivers can also work using a microcontroller like ESP32 and a Digital to Analog Converter (DAC). The microcontroller needs to be programmed to decode internet radio packets. When connected to the internet using WiFi, the user can tune to an internet station using the controller interface and the station information is displayed on the
display device connected to the microcontroller. The decoded signals are fed to DAC and converted to analog audio, which is played using a connected speaker.
The first SDR was developed by the research team of an American entrepreneur and scientist called Ulrich L. Rohde, While working under a US Department of Defense contract at RCA in 1982, and it used the COSMAC (Complementary Symmetry Monolithic Array Computer) chip. However, the practical commercial application of SDR was made possible by a company called Broadcom, with the help of RF CMOS technology. The company demonstrated this by integrating a SDR on a single mixed-signal System-on-a-Chip (SoC) with the BCM21551 processor in 2007.
Since then many companies have introduced SDR receivers in the market for ameture use. Any USB dongle with the Realtek RTL2832U/R820T2 demodulator chip can be used as a SDR receiver with the help of a computer and SDR software like SDRSharp. It has a frequency range of 25MHz up to 1800MHz and supports both analog (AM/FM) and digital (DAB) radio reception. More information is available at https://www.rtl-sdr.com/.
The SDR receiver hardware works along with the hardware of the connected computer. Various components of the receiver are controlled by the computer hardware according to the software configuration. The radio signals received by the antenna connected with the SDR hardware is used by the flexible RF hardware of the SDR. Only the flexibility of the RF hardware makes it possible to work in many different modes with the help of a software. The filtered radio signals are converted to digital data and are used for channelization and sample rate conversion. This data is then used by the computer for further processing to output the data for audio.
Many AM/FM radio stations have resorted to digital transmission, and are also running internet radio channels. Even though the audio quality of digital radio transmission is of superior quality, digital transmission is still having some disadvantages when compared with the traditional analog transmission. And one of the biggest disadvantages is that digital transmissions like DAB have limited coverage range. AM analog radio signals (especially SW) can be transmitted to thousands of miles from one country to another, but that’s not possible with digital radio transmissions like DAB. Moreover, to use an internet radio receiver, one must have an active high speed internet connection, which is not free.
Therefore, analog radio technology has some good features that makes it a winner in some worst case scenarios like network failure (for internet radio) and electromagnetic interference (that causes data loss for digital transmissions), and it’s one of the best technologies ever made.
Author: Debojit Acharjee
The author is a software engineer and likes to geek about various software technologies. Apart from that, he also likes writing articles related to science and technology. He has written many articles related to software technology and computer science, and has knowledge about various software technologies like Robot Process Automation (RPA), Artificial Intelligence (AI) & Machine Learning (ML), blockchain, DevOps, database management, and also knows many programming languages. Besides that, he also knows about various multimedia software used for audio/video editing and production purposes. His passion for computers makes him work hard, and he believes that success comes in life only through hard work and good skills.
Contact: firstname.lastname@example.org or Twitter: @debojitacharjee
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