21st Century Radio Technology
I think the topic is worth starting with what is the receiver for you? This is such a contraption with a bunch of parts, always with coils and frequency control. It doesn’t matter if the receiver has a digital display, or just a knob to select the frequency, or is it a TV tuner installed in your computer and controlled from the computer. They all have a common construction principle, it would seem impossible to come up with something new. Now we will turn your idea about the receivers, what they were and what they became, without particularly delving into subtleties.
Take a look: the receivers shown in the figure (No. 1 - a professional connected receiver, No. 2 - a receiver assembled using the new digital modeling technology) are equal in characteristics; In addition, receiver No. 2 is also a multifunctional MEASURING device! (Of course, a computer is needed for the new receiver to work, but more on that later.)
How can I replace a professional receiver with a small scarf, and even with equal characteristics? It would seem impossible! This was before the advent of software-defined radio (SDR) - a radio communication system in which software is used both for modulation and for demodulation of radio signals. SDR changes priorities, and the personal computer becomes the core of an amateur radio station.
Let's start with the name of the new technology: SDR (Software Defined Radio). Translated into Russian, this means "software-defined (dependent) radio." Why is this radio “definable” and on what programs does it “depend”? Unusual looks the very principle of building a receiver, which consists of two parts: a small circuit part and software. That's the software and the main burden.
In fact, the computer simulates all the nodes of the receiver programmatically. And he does it with the highest quality. Only the first three “squares” in the figure remain on the share of “iron”: brown, blue and red, but they are also simplified to the limit. Even power can now be taken from the computer’s USB port.
The figure below shows a diagram of a simple SDR receiver.
So, the signal from the antenna is fed through the filter (it is also possible through the low-pass filter) to high-speed keys. Much depends on these keys, therefore they must be of good quality (high-speed, with a small transitional and high resistance of the disconnected state, etc.). Two operational amplifiers are connected to the key outputs. Amplifiers also have high demands. There is nothing to write about a local oscillator (synthesizer).
Using a standard DDS synthesizer chip (Direct Digital Synthesis) and dividers with signal outputs shifted 90 degrees, you can cover the range that you need. That's the whole receiver, in its simplest version.
For comparison, below is a block diagram of a modern receiver.
So, back to the consideration of the digital SDR receiver, fig. 1. From the output of the operational amplifiers, the signal is transmitted to the left and right channels of the audio card. The program does everything else: it processes the signal, rebuilds the receiver according to the range (controlled by DDS is used), models the necessary filters (and with the characteristics that cannot be obtained in hardware), simulates the AGC operation (much better than in the "real" receiver), has a panoramic indicator that displays a spectrogram (which shows the situation on the air), measures signal levels and much, much more. That is, using digital signal processing, we can implement what we would like, as well as adjust parameters over a wide range.
SDR technology offers a panoramic view; at the same time, the operator has access to real-time visual monitoring on a computer monitor of signals in the frequency band determined by the sampling rate of the sound card (48, 96 or 192 kHz), as well as the ability to improve the functionality of the SDR receiver by improving the software. Imagine that now you do not need to buy a new device every time - just download and update the program.
Here's what the interface of the SDR receiver looks like, looking at the picture you can imagine what powerful functionality is embedded in this technology. Impressive, isn't it? Especially if you understand why all these buttons;)
In addition to monitoring with very good visibility, SDR control programs allow for high-quality recording of the received signal and relay it to your correspondent, record the state of the ether in the frequency band and subsequently reproduce it, select any filter bandwidth from 10 Hz to 20 kHz with a good slope slope, as well as any operating modes.
In addition, the SDR receiver is also a spectrum analyzer that allows the operator to comprehensively evaluate the signals of the received radio stations. Special perspectives of the SDR technique can give those who work on the VHF bands. By connecting a VHF transverter to an SDR transceiver, it becomes possible to monitor the presence and activity of radio stations in a fairly wide frequency band.
This is not to say that Software Defined Radio technology is young, since the military has long been using it in their equipment. From a commercial point of view, the technology can be considered quite young and rapidly developing. Components for digital signal processing, analog-to-digital and digital-to-analog conversion are being improved and are getting cheaper every day, which constantly brings SDR technology to the masses. As was shown in this article, the complexity of the design of traditional receivers is significantly higher than that of the SDR, not to mention the lack of flexibility of the former, which is so necessary in modern conditions of rapidly changing standards. Therefore, a total transition to the SDR architecture is inevitable, it is only a matter of time.
Several sources have been used to write this text. You can read more about technology here.
offline.computerra.ru/2007/685/318163
And for those who want to try to control and take on the air with such a receiver without getting up from a computer, I suggest visiting this link
http://websdr.ewi.utwente.nl:8901/ . To work, you need a JRE (Java Runtime Environment) and a channel of at least 512 kbps. I managed to receive amateur radio from Russia and the CIS. The receiver itself is located in the Netherlands and allows access to as many users as the outgoing channel allows. All signal processing takes place on your computer.
Take a look: the receivers shown in the figure (No. 1 - a professional connected receiver, No. 2 - a receiver assembled using the new digital modeling technology) are equal in characteristics; In addition, receiver No. 2 is also a multifunctional MEASURING device! (Of course, a computer is needed for the new receiver to work, but more on that later.) How can I replace a professional receiver with a small scarf, and even with equal characteristics? It would seem impossible! This was before the advent of software-defined radio (SDR) - a radio communication system in which software is used both for modulation and for demodulation of radio signals. SDR changes priorities, and the personal computer becomes the core of an amateur radio station.
Let's start with the name of the new technology: SDR (Software Defined Radio). Translated into Russian, this means "software-defined (dependent) radio." Why is this radio “definable” and on what programs does it “depend”? Unusual looks the very principle of building a receiver, which consists of two parts: a small circuit part and software. That's the software and the main burden.
In fact, the computer simulates all the nodes of the receiver programmatically. And he does it with the highest quality. Only the first three “squares” in the figure remain on the share of “iron”: brown, blue and red, but they are also simplified to the limit. Even power can now be taken from the computer’s USB port.
The figure below shows a diagram of a simple SDR receiver.
So, the signal from the antenna is fed through the filter (it is also possible through the low-pass filter) to high-speed keys. Much depends on these keys, therefore they must be of good quality (high-speed, with a small transitional and high resistance of the disconnected state, etc.). Two operational amplifiers are connected to the key outputs. Amplifiers also have high demands. There is nothing to write about a local oscillator (synthesizer).
Using a standard DDS synthesizer chip (Direct Digital Synthesis) and dividers with signal outputs shifted 90 degrees, you can cover the range that you need. That's the whole receiver, in its simplest version.
For comparison, below is a block diagram of a modern receiver.
So, back to the consideration of the digital SDR receiver, fig. 1. From the output of the operational amplifiers, the signal is transmitted to the left and right channels of the audio card. The program does everything else: it processes the signal, rebuilds the receiver according to the range (controlled by DDS is used), models the necessary filters (and with the characteristics that cannot be obtained in hardware), simulates the AGC operation (much better than in the "real" receiver), has a panoramic indicator that displays a spectrogram (which shows the situation on the air), measures signal levels and much, much more. That is, using digital signal processing, we can implement what we would like, as well as adjust parameters over a wide range.
SDR technology offers a panoramic view; at the same time, the operator has access to real-time visual monitoring on a computer monitor of signals in the frequency band determined by the sampling rate of the sound card (48, 96 or 192 kHz), as well as the ability to improve the functionality of the SDR receiver by improving the software. Imagine that now you do not need to buy a new device every time - just download and update the program.
Here's what the interface of the SDR receiver looks like, looking at the picture you can imagine what powerful functionality is embedded in this technology. Impressive, isn't it? Especially if you understand why all these buttons;)
In addition to monitoring with very good visibility, SDR control programs allow for high-quality recording of the received signal and relay it to your correspondent, record the state of the ether in the frequency band and subsequently reproduce it, select any filter bandwidth from 10 Hz to 20 kHz with a good slope slope, as well as any operating modes.
In addition, the SDR receiver is also a spectrum analyzer that allows the operator to comprehensively evaluate the signals of the received radio stations. Special perspectives of the SDR technique can give those who work on the VHF bands. By connecting a VHF transverter to an SDR transceiver, it becomes possible to monitor the presence and activity of radio stations in a fairly wide frequency band.
Conclusion
This is not to say that Software Defined Radio technology is young, since the military has long been using it in their equipment. From a commercial point of view, the technology can be considered quite young and rapidly developing. Components for digital signal processing, analog-to-digital and digital-to-analog conversion are being improved and are getting cheaper every day, which constantly brings SDR technology to the masses. As was shown in this article, the complexity of the design of traditional receivers is significantly higher than that of the SDR, not to mention the lack of flexibility of the former, which is so necessary in modern conditions of rapidly changing standards. Therefore, a total transition to the SDR architecture is inevitable, it is only a matter of time.
Several sources have been used to write this text. You can read more about technology here.
offline.computerra.ru/2007/685/318163
And for those who want to try to control and take on the air with such a receiver without getting up from a computer, I suggest visiting this link
http://websdr.ewi.utwente.nl:8901/ . To work, you need a JRE (Java Runtime Environment) and a channel of at least 512 kbps. I managed to receive amateur radio from Russia and the CIS. The receiver itself is located in the Netherlands and allows access to as many users as the outgoing channel allows. All signal processing takes place on your computer.