Personal radio communication. What? How much? What for?

[CarderPlanet]

Complication and rise in price from left to right

There will be no diagrams or boring lectures on the basics of radio here. The purpose of this article is to explain the difference between the models available on the market. Why the price can be so different, and how it affects the consumer characteristics.

A little excursion
Almost every time when it comes to personal radio communication in the non-core community, there is someone who is very surprised that such devices are still actively used. And the argumentation of such skeptics is always the same: why do we need all these walkie-talkies, if everyone has a mobile phone with GSM, UMTS, LTE, WiFi, GPS, and a dozen other terrible words in the kit in their pocket.

I want to apologize right away for some snobbery, but for "religious" reasons, in this article I will still use the word radio station.

Of course, outdoor enthusiasts, as well as professionals working in groups somewhere far beyond the warm offices, do not need to explain anything. These people regularly use personal radio communication and its convenience is obvious to them. But, nevertheless, for the rest I will explain the key differences between mobile phones and radio stations. First, about the advantages of the latter.
Autonomy. In most cases, personal radio communication is carried out in the so-called forward channel, directly from the transmitting device to the receiving one. Accordingly, no external infrastructure is required for such communication. Radios work great at the pole and in the middle of the ocean, where there are no cellular networks. A byproduct of autonomy is the absence of any communication fees.
Instantaneousness. The radio does not require dialing and waiting for an answer. You just press a button, speak, and your words are immediately heard from any receiving device tuned to the same frequency channel. This can be very important in extreme conditions, where poking into the touch screen while hanging from the edge of a cliff is not always convenient.
Broadcasting. One transmitting radio station is received by everyone who is in its coverage area and tuned to its channel. That is, this is a one-to-many relationship, where the number of receivers is not limited at all. At least ten, at least a thousand. It is extremely convenient when working in a large group, where you would have to call everyone with an ordinary phone, spending a lot of time on it.

I am aware of PTT and Zello-like services, but few people know that a message through such a channel can arrive with a delay of up to tens of seconds. In a firefighting environment, for example, this is eternity.

Now for the main disadvantages.
Limited range. The downside of autonomy. The signal of a portable radio station in the conditions of the earth's surface usually spreads over a distance from several hundred meters to a couple of kilometers. Depending on the height, terrain, and other factors. There will be no connection for many tens of kilometers, as is sometimes shown in the movies or on the pages of sellers.
Instantaneousness. Yes, this is also a disadvantage. With an incoming phone call, you can slowly take it out of your pocket, psychologically tune in to receive information. But the radio station can start talking immediately and to the point, without preliminary caresses, so to speak. As a result, the pioneer must always be ready.
Lack of targeting. The downside of broadcasting. When communicating in a group, you cannot call an individual person. The maximum that can be done is to offer the subscriber to switch to another channel in the general channel, where they can discuss personal issues. This is, of course, much less convenient than a direct telephone call. And you also need to remember to return to the general channel later.
There is no confirmation of delivery. It is far from the fact that the transmitted information was received by its addressee. Not the fact that at least anyone accepted it. For example, all subscribers are too far away, or their radio stations are tuned to a different channel. That is why, with such a connection, the rule of good manners is to confirm the fact of reception by the word "accepted" or in some similar way.
Simplex. This is when you cannot speak and listen at the same time. Also press the button. Moreover, when one speaks, no one else can speak either. More precisely, it can, but which of several speakers will be heard by this or that subscriber - the will of the case. A close transmitter will block the far one, but the signals of equidistant transmitters will not overlap like ordinary voices, but will make each other completely unreadable.
Limited number of channels. Unlike cellular communications, where the network is responsible for the dynamic allocation of channels, here people choose the channel, and its change is often associated with organizational and, perhaps, technical difficulties. All this often leads to conflicts on the air. To reduce the influence of this factor, subtones were invented (CTCSS, DTS and the like "subchannels"), which allow at least not to listen to other people's chatter.

Attention! Closing to subtone is not a means of encryption or any other way to restrict access to your conversations. This technology just shuts your receiver off from other people's signals on the same frequency. In other words, it is you who stop hearing the transmissions of your neighbors, not yours.

Lack of privacy. If you do not go into the high matters of encrypted digital communication, then all your conversations can not only be easily heard by outsiders, but also disrupted by someone else's interference. Some radio stations have in their composition an analog signal obfuscator - a scrambler, but this is a comparative rarity, and as an encryption it is so-so, something like WEP from the WiFi world, who wants to - easily decodes. Therefore, do not forget the old army wisdom.

As you can see, the disadvantages are above the roof. Some of them have been eliminated in professional equipment, but it is still clear that radio stations are not about household or business communications, i.e. not a replacement phone.

I really like the analogy with network protocols.
A cell phone is TCP. Point-to-point communication; pre-connection is mandatory with obtaining consent for communication from the receiving party; guaranteed package delivery; notification of the parties about the emergency rupture of the channel; used in both local and global networks.
The radio station is UDP. Point-to-point and point-to-multipoint communication; no preliminary connections, just send packets and that's it; there is not only a guarantee of delivery, but also a guarantee that someone is listening to a given port at all; an emergency channel break is detected only by the absence of incoming traffic; more often used in local networks.
At the same time, no one says that TCP should replace UDP. Moreover, in "difficult" network conditions, it is recommended to use just the same UDP.

But, despite all the shortcomings, such a connection has gained popularity among the categories of users mentioned above. Now let's move on to the topic of the article.
A little over ten years ago, there was virtually no choice of radio stations. Of course, there were and are a dozen manufacturers offering similar solutions at a similar (high) price. But the difference between these products is mainly in the design and service functions. They are all built according to the same principle and work in about the same way.
The receiving path of these radio stations is built according to a superheterodyne circuit on discrete elements or analog microcircuits of a small degree of integration. The transmitter consists of a master oscillator combined with a modulator, several stages of frequency multiplication, and a power amplifier. Separate transistors or simple microcircuits (as well as hybrid assemblies) are also used here. That is, the transmitter and receiver are analog devices, and due to the fact that some parts of the circuit are used by them together, radio stations of this type are also called transceivers.
I will further call such devices "classical", because the principles of their operation have been known for more than a hundred years.
Today, thanks to our Chinese comrades, there are about a hundred models on the market. Sometimes similar to each other as twins, sometimes very different. But, most importantly, the prices of different models also sometimes differ by almost an order of magnitude. Is it about marketing and whistles, or not only?

RDA and all-all-all

A real bestseller

Let's start with the most delicious for the price and therefore very popular brand called Baofeng. I will not deny, he just turned the market upside down. Thanks to him, portable radios have gone from gadgets to consumables. Now there is no need to save a whole salary for a radio station; it is enough not to go to a restaurant once. What's the secret?

The secret is in this small microcircuit, only 5x5 mm, one notebook cell
Despite some antagonism between radio stations and mobile phones, Baofengi owes its birth to developments in the field of cellular communications.
Once, one engineer asked himself: if in any cheap mobile phone a transceiver with good characteristics is built right into the processor, then why are radio stations so complicated and expensive? Could it be possible to use the developments of mobile communications to build the same cheap radio station?
And naturally it turned out that it is quite possible. After all, the transceiver of a radio station is structurally much simpler than a transceiver of a cellular terminal. Here the frequencies are lower, and the transmission-reception switching is simpler, and the requirements for stability of characteristics are an order of magnitude softer. Why not?
As a result of all these logical conclusions, and then engineering efforts, a wonderful RDA1846 microcircuit was born, which includes almost the entire radio station. There is a frequency synthesizer, and receiver and transmitter paths, which include all key nodes, and even SPI and I 2 C interfaces for communication with an external microcontroller, which are more typical for Arduin peripherals with blackberries.
In short, the idea worked 200%. Radio stations based on this microcircuit turned out to be about the same price as the most deshman mobile phones based on highly integrated all-in-one SoCs, that is, literally from two dozen dollars. And, which is also very important, in some respects they even surpassed the classic entry-level products at a multiple lower price!
But our world is arranged so that does not happen that all was well. There must be a catch somewhere. And, unfortunately, there is.
What's inside a two hundred dollar Motorola or Kenwood radio? There are a lot of different parts, including a lot of capacitors and coils. Moreover, some of the coils are also with variable inductance, which must be manually adjusted in each instance at the production stage. There are also usually several weighty quartz resonators and ceramic filters.
All these parts cannot be crammed into the microcircuit crystal. Especially the trimmers. And if you just take them outside, it will not be much easier and cheaper to consider it a revolution.

Analog microcircuits for transmitters and receivers, which contain everything that can be placed on a chip, of course, have existed for a long time. But their use does not provide radical advantages, so many classic radio stations are still based on discrete transistors in their high-frequency part.

Motorola actively uses analog microcircuits of its own design

It is for this reason that integrated receivers and transmitters are built on a different principle. In them, the analog signal is subjected to only the most minimal processing.
To simplify somewhat, the receiver, after a short preparation, transfers the signal to a lower frequency, simultaneously dividing it into components, and immediately digitizes. All subsequent manipulations are performed on the digital stream. Exactly the same principle as in SDR, only the built-in DSP-core is engaged in algorithmic processing, and not a separate computer.
The transmitter, on the contrary, generates the target signal completely "in digital", and only before its output to the chip leg, it undergoes digital-to-analog conversion and transfer to the desired frequency.
This approach allows you to get rid of 90% of those parts that cannot be etched on the surface of the silicon substrate, and at the same time from all those that need to be tightened up during the setup process.
Of course, in terms of the number of elements, the circuit of such a transceiver turns out to be three orders of magnitude more complicated than an analog one. But thanks to the fact that all of it is now placed on a crystal that can be stamped in millions of copies, the final price turned out to be very low.
The result is an excellent transmitter, and a receiver that has very good sensitivity, but has some problems ...
Anyone who has used RTL-SDR receivers in the city knows well how they behave in the presence of a powerful interfering signal on the air. This signal begins to be received everywhere, and not only at its own frequency. And at the moment of appearance of such interference, the entire spectrum "sags", as if the level of all other signals had sharply decreased.
This is due to the fact that the range of input voltages that such a receiver can process is limited by the circuitry of the input circuits and the ADC capacity. If the typical receiver sensitivity is about 0.1 μV, then even under ideal conditions a 16-bit ADC will hit the upper limit of its dynamic range even with an input voltage of only about 3 mV. In reality, it is several times lower. And such a signal can easily be "caught" even a few kilometers from its source, especially on an external antenna.
What happens when the ADC overflows with a powerful signal? It's about the same as when the camera is exposed to direct sunlight. Everyone has seen this kind of footage.

There are branches and leaves inside the bright circle, but they are not visible.

In the photo, we can see that due to the sun, all the colors have changed. Dark tones have turned to gray, and the closer to the sun, the more the color is distorted. And starting from some degree of approximation, all pixels merge into a solid white color and information about them is completely lost. This threshold of brightness is the limit of the capabilities of analog cells or ADC matrix.
Exactly the same effects occur in the "blinded" receiver. A strong signal noticeably suppresses even that which is far from its frequency. At the same time, weak signals begin to drown in noise. And everything that turned out to be near the frequency of the "illumination" is completely covered by the interference.
These are far from all the negative consequences of overloading the receiver, but it is already enough to explain such an unpleasant feature of the Baofeng as the ability to receive interference from car alarms at any frequency, even with a large detuning from the garbage 433.920 MHz channel. In this case, the signal from a nearby hummer plays the same role as direct sunlight in a damaged photograph.
You can, of course, increase the ADC capacity to 24 bits and get a good dynamic range from 0.1 μV to 0.7 V, but then you will need to transfer to 24-bit rails and DSP. And at the same time, do not forget about the analog circuits at the input, which must consume a significant current in order to pass almost a volt of the input voltage through themselves without distortion. All this can be done, but the resulting price and power consumption of such a chip already makes it almost meaningless in comparison with the analog "classic".

By the way, such solutions are actively used, for example, in the market of shortwave radio stations, where the problem of dynamic range is much more acute. But their price, as I have already said, is even higher than that of classical devices, and all the fuss was started not to reduce the cost, but for the sake of the huge possibilities provided by digital signal processing.

So what do we have? Baofengs are cheap, compact, economical, sensitive in reception, but feel bad in the busy city air.
Their ideal "habitat" is in nature, in the sea, in the desert, at the pole. In short, away from interference, where the potential of their sensitive receiver can be fully revealed.
Accordingly, where they do not need to be used - this is in aviation and aeronautics, in electric transport, and in urban conditions, be ready to listen to all alarms within a radius of one hundred meters. And in no case even think about connecting an external antenna, including an automobile one. In general, I do not recommend connecting anything other than the standard "rat tail". The better the antenna, the more pronounced all the disadvantages of the RDA chip. Up to the point that the reception of weak signals on an external antenna will be worse than on a standard one.

RDA on steroids
The disadvantages described above made some manufacturers go for a slight complication and increase in the cost of the radio station in order to improve its reception characteristics.
The essence of the improvement is simple. Since a single-chip receiver is so afraid of strong interference, it should be protected from them as much as possible. For this, additional filters are placed at the input of the receiver, consisting of inductors and electrically controlled variable capacitors - varicaps.

In fact, a varicap is a simple diode, but that's not about that now.

When setting the frequency, the processor, using the built-in DAC, changes the voltage on the varicaps so that their capacitance, in combination with the inductance of the coils, forms LC circuits tuned to approximately the same frequency. Literally a pair of such circuits, connected in a chain, form a filter that makes it possible to effectively filter out all signals that are more than a few megahertz away from the operating frequency right at the receiver input. As a result, the radio station ceases to hear alarms over the entire range and generally works much better for reception.
Apart from the rise in price, the price of improvements is a slight deterioration in the receiver sensitivity due to losses in the filter (after all, the rest of the circuit, in particular the RF amplifier, remained unchanged). But these losses are more than compensated for by improved noise immunity, as a result of which the ability to receive weak signals in urban conditions only gets better.

ShiQun SQ-UV25 looks exactly the same

It is not easy to distinguish between radio models equipped with a filter. Their price is slightly higher than that of the classic Baofeng, by about $ 10. But it is obvious that you cannot be guided by the price alone, you need to look for reviews from specialists. So far, only two such models are known to me for certain: Quansheng UV-R50 and ShiQun SQ-UV25.
What are the conclusions? In terms of receiver quality, these radio stations occupy an intermediate position between Baofeng and superheterodyne. They can be used quite comfortably in the city with a standard antenna. And in remote areas, even connect an external antenna if necessary.
The RDA still feels bad in the city with an external antenna, and on electric vehicles.

Classic

I won't write much here. The cost of these radios from the Chinese starts at $ 80. Now the market for cheap portable superheterodyne devices is actually monopolized by several models of only two manufacturers. This is Wouxun with the KG-UVD1P model and the KG-UVxD line, as well as Quansheng with the TG-UV2 and TG-UV2 Plus models. There are a number of sophisticated models with a price of under two hundred dollars, but this is a completely different category, which we will not touch upon.
Classical circuitry allows the receiver to work in the difficult conditions of the city air and on electric transport, where the interference is even greater. But in everything you need to know when to stop. The input circuits, even for a superheterodyne receiver of a portable radio station, are sharpened primarily for sensitivity and economy. Although the ability to withstand strong interfering signals is better than that of the RDA, care must be taken when using an external antenna.

For operation with full-size antennas, only stationary and some automotive devices are recommended. Their developers did not need to save every millimeter on the board. Even in reception mode with a closed noise suppressor, these devices consume a current of up to several amperes from the power source. It is at this price that a wide dynamic range is achieved, and therefore a portable radio station will never compare with them in this parameter.

What's the bottom line? Classic devices can be used almost without restrictions in any conditions except for the version with an external antenna in a particularly busy broadcast.
The disadvantages are higher price and power consumption, usually fewer different service functions.
PS I also wanted to include digital radio stations in the article, but it was too long. If the topic of digital personal radio is interesting, then there will be a similar article, but already about inexpensive digital radio stations.

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