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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Radiotelephones and all about them. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Telephony We owe the appearance of this useful thing in our everyday life to the passionate American inventor, scientist and radio amateur - Al Gross. Although, of course, one might think: "Eka unseen - to offer to use the radio station, in fact, for its intended purpose." Everything seems to be correct, but if we consider that this idea was expressed back in 1950, then the situation becomes completely different. All electronics at that time was made on lamps, and a typical army "portable" radio station was a shoulder pack weighing about 20 kilograms. It is hard to imagine a fan of "conveniences" who would agree to carry a kind of "chest with an antenna" around the apartment instead of a small wired phone! And Gross had to try hard to prove that his idea was not at all absurd and would subsequently be widely demanded by people, although even then he could not offer anything better than a design that received the eloquent nickname "brick" for its size and weight. To feel how far the idea of a radiotelephone was ahead of its time, suffice it to say that by the time the first serial models of home radiotelephones appeared - in the early 70s of the twentieth century - Gross's patents had already expired! On this occasion, the inventor even joked with irony: "If my patents had not expired, then I would have been a millionaire several times ... and Bill Gates would have stood behind me." Indeed, radiotelephones today are produced in huge quantities by many companies, and the convenience and ease of use of them, it seems, no longer require any explanation. But it turns out that this is not always the case, and questions still remain here. To make the phone work not only at night ... This story happened several years ago, when in the midst of the white nights in St. Petersburg, my old friend called me and asked the question: "What could happen to the radiotelephone during its transportation by plane, that it began to work only after sunset?" I can honestly say that this question has puzzled me. I have always known this woman (humanities by education) as a very attentive and accurate person, besides, she always expresses her thoughts well and clearly, but her question seemed to me complete absurdity! No, of course, the Sun affects radio communications, and radio astronomers and many other specialists are well aware of this, but it was absolutely impossible to suspect a home radiotelephone of such sensitivity ... From further inquiries, I managed to find out that my friend bought the radiotelephone during a trip to Europe and even managed to test its operation abroad in practice. But after returning home, something incomprehensible began to happen with the phone: a normal conversation was possible only at a distance of several steps from the base, and when moving away from it, noise, background appeared in the handset, and the connection was cut off. But with the advent of darkness (which at this time of the year in St. Petersburg only comes for a short time in the dead of night), the telephone began to work perfectly and it was possible to walk even around the block with it. The solution to this "mystical" story turned out to be extremely simple, it was enough just to compare the intervals of "whims" in the behavior of the phone with the time ... of the first television program. It was the signals of television broadcasting (and my friend lives not far from the TV tower) that interfered with the operation of the phone in the daytime. And the reason for this was that the acquired radiotelephone was designed to operate in the frequency range that is used in our country for TV broadcasting. This is how ignorance about the differences in the use of radio frequencies in different countries made a fully functional cordless telephone just a beautiful toy. So what do you need to know to avoid this and other similar problems? First of all, it should be borne in mind that for the operation of cordless radiotelephones in our country, frequencies are allocated in the ranges: 31-40 MHz, 814-960 MHz and 1880-1900 MHz. Owners of devices operating on other frequencies may encounter the described or other similar situations when the radiotelephone will interfere not only with neighbors when watching television, but also with other organizations using radio communications. And from here it is not far from serious troubles. To avoid this, when going to buy a phone, it is not necessary to memorize the indicated radio frequency ratings, but it is enough to make sure with the seller that the phone you like is certified for use in our country. In this case, you can be calm - everything is in order with the operating frequencies (and other parameters) of the phone. Speaking of other options. During certification, quite specific requirements are imposed not only on the operating frequencies of telephones, but also on the power of their transmitters, the types of antennas used, etc. That is why those who, for example, wanting to increase the range of a radiotelephone, begin to make changes to it, immediately deprive his certificate and risk coming into conflict with the law. Now about other features of cordless phones. First of all, it should be noted that many of the users of the radiotelephone are not fully aware of the fact that, in fact, it is an ordinary communication radio station, and its signals can be received by anyone. And if we take into account that the vast majority of radiotelephones operating in the first two indicated frequency ranges do not have any means of voice coding, then you can simply eavesdrop on such conversations using a specialized receiver. The special "codes" that are exchanged when establishing a connection between the base and the handset, designed to exclude erroneous alarms from other people's signals, are not the best protection either. All these digital codes are transmitted over the air in the clear and therefore can be easily intercepted. It is on this circumstance that the work, which has received a fairly large scale, of "inflating" tubes is based, providing the possibility of pirated connections to the bases of other people's phones and conducting conversations at someone else's expense. From all these shortcomings, DECT standard radiotelephones operating in the 1880-1900 MHz range are free. These phones operate in digital mode and provide signal processing similar to that adopted in the GSM cellular standard. In general, such phones, perhaps, can be considered the most promising, especially since a slightly modified version of DECT is even included by the International Telecommunication Union in the number of standards adopted for use in third-generation mobile communication systems. Apparently, the only limitation on the use of DECT phones is a relatively short range: on the street - up to 300 m, and even less in buildings - about 30-50 m, and "vertically" - just plus or minus one floor. Although for many purposes such values are quite enough. Another factor that initially held back the spread of DECT phones in our country - their somewhat higher cost - is now fading away, because prices are almost the same. A little about the functions It should be noted right away that the number of varieties of various functions and their nuances in modern phones is huge. Therefore, we will focus only on the main ones. More recently, the standard option for the operation of radiotelephones was the "one base - one handset" mode. It is such a set (a base connected to a telephone line and a handset - from the user) that was usually understood by the word "radio telephone". However, now most radiotelephones provide the ability to connect several (usually up to 8) handsets to the base, as well as the "registration" of the handset on several (4 or 8) bases. At the same time, some handsets can also communicate with each other (bypassing the base) like ordinary radio stations. Therefore, even such types of radiotelephone equipment as "base with handset" and additional handsets are now distinguished. Additional handsets function in the same way as the main one, and they are purchased in cases where it becomes necessary to expand the number of users of the radiotelephone. The only thing to remember is that all elements of the radiotelephone must be able to understand each other, that is, that they be compatible with each other in terms of parameters. Moreover, in many cases they can no longer only refer to different phone models, but also be manufactured by different manufacturers. Modern models have most of the already traditional telephone functions: dialing in pulse and tone mode; handset volume control and ringer volume control; hands-free mode ("speakerphone") and a button to temporarily mute the microphone; electronic memory (notebook) of telephone numbers and keys for "one-button" dialing of telephone numbers and repeating the last dialed number; displays (there are both bases and handsets) for displaying various information - date, time, number, call duration, etc. But radiotelephones also have specific functions. One of them - "Handset search" - allows the owner of the radiotelephone to send a call from the base, to which the handset will respond with an audible signal that ensures its detection. A more advanced version of this function is "Intercom" (connection between the base and the handset without access to the telephone line), which allows you to send a call to the base from the handset and talk to the people there; the reverse option is also possible - a conversation on a call from the base. Also specific to cordless handsets is the low battery indication function, indicating that the handset needs to be returned to the base for recharging. But only in this case it must be remembered that you should not always keep the handset on the base, as this leads to premature failure of the batteries. The designs of radiotelephones are also very different. Among the interesting design solutions for radiotelephones, the Goodwin Lund series of telephones should be noted. In them, the base unit is made as "invisible" as possible and is made in the form of a frame for a small picture or photograph, which can simply be placed on a table or hung on the wall and it will participate in interior design. But a completely opposite idea is implemented in the design of another group of phones. Models such as Sanyo CLT-2032, LG GT-9540A, 9720, 9751A, 9760A, 9770, a number of Siemens Gigaset models, etc. - contain essentially two phones: a wired stationary device combined with a base unit, and a wired handset. Such models, which allow dialing and calling both from the base and from the handset, can be convenient for use by a group of people - in a family or a small work team. A common element of modern radiotelephones has become a cassette or electronic answering machine, but the function of creating independent voice mailboxes for several users in modern devices is not always found. Similar progress has been made with features such as Auto Redial and Baby Call. Previously, many phones did not provide reliable performance of the auto-dial function, and the goal could only be achieved by repeatedly pressing the redial button of the dialed number, now this process has been successfully automated in most models. No less important is the second of the mentioned functions. The Baby Call mode allows you to pre-program a phone number that will be dialed after pressing any key on the phone - and this is within the power of a very small child. That's just together the functions of "Auto redial" and Baby Call for some reason are not found in all phones. Phone developers also took care of another function - Baby Phone, which allows you to listen to the room where the child is. It is implemented using the standard "Intercom" mode and is most convenient when it can be initiated both from the base and from the handset. But for those who prefer to talk on the phone and at the same time continue to do something while moving around the apartment (for example, while cleaning or preparing dinner), Samsung has specially released the SP-R6100 model. Here, a miniature handset (outwardly very reminiscent of a cell phone) allows you to connect a headset containing an earpiece, a microphone and a call answer button. At the same time, the tube itself can be safely placed in your pocket - all buttons are protected from accidental pressing by a hinged lid. And when using the handset without a headset, you can answer the call simply by opening this cover - you do not need to press any buttons. How to choose a radiotelephone? Well, first of all, we can say that for the home you can choose any phone that you just like more. The only remark here must be made regarding phones in the range of 31-40 MHz: if they are located near a working TV or computer, communication may be accompanied by interference. If a long communication range is important, then the choice must be made among phones in the 900 MHz band. Well, for the office, of course, it is better to purchase DECT phones, which are distinguished by an abundance of features, including the functions of a mini-PBX. As for the choice among various brands and manufacturers, now this is no longer very important. The point here is that at the current level of development of microelectronics and international cooperation, similar devices of various manufacturers turn out to be made on the basis of very similar technical solutions, or even simply on the basis of the same sets of integrated circuits. And if we take into account that the processes of assembling serial products are already usually extremely automated, then it becomes completely unimportant where the production is geographically located. Thus, the reliability of the work of different models is actually the same. An exception here can only be some little-known firms, for the sake of economy, for example, not performing the necessary quality control of used parts and finished products. It is better to avoid buying such products. This group also includes the so-called "restored" phones, which have already been used somewhere for some time, and then in small workshops were trivially washed, repaired and put on sale. You can distinguish such devices either because they are already outdated models, or by the presence of an additional marking of the company, by whose order they were made and where they were previously used. At the time of sale, all these phones, as a rule, work normally, but their technical resource has already been thoroughly used up. Buyers notice this drawback only after some time due to rapidly discharging batteries, non-working buttons, reduced range and resulting breakdowns. In general, in order to choose the most correct radiotelephone, it is necessary to determine very precisely the requirements that it must meet. Therefore, proceeding to specific models, taking into account the comments made, the following general recommendations can be made. If you need to purchase the cheapest radiotelephone, then you should pay attention, for example, to models such as Alcatel One Touch First 10 and 20, LG GT-9160 and GT-7101, Panasonic KX-TC1005RU, KX-TC1019RU, KX-TC1025, KX -TC1045, KX-TC1403, KX-TC1405, KX-TC1455, KX-TCD951, Philips KALA 6120, Sanyo CLT-138, CLT-538 and Siemens Gigaset 100. If, according to the operating conditions, the most important parameter of a radiotelephone is its range, then we can recommend phones manufactured by LG, models GT-9130, GT-9140A, GT-9540A. Claimed indoor range for them is up to 400 m, which guarantees communication even within very large buildings. Well, if you want to use the most feature-rich phone, then it can be one of the following models: LG GT-7710, LG GT-9771A, LG GT-9780, Panasonic KX-TCD735RU-M or Siemens Gigaset 3035. Publication: cxem.net
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