Digital DX

bonou2 · Trimis: 30/12/2021 15:59 Titlul subiectului: Czech Radio

Czech Radio stops medium and long wave broadcasting at the end of the year

On December 31, 2021, the medium and long wave transmitters of the Czech Radio (ČRo) will cease to operate. The Czech Radio currently broadcasts its programs ČRo Dvojka and ČRo Plus on medium wave and ČRo Radiožurnál on long wave. All listeners who hear via the distribution channels have to switch to a more modern type of reception.

For this purpose, the Czech Broadcasting Corporation recommends switching to FM, DAB +, DVB-T2 or the respective station streams.

BY STEPHAN MUNDER TUESDAY, DECEMBER 28, 2021

bonou2 · Trimis: 01/01/2022 01:06 Titlul subiectului:

THE LONG WAVES OF CZECH RADIO ARE COMING TO AN END. WE VISITED THE TOPOLNÁ TRANSMITTER, WHICH WILL DEFINITELY SHUT UP ON NEW YEAR'S EVE

INSIDE THE GALLERY - The end of the long-wave broadcast was planned several times, but each time the situation was re-evaluated. This year, the end is really final. On December 31, the 70-year history of the Topolná transmitter will end.

Like other medium-wave transmitters, the only long-wave transmitter in our country will end the broadcasting of the Czech Radio Radio Journal for the Zlín Region, the entire Czech Republic and at night for a large part of Europe. After several delays in the closure of Topolná's operations in the recent past, the last day of this year will really happen, and we have tried to convey its last operating days to our readers.

Already on the way from Napajedel near Otrokovice, we noticed two broadcasting towers, 430 m apart, in the cadastre of the village of Topolná. The inhabitants of the surrounding villages - Babice, Spytihněv or Kněžpole - have had a similar outlook for 70 years. The construction of the transmitter began in 1951 shortly after the adoption of the Copenhagen Frequency Plan, where the then Czechoslovakia acquired the frequency 272 kHz in one of the longwave bands reserved for radio. Its main goal was to cover the entire territory of the state from west to east from Aš to Michalovce in Slovakia. This corresponds to the orientation of both 270 m high masts.

The construction site of the Topolná transmitter was chosen in the middle of Czechoslovakia. The map at the entrance to the transmission center shows the coverage and attenuation values of the field strength.

Propagation of electromagnetic waves
To understand the uniqueness of long-wave radio broadcasting, it is important to realize that the propagation of electromagnetic waves is affected by both the frequency and the Earth's atmosphere, which consists of several layers. Electromagnetic waves propagate through spherical wavefronts, but the higher the frequency, the more the influence of obstacles on the path between the transmitting and receiving antenna will be applied. Long waves, sometimes called kilometer waves, have a length of 2000 - 1000 m in the band 150 - 300 kHz. Their part, the space wave, is absorbed during the day by the so-called layer D of the Earth's atmosphere (at an altitude of 60-110 km above the Earth), while the surface ground wave follows the Earth's surface and thus the range of the longwave transmitter, it can be up to several thousand kilometers depending on the power of your own transmitter. Layer D is formed mainly by the influence of solar radiation, and therefore disappears overnight and at night allows waves to pass to the "hard" layer E at an altitude of up to 140 km, which does not absorb electromagnetic waves, but reflects them almost without loss. Although this phenomenon is particularly pronounced in the case of short waves, it is possible to explain the reception of the Topolná transmitter in countries as far away as China or Madagascar, which has occurred in the past. After dark, when the long waves spread best, the signal from Topolná can still be picked up in a large part of Europe and in the past, at higher power and favorable conditions, it reached as far as Japan or India. it is thus possible to explain the reception of the Topolná transmitter in countries as far away as China or Madagascar, which took place in the past. After dark, when the long waves spread best, the signal from Topolná can still be picked up in a large part of Europe and in the past, at higher power and favorable conditions, it reached as far as Japan or India. it is thus possible to explain the reception of the Topolná transmitter in countries as far away as China or Madagascar, which took place in the past. After dark, when the long waves spread best, the signal from Topolná can still be picked up in a large part of Europe and in the past, at higher power and favorable conditions, it reached as far as Japan or India.

Mr. Jan Krčmář , who spent most of his professional life on the Topolná transmitter since 1978, informed us about this . We recorded his story, from which we will bring an interview in a future issue.

From the history of the Topolná broadcasting center
But we're ahead of it. Let's go back to the beginnings of broadcasting in the fifties. Exactly seventy years ago, in December, the Tesla DRV 200 transmitters launched a test broadcast with a power of 2 × 200 kW at a frequency of 272 kHz in the operating room of the broadcasting center. It was a program of Czechoslovak Radio "Czechoslovakia I". Topolná remained faithful to this program, albeit with various changes in performance, until 1970, when the program was renamed "Hvězda". Both transmitters did not always work at full installed capacity. In the period 1953–1960, one of the transmitters was adapted to transmit the frequency 173 kHz to jam the Voice of America from Munich in singular operation, which was repeated briefly in 1963. A similar situation of "special operation" was ordered in the period from 1969 to 1973, when the program Radio Maják from the USSR was broadcast. Details can be foundhere .

In the years 1975–1978, an extensive reconstruction took place, which included new Tesla DRV 750 transmitters, which operated with an output of 1,500 kW in combined operation into the ARPO antenna system with controlled current lining, as in Liblice or Mělník and Dobrochov. They allowed the switch to operate independently to only one antenna.

In 1989, the transmission frequency was retuned to today's 270 KHz, which corresponds to a wavelength of 1110 m, but the autentic wavelength was indicated on most scales of analog radios. Since 1990, the transmitter has been broadcasting the Czech Radio station "Radiožurnál". However, the energy intensity of transmitters (estimated at 3 MW) has long been unsustainable from a financial point of view, to which the division of the federation and the loss of listeners in Slovakia have contributed. Thus, in 1994, the power was first halved, when both transmitters alternated in the broadcast after a week. The power reduction has also been reduced after switching to controlled carrier (DCC) operation, in which the carrier level is regulated to ensure undistorted reception by a conventional receiver, so that the power consumption of quiet music is only a fraction of the nominal value. The innovation of the main rectifier also served to further reduce the power input,

The floods in 1997 also affected Topolná. The stairs of the operating building were flooded, but the architectural design provided for a century of water, so the transmission room and technology were built upstairs, so only the operating workers had to use boats to get to and from work. The broadcast was not interrupted and listeners in the flooded areas of Moravia still had a source of important information. Since January 2002, the power of the transmitter has been reduced to 650 kW, which was the lowest possible power for the installed technology. Already at that time, for economic reasons, consideration began to be given to shutting down. However, this was averted in 2014 by the installation of a modern transmitter from TRANSRADIO SenderSysteme Berlin AG with an output of 50 kW. This company, Telefunken's successor, with its "TRAM" transmitter model, enabled operation with either amplitude modulation or digital DRM. Due to customers' lack of interest in longwave transmitters, the company no longer exists today. One of her last transmitters will be silent on the last day of 2021.

Visiting the Topolná Czech Radiocommunications broadcasting center
The center building itself, which survived the floods, does not deny the character of its creation in the fifties: a huge entrance hall with a sculpture "Modulation", a staircase, abandoned offices and a meeting room, which at the time of prosperity who on duty bypassed a huge plot of land with dogs. It's perfect retro, with the atmosphere of forgotten years. This is underlined by the main transmission hall, similar to the one in Liblice, but the individual cubicles, where modulators, low-frequency amplifiers and output stages based on half-meter heavy tubes were located, are empty, with a few exceptions. Only the control circuits of the protections are visible from the original installation, the others are dismantled.

In the middle are several stands of the last functional TRAM 50L transmitter and an operator's control room. Today, the only technician works at the entire center, whose work is facilitated by remote monitoring and control software. The guide to the technologies was the already mentioned Jan Krčmáč, who explained the procedures for starting both 750 kW transmitters, which took place daily after a night break at 5 o'clock in the morning. The control panel lights had to turn green according to the întocmai turn-on: cooling water, full glow, grid preload, anode voltage.

Fault conditions were indicated by a red light. The combiner gave signals from both transmitters together for the full allowed power of 1.5 MW, or the output from only one transmitter was used in the mechanical switch. Subsequently, the transmitter was switched on for remote monitoring via a special computer network.

Topolná is one of the last long-wave transmitters in Central Europe. In Germany, analogue amplitude modulation broadcasting ended in 2014. The audience of long (and medium) waves is everywhere and we will not do anything about it. We will no longer listen to Radiožurnál on holiday in Europe, and organized amateur radio clubs abroad will no longer send their income reports. Confirmation "Oves" resp. They don't even have a QSL (Qualified Suppliers List) on the Topolná transmitter. However, if we poză rising energy prices, we must acknowledge that the costs of operation and maintenance of such a transmitter will not be small and negligible in the budget of Czech Radio. Although the entire center is carefully maintained and in good technical condition, this decision is understandable, albeit painful for some, and there is no choice but to come to terms with it.

29.12.2021 / VACLAV UDATNY

bonou2 · Trimis: 01/01/2022 01:09 Titlul subiectului:

THE ICONIC RADIO TRANSMITTER IN LIBLICE NEAR ČESKÝ BROD IS COMING TO AN END. WE VISITED HIM A FEW DAYS BEFORE THE SHUTDOWN

On December 31, the Czech and medium-wave broadcasts of Czech Radio will definitely be silenced. The era of well-known radio transmitters in Liblice near Český Brod, which are the tallest building in the Czech Republic, ends with it.

We went to see what it looks like today on the broadcasters on which Czech Radio will end the broadcasting of its programs ČRo Dvojka and ČRo Plus with historical amplitude modulation (AM) on medium waves and Radiožurnál on the only long-wave transmitter, on which we will bring information in another article.

Thus, one historical stage will end, which began after the First World War on the occasion of the first anniversary of the founding of the republic in 1919 from the radiotelegraph station on the Petřín Lookout Tower. However, the regular one-hour radio broadcast dates back to 1923 from the station in Kbely and subsequently continued from the transmitter in Prague - Strašnice. Today, a total of 12 medium-wave transmitters are in operation in the Czech Republic, four of which with outputs of 5 - 20 kW will continue to distribute the Český Impuls, Country radio and Rádio Dechovka programs. The following table shows the AM transmitters of České Radiokomunikace, including the 270 kHz long-wave transmitter, from which Czech Radio's programs are broadcast and which will be silenced at the end of the year:

However, this does not mean that the popular Czech Radio programs will disappear from the air, they continue with frequency modulation (FM) on VHF, a much larger offer in the digital standard DAB +, or in multiplexes DVB-T2 and of course as streaming services via the radio application. cz.

From the history of AM broadcasting in the Czech Republic
Until the end of II. During World War II, a network of 12 transmitters with outputs from 0.5 to 200 kW was established on the territory of today's Czech Republic, while during the Protectorate during the war four of them were put into operation and served to spread German propaganda outside our country. It is interesting from this time that the owners of radio receivers, which were equipped with short waves, had to have the entire range of HFs removed for these receivers (due to the spread of Czech broadcasting from London on this wavelength). The retreating German army seriously damaged or even completely destroyed some of the operated transmitters. After the war, but especially at the end of the 1940s, there was a time of intensive construction of a network of medium-wave transmitters, which was to ensure sufficient quality reception of two national programs throughout the territory, followed by regional programs and broadcasting abroad. In the period from 1949 to 1978, 18 transmitters in Bohemia and Moravia were renewed or built. These were mostly transmitters with outputs of 3 to 30 kW. However, another transmitter with the same power was added, not as a backup, but as a 719 kHz mid-wave jammer, on which Free Europe was broadcasting from Munich. The construction of AM transmitters was completed in 1976 with the Liblice transmitter and in 1978 with the Topolná transmitter.

Without frequency coordination, there would be no broadcasting
From a historical point of view, it is interesting that the first coordination of radio frequencies took place in Prague from 4 to 13 April 1929 within the then European Radioelectric Conference and Czechoslovakia acquired the following frequencies: 617, 878, shared 1022, 1076, 1139, 1202 kHz in accordance with the so-called Prague plan.

This enabled the rapid development of the construction of transmitters during the First Republic and subsequently in the Protectorate. After the war, the assigned frequencies were reworked according to the Copenhagen Plan, which in principle applies from September 15, 1948 to the present day. On long waves, Czechoslovakia acquired a frequency of 272 kHz with an output of 200 kW, on medium waves with outputs of 150 kW 638 kHz for the Prague 1 station, 701 kHz for Bánská Bystrica and a synchronized network with 5 kW, for the Morava station 953 kHz, 1097 for Bratislava ( 5 kW for synchronized network), 1232 kHz for Prague II (100 kW), Budějovice and Bohemia West and Moravia East, for Košice frequency 1286 kHz with power 100 kW, as well as for smaller transmitters 1520 kHz in Jihlava, Ostrava and Pilsen up to power 25 kW.

The term "transmitter" is often understood by the general public only as an antenna system, or a mast or tower. However, the transmitter is a complex technological device, which consists of a modulator, high-performance transmitter tubes, cooling systems and power supply. The development of these technologies is described in detail in the lecture by Ing. Gregory from the Pardubice conference Radiokomunikace 2013 and from which the author drew some data.

Historical transmitter Liblice I
The original transmitter, including the antenna mast, which began to be built in 1929 on land closer to the village of Liblice than where it is now, began regular broadcasting on the last day of 1931. It will be exactly 90 years since mid-wave broadcasting spread from it. It is said that even before the launch, there were very negative moods in the village about the construction of the transmitter. However, soon after the broadcast began, residents in the vicinity pulled on a wire like an antenna, made a crystal from galena and tungsten, grounded and listened to the Radiojournal program. At first they were afraid of the new techniques, then they were happy to have a cheap income without a concession.

The first antenna from 1931 took the form of a T-antenna, a rope stretched between two masts with a span of 250 m and a height of 150 m. Then in 1937 it switched to a type of vertical unipole. It was a Blaw-Knox type anti-fading antenna with a height of 247 m, which could also be extended by a 30 m extension rod used to fine-tune the antenna. It was then the first and highest antenna of this type, which allowed the operation of the strongest transmitter in Europe. Today, this antenna no longer exists, in 1974 it was dismantled. On the occasion of the 40th anniversary of radio broadcasting, an article about the then transmitter technology was published in the magazine Amateur Radio (issue 5/1963) and can be found here today .

The first transmission, as shown in the table, began in 1931 with an output of 120 kW. The supplier of the technology was Standard Electric. Anode modulation with a single modulation tube and a low power high frequency modulation choke followed by one or more other linear amplifiers was used as the modulation. However, their efficiency was small and nonlinear bias was kept below 10%. On the other hand, this autentic transmitter worked for 28 years until 1959, when it was replaced by a Tesla 2x150kW transmitter with a modulator in the output stage with negative feedback to improve parameters - distortion around 1% and noise below -60 dB.

Throughout the twentieth century, high-performance tubes were an indispensable part of every transmitter. At the same time, it was necessary to solve the heat dissipation in connection with the construction of these tubes, the location of the anode and cathode. After the war, all Czech transmitters were equipped with tubes from Tesla Vršovice. The largest of them, for outputs of 750 kW, marked RD 250 VM and weighing 73 kg was located in the last transmitter in Liblice in 1976 and in Topolná (1978). Until 1954, the cooling of high-performance tubes was performed with water (distilled) and the flows reached up to 150 l / min. The original Libl transmitter until 1959 with an output of 150 kW, however, was equipped with air cooling, in the seventies then there were tubes cooled by the cooling liquid, the so-called vapotrons, which cooled by evaporation. This resulted in lower demands on the fluid flow.

All these devices required a significant supply of electricity, which had to supply all stages with DC and well-filtered voltage. For high powers, it was not possible to use conventional selenium rectifiers, so the Libl transmitter was solved by a DC dynamo, which supplied from its own engine room 800 V for grid bias, auxiliary 1000 V and 5000 V for anodes and heating voltage 24 V / 1000 A in redundant connection. However, the main anode sources could not be solved in this way, so the Liblický transmitter used a set of three-phase glass lamps placed in steel oil vessels and connected in series so as to achieve a DC voltage of 18 kV at 24 A.

Today's transmitter Liblice II
With its power, this transmitter covers 80% of the territory of the Czech Republic and at night it can be captured in a large part of Europe. The current two steel anchored masts reach a height of 355 m and are the tallest building in our country. The antenna is of the ARPO type with regulated current lining, which to some extent allow to control the vertical radiation diagram and do not require the installation of a foot insulator, such as unipole antennas. However, part of the power is lost in the ground, which is evident in the winter, because the snow layer, when kept at an altitude of about 250 m, always melts along the antenna radiators.

At the invitation of České Radiokomunikace, we did not miss the opportunity to visit this broadcasting center and take current pictures of "heavy radio equipment", which works with ten kilovolts and hundreds of amperes.

The transmitters were protected by the military in the past
The ninety-year history of the Liblice broadcasting center is not just about construction, building and routine operation with today's archaic technology. There is also a monument near the Liblice II towers, which commemorates the days of May 1945, when 18 Czech insurgents fell while trying to control a transmitter occupied by Nazi soldiers. August 1968 found the broadcasting center out of operation as a result of work on the coating of the antenna systems and maintenance of the technology carried out since June. When the republic was attacked by Soviet troops on August 21, the maintenance work of one of the SRV150 transmitters was completed, and from half past eleven, this transmitter was put into operation. Subsequently, at the behest of various authorities, it was then alternately turned off and on until silent at 20:30. Soviet troops did not occupy the center until the following afternoon, when the guard section of the Czechoslovak Army withdrew at the command of the barracks. The broadcast was not resumed, although in the following days the occupiers imported about 20 civilian employees from transmitters from Ukraine and the Baltic republics with the intention of putting the transmitter into operation with the help of the left documentation. It was not until the afternoon of Tuesday, August 27, at the request of the centre's chief engineer, that the commander of foreign troops allowed the technicians of the then Radiocommunications Administration to resume broadcasting the Czechoslovak Radio program with speeches by state officials who returned from an involuntary stay in Moscow. How difficult the work of our technicians was until Sunday, September 1, when the foreign soldiers finally left the center, and what condition the partea interioară of the transmitter was after their departure is difficult to imagine today. Diary of the center, which was established in 1981 to 50.

How will the medium waves be used?
The medium wave band uses frequencies in the range of approximately 520 - 1605 kHz for radio transmission, which corresponds to wavelengths in the range of 185 - 575 m. Amplitude modulation is used for audio signal transmission. The spacing of neighboring frequencies in Europe is 9 kHz. From the pages of the Czechoslovak DX Club, we took a picture of the scale of an old radio receiver with red marked ČRo switched stations on medium and DV waves:

From next year, Czech Radio's analogue programs will be poorer. The band will be significantly freer and it is questionable whether DRM (Digital Radio Mondial) broadcasting, which is already in operation in some countries, will gain ground.

22.12.2021 / VACLAV UDATNY