The Vakarel Transmitter was a large broadcasting facility for long- and medium wave near

Vakarel Vakarel ( bg, Вакарел) is a village, away from Sofia, the capital of Bulgaria. Population: 1984 people. It is situated in the Sredna Gora mountains, within Ihtiman Municipality. The village is an important transport knot along the Sofia ...

Bulgaria Bulgaria (; bg, България, Bǎlgariya), officially the Republic of Bulgaria,, ) is a country in Southeast Europe. It is situated on the eastern flank of the Balkans, and is bordered by Romania to the north, Serbia and North Macedon ...

. The Vakarel Transmitter was inaugurated in 1937. It had one directional antenna consisting of three guyed masts and another consisting of two masts. The most remarkable mast of the Vakarel Transmitter was the

Blaw-Knox tower The Blaw-Knox company was an American manufacturer of steel structures and construction equipment based in Pittsburgh, Pennsylvania. The company is today best known for its radio towers, most of which were constructed during the 1930s in the ...

, built in 1937 by the company

Telefunken Telefunken was a German radio and television apparatus company, founded in Berlin in 1903, as a joint venture of Siemens & Halske and the ''Allgemeine Elektrizitäts-Gesellschaft'' (AEG) ('General electricity company'). The name "Telefunken" app ...

. Along with

Lakihegy Tower The Lakihegy Tower is a 314-metre-high (1,031 ft) radio mast at Szigetszentmiklós-Lakihegy in Hungary. The Blaw-Knox type tower was built in 1933 and was one of Europe's tallest structures at the time of construction. It was designed to p ...

Hungary Hungary ( hu, Magyarország ) is a landlocked country in Central Europe. Spanning of the Carpathian Basin, it is bordered by Slovakia to the north, Ukraine to the northeast, Romania to the east and southeast, Serbia to the south, Croatia a ...

Riga LVRTC Transmitter The Riga LVRTC Transmitter was a mediumwave transmitter in Ulbroka near Riga, Latvia, which broadcast on 945 kHz a music program in Digital Radio Mondiale, DRM-simulcast mode, which was receivable at night time in wide parts of Europe. It ...

Latvia Latvia ( or ; lv, Latvija ; ltg, Latveja; liv, Leţmō), officially the Republic of Latvia ( lv, Latvijas Republika, links=no, ltg, Latvejas Republika, links=no, liv, Leţmō Vabāmō, links=no), is a country in the Baltic region of ...

and Lisnagarvey Radio Mast,

Northern Ireland Northern Ireland ( ga, Tuaisceart Éireann ; sco, label= Ulster-Scots, Norlin Airlann) is a part of the United Kingdom, situated in the north-east of the island of Ireland, that is variously described as a country, province or region. Nort ...

it was one of the few Blaw-Knox towers in Europe until its demolition on 16 September 2020. The transmitter was shut down at 22:00 UTC on 31 December 2014.

Transmitter internal structure

The modulation method used by the transmitter in Vakarel is called a tube voltage modulation and was successfully used in all powerful AM transmitters at that time. The Vakarel transmitter is supplied with electricity from a substation in

Samokov Samokov ( bg, Самоков ) is a town in Sofia Province in the southwest of Bulgaria. It is situated in a basin between the mountains Rila and Vitosha, 55 kilometres from the capital Sofia. Due to the suitable winter sports conditions, Sam ...

via a medium voltage transmission line. The transmitter uses six stages of amplification. The first stage contains a single radio tube, which generates alternating current at a

carrier frequency In telecommunications, a carrier wave, carrier signal, or just carrier, is a waveform (usually sinusoidal) that is modulated (modified) with an information-bearing signal for the purpose of conveying information. This carrier wave usually has a m ...

of 850

kHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that on ...

. The electrical oscillations of the anode circuit in the tube are coupled in series to the second and third stage. The signals in these three stages are only amplified, without any other changes. In the special fourth modulation stage, the form of signals is modulated with speech or music. The audio recordings are sent to the transmitter with an underground communication cable from the main radio studio in Sofia. Due to the large distance of almost , the audio signal is amplified at both ends by separate blocks of amplifiers. The fifth stage consists of six transmitting tubes, two of which are in reserve, and four others can be switched on, if necessary. All of them are water-cooled. The final sixth stage consists of four high-power transmitting tubes amplifying the final output up to 100 kW. The energy is filtered by a high-power tuned circuit and sent to the feeder of the antenna, which is mounted on a large insulator on the ground and suspended with four guy lines with strain insulators.

References

External links

* http://www.skyscraperpage.com/diagrams/?b46739 * http://www.predavatel.com/bg/istoriya/predavatel-vakarel * Towers completed in 1937 Broadcast transmitters Radio masts and towers in Europe Buildings and structures in Sofia Province Towers in Bulgaria 1937 establishments in Bulgaria {{Europe-mast-stub

Transmitter internal structure

See also

References

External links