Question: How long did the channel that shows I Dream alternate different broadcasting systems?

full_context: Document 1: BBC Television: After a series of test transmissions and special broadcasts that began in August 1936, the BBC Television Service officially launched on 2 November 1936 from a converted wing of Alexandra Palace in London. ``Ally Pally ''housed two studios, various scenery stores, make - up areas, dressing rooms, offices, and the transmitter itself, which then broadcast on the VHF band. BBC television initially used two systems on alternate weeks: the 240 - line Baird intermediate film system and the 405 - line Marconi - EMI system. The use of both formats made the BBC's service the world's first regular high - definition television service; it broadcast from Monday to Saturday between 15: 00 and 16: 00, and 21: 00 and 22: 00. The first programme broadcast -- and thus the first ever, on a dedicated TV channel -- was`` Opening of the BBC Television Service'' at 15: 00. The first major outside broadcast was the coronation of King George VI and Queen Elizabeth in May 1937.
Document 2: BBC Television: After a series of test transmissions and special broadcasts that began in August, regular BBC television broadcasts officially resumed on 1 October 1936, from a converted wing of Alexandra Palace in London, which housed two studios, various scenery stores, make-up areas, dressing rooms, offices, and the transmitter itself, now broadcasting on the VHF band. BBC television initially used two systems, on alternate weeks: the 240-line Baird intermediate film system and the 405-line Marconi-EMI system, each making the BBC the world's first regular high-definition television service, broadcasting Monday to Saturday from 15:00 to 16:00 and 21:00 to 22:00.
Document 3: The Adventures of Rocky and Bullwinkle and Friends: The Rocky and Bullwinkle Show remained in syndicated reruns and was still available for local television stations through The Program Exchange as late as 2016; WBBZ - TV, for instance, aired the show in a strip to counterprogram 10 PM newscasts in the Buffalo, New York market during the summer 2013 season. The underlying rights are now owned by Universal Pictures, which holds the library of predecessor companies DreamWorks Animation and Classic Media, and who in turn with copyright holder Ward Productions forms the joint venture Bullwinkle Studios, which manages the Rocky and Bullwinkle properties; Universal's purchase of Classic Media coincided with The Program Exchange's shutdown.
Document 4: BBC Television: As a division within the BBC, Television was formerly known as BBC Vision for a few years in the early 21st century, until its name reverted to Television in 2013. It is responsible for the commissioning, producing, scheduling and broadcasting of all programming on the BBC's television channels, and is led by Danny Cohen.
Document 5: American Idol: In 2001, Fuller, Cowell, and TV producer Simon Jones attempted to sell the Pop Idol format to the United States, but the idea was met with poor response from United States television networks. However, Rupert Murdoch, head of Fox's parent company, was persuaded to buy the show by his daughter Elisabeth, who was a fan of the British show. The show was renamed American Idol: The Search for a Superstar and debuted in the summer of 2002. Cowell was initially offered the job as showrunner but refused; Lythgoe then took over that position. Much to Cowell's surprise, it became one of the hit shows for the summer that year. The show, with the personal engagement of the viewers with the contestants through voting, and the presence of the acid-tongued Cowell as a judge, grew into a phenomenon. By 2004, it had become the most-watched show in the U.S., a position it then held on for seven consecutive seasons.
Document 6: I Dream: The lead production company was 19 Television, a subsidiary of the corporation 19 Management, which is owned by the show's executive producer, Simon Fuller. The first episode of "I Dream" aired on Wednesday 22 September 2004 on BBC One. From the week of 23 November episodes were aired on Thursday instead of Wednesday, and the thirteenth and final episode aired on 16 December and featured Laila Rouass. Reruns of the show in the UK were broadcast on the CBBC Channel.
Document 7: The X Factor: The similarities between "The X Factor" and "Idols" prompted "Idol" creator Simon Fuller, along with 19 Entertainment, to file a lawsuit against Cowell, SYCOtv, and FremantleMedia in 2004. An out-of-court settlement was reached in 2005 allowing Fuller to gain a 10 per cent share in "The X Factor" format, and preventing an American version until 2010. Fuller later filed another lawsuit in 2011, claiming that he had also been promised that he would be credited as an executive producer of "The X Factor USA", but that Syco, FremantleMedia, and Fox Broadcasting Company had failed to fulfill that promise; that lawsuit is pending.
Document 8: Dream Destinations: Dream Destinations is a Hindi language adventure tourism television series produced by i-Stylus Productions. The series was aired both on Zee News and Zee TV channel's. Each episode features the host of Dream Destinations going to a different places within India, and exploring the geography and culture of the areas. Besides, the show often goes far beyond popular tourist destinations in order to give viewers a more authentic look at local culture.
Document 9: High-definition television: Colour broadcasts started at similarly higher resolutions, first with the US NTSC color system in 1953, which was compatible with the earlier monochrome systems and therefore had the same 525 lines of resolution. European standards did not follow until the 1960s, when the PAL and SECAM color systems were added to the monochrome 625 line broadcasts.
Document 10: BBC Television: The two systems were to run on a trial basis for six months; early television sets supported both resolutions. However, the Baird system, which used a mechanical camera for filmed programming and Farnsworth image dissector cameras for live programming, proved too cumbersome and visually inferior, and ended with closedown (at 22:00) on Saturday 13 February 1937.
Document 11: BBC Television: Baird Television Ltd. made Britain's first television broadcast, on 30 September 1929 from its studio in Long Acre, London, via the BBC's London transmitter, using the electromechanical system pioneered by John Logie Baird. This system used a vertically-scanned image of 30 lines – just enough resolution for a close-up of one person, and with a bandwidth low enough to use existing radio transmitters. Simultaneous transmission of sound and picture was achieved on 30 March 1930, by using the BBC's new twin transmitter at Brookmans Park. By late 1930, 30 minutes of morning programmes were broadcast Monday to Friday, and 30 minutes at midnight on Tuesdays and Fridays, after BBC radio went off the air. Baird broadcasts via the BBC continued until June 1932.
Document 12: Sueña Conmigo: Sueña Conmigo (in English "Dream With Me") is an original telenovela produced by Nickelodeon Latin America, Illusion Studios and Televisa. This is the 5th Latin American production for Nickelodeon. The first announcement was after the last episode of the telenovela of the same channel "Isa TK+". In Hispanic America, the sneak preview was on July 20, 2010, the official release was on August 23, 2010.
Document 13: High-definition television: Since the formal adoption of digital video broadcasting's (DVB) widescreen HDTV transmission modes in the early 2000s; the 525-line NTSC (and PAL-M) systems, as well as the European 625-line PAL and SECAM systems, are now regarded as standard definition television systems.
Document 14: Color television: After a series of hearings beginning in September 1949, the FCC found the RCA and CTI systems fraught with technical problems, inaccurate color reproduction, and expensive equipment, and so formally approved the CBS system as the U.S. color broadcasting standard on October 11, 1950. An unsuccessful lawsuit by RCA delayed the first commercial network broadcast in color until June 25, 1951, when a musical variety special titled simply Premiere was shown over a network of five East Coast CBS affiliates. Viewing was again restricted: the program could not be seen on black - and - white sets, and Variety estimated that only thirty prototype color receivers were available in the New York area. Regular color broadcasts began that same week with the daytime series The World Is Yours and Modern Homemakers.
Document 15: BBC Television: Mechanically scanned, 30-line television broadcasts by John Logie Baird began in 1929, using the BBC transmitter in London, and by 1930 a regular schedule of programmes was transmitted from the BBC antenna in Brookmans Park. Television production was switched from Baird's company to what is now known as BBC One on 2 August 1932, and continued until September 1935. Regularly scheduled electronically scanned television began from Alexandra Palace in London on 2 November 1936, to just a few hundred viewers in the immediate area. The first programme broadcast – and thus the first ever, on a dedicated TV channel – was "Opening of the BBC Television Service" at 15:00. The first major outside broadcast was the coronation of King George VI and Queen Elizabeth in May 1937. The service was reaching an estimated 25,000–40,000 homes before the outbreak of World War II which caused the service to be suspended in September 1939. The VHF broadcasts would have provided an ideal radio beacon for German bombers homing in on London, and the engineers and technicians of the service would be needed for the war effort, in particular the radar programme.
ground_truth: six months
sub_queries: Where can you find the show I Dream? Answer: BBC
For how long did the BBC alternate different broadcasting systems? Answer: six months