#1
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TV IF frequency change
Simple question...When did most TV IFs change from the vicinity of 24 mhz to 43 mhz and why? Which brands were the leaders and which took a few years to catch up?
jr |
#2
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Quote:
IIRC, the firms that changed right away were GE, RCA, Westinghouse and maybe, Stromberg Carlson. |
#3
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Moving the IF from 21.25MHz aural/25.75MHz video to 41.25MHz aural/45.75MHz video was to eliminate local oscillator radiation interference with other TVs. For example, a TV tuned to channel 7 with the 20MHz region IF would have a local oscillator frequency of 175.25MHz+25.75MHz=201.00MHz. 201MHz falls into and will interfere with channel 11.
By moving the IFs to the 41.25MHz aural/45.75MHz video, the local oscillator for channel 7 will be 175.25+45.75MHz=221.00MHz which is above channel 13 hence out of band. Of course the more densely populated UHF band would suffer. But in the early days, the FCC would avoid allocating a channel which would suffer from local oscillator interference. The same reasoning applied to FM on the old band (42MHz-50MHz with 4.3MHz IF) and the new band (88MHz-108MHz with the 10.7MHz IF). These were not simply arbitrary numbers. |
#4
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Interesting article in a publication of the time on this topic
taken from "Radio & Television News." -. january 1953 pag 47 http://www.americanradiohistory.com/...Page_Guide.htm Last edited by telescopio08; 06-05-2014 at 01:57 PM. |
#5
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This became possible when channel 1 was eliminated. As channel 1 would have overlapped the new IF frequencies.
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Audiokarma |
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