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

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

I remember reading somewhere, that the FCC was meeting with RETMA, to change the IF frequency of TV sets, to minimize interference with other services. That was in the early 1950's.
IIRC, the firms that changed right away were GE, RCA, Westinghouse and maybe, Stromberg Carlson. :scratch2:

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.

Interesting article in a publication of the time on this topic
taken from "Radio & Television News." -. january 1953 pag 47 http://www.americanradiohistory.com/Radio_News_Master_Page_Guide.htm

Moving the IF from 21.25MHz aural/25.75MHz video to 41.25MHz aural/45.75MHz video

This became possible when channel 1 was eliminated. As channel 1 would have overlapped the new IF frequencies.