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 |
Quote:
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. |
1 Attachment(s)
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 |
Quote:
|
All times are GMT -5. The time now is 09:30 AM. |
Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
©Copyright 2012 VideoKarma.org, All rights reserved.