Videokarma.org

Go Back   Videokarma.org TV - Video - Vintage Television & Radio Forums > Vintage TV & Radio Tech Forum

We appreciate your help

in keeping this site going.
Reply
 
Thread Tools Display Modes
  #1  
Old 03-03-2014, 02:31 PM
jr_tech's Avatar
jr_tech jr_tech is offline
VideoKarma Member
 
Join Date: Sep 2009
Posts: 4,510
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
Reply With Quote
  #2  
Old 03-03-2014, 06:07 PM
dieseljeep dieseljeep is offline
VideoKarma Member
 
Join Date: Jul 2010
Posts: 7,562
Quote:
Originally Posted by jr_tech View Post
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.
Reply With Quote
  #3  
Old 04-19-2014, 09:20 PM
Penthode's Avatar
Penthode Penthode is offline
VideoKarma Member
 
Join Date: Jun 2009
Location: Kitchener/Waterloo Ontario Canada
Posts: 1,059
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.
Reply With Quote
  #4  
Old 06-05-2014, 01:47 PM
telescopio08 telescopio08 is offline
VideoKarma Member
 
Join Date: Mar 2008
Posts: 2
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
Attached Images
File Type: jpg IF40mccomp.jpg (79.3 KB, 20 views)

Last edited by telescopio08; 06-05-2014 at 01:57 PM.
Reply With Quote
  #5  
Old 06-05-2014, 08:10 PM
wa2ise's Avatar
wa2ise wa2ise is offline
VideoKarma Member
 
Join Date: Dec 2002
Location: USA
Posts: 3,147
Quote:
Originally Posted by Penthode View Post
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.
__________________
Reply With Quote
Audiokarma
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 10:10 AM.



Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
©Copyright 2012 VideoKarma.org, All rights reserved.