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Why these values 10.7Mhz 455khz?

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twinsen

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455 khz

I have just always accepted these as IF values simply because you get filters for them etc.

Why are these values "standard"? I can only presume it has something to do with harmonics and broadcast frequencies of times gone by?
 

klug

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electromechanical filter 455khz

Hi Twinsen!

I think that it was not standard from beginning. At 30th of last centery Radio Company named as "Collins" has made mechanical filter on 455 kHz for their receivers. This filter has great success and other companies have used it in their receivers. As this frequency became popular it was needed to keep it clean - any signal on air of 455 kHz will be big problem for receivers. So it become standard and silent forever.

To be precise i need to tell about other standard frequencies. So in USSR it was 465 kHz for IF. I do not know the history of this 10 kHz split :). Also you should know a popular HAM radio IF 500 kHz. Standard electro-mechanical filters on 500 kHz were a heart of 90 % home-made tranceivers in USSR.

Wish you good luck! 73's! Klug.
 

flatulent

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if 10.7 mhz 455 khz

These IF frequencies were standardized when AM and then FM broadcasting was introduced in the USA. 455 was chosen because it was below the 540 end of the AM broadcast band. The 5 on the end was because mixing products of stations spaced 10 apart would not get into the IF and the local oscillator radiation would fall between stations. Once this was used, the frequency assignments were made so that local strong signals would not have a combination of IMD frequencies that fell in the IF or be at the image frequency of any station. Another consideration at the time was what high power stations were in that frequency range that would leak into the IF.

On the FM band, the 10.7 is high enough that the image is out of the broadcast band. Since stations are spaced 0.2 apart the mixing products would not fall in the IF and the LO radiation will fall between stations. Cost of components etc kept the frequency from being higher.

In both these cases there was an economic regeneration cycle where the more sets were produced with these IF frequencies the lower price the components for them were which made using something different more expensive.
 

pool_77

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intermediate frequency range 455khz,why

I think thst is because 450, 455 nad 460 is beetwen LW and MW radio bands.

pool_77
 

flatulent

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why 455 khz

In the USA the superhetrodyne method is credit to then US Army Major Armstrong. This is in spite of previous issued patents in France, Germany, and England. A similar thing has happened in mixers. A vacuum tube topology was converted to transistor form and patented by Jones of Honeywell Corp. This topology is now credited to Gilbert.
 

riz_aj

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500khz collins mechanical filters

Hi,

TH Lee book, Design of CMOS RFIC has a chapter on history of RF since vacuum tube era and etc. You may find reading this chapter interesting for RF historian. :D
 

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