why INTERMEDIATE FREQUENCY for fm is 10.7M only??

[bvishwanath]

Why intermediate frequency for fm is 10.7 mhz and for am 455k hz??
One reason is it should not be in tuning range 0f am and fm 88to 108mhz
why only that number 10.7m ,455k why not other numbers LIKE 9.7m 11.7m etc??
Plz explain me...
Thanks in advance

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HOW TO AVOID IMAGE FREQUENCY IN SUPERHETRODYNE RX??

 

[godfreyl]

why not other numbers LIKE 9.7m 11.7m etc??

It's just easier if everybody uses the same standard frequency. Then they can all use the same filters and IF transformers etc instead of having to make custom parts.

10.7 MHz is about the lowest frequency you can use as IF for the FM band without having problems with image frequencies. For example, if you use exactly 10MHz, then when you tune the radio to 88MHz, it will also receive 108MHz (or vice versa).

Similar logic for the AM standard.