[HomeBrew] why 455 khz?

[Jim Kearman]

 -------------- Original message ----------------------
From: bhat srikanth <emailsbbhat at yahoo.com>

> Pls excuse if this is a trivial q. Why do
> conventioinal BC Rxs have their IF as 455 khz? Whats
> special about this number?

Sri,

I believe 455 was chosen as a compromise that gave reasonable image rejection, and was also an unused frequency, so less chance of IF-breakthrough. Earlier receivers used 85 kHz, but on the standard broadcast band in the U.S., extra front-end selectivity would have been required to eliminate images.

73,

Jim, KR1S
http://kr1s.kearman.com/