04-15-2019, 09:05 PM
Theory says that the lower frequencies allow for tighter selectivity. I think for that reason some communications receivers have double conversion - a high first IF frequency to improve image rejection, then a low IF where bandwidth can be well controlled.
In early sets, low frequencies probably made it easier to derive lots of IF gain with reasonable stability.
Another aspect to the choice of frequency is the potential for interference caused by the local oscillator. If the IF is 460 kHz, then a set tuned to 1000 kHz will have the oscillator running on the 1460 kHz channel. The move to 455 kHz put the LO from a correctly tuned and aligned radio inbetween stations - at least in the USA where channels are 10 kHz apart. In UK and europe, the channels are separated by 9 kHz. I'd have to do some arithmetic to see how that worked out.
In early sets, low frequencies probably made it easier to derive lots of IF gain with reasonable stability.
Another aspect to the choice of frequency is the potential for interference caused by the local oscillator. If the IF is 460 kHz, then a set tuned to 1000 kHz will have the oscillator running on the 1460 kHz channel. The move to 455 kHz put the LO from a correctly tuned and aligned radio inbetween stations - at least in the USA where channels are 10 kHz apart. In UK and europe, the channels are separated by 9 kHz. I'd have to do some arithmetic to see how that worked out.
I don't hold with furniture that talks.
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