KISN gets on the Web

Tagged: ,

Viewing 2 posts - 16 through 17 (of 17 total)
  • Author
  • #49257

    Yeah, any superhet AM rig with a 455 kHz IF does it on 910. It may be less pronounced on better systems (like stereo tuners) because of tighter filtering and beat cancellation that may be minimal or absent in cheaper tuners, but it’s still there. Self-interference isn’t just limited to low-end receivers; it’s part of the physics of superheterodyne receivers.


    I still rack my brain over all the possible ways that internal signals in a superheterodyne radio can make their way back to the RF stage and cause heterodynes. The makers of one Japanese receiver IC called this deficiency “tweet.”

    Car radios often used intermediate frequencies near 260 kHz. In my recollection, the nominal IF for variable-inductance tuned radios was 262.5 kHz. The IF in our 1986 Dodge Caravan (with AM stereo) was 255 kHz. I determined the latter when I discovered that parking the minivan a few blocks from a 1230 kHz transmitter site produced an image at 720 kHz. These low intermediate frequencies have the benefit of placing the 2x intermediate frequency birdie out-of-band.

    I once had a chance to look inside that Caravan radio, and I saw that they were using the tall, old-fashioned IF cans. Radios moved to 450 or 455 kHz when ceramic filters became the norm. However, it is my understanding that extremely low IF techniques have made a comeback in the current generation of DSP-based radios; the mixer in these radios is of an image-reject design, so the tradeoff between the value of the intermediate frequency and image rejection doesn’t exist.

Viewing 2 posts - 16 through 17 (of 17 total)
  • You must be logged in to reply to this topic.