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Comment by phkahler | Hacker News Reader

Can we get the aircraft band too? It's a little above the FM frequencies.

Aircraft bands use AM rather than FM because of the FM capture effect. When there is a double transmission with FM, the receiver will lock on to one signal and exclude the other. With AM, you will hear both as well as, possibly, a heterodyne tone if the carriers aren't exactly the same frequency which is much preferable.

FM demodulators can't really demodulate AM signals. AM demodulation can demodulate FM by tuning a bit off the carrier frequency thanks to the fall-off of the filters but the quality isn't great.

> FM demodulators can't really demodulate AM signals. AM demodulation can demodulate FM by tuning a bit off the carrier frequency thanks to the fall-off of the filters but the quality isn't great.

By "isn't great" you mean, "I might be able to understand something with a tailwind, downhill" - right? :-P

The mode of operation for an AM radio listening to FM is akin to a slope detector.

Why can't we just get a software-defined radio in the hardware...

That's because SDRs hog a lot more power than discrete components. For something like a phone stand-by/screen-off power usage is a pretty critical component.

Some phones have optional removable components like extra batteries, higher-quality speakers/cameras, or even projectors. It would be cool if someone made a SDR add-on for these phones.

Ive used a cheapo SDR on my phone before, with a microusb adapter. There aren't a ton of Android apps but IIRC I was able to look at ADS-B transponder data

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