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A comment on Congress wants AM radio in all new cars–trade groups say that’s a mistake.

Re:Congress wants AM radio in all new cars–trade groups say ... by elromulous on Tuesday May 23, 2023 @12:09PM (#36046350)
While it's true AM radio is very easy receive, I imagine it's a much less effective use of bandwidth compared to the amount of information (the shannon kind) modern digital communication can cram on there, no?

Wouldn't it be better to repurpose those frequencies for country wide digital broadcast that could also send other data during emergency situations?

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Re:Congress wants AM radio in all new cars–trade groups say ... by riskable on Tuesday May 23, 2023 @12:20PM (#36046505)
AM radio's band isn't suitable for modern high-speed communications. The most you can extract out of it is ~1200 bps:

https://www.diffen.com/difference/AM_vs_FM

Even if you multiplexed all possible amplitudes into one it still wouldn't be worth it for (two-way) digital communications.

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Re:Congress wants AM radio in all new cars–trade groups say ... by hotpotamus on Tuesday May 23, 2023 @12:32PM (#36046688)
That seems unintuitive given that we had 56K modems running over telephone systems also designed to carry human-audible audio.
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Re:Congress wants AM radio in all new cars–trade groups say ... by MrRadar on Tuesday May 23, 2023 @12:52PM (#36047054)
Indeed. The US "HD Radio" system has AM support in addition to FM and on AM it can broadcast up to 60 kbps (though most stations chose a 40 kbps mode with additional error correction to improve reception)[1]. Digital Radio Mondiale [2] (with the unfortunate acronym DRM) is another competing digital system system that can be used in the AM and shortwave broadcast bands, supports similar bitrates.

[1] https://en.wikipedia.org/wiki/HD_Radio#AM

[2] https://en.wikipedia.org/wiki/Digital_Radio_Mondiale

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Re:Congress wants AM radio in all new cars–trade groups say ... by ianburrell on Tuesday May 23, 2023 @12:45PM (#36046921)
The radio bands are small. Each AM HD station uses 30 kHz which gives 40-60 kbit. That isn't enough for full fidelity music. And that is using more than one frequency since analog AM is 10kHz stations.

AM band uses a large frequency range, 530-1700 kHz, but the total bandwidth is small, slightly more than 1MHz.

Telephone is bad compared to AM and really bad compared to FM or CDs. Human voice fits in much smaller bandwidth than music.

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Re:Congress wants AM radio in all new cars–trade groups say ... by cf100clunk on Tuesday May 23, 2023 @01:16PM (#36047500)
> Each AM HD station uses 30 kHz which gives 40-60 kbit. That isn't enough for full fidelity music

That's part and parcel of station management's programming decisions for HD Radio subchannels on the AM band, hence the focus on ''talk''.

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Re:Congress wants AM radio in all new cars–trade groups say ... by poo-yie on Tuesday May 23, 2023 @01:01PM (#36047227)
One is going over the air and the other was going over copper lines. I don't know if that makes a huge difference, but I suspect it makes some difference (especially in inclement weather).
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Re:Congress wants AM radio in all new cars–trade groups say ... by jalk on Tuesday May 23, 2023 @01:51PM (#36048084)
I guess that figure is set by some ancient standard for transmitting bits semi reliable on AM, which doesn't employ the same encoding tricks that modems did. POTS lines had a max baud rate of 2400, and the higher speeds were accomplished by encoding more bits pr baud. Parts of the modem noises was to establish which encoding scheme to uses, based on capabilities of the two devices and the line quality. AM broadscasting can't really make such handshakes, so my guess is that 1200 bps was some lowest common denominator.

edit: wasn't too clear that I meant to say that the 1200 bps must be from an old standard

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Re:Congress wants AM radio in all new cars–trade groups say ... by icehawk on Tuesday May 23, 2023 @02:46PM (#36048945)
The SNR from an AM radio station at about ~30mi is 13dB and if you plug that into the Shannon capacity calculation for regular 15kHz AM radio (not HD AM) you get about 57kBps at ~100mi, that drops to 4kB/sec.

56K modems also had the advantage that the noise floor for the downstream direction was much lower than the upstream direction.

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