Radio 101: Why AM stations reduce power at night | Hacker News Reader

Radio 101: Why AM stations reduce power at night

relevantradio.com

25 pointsthunderbong19 comments

It might make sense to link the FCC website[0] directly instead of this blog post which is equal parts copying from the FCC website and advertising its own service.

[0] https://www.fcc.gov/media/radio/am-stations-at-night

That would be a good idea indeed. It's also much better referenced (which has the side-effect of going into yet another broadcasting rabbit hole).

A warning to those who may be bothered by it (as I am) - while the article is nice, it's hosted on a Christian radio website, and the top banner boldly declares how many "Prayers to End Abortion" there have been (however that's calculated...). I would not have wanted to contribute my visit count to this website.

Same here. The article itself is pretty good, but everything alongside it is... not for me.

Lately I've been in a bit of a rabbit hole on YouTube looking at AM transmitter tours for facilities ranging from 2000 to 50000W transmitters (and beyond! Look up WLW for an insane facility that seems like it was built by mad scientists!), and it was interesting the variety of methods they used to control their AM signals.

Some stations have highly complex phased antenna arrays designed to distribute the signal more north, or in a certain pattern, to avoid certain cities.

Others turn off completely at night, and yet others have transmitters that shed load at night to just reduce overall coverage with a simpler antenna system.

And all that, while companies like Tesla have started not even including support for the AM band on their car radio tuners...

>>And all that, while companies like Tesla have started not even including support for the AM band on their car radio tuners...

Seems like a safety issue. Some localities share traffic and safety information on an AM frequency when you're driving through the area.

Example: https://upload.wikimedia.org/wikipedia/commons/b/b9/Thruway_...

You’re supposed to get your important information from twitter now

- Tesla, probably

It’s due to EM interference. BMW, Tesla, Audi, Porsche, Volvo, and Volkswagen have all removed AM radio from their electric vehicles. Ford is dropping it from the 2023 F150 Lightning.

There is a cost to improve shielding for a good AM UX in EVs, so cheaper to drop it.

https://archive.ph/2022.12.10-142534/https://www.nytimes.com...

> And all that, while companies like Tesla have started not even including support for the AM band on their car radio tuners...

I would assume the percentage of drivers that listen to AM radio to be very small.

And even smaller for the Tesla audience, who likely uses some internet based radio or music service.

I was about to share your own SuperTower video to you, before I saw your username lol.

for the uninitiated: https://www.jeffgeerling.com/blog/2022/1-million-watts-rf-ho...

Yes, sometimes weird things happen at night with propagation: https://blog.jgc.org/2021/07/receiving-wwvb-time-signal-in-p...

I was measuring a delicate electronic device at MagLab in Tallahassee. They warned me that the best data would be had at night, because of reduced noise from a nearby radio station. Precisely at 8 PM every night my data became noticably sharper.

This is known as Ionosperic Skywave Propogation Phenomenon. I managed a small class C “day-timer” AM station in the early 90s and we had to reduce power based on a very specific schedule of dates and times. For example, start the day at 6:00 AM at low power (50 watts) and increase to full power (1000 watts) at 6:15 AM. This was to “protect” the class A station which had the rights to broadcast in our area at night. I believe the class A was KGO in San Francisco. My station was 810 KKGD in western Colorado (no idea if it is still broadcasting).

Not related to the story but one of my fondest childhood memories was one stormy night listening to AM radio and hearing the crackle of thunder on the audio (and seeing the lightning at the same time), then switching to FM and noticing I couldn’t hear it anymore. I was so intrigued then as to why FM was unaffected.

https://web.archive.org/web/20221219161045/https://relevantr...

The day/night propagation differences pretty much govern amateur radio as well. "Greyline" effect around dusk or dawn also greatly enhances propagation, as more signal paths open up for some frequencies.

Amateur radio is an amazing sandbox for radio science. It has worldwide frequency allocations from 2200m (136kHz) all the way up to visible light, including an allocation on the 160m (1.8MHz) band that behaves almost identically to the AM broadcast band.

Beyond ~30-50 MHz (depending on solar activity (solar flux and/or sunspot number)), the rules of propagation change from mostly ionospheric to line-of-sight, but can still have some interesting long-range propagation phenomena like tropospheric inversion ducting, rain/hail/airplane/building/mountain/water tower scatter, earth-moon-earth, Sporadic-E, etc.

Ham radio has kind of a bad rap for being an expensive hobby full of crotchety geriatric men, but it really has a lot more going for it. It's like the national park of radio spectrum. Some people litter and cause problems, but the sheer beauty and utility of the spectrum outshine them.

> It's like the national park of radio spectrum.

Well put.

I used to enjoy how many AM stations you could get at night.

Perhaps this should be "why AM stations have to increase power during the daytime." ;-)

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