Why Some AM Radio Stations Don't Work at Night 

Because it's AM duh! You'll need PM station to listen at night

"The Earth supposedly curves" XD

AM frequencies can also bounce off water. So you can get cases where it hops into the atmosphere, off the ocean (or lake), back off the atmosphere, etc. and gets half way around the planet. In the military, we'd occasionally tune in our HF into a local AM station for music. Half-hour later, you could hear a faint signal, re-tune it a few hundred megahertz and you'd be listening to an Iranian station. You could often guess the station by where it was dark at the time of day you are hearing it and eliminating languages you could identify. We had a big chart of world stations which could finally tell you who it was.

2:35 "Much-loved FCC"

"Earth is 'supposedly' curved" lol you're savage edit; wow thanks for the likes. i opened up this comment after 2years and saw 1.9k likes. wow!

"much like stab wounds" lol had to double take on that one

"With wavelengths, much like stab wounds, smaller is better."

One night, during a vacation in the US, I remember waiting in the car for our parents who were visiting with family (listening to old people talk gets boring, obviously). We decided to turn on the AM radio. We were able to pick up two or three stations conflicting with each other. It kind of sounded like they were arguing too. So that was entertaining.

0:54 jesus fucking hell man, metaphor of the year

You and Wendover Productions should make podcast and pretend to be the same guy. It will blows people mind, you guys sound alike.

0:54 That's an interesting comparison 🤔

I'm Venezuelan and I live in the central coast. During last month's blackouts I realized my car picked up an AM radio station from New York that I later identified as WCBS 880 and I was really really really puzzled about it, because I didn't understand how in heavens could I listen to the same thing that people in NYC were listening to. Thanks for explaining why, I can rest easier now.

In the last week of November 1994 I picked up an AM radio signal late at night being broadcast from Denver, Colorado while driving in Southern Illinois. The station identified itself as "The Blow Torch of the West".

KOMO in Seattle is correct, but for Chicago it’s WMVP for our radio station. All radio stations in the US are split by prefix along the Mississippi River. K to the west, W to the east.

Its because they don't turn into PM waves. I'll see myself out.

"Learn how to think" Oh thank god, I need this.

Perhaps too technical for your target audience, but you failed to mention that many AM stations, rather than signing off or drastically reducing power, shift to directional antenna patterns after sunset. I worked in broadcasting for a few years in the early ‘70s. The first place I worked was a small town AM & FM outlet, WCOR in Lebanon, TN. They were 1000 watts on AM and 10,000 watts FM. At sunset, the AM shut down and the FM continued. They simulcast, broadcasting the same content on both transmitters. Later I worked for WLAC in Nashville. Their AM & FM were separate operations. The FM at 105.9 MHz broadcast 24 hours with 100,000 watts ERP. The AM was 50,000 watts at 1510 KHz. Both were the maximum legal power for U.S. stations. At sundown the AM shifted to a directional pattern, oriented north/south if I remember correctly. Another Nashville station, WSM at 650 KHz, broadcast 24 hours with their full licensed 50KW and an omnidirectional pattern. The power and reach of WSM, “clear channel 650,” is one of the reason the Grand Ole Opry, and country music in general became so popular. A bit of radio trivia for you. Did you know that WLS 890 KHz in Chicago was started by Sears, Roebuck and Co. to encourage people to buy radio receivers? The call letters were an acronym for Sears slogan, the World’s Largest Store. Mid-1920’s editions of the Sears catalog contain full page ads for WLS opposite the page selling radio sets.

What's a radio? Is that kinda like a podcast?

As an engineer in the commercial broadcast sector I must say this was a very well done explanation!

Much loved FCC lol xD

WABC 770 AM in NYC was always on my sister’s car radio when I was a kid growing up in the early 70’s in Connecticut. After we’d moved to Pittsburgh in 1981 I put a TV antenna atop the back porch of our house and connected it to my AM/FM stereo receiver. I did it to get better local FM but I was stoked to discover that at night I could pick up WABC in NYC. I thought it was the coolest thing to get that familiar signal from 400 miles away.

*”Earth is supposedly curved”* *Wait a minute... -.-*

Video killed the Radio Star

But where are the airplanes? Do airplanes use AM signals?

I remember when I was a kid and had an old 'ghetto blaster' stereo with one of those old school retracting antennas on it. I found that at night, and with some strategic placement of aluminum foil on the antenna, I could pick up WGN radio in Chicago, the aforementioned KOMO 1000 radio from Seattle, KNX 1070 in Los Angeles, and an AM news radio station from Vancouver, Canada. Mind you, I was living in Billings, MT at the time. I thought it was kinda cool getting AM stations from all over the country.

"In this video you might actually learn something" I always learn something from these videos Double as Interesting?

"Much-Loved" FCC

As a kid in Minnesota in the 1980s I discovered that at night I could regularly tune in KOA from Denver and WLS from Chicago, and occasionally I even picked up WOR from New York, and over the years I learned about 'clear channel' (lowercase) stations, but I don't think I really understood *why* they were stronger at night until I watched this video today.

Should of mentioned 650 Am WSM Nashville TN, One of the most well known and oldest and power full Am towers currently that operates 24/7. I could hear them almost perfectly 9pm up in NH and ND

As I am old (40+), I remember playing with my radio and the antenna some nights as kid, trying to pick up radio stations from as far away as possible. Past AM, you move into SW, MW and LW (short, medium and long wave) territory... but thats another story for another time or for a doomsday scenario.

AM is capable of comparable sound quality to FM under the right conditions there is also an AM stereo broadcast standard (though it came so late it has very poor adoption). There are 2 factors that normally limit AM audio quality Bandwidth and noise. Bandwidth comes down to transmitter and reciever design and use. Prior to the 70's AM was the major music medium and there were AM stations with better fidelity and bandwidth than FM stations...An example of this is WLW which after the FCC told them you "can no longer transmit at 500KW as the world's strongest AM station" decided "if we can't be the strongest then we'll be the highest fidelity"...HH Scott certified their AM station as having better fidelity than most FM stations at the time. Most stations and radios used on AM today are expected to be used for talk radio which prompts many stations and receivers to limit bandwith and fidelity to land-line phone like lousiness for cost savings. FM has the advantage of being mostly immune to RF noise. Most RF noise is more of a varying amplitude impulse than a varying frequency so FM recievers are basically designed to ignore it (called capture ratio)...FM recievers also tend to ignore whichever station has a weaker signal...So unlike the AM band the FM band will have closer spaced stations that effectively interfere with eachothers geographical outer fringe coverage...Case in point ever listen to FM on a long road trip and after a moment of noise (say while cresting a hill) suddenly your hearing a different station despite not changing the frequency?...That's capture ratio in action. In the last 20-30 years switchmode power supplies have become more prevalent (in every device you plug in) and those tend to be basically huge RF noise polluters and tend to disproportionately affect AM because of AMs lower frequency. A switchmode supply usually creates (and doesn't bother to contain) a 17KHz square wave...And if enough of my college electrical engineering Fourier analysis class is still with me, a square wave consists of a STRONG sine wave at its fundamental frequency (in this case 17KHz) and an infinite series of harmonic (read that multiples fo the fundamental) frequencies above that (for example 34KHz, 51KHz, 68KHz, etc all the way up to infinity Hz ) and as the harmonic frequency decreases its intensity decreases so a 17KHz CFLor phone charger, or computer power supply, etc will generate louder RF noise in the AM and frequencies than at the FM band frequencies. A final mind blower to some people: AM and FM are just interchangeable techniques to place audio on an RF carrier...So you could modulate an RF signal in the AM band with FM modulation or an RF carrier in the FM band with AM modulation....In fact in the Ham radio world, there are frequencies that are/have been used interchangeably with AM or FM modulation.

What's with that statement? Aren't bigger stab wounds better if you're doing the killing?

the chicago am 1000 station is not KMVP, it is WMVP. This is because all stations east of the mississippi river start with a W, and every station west of the mississippi start with a K.

There's a station based in denver that runs on 850khz (850KOA) that is nicknamed the "blowtorch of the rockies". It is so ludicrously powerful to get through all our mountains that it can be picked up in Siberia.

Because there are not enough TOYOTA COROLLA.

FYI - There’s a mistake in the narration starting at 01:44. After he shows the green lines going upward and correctly says “the FM waves go right through (the ionosphere”), the RED lines that appear represent an AM signal but the narrator inadvertently refers to it as an FM signal. Indeed it is an AM signal which, at night when the lower level ionosphere dissipates, the AM signal bounces off the upper level ionosphere and can travel a much longer distance.

I'm pretty sure that the channel in Chicago is not "KMVP", since that call sign is for a station in Arizona (that recently switched from AM to FM. Also, radio stations broadcasting from East of the Mississippi all begin with the letter "W" (For the most part, there are a few exceptions like for instance in cities that straddle the river like the Twin Cities in Minnesota, which use "K" even if the tower is on the East side of the river, like for instance KSTP in St Paul, which I used to live across the street from)

This is INCREDIBLY fascinating!! Thank you for putting so much work into these videos - we all appreciate it!

8 people are flat earthers

Fun fact: You can also sometimes hear meteors enter the atmosphere at night on AM radio

But what about TC? (Toyota Corolla)

I sleep everyday listening to your podcast... when are going to upload a new episode? I really enjoy listening it at night. Greetings mate.

I’ve always wanted to start a radio station that plays Video Game music unfortunately I learned about copyright later in life and my dream may never become a reality. :/

Excellent video as always, but I noticed a little mistake. There is no station called KMVP in Chicago, but there is a station called WMVP. Generally in the US, stations west of the Mississippi have a call sign starting with K (although there are some exceptions like WFAA in Dallas) and stations east of the Mississippi have a call sign starting with W (there might be some exceptions, but I'm not sure).

30-40 mile range for FM? I've picked up FM radio in my car from 60-70 miles away from the tower. Apparently 103.5 BOB-FM Austin has a big antenna (like 1200 ft) and the place I got it from that far away is around 150 ft lower in elevation

Some nights, you used to be able to hear an AM station from Boston all the way down in Florida on a walkman.

I love how we can see your style evolve in your videos. Your currently ones are way more animated

"Much like a stab wound" LOL, this channel is one of the best I have ever seen. You make the boring stuff from a textbook seem WAY more interesting. You have a great talent, and I love your dry sense of humor. Keep up the good work.

Huh. This explains a weird thing that happened when I was a kid. My grandparents live ~12 hours away from me and I spent many hours in the back seat of a car riding to and from their house. One time as we were returning from their house, we were flipping channels on the radio and were able to tune in to their local talk radio station some 600+ miles away.

I don't know if this is a normal occurrence, but I was able to pick up WJR 760 AM out of Detroit all the way from Rochester, NY, through Western Pennsylvania and the entirety of Ohio, all the way to Indianapolis, IN, during a drive during daylight hours. Of course if you look at a map during that journey you are never super far from Detroit, but still that is pretty impressive.

Back in the 60s, in my teens, I had a hobby of tuning for, and catching am radio stations at night. There used to be a LOT more of the "clear channel" stations than there are today. A few years ago the FCC removed a bunch of the 50,000 watt clear channel stations from being "clear channel". If you sent a letter/postcard to most of these stations, reporting what you heard and the time, they'd send you a return postcard, known as a QSL card, proving you heard that station. I had quite a collection of these cards, with the farthest away station I received being KDKA in Pittsburg PA, with me being in San Diego CA. That station was somewhat of a hard one to get as there was another station on the same frequency in Los Angeles. What it took to catch KDKA was, the LA station would go off the air late sunday night-early monday am for maintainance and one early monday morning I caught KDKA. KDKA is better known as the first actual commercial radio station in the US, on Nov 2, 1920.

Here in Brazil, a former radio station used 10 kW at day and 1 kW at night, with their transmissions reaching almost the same distance (slightly better at night, of course). The transmitter operator always received a letter from a government agency with a schedule indicating the precise time to change the transmitters along the year to avoid conflict with another stations from the region.

I guess this explains why my PC speakers start picking up French radio after the sun sets!

2:20 this is completely true, I work for a AM station in Boston and someone got our signal in Norway and sent us a audio recording a couple months ago.

Editor/Director: I like your use of info-graphics. Also it’s cool how you use what looks like NASA “blue marble next-gen” imagery of the Earth surface. It really adds to your videos. Thanks!

Close but no cigar. The ionosphere does play a major part in this, however it's the lowest layer, called the D-Layer, that makes it possible. Or rather the *absence* of the D-Layer. At sunrise the D-layer forms and lower frequencies are absorbed by it, so the station remains ground-wave only and covers the local listening area. At night the D-Layer disappears and the signals can get to the higher layers of the ionosphere where they bounce back to Earth. Also, most AM broadcast stations operate directional arrays changing pattern at daybreak and twilight.

I'm a little concerned that I knew 100% of the technical stuff in this video.

Oh shit I might actually have to learn something.

You deserve a million subs for both channels because of your exact quality of each vids

2:36 Wrong. The AM band starts at 530 kHz, but that frequency and 1610 kHz is only used for traveler information stations. 3:16 WMVP not KMVP. Chicago is located east of the Mississippi River. Stations east of the river have callsigns that begin with W, whereas stations west of the river have callsigns that begin with K.

I presume this is why one of the largest companies that own an operate radio stations is called "Clear Channel Communications". Even though most of their stations are FM, naming the company after the most powerful and highest status AM stations is definitely a power move.

“you might have to learn something this episode” *clicks off*

Wow. Keep posting those informative brilliant videos!

When I was a kid, a friend gave me a large console tube radio from the 30's. I was able to get it working and found new tubes for it, built a high gain antennaand started listening. I was able to get Radio MOSCOW from Long Island.

Supposedly curves.... Doesn't want to lose views from flat earthers

I live in the Philippines and when I turn on the AM radio at night occasionally, I hear chinese radio stations hahaha

You've left out a LOT of important details! KOMO and WMVP (not KMVP) are both directional Class A, but they both use directional antenna arrays at night (KOMO actually provides a signal with more than 50,000 effective watts, but almost no signal to the West, WMVP (not KMVP) sends it's power eastward, in fact, WMVP actually bought billboards in Detroit to advertise Bulls basketball when the Bulls dominated the NBA. They send almost no signal westward at night. The coverage of seemingly similar AM stations can vary drastically. A 5,000 watt station in North Dakota, near the bottom of the band, can carry through ND, SD and a lot of Saskatchewan, whilst a 5,000 watt station in Georgia at the top of the band may only go out to 15 miles. Most of the regional channels were given out on a "first come, first served" basis, the first station on the channel will have good coverage, every other station on said channel tolerates the first station's interference, and has to build an expensive directional array so it doesn't affect the "senior" station. You'll know an AM station is directional by seeing more than one tower (as many as twelve!) at its site. Also, there are six "local" channels (1230, 1240, 1340, 1400, 1450 and 1490) where Class C "local" stations are 1,000 watts all day and night. By day, these stations go out as far as the soil under the station can carry the daytime signal. If you look up the FCC's "M3 soil conductivity map", you'll get to know which local stations have good or bad daytime coverage (at night, all of these stations interfere with each other, leaving only their small town with a good signal) For what it's worth, there are cases where FM stations can be heard FAR beyond the line-of-sight. Often, an "air inversion" can "trap" an FM signal into following the curve of the earth (most often observed late at night or early morning). This is particularly true over lakes and oceans. Sporadic-E skip will sometimes reach the FM broadcast band. It is not as common as it is on the 6m amateur band or TV Channels 2-6, but it is a true ionospheric skip mode, allowing FM reception from stations about 1,000 miles (1,600km) away, and not the stations between your site and 700 miles. Look for it late May through early August, in late mornings and around sunset.

KMVP, Chicago's ESPN radio affiliate, broadcasts from my hometown of Downers Grove! I never knew I could have such a jolt of excitement in a video about clear channel AM radio.

Half Toyota Corolla references and Half Plane references

Because it's pm!

I was just thinking about this last night. Thank You!

one of the best HAI episodes! Bravo!

and thats why the world is switching to DAB+, also can you do a vid on the naming of us radiostations? the names seem a bit wheird to me as a european.

If the circumference of Earth was 25,000 miles, it would calculate to a curvature of .75 x #miles squared; which means that for a FM radio signal to reach 35 miles the transmitter tower would have to be over 900 feet tall, as tall as the Empire State building in NYC. DO YOU SEE ANY RADIO TRANSMISSION TOWERS AS TALL AS THE Empire State BUILDING?

With high power HF (using a form of AM) you can get some really impressive bounces. I've heard broadcasts from as far away as Diego Garcia in Washington DC. At that point it's probably a multi-hop one. (bounces off ionosphere, off the ocean[sometimes land but more often ocean] then off the ionosphere again)

This is very important for people who work out in the open ocean, as one the ways of sending a distress/safety message is using HF equipment (basically AM). We work out a distance to a coast station, from that we know the frequency to use. For 500NM it’s 8kHz, but if it’s night it’s 4kHz. So it’s important to always remember this, as the last thing you want is for your mayday to bounce miles away from station you wanted to get in contact with.

I had no idea AM radio was still a thing? I don't think I've heard any AM radio for decades. In my country FM radio is also dying out, we're switching to digital radio (DAB+)

Very interesting... but how does this affect planes?

Long these same lines (annealing), I've just fumbled upon a.m. buzzing static for 2 prong stereos. I couldn't get through the myriad of uploaded sound waves so I ran a 10 minute very quiet (honey bee loud) buzz through the plug then flipped an d.m. station on a d wow! First it turns the existing Soundwave into a watery human voice sound then it ran the station through and it's crystal clear. Very clean and balanced. In some parts of California it's gotten difficult to get clean sound so that just gets right through, whether it's a.m. or f.m.. Clean! Rich! I'm looking forward to listening again. I just ran a Spanish music station through at approx. 3:50 p.m. from the central san joaquin Valley and the freeway imbalance I was hearing and that dawned on us here just went away. . I've also found that metal string songs are really complimentary to copper wires. The wires just purr. A.M. is also very Matt sounding (dry) compared to F.M.s wetness, here. I've yet to listen far off so perhaps that's the case elsewhere? Thanks.

Your videos are amazing. This video killed my mind. most of your videos are simple and easy, this you made very complicated!

Wait "Since the Earth is supposedly curved," Wendover is a Flat Earther confirmed?

I think you mean WMVP not KMVP

Informational but super simplified. AM and FM are only modes and have very little to do with propagation. As for the FM sounding better because of the higher frequency, that in itself real doesn't have much to do with it. It has to do with the mode. Wide FM takes up over 100kHz of bandwidth, while an AM station is only 1/10th that. As far as the distance AM signals travel during the day, there is also a lower layer of the ionosphere that absorbs RF energy with wavelengths generally below 10Mhz during the day, but is one of the first layers to dissipate around sunset. Its all a lot more complicated than a short 5 minute video can address, but it gives the general gist of it.

Living in Chicago, I have to make a correction to this video. At 1000 am, the radio station is actually WMVP, which is ESPN. KMVP is actually Arizona sports radio. Just letting you know!

So what happened to radio stations during the solar eclipse?

Yess!!! Finalyy smaller is better

So much of it is based on geography. In the 1980s, I lived in Maryland but attended graduate school in Ames, Iowa (ISU). When driving west from Maryland to Ames, in the twilight hours in Illinois and Iowa I could hear Phillies games on what was then WCAU (1210 AM), at the time the Phils' 50,000-watt flagship. While in Iowa, I could pick up major AM stations west of Ames (though none on the West Coast) such as KOA (850) in Denver and KSL (1160) in Salt Lake City.

The subtle humor is hilarious. Well done.

because if they did work they would be called PM's

at 1:44 you say 'FM' but you mean AM

Fun fact my grandpa when he was in college he actually helped with the radio station at his college, and one night they got together and got a am radio signal from hongkong(he lived on the west coast the time.

What isn't mentioned is, just like propagation (or skip) with CB and HAM operators, people outside the line of sight but not along the outer edge of that circle may not even know that station exists because the signal passes right above them while bouncing.

What was meant by "the earth curves, supposedly", flat earther on this channel?

Cool

FM radio isn’t only line of sight. That is an old wives tale. I’m originally from Hartford, Connecticut and can remember back in high school I used to routinely pick up FM stations from New York City and Boston, Massachusetts which are both just over a hundred miles in either direction from Hartford. My favorite stations were KISS 108 (WXKS 107.9) in Boston and the now defunct KISS FM (WRKS 98.7) in New York City. I could also pick up WBLS 107.5 in New York City. When my brother went away to college. He went to Purdue University, which is in West Lafayette, Indiana. That is about a hundred miles outside of Chicago. He used to pick up the now defunct WBMX 102.7 as well as WGCI 107.5 on the regular on his boom box and record their house music mixes on cassette and bring them home.

That ad transition targeted me directly. I'm in the process of starting a radiostation😂

@0:03 I already know how to think so I don't need brilliant. Brilliant! 😋 (worst pun ever)

America still uses AM? Maybe for the sparsely populated areas it's better with its range, but FM has better quality, no?

there is no other creator's videos i get more excited about than yours (sorry RLL and second thought) ill get the notification and i know i'm going to learn something really interestinG

I live in Phoenix, and I can pick up AM stations from as far west as Los Angeles and San Francisco, as far north as Denver, and as far east as Dallas-Ft. Worth.