Here’s a question: when did you last listen to an AM radio station? If your answer is “recently”, chances are you are in the minority.
You might ask: why should you listen to AM? And you’d have a point, after all FM, digital, online, and satellite stations offer much higher quality audio, stereo, and meta information, and can now be received almost anywhere. Even digital receivers are pretty cheap now, and it’s by no means uncommon for them to not even feature the AM broadcast band at all. Certainly this has driven an exodus of listeners to the extent that AM radio has been in slow decline for decades, indeed it’s disappearing completely in some European countries.
Amplitude Modulation
On your radio receiver “AM” will probably refer to the broadcast band between about 550KHz and 1600kHz depending on where you are in the world, also known as “Medium Wave”. But AM itself is not related to a particular frequency, instead it refers to “Amplitude Modulation”, and was the original modulation mode for conveying speech and music. You’ll also find it on the shortwave (HF) broadcast bands and in CB radio. With a modified sideband structure it provided the modulation scheme for analogue television.
![Amplitude modulation in the time domain. Ivan Akira [CC BY-SA 3.0], via Wikimedia Commons](https://hackaday.com/wp-content/uploads/2016/05/illustration_of_amplitude_modulation.png)
![Amplitude modulation in the frequency domain. Heron2 [CC BY-SA 3.0], via Wikimedia Commons.](https://hackaday.com/wp-content/uploads/2016/05/am-sidebands.png?w=400)
In the time domain, the varying amplitude of the signal means that it is vulnerable to interference from any other RF sources within its bandwidth whose amplitude also varies. Lightning strikes, switching transients, noise from faulty switch-mode power supplies and more can all be heard when they occur in the background of an AM transmission. It’s not all bad, if you live on a farm you might have found it useful to always know when your electric fence is working from the tick… tick… tick… on your radio.
Meanwhile, in the frequency domain, the width of those sidebands is proportional to the bandwidth of the audio being modulated. For a higher quality audio source with a 15kHz bandwidth for example, the total AM bandwidth would be 30kHz. The demands of the spectrum regulators to fit as many broadcast stations as possible into the available bandwidth mean that depending where in the world you live each channel will be allocated only 9 or 10 kHz, so the practical audio bandwidth is reduced to around 5kHz. Thus as well as being vulnerable to interference, the AM broadcast also sounds poor, especially for music, compared to its FM competitor.
Cheap Plastic
The final nail in the coffin for the quality of AM broadcasts comes from the typical modern AM receiver. In AM broadcasting’s early years, a radio receiver was a premium product, comparable perhaps to a modern 4K TV set. The radio manufacturers of the 1920s and 1930s were in fierce competition to deliver technical innovations to improve their product’s sound quality in all areas, and the best radios had extremely high quality amplifiers and speaker cabinets. This was the golden age of AM broadcasting, when AM stations had more bandwidth in a less crowded band, and were a primary entertainment medium.
By contrast a typical plastic portable AM radio of today is built at as low a cost as possible with very little attention to the quality of the sound it delivers. Even with a bandwidth-restricted modern broadcast station it is obvious just how poor quality its sound can be if you compare a cheap plastic portable with a high-end 1930s radio or a modern high-end AM receiver like the Tivoli Model One. If most people’s experience with AM is low-bandwidth audio accompanied by electrical noise and played back on poor quality electronics through a cheap speaker, is there any wonder it’s taken up by ever fewer people?
Golden-Eared Hams
When AM is treated with some care and attention in both transmitter and receiver though, it is capable of delivering very good results. Surprisingly there is a small area where you will find AM enthusiasts hard at work refining their art, though you won’t find them on your broadcast radio. The golden age of AM in amateur radio is long past, but there is a dedicated band of AM diehards for whom the quality of the received audio is more important than achieving distance at all costs. Some of them maintain huge “boat anchor” transmitters from many decades ago, while others are at the cutting edge with DSP-based AM generation at low-level, or class D modulators driving class E RF amplifiers. They do this in spite of considerable institutional opposition from their national amateur radio lobby groups, or maybe in some cases even because of it.
Whether or not we still have AM broadcasts in the coming decades will depend on whether or not a viable niche can be found for them. Sometimes, as in the case of the British long-wave BBC Radio 4 on 198kHz, it has even attained a cult status, sparked public demonstrations when its demise is predicted, and become a National Treasure. But that is the exception, the overall picture is one of decline, which leaves one wondering whether it is not the medium that is at fault but its regulation. The AM broadcast bands are still run according to rules and expectations with their roots in a different century, when a medium-wave frequency was a valuable asset and so-called “clear channel” high-powered stations covered entire continents. Perhaps if we recognised that those days have passed, allowed a slightly higher bandwidth at the expense of a lower channel count and created a constellation of low-power local stations with better quality sound, it might have a future. Otherwise if its current decline continues it can’t be long before we’ll be faced with a young relative approaching with a dusty transistor radio and asking “What does this do?” And as we start to explain to the child it’ll dawn on us that with no broadcasts left to receive we’ll no longer be able get them into electronics the way so many of us did, with a crystal set.
Farmer listening to crystal radio image: public domain via Wikimedia Commons.
Still a number of stations transmitting AM signals on shortwave although most now use some form of dynamic carrier control like Modulation-Dependent Carrier Level (MDCL) control, so are not classic AM as described above.
Radio Free Havana is a really good one to listen to, and it covers most of the USA and south america. American radio is more about profits and less about communicating, otherwise we would have a nation wide NPR station that covers all of CONUS.
It is interesting to note that communication in aviation is done entirely using AM radios. One of the reasons for this is the lower bandwidth required in comparison to FM. Another reason is that its vulnerability to interference means that if two pilots accidentally transmits at the same time, the air traffic controller can always hear that this is the case.
True, I’d forgotten pilots use AM. Thanks for that!
Wouldn’t SSB be superior for all the reasons you just named?
AM handles frequency error better than SSB. A small frequency error between the transmitter and receiver won’t be noticed as much.
To use SSB one have to change ALL the transceivers, necessitating a long period of switch-over. The other proble is that having a missing carrier, one must tune precisely to receiving a single station, so if the tower have to listen a lot on aircrafts on the same frequency with sightly off oscillators, it must continuosly use the clarifier to get an intellegible conversation.
To transmit a 10 kHz audio signal over a 100MHz SSB channel you need a crystal precision of 0.0001 – say your local oscillator is 10 kHz out – well you have completely missed the signal.
For that reason SSB transceivers had an adjustment so that a human could adjust the local oscillator by ear.
There are ways of making SSB more friendly. There is Extended single sideband (eSSB) a mode that expands the 2.9 kHz audio bandwidth of standard or traditional SSB and Amplitude-companded single sideband (ACSSB), a narrowband technique using a single sideband with a pilot tone, allowing an expander in the receiver to restore the amplitude that was severely compressed by the transmitter as well as allowing AFC.
There is today but there wasn’t that much back then.
We used to bunch 960 SSB channels together and send them over microwave. On one single channel out of the 960 we would send tow-tone which was 1.5kHz signal mixed with a 2.5kHz signal and it was used to synchronize the local oscillator at the other end. The 1.5 kHz was subtracted from the 2.5kHz to give the 1Khz reference. If they drifted then they drifted by the same amount. ie 2.6kHz – 1.6kHz still yielded the 1kHz reference.
Unfortunately the bottom line is that there isn’t much you can do with analogue modes that you can’t do better with digital these days, and while the former will always have their niches they are the past, not the future.
Exactly. Therefore I listen to AM all the time because I listen to airband radio A LOT
Otherwise known as “Ancient Modulation”. There’s a group that regularly do AM around 7120kHz here in Brisbane.
Huh, What time does that happen and who runs it?
Until an emergency happens and the internet goes down. AM radios, including and especially those continental blow-torches will be important. They aren’t useless, but you probably don’t listen to talk-radio.
Below 30MHz includes citizens band, and a lot of the Amateur bands – which you can talk across the country on. Right now “Cascadia Rising”, a simulation of a major earthquake and tsunami along the oregon/washington coastline is going on. Katrina also had ham radio. CW – morse code – is the original digital mode (let your fingers do the talking?), but there are now many more and things like slow-scan TV.
AM (550kHz-1700) has its niche, and is unlikely to go away. If things should change, it would be from 1.7-30MHz, but that would require worldwide cooperation
The way a lot of countries are abandoning their international radio broadcasting services it won’t need even that.
There are some hams around here that have regular HF nets using AM. I don’t think it will ever completely die out as long as there are amateur radio operators around.
Goodbye France Inter, on 162kHz…
This brings back so many memories. Without internet, this is one of the only french radio stations you can still manage to hear in Belgium (along with Europe 1, RTL and Radio Monte Carlo). The audio of this station is so warm, bass-rich, you can recognize it just by its sound!
I guess it’s for the best, but it is still amazing to receive LW stations in tunnels or underground garages where the FM (VHF) stations have no coverage…
As a teenager I used France-Inter to help with my school French exams. I probably don’t have the level of comprehension now that I had then.
An interesting fact about AM hams… it goes even larger than boat anchors. Some of them actually have converted old comercial broadcast transmitters to ham bands! I’m talking big rack mount transmitters with ceramic tubes that do legal limit as easy as though they were just sitting on standby.
Check YouTube, there are recordings of some AM nets where the hams audio sounds like comercial broadcast quality. It turns out it’s because it is! There is this one guy who I could have sworn sounds just like Howard Stern…
Well… I’m sure not everyone is impressed but it blew my mind to learn of it.
Oh.. and I have even seen one mount the thing inside a trailer and take it mobile!
MW AM broadcast radio, working like the AM audio we use to communicate, is subject to interference true.
But VHF AM air band is enhanced by the ability of two people being able to transmit simultaneously and be heard like two people talking over each other in a room, this is apparently why we still use them when we fly rather than FM, though on transoceanic flights they do use HF SSB with a tone squelch not unlike the famous CRM-114 of Doctor Strangelove fame or an old volunteer firefighter’s audio pager.
I hope AM sticks around though it would be fun to have it as an amateur band, but it is also nice to have something fun to receive when demonstrating a crystal radio.
There are a number of reasons that airplanes still use AM.
1. A weak FM signal is unintelligible. A weak AM signal is noisy but you can hear it.
2. Two FM signals on top of each other, like two pilots transmitting at the same time, even a slight difference in received power and the weaker one disappears. With two AM signals at the same time, you hear them both and know.
3. Although SSB can carry further as all the power is concentrated in one sideband, you must be right on frequency or the signal is garbled. Even a few 100Hz or so off.
The real reason AM is used for aircraft is due to doppler shift. Planes especially jets move at speed relaive to ground recevers fast enough to produce a shift in frequency. SSB and FM do not work reliably when this occurs. AM does not require the receiver to be perfectly on frequency
http://www.animations.physics.unsw.edu.au/jw/electromagnetic-radiation-doppler.htm
fshift = fradio x C/(C-V) where C is the speed of light, V is the relative velocity between the two radios, fradio is the frequency of the radio signal, and fshift is the received signal. When V is positive, moving towards each other, it shifts up, and vice versa.
Of course, for the answer to be in Hz, the velocity must be in m/s and the speed of light c in m/s. Or miles per second and miles per second. A jumbo jet’s typical speed is 885km/hr or about 246m/s. Speed of light is about 3×10^8m/s.
The highest frequency listed on the Wikipedia page for aircraft is about 380MHz.
fshift = 3.8e8 x 3e8/(3e8-246) = 380000311Hz
A shift of 311Hz. Narrowband FM has a deviation of about +-2.5kHz, so I think you are on to something.
SSB would definitely be messed up by this much frequency shift.
If we want to save AM then we need to start cracking down on the rules. Class D’s need to stop being allowed to act like Class B’s and C’s at night. Interference specifically from power lines should be taken more seriously and fines need to be given for violators. The Class D’s receiving a translator should be given the option to stop broadcasting on AM during their evening hours or even altogether to clear up some space and reduce interference. Once we get more space then we can look into power increases like many groups have requested. Vacant Clear Channels should not continue being protected simply because a clear channel station existed at one point. We have stations required to power down because of former Class A and large class B stations in Canada even though the stations they were protecting no longer exist. And IBOC should be completely banned in the evening hours.
For SW legacy rules need to simply be eliminated. There are still rules in place that prohibit US broadcasters from specifically broadcasting to US audience. These rules, partly in place to prevent major broadcasting companies from covering the entire US with a single station are no longer valid. New technologies like DRM need to be more openly explored. The SW bands are large enough that multiple technologies can coexist.
IBOC shouldn’t just be banned in evening hours on AM. It should go away entirely! Broadcast spectrum should be considered more of a public resource. What I mean is one company shouldn’t own the encoding format used in every radio receiver in the nation. Even when IBOC’s patents are all up you will only be able to make an IBOC receiver by paying iBiquity for the privilege because it is encrypted. That is rediculous! The broadcast bands should use an open codec.
I truly doubt that the iBiquity IBOC encryption will hold for very long… it’s not particularly robust (at least by today’s standards, let alone those of the future dates when the relevant patents expire). Some of the key patents are due to expire between 2018 and 2022, so we’re getting close. Of course, DTS (iBiquity’s new corporate overlords) will doubtless continue to file additional patents, but the core patents (the ones that are “essential for someone skilled in the art to manufacture NRSC-5 compliant transmission and reception devices”) are the ones that matter in terms of competition. I’d expect the competition would largely come from overseas (first from the receiver side, eventually from the transmitter side and likely accelerated by iBiquity’s inevitable price/fee hikes as they try to keep their profits up in the face of a declining market).
I’m guessing that iBiquity’s original plan was all rosy and assumed they’d be able to be on v2 of IBOC by now (in order to ensure a fleet of new patents for another generation of exclusive profit), but to the extent that they may have thought that, they badly underestimated the state of the US radio broadcast market. As to what DTS might have up their sleeve in terms of future IBOC development, that’s hard to speculate about. The acquisition seems to have been more of a portfolio builder than a market changing profit maker. I’m hopeful that DTS will do some degree of good with the iBiquity intellectual property, but that remains to be seen.
I think it’s sad to see AM die even though that death began before I was born. AM crystal radios make an awesome first build to get a kid into electronics. You can actually identify and explain each individual part. FM kits for kids generally have a little black-box PCB that gets little or not explanation. Sure the manuals describe the waveform well enough but there is no way you are going to explain the detector to a first-time builder.
Those kits were almost always broadcast band but the same goes for shortwave. I never understood why shortwave kits were not more popular. Sure, back in the 70s and earlier when the AM broadcast was popular it made sense that the kits would tune that. In the 80s and 90s when all we knew was FM shortwave was at least a little interesting (compared to AM broadcast) because those signals were coming from all over the globe.
Today I suppose most kids wouldn’t be impressed with that given the internet and all. It’s too bad though, people don’t appreciate the difference between being able to communicate across the planet over free airwaves using something built from a handful of simple components vs accessing the world via a multi-billion dollar network which you don’t own, don’t control and pay a monthly fee just to get access to. Don’t get me wrong… I wouldn’t trade the internet for the world but I think the ability to communicate without it is very much worth preserving.
Ironically is possible to make a FM crystal radio, http://solomonsmusic.net/FM_CrystalRadio.html , it works by slope detection.
The reason that AM is left out of modern gadgets is because the little ferite loopstick antenna is built in and next to a screaming harmonic laden digital controller. Sports and talk are keeping it alive. Many local NPR stations have one each AM/FM for talk/music.
Unless you want to pay for and listen to nearly as bad sounding satellite radio, cross country listening is long range AM. All of the future microwave modes will be worse than FM at being line of sight. To have a chain of these spreading thru that wide open country will cost. Unless government run, single site legacy stations will fight. In other words someone will have to make a big change where substantial loses will occur.
I have a pocket radio with only FM being of any use. The AM is wide band, it sounded like FM till our local NPR AM went HD. It was 10k wide! Now it is useless I could mod it to narrow band for talk but WBAA is gone for good. The other band it used to receive is NTSC TV audio, we all know where that went along with the biggest e-trash dump in history.
From memory – lower side band isn’t lower side band and upper side band isn’t upper side band when you are talking about AM because in AM they must both exist together (with the carrier) to fulfill the definition of AM.
If (however) you suppress the carrier then they can be individual transmitted as a “side” band or both as double side band.
No.
One of the problems was that there was “AM”, and then later things changed. For a long time, there wasn’t a unified explanation. Even after SSB came long, it was in a different chapter from “AM”. Even today, many don’t see that there’s a continuum.
Jenny rightly described the process of modulating the transmitter as “mixing”. The output stage is a mixer, translating audio up to radio frequency. Since there is no way to remove one sideband, you have the image too, just like any heterodyning process. Since the mixer isn’t balanced, the carrier feeds though to the output, along with those two sidebands. That’s double sideband with carrier, euphemistically called “AM”. When it came long, people did believe the carrier varied amplitude as the audio signal amplitude varied, after all a power meter at the output did show a varying signal.
When that “AM” signal gets to the detector in the receiver, it’s not following the envelope. The detector is mixing the carrier with the sidebands to translate the radio signal back down to audio. If it just followed the envelope, information would be missing.
Listen to fading “AM” station, it can fade enough that it sounds distorted, and it is. The carrier fades differently, so there may not be enough to cause mixing in the receiver’s detector.
When “SSB” came along, it was a subset of that signal, still an “AM” signal but a variant. It took away the carrier by making the mixer balanced (so the carrier doesn’t feed through to the output of the mixer). The carrier isn’t needed, except at the receiver (where it mixes back down to baseband). Since the two sidebands contain the same information, one being the “image” of the other, one can be eliminated by a very narrow filter, or by the “phasing method”.
So you have just a sideband, the carrier only needed to heterodyne the audio up to radio frequency. The output meter will go up and down as the audio does.
You do need to have a locally generated “carrier” at the receiver to mix the sideband back to audio.
If you listen to an SSB signal in an “AM” receiver, you will be hearing just the envelope (you can’t really understand what’s said), proving the carrier is needed to translate back to baseband.
And there are all the variants in between, DSBsc (double sideband suppressed carrier, you either convert it in the receiver to SSB with a narrow filter, or need a fancy detector that locks the locally generated “carrier” to the right point), SSB with carrier (only one sideband sent, but the carrier too so no special detector), SSB with reduced carrier (so expect distortion with fading, though the weaker carrier makes it easier to tune, the carrier showing where the locally generated carrier should be) and ISB (independent sideband, without carrier but I think the carrier can be sent; here two ingle sideband signals are generated, each with different content. Used in the military to send voice and rtty, one per sideband, and was used in some early AM stereo experiments).
I think I got them all, every one has the signal going up and down, amplitude modulation (as opposed to FM where only frequency varies). in the old days it was all labelled “A3”, with a letter appended to show the variant, but some new nomenclature is in use.
Michael
Even low power AM stations can create skywave interference over surprising distances at night, and local low power AM stations suffer at night from reduced coverage and skywave interference . I favor having most of the low power AM stations move to FM, as the line-of-sight VHF frequencies are ideally suited to local service, and make room for more of the clear channel “blowtorches”. Broadcasters are always clutching for some magic technical fix that will bring listeners back. Some time ago it was AM Stereo, currently it is HD Radio, which brings with it a whole new bag of technical and interference problems.
Ultimately, though, “It’s about the content, stupid!” A big reason for the current doldrums in AM radio (and to a certain extent in FM as well) is the insipid, formulaic, limited playlist, cost cutting programming most radio stations air these days. I believe that a return to something similar to the “personality” radio of the past or what used to be known as “program driven” broadcasting could bring the listeners back. To me, the most outstanding example I have ever experienced was what WJR was when I listened to them in the 1970s.
A high power, broad coverage AM station could draw revenue from a wide enough area to afford to pay the talent for such programming, although where the talent would come from is problematic, since the small station “farm system” that allowed talent to work their way up to larger and larger markets is mostly gone. (That’s the same problem that faces the broadcast industry with regard to where the next generation of competent broadcast engineers will come from, as the now mostly older guys retire out in the next few years.)
Over-the-air broadcasting is a vital and indispensable part of the national infrastructure. It may be considered increasingly archaic in this internet age, but I have lived through natural disasters where, if the internet had been around at the time, it would have been gone for the duration, but over-the-air radio and battery powered receivers remained our mainstay.
” in the time domain with the supposition of a pair of waveforms to form a modulation envelope”
supposition should be superposition
Why didn’t they ever develop a dual channel differential version of AM, or did they? Like Ethernet, but over the “aether”.
I’m not sure what you mean. Do you mean two separate AM signals? Takes up twice the bandwidth.
Yes, it would as the second signal is the inverse of the first, but did anyone ever use it to ensure a less noise vulnerable AM transmission? I guess they just went with the “MORE POWER!!!” solution?
With two sidebands, the information in one is redundant. With the right detector, that redundancy becomes valuable, interference to one sideband is not a problem.
Remember, “AM” goes back to the 1910s, anything complicated was bulky and expensive. It took decades for variants to become commonplace. So even if your idea would work, it probably wasn’t viable in the early days, and then later it would mean new receivers (so expensive to make the changeover).
Howard Armstrong came up with the regen receiver, the superheterodyne receiver, and the superegenerative receiver by 1922. Soon he turned to FM, already known about, to get rid of noise. Since there is no amplitude data, any noise can be limited out, so it’s a logical path to go down. There was FM broadcasting in the thirties, unfortunately WWII came along, halting growth, and after the war the relocation of the FM band meant people generally had to buy new receivers.
Michel
Thanks for explaining that, it is very useful to have it explained by a person who actually has more than a Wikipedia level knowledge of the subject.
So using the redundant sideband to detect and remove noise sounds like what I was asking about, except the differentials symmetry is about the central carrier frequency rather than a copy inverted and shifted up to a higher band. That actually sound hard to do, how to you effectively reflect one on to the other and compare them? I don’t have a deep knowledge of valve tech, and then more as they apply to digital circuits so can you explain to me how on earth they manage to do that?
There have been experiments done in the last few decades using narrow-band FM on the AM broadcast band. From what I understand the results were fairly positive.
I agree. It would be pointless.
It is prehipster technology, you wouldn’t understand.
Differential AM. Amazing idea. Each sideband containing each part of the pair. That would definitely help with interference reduction just like it does in so many wired PHYs (RS485, Ethernet, LVDS, USB, etc).
There weren’t / aren’t any experiments on that? Of course it wasn’t possible back in the day, but today?
Wouldn’t that be very interesting?
I’m sure GNU Radio could do it on a PiZero, I just don’t know enough about how it could be done in analogue hardware.
Get your ham radio license, build a Michigan Mighty Mite – share your radio waves with the world.
I wonder how much effort is done these days to find ‘illegal’ HAM radio users.
I mean with few people using it and even fewer illegal users do they even keep up anybody to control it? Sitting there twiddling his fingers 8759.5 hours a year.
Licensed Ham radio operators do a pretty good job of that. I understand the FCC has some pretty good direction finding equipment.
I was illegal for a while (in a foreign country) – just couldn’t resist the temptation. I don’t think much would happen until some licensed user made an issue of it. Just guessing.
There’s been a slight resurgence of AM in the US over the last decade or so. The FCC doesn’t “like” to license new lower-power FM stations. So if someone doesn’t have the deep pockets for a 100KW FM station, it’s much easier to launch an AM station.
Good AM receivers were built still in the nineties. I have a Kenwood PLL an a Technics analogue receiver for a separate Hi-Fi system, and connected to decent amplifiers and loudspeakers or headphones, they both deliver an excellent audio in AM.
The biggest problem I find now to listen to AM radio is the elecromagnetic pollution generated by cheap switching power supplies or electronics gadgets like the smartphones or tablets, that are now filling the bands with birdes.
In the nineties I remember hooking a capacitor to the red wire of the telephone line, in my home in the countryside we had a 2 km line on poles, the reception was extremly good.
The main reason I like AM is because I can I listen to my favorite sports team and one of the (many) talk radio stations from 200+ miles away, whereas the FM stations generally have about a 100 mile radius. For this reason, I don’t think AM will die out in the States. Too many people love their sports. Too many also love to hear themselves talk.
In regard to music, anybody remember AM Stereo? :-)
C-QUAM is severely underrated. There are a number of videos on Youtube showing AM Mono vs. AM Stereo The results are significant. Unfortunately the number of stations broadcasting in AM Stereo and the number of receivers available are both nearing zero.
With all the conceptual simplicity of AM it might be surprising that (aside from the IF amplifier bandwidth) the detector is often the primary source of distortion. Passing the audio through a diode only works best in theory, in reality its THD can reach several percent! Most cheap AM radios apparently still use the diode detector, even though numerous alternative, higher quality methods are available: Synchronous detector, infinite-impedance detector or fast op amp-based ideal rectifier could improve things a lot! See excellent write-up by Mr. Elliott: http://sound.westhost.com/articles/am-radio.htm
Sometimes I switch on a family heritage late 60’s portable transistor receiver – it still works and still picks up the same station it was primarily bought for (Polish Radio Program I). Perfect UI simplicity and usability after all those years.
A lot of people still listen to AM radio because in some areas the typical headline/traffic/weather news stations are AM stations.
The San Francisco Bay Area doesn’t have any spare FM broadcasting slots, as far as I could tell by trying to use an audio-jack-to-FM adapter with my car radio, but I don’t think there’s much of any spare AM space either. The sound quality’s good enough for talk, even if FM does music better, and it doesn’t die out in the mountains as badly as FM does. My car radio (about 4 years old) has two FM and one AM band, and I normally leave the first button on the AM tuned to traffic/news/weather radio, and the next button to the talk/some-traffic station in case I’ve just missed KCBS’s traffic, and the two FM stations I listen to most are the first button on the other bands.
It’s been a while since I’ve driven cross-country, but AM radio used to mean you could listen to WOWO in Ft. Wayne Indiana for about 2000 miles, and a few other high-power stations for a long distance.
AM on the MW broadcast band still has a place. The propagation characteristics of the band are suited to covering wide areas, which is particularly valuable for talk radio, news services and sports, where getting the information out is more important than sound quality. AM receivers are still conceptually simple devices. When things go pear shaped, simplicity rules. In regional and rural Australia, broadcast AM will always have the advantage of propagation over other broadcast media, as even a drive into “town” might be enough to go in and out of the coverage of the nearest FM station, but AM will be going strong the whole way.
As for audio quality, I have listened to some of the old valve radios of the 1930s era, and they certainly do sound rather nice, given the limitations of the audio being broadcast. What commercial broadcast radio lacks is decent content. I rarely listen to commercial stations for that reason. My preferences are either local community FM stations, which are volunteer run and feature locally made content, or the national public broadcaster, the ABC. There are community AM stations, but they can be tough to receive, due to low power and the high noise level on the MW band these days. :(
The day AM dies as a broadcast medium will be a sad day indeed, but I’m sure the hams will keep AM alive long after that time. I modded my Icom IC-745 for AM transmit on the amateur bands on principle. For some strange reason, Icom chose to offer only AM receive in this radio on all frequencies.
What annoys me, and it requires you to look at how the bandwidth is divided up by ofcom (uk readers ), is how much bw is spared for us mere mortals and how much the military and government has. They just not give a crap about optimal modulation schemes. Bloody disgrace.
” in the time domain with the supposition of a pair of waveforms to form a modulation envelope”
supposition should be superposition
please fix this…