# AM vs. FM radio and their content **URL:** \ **Category:** Factual Questions\ **Created:** [December 14, 2009, 2:55am UTC](https://boards.straightdope.com/t/am-vs-fm-radio-and-their-content/521178 "2009-12-14T02:55:40Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![KellyM](https://avatars.discourse-cdn.com/v4/letter/k/57b2e6/32.png) [@KellyM](https://boards.straightdope.com/u/KellyM)\ **Post date:** [December 14, 2009, 9:31pm UTC](https://boards.straightdope.com/t/am-vs-fm-radio-and-their-content/521178/21 "2009-12-14T21:31:33Z")
> [@kunilou](#): > > Yes, because farmers still don’t have the Internet in their tractors, combines and pickup trucks. That’s changing. More and more farmers have satellite receivers in their equipment, for weather and financial information. That said, broadcast AM remains the most consistently reliable way to reach this demographic, and the crop report remains a very real part of the program for many AM stations in the Midwest. They tend to fill the void with talk radio because talk radio is _cheap_. The FCC doesn’t allow AM stations to go dark; you have to be transmitting some sort of programming at all times that your license specifies that you will be in operation or the FCC will yank your ticket, and the FCC stopped issuing new “limited time” station licenses quite a while back. Talk radio is cheaper than music for this purpose; for music you have to pay royalties, but many of the talk radio programs are available for almost nothing (I think in some cases they actually pay you to run it) and so they’re a great way to fill gaps in the program schedule. ---
**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\ **Post date:** [December 14, 2009, 9:37pm UTC](https://boards.straightdope.com/t/am-vs-fm-radio-and-their-content/521178/22 "2009-12-14T21:37:18Z")
Obscure _All the President’s Men_ reference. ---
**Author:** ![sqweels](https://avatars.discourse-cdn.com/v4/letter/s/f19dbf/32.png) [@sqweels](https://boards.straightdope.com/u/sqweels)\ **Post date:** [December 14, 2009, 9:41pm UTC](https://boards.straightdope.com/t/am-vs-fm-radio-and-their-content/521178/23 "2009-12-14T21:41:25Z")
> [@Musicat](#): > > Define “blocked”. Opposed? Jammed. ---
**Author:** ![Derleth](https://avatars.discourse-cdn.com/v4/letter/d/b9e5f3/32.png) [@Derleth](https://boards.straightdope.com/u/Derleth)\ **Post date:** [December 14, 2009, 10:48pm UTC](https://boards.straightdope.com/t/am-vs-fm-radio-and-their-content/521178/24 "2009-12-14T22:48:31Z")
> [@Exapno\_Mapcase](#): > > most FM stations up through the 60s were owned by AM stations and just rebroadcast the material to the small listener base Do you have a cite for this? I seem to recall that the whole reason FM was such a wonderland in the 1960s was because it was forbidden for AM stations to merely rebroadcast their signals on the FM band. Thus, you got radio stations owned by companies at a loss to fill the air time hiring a DJ to spin whatever those crazy kids were listening to (and make money via payola). [This seems to agree with me:](http://radiomagonline.com/fcc/radio_fcc_approves_am/) > [@](#): > > In an effort to provide a lifeline to an AM radio, the Commission has changed its rules to permit AM stations to rebroadcast their signals on FM translators under certain conditions. This article dates to September 1 of _this_ year. ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [December 14, 2009, 10:51pm UTC](https://boards.straightdope.com/t/am-vs-fm-radio-and-their-content/521178/25 "2009-12-14T22:51:26Z")
> [@KellyM](#): > > It’s obviously possible to put tube radios into a car (we put tube radios into airplanes during WW2, after all) but there are all sorts of difficult issues involved. It does occur to me that many of the hard problems with tube radios in mobile environments are limited to transmitters, which generally require high voltages. I’d be curious, though: did those radios carry their own batteries, or were they driven from the car’s electrical system? the DC was chopped with a mechanical vibrator (like a door bell or buzzer) and then run into a transformer. for portable radios, like for a picnic, you used a B battery which could be 22.5, 45 or 90V for the plate voltage. ---
**Author:** ![Hari\_Seldon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hari_seldon/32/5173_2.png) [@Hari\_Seldon](https://boards.straightdope.com/u/Hari_Seldon)\ **Post date:** [December 14, 2009, 10:52pm UTC](https://boards.straightdope.com/t/am-vs-fm-radio-and-their-content/521178/26 "2009-12-14T22:52:02Z")
> [@](#): > > It’s obviously possible to put tube radios into a car (we put tube radios into airplanes during WW2, after all) but there are all sorts of difficult issues involved. It does occur to me that many of the hard problems with tube radios in mobile environments are limited to transmitters, which generally require high voltages. I’d be curious, though: did those radios carry their own batteries, or were they driven from the car’s electrical system? It ran off the car battery. But car batteries were only 6 volt (although the majority of vacuum tubes used that for the heater supply) and did not hold that many amp-hours. And of course, you needed a hundred volt or so DC plate supply so you had to chop it transform it and rectify it and, I assume, filter it to get that. An hour or so of listening with the engine off could run the battery down to the point of not being able to start the car. I think that standard portable radios used 9 volt batteries and used them up quickly. Transistors made a huge difference to portable radios. A really primitive AM radio didn’t need any circuitry at all, just a crystal and a cat’s whisker and got its power from the signal itself. But that was really primitive. I am not sure an FM receiver is that much more complicated than an AM receiver. They both needed a detector, an IF mixer (you know I assume that AM tuners also used an IF mixer), hi-Q filter and then one or more stages of amplification and power amplification. I built several FM tuners around 1960 (from Dynakit) but I don’t really know how AM tuners worked. In the 50s, there was one FM station, WFLN in Philadelpha, a classical music station, that sold an untunable FM radio just for listening to it. ---
**Author:** ![KellyM](https://avatars.discourse-cdn.com/v4/letter/k/57b2e6/32.png) [@KellyM](https://boards.straightdope.com/u/KellyM)\ **Post date:** [December 14, 2009, 11:27pm UTC](https://boards.straightdope.com/t/am-vs-fm-radio-and-their-content/521178/27 "2009-12-14T23:27:44Z")
> [@Hari\_Seldon](#): > > A really primitive AM radio didn’t need any circuitry at all, just a crystal and a cat’s whisker and got its power from the signal itself. But that was really primitive. I am not sure an FM receiver is that much more complicated than an AM receiver. They both needed a detector, an IF mixer (you know I assume that AM tuners also used an IF mixer), hi-Q filter and then one or more stages of amplification and power amplification. I built several FM tuners around 1960 (from Dynakit) but I don’t really know how AM tuners worked. Virtually all commercial radios these days are superheterodynes, yes, mainly because such designs can be made more stable than direct-conversion or regenerative receivers. Downconverting doesn’t change what you have to do to recover the modulating signal, though. You actually can use an AM detector to demodulate FM (a so-called “slope detector”), but doing so requires very precise tuning (for which you cannot use a PLL off the carrier all that well, either), and the recovered signal is not of very high quality. In addition, you lose the main advantage of FM when you do that. One of the major annoyances with AM is that signals in AM are additive; if you have two stations overlapping you’ll get pieces of both of them, and impulse noise (e.g. lightning) is very audible. However, in FM the receiver will grab the strongest signal and demodulate only that signal, rejecting the others (the “FM capture effect”), and impulse noise tends not to make it through as much because you’re detecting changes in the phase, not amplitude, of the received signal. But you only get that if you use a phase detector, which is inevitably more complicated than an AM envelope detector. The other main feature of FM is that audio volume is independent of received signal strength; the station doesn’t fade as it gets weaker the way it does in AM; again, you have to use a phase detector to get this benefit. The deviation ratio used in FM broadcasting is quite high (5), giving a wide capture range and therefore allowing receivers to have relatively imprecise local oscillators. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [December 15, 2009, 3:30am UTC](https://boards.straightdope.com/t/am-vs-fm-radio-and-their-content/521178/28 "2009-12-15T03:30:10Z")
> [@Derleth](#): > > Do you have a cite for this? I seem to recall that the whole reason FM was such a wonderland in the 1960s was because it was forbidden for AM stations to merely rebroadcast their signals on the FM band. Thus, you got radio stations owned by companies at a loss to fill the air time hiring a DJ to spin whatever those crazy kids were listening to (and make money via payola). > > [This seems to agree with me:](http://radiomagonline.com/fcc/radio_fcc_approves_am/)This article dates to September 1 of _this_ year. Yes and no. The prohibition was broadcasting simulcasts 24 hours a day. I believe the limit was 12 hours. But in those days many AM stations did not broadcast 24 hours a day in the first place. Low power stations normally stopped at night because of the long distance effect. Other, stronger, stations on the same wavelength would interfere with the signal. There weren’t as many listeners at night, either, and no real economic incentive to broadcast 24 hours. Most stations had elaborate sign on and sign off rituals involving the national anthem or some special song or taped bit. No doubt some stations filled up any time over 12 hours with that noise the kids were listening to. But the history of FM rock doesn’t depend on that. It evolved from dedicated stations. ---
**Author:** ![Derleth](https://avatars.discourse-cdn.com/v4/letter/d/b9e5f3/32.png) [@Derleth](https://boards.straightdope.com/u/Derleth)\ **Post date:** [December 15, 2009, 4:58am UTC](https://boards.straightdope.com/t/am-vs-fm-radio-and-their-content/521178/29 "2009-12-15T04:58:13Z")
**Exapno Mapcase** : That makes sense. Thank you. Just for reference, there _are_ AM stations that play mostly music, but only music aimed at people at least 50 years old: There’s an Oldies-heavy Easy Listening AM station in Havre at 610 kHz, I think there’s still a Beautiful Music\* AM station in Great Falls, and until recently there was a Beautiful Music station in Missoula. \*(Beautiful Music is Big Band, Great American Songbook, and some of the softest of the modern Singer-Songwriter stuff. Think Perry Como, Frank Sinatra, and other stuff just a hair edgier than Lawrence Welk’s Champagne Music. If anyone still played music in elevators, it would be Beautiful Music.) Now, in Havre the utility of an AM station is obvious: Crop prices, weather, livestock prices, tradio (eBay/Craigslist for the AM set), some more crop prices, and music to fill the gaps. In Great Falls and Missoula, I fail to see the business model. (The Missoula station didn’t, either. But it _was_ around just a few years ago.) My only guess is that the overhead and license competition for AM stations is so much less than for FM stations that it makes sense for companies that want to chase niche markets (old people) to do so on the AM band. ---
**Author:** ![jasonh300](https://avatars.discourse-cdn.com/v4/letter/j/46a35a/32.png) [@jasonh300](https://boards.straightdope.com/u/jasonh300)\ **Post date:** [December 15, 2009, 5:43am UTC](https://boards.straightdope.com/t/am-vs-fm-radio-and-their-content/521178/30 "2009-12-15T05:43:31Z")
> [@Hari\_Seldon](#): > > In the 50s, there was one FM station, WFLN in Philadelpha, a classical music station, that sold an untunable FM radio just for listening to it. Back in the 80s, one of the New Orleans stations distributed a little walkman style radio with headphones that couldn’t be tuned. It had the station’s logo screen printed on the front of it and one wheel that turned it on and controlled the volume. I remember a friend of mine took his apart and found a pot inside that could be turned with a small screwdriver to change the frequency, although I’m pretty sure it still couldn’t be tuned across the whole FM dial. ---
**Author:** ![qazwart](https://avatars.discourse-cdn.com/v4/letter/q/5fc32e/32.png) [@qazwart](https://boards.straightdope.com/u/qazwart)\ **Post date:** [December 15, 2009, 5:46am UTC](https://boards.straightdope.com/t/am-vs-fm-radio-and-their-content/521178/31 "2009-12-15T05:46:44Z")
> [@Thudlow\_Boink](#): > > Is this still true, and if so, why do some MP3 players have the capability to receive FM but not AM radio? In the 1960s, you had to build circuits transistor by transistor. We now have “radios on chips”, so there’s not much difference in the price. You want FM radio? You put in the FM radio ic chip. I’ve found them priced about $1.50/each in lots of 100. Since FM has better sound quality and is the station most music is played on, that’s the one that people want to listen to on their MP3 players. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [December 15, 2009, 6:12am UTC](https://boards.straightdope.com/t/am-vs-fm-radio-and-their-content/521178/32 "2009-12-15T06:12:55Z")
From the OP 'black art": This is great stuff, and I am following it. As an side anecdote (to cut into the level of your healthy back-and-forthings) I’d like to mention the comments of a friend of mine, now cognitively disabled, alas, who graduated from MIT in the 60s as an E.E. When I brought him over to see my new oh-so-cool and expensive stereo components, he said the speakers were difficult and had a lot of personal choice; that my amplifier (tube of course, that’s how cool I am) he gave a “meh”; but he said that designing the receiver was where the absolute hardest engineering went, going so far as to call it “a black art.” Just passing this along. ---
**Author:** ![elmwood](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/elmwood/32/3060_2.png) [@elmwood](https://boards.straightdope.com/u/elmwood)\ **Post date:** [December 16, 2009, 5:59am UTC](https://boards.straightdope.com/t/am-vs-fm-radio-and-their-content/521178/33 "2009-12-16T05:59:43Z")
> [@Derleth](#): > > My only guess is that the overhead and license competition for AM stations is so much less than for FM stations that it makes sense for companies that want to chase niche markets (old people) to do so on the AM band. Interesting that you mention “old people”. I would imagine they stick with AM not because they’re all stuck with ancient cathedral radios that can’t tune FM, but rather because they’re creatures of habit. FM is a strange, mysterious land full of that rolling and rocking music these kids listen to nowadays. AM is familiar and comfortable, where they first heard about the Japs bombing Pearl Harbor. Their Buicks may boast impressive factory audio systems, but they’ll never take full advantage of it, instead sticking to the Music of Your Life and all-news stations on AM, and wondering why that slot by the stereo is too narrow to fit the sermon on tape from St. Gustavus Lutheran Church. Likewise, despite that V8 engine, they’ll never drive that Buick over 45 MPH. ---
**Author:** ![Terry\_Kennedy](https://avatars.discourse-cdn.com/v4/letter/t/c57346/32.png) [@Terry\_Kennedy](https://boards.straightdope.com/u/Terry_Kennedy)\ **Post date:** [December 16, 2009, 9:08am UTC](https://boards.straightdope.com/t/am-vs-fm-radio-and-their-content/521178/34 "2009-12-16T09:08:43Z")
> [@johnpost](#): > > the DC was chopped with a mechanical vibrator (like a door bell or buzzer) and then run into a transformer. 4-pin and 5-pin vibrators were the most common types, though there was a 6-pin variant as well. [This page](http://www.leedsradio.com/parts-odds.html) lists some for sale and has links to pictures. By the mid-70’s, the originals were failing, mostly due to the vibration-absorbing foam in them decaying, leading to short circuits and excessive (mechanical) noise. > [@](#): > > for portable radios, like for a picnic, you used a B battery which could be 22.5, 45 or 90V for the plate voltage. Some of those batteries are still being made. If you go to the Energizer [web site](http://data.energizer.com/) and select “Industrial Carbon Zinc”, you’ll get an amazingly large list of still-produced B batteries. However, most of the types that are still manufactured are for photo flash units, radiation counters, and so forth. The vintage radio collecting hobby has developed various electronic converters which are packaged inside vintage battery housings (or reproductions). Regarding the cost of AM vs. FM receiver designs, the classic tube radio design for AM uses 5 tubes. These were either all 12V tubes for auto applications or a variety of oddball voltages that added up to 117 for home use. The equivalent FM design used 7 tubes. ---
**Author:** ![MsRobyn](https://avatars.discourse-cdn.com/v4/letter/m/90ced4/32.png) [@MsRobyn](https://boards.straightdope.com/u/MsRobyn)\ **Post date:** [December 16, 2009, 12:36pm UTC](https://boards.straightdope.com/t/am-vs-fm-radio-and-their-content/521178/35 "2009-12-16T12:36:16Z")
> [@elmwood](#): > > Interesting that you mention “old people”. I would imagine they stick with AM not because they’re all stuck with ancient cathedral radios that can’t tune FM, but rather because they’re creatures of habit. FM is a strange, mysterious land full of that rolling and rocking music these kids listen to nowadays. AM is familiar and comfortable, where they first heard about the Japs bombing Pearl Harbor. Their Buicks may boast impressive factory audio systems, but they’ll never take full advantage of it, instead sticking to the Music of Your Life and all-news stations on AM, and wondering why that slot by the stereo is too narrow to fit the sermon on tape from St. Gustavus Lutheran Church. Likewise, despite that V8 engine, they’ll never drive that Buick over 45 MPH. This is another chicken-and-egg problem. In my market, there are few, if any, FM stations that play music that appeals to anyone over 60. Conversely, there are several AM stations that program for that demographic. So do older people listen to AM because they’re comfortable with the technology, with AM stations programming accordingly, or are older listeners listening to AM because there’s nothing for them on FM? ---
**Author:** ![CurtC](https://avatars.discourse-cdn.com/v4/letter/c/ce73a5/32.png) [@CurtC](https://boards.straightdope.com/u/CurtC)\ **Post date:** [December 16, 2009, 2:46pm UTC](https://boards.straightdope.com/t/am-vs-fm-radio-and-their-content/521178/36 "2009-12-16T14:46:52Z")
> [@elmwood](#): > > Interesting that you mention “old people”. I would imagine they stick with AM not because they’re all stuck with ancient cathedral radios that can’t tune FM, but rather because they’re creatures of habit. FM is a strange, mysterious land full of that rolling and rocking music these kids listen to nowadays. AM is familiar and comfortable, where they first heard about the Japs bombing Pearl Harbor. Except the first stations to air on the FM band targeted old people, or at least middle-aged. In my recollection, when the FM dial was first being populated with stations, they were mostly “easy listening” format. ---
**Author:** ![Tom\_Tildrum](https://avatars.discourse-cdn.com/v4/letter/t/e95f7d/32.png) [@Tom\_Tildrum](https://boards.straightdope.com/u/Tom_Tildrum)\ **Post date:** [December 16, 2009, 3:35pm UTC](https://boards.straightdope.com/t/am-vs-fm-radio-and-their-content/521178/37 "2009-12-16T15:35:39Z")
> [@CurtC](#): > > Except the first stations to air on the FM band targeted old people, or at least middle-aged. In my recollection, when the FM dial was first being populated with stations, they were mostly “easy listening” format. That can’t have lasted long. By 1978, Steely Dan was singing about how women would put out if you played them FM music. 😃 ---
**Author:** ![Sparky812](https://avatars.discourse-cdn.com/v4/letter/s/eb9ed0/32.png) [@Sparky812](https://boards.straightdope.com/u/Sparky812)\ **Post date:** [December 16, 2009, 3:54pm UTC](https://boards.straightdope.com/t/am-vs-fm-radio-and-their-content/521178/38 "2009-12-16T15:54:12Z")
The nostalgia is really hitting me. Anybody else missing the old FM album oriented format these days? I can’t stand to listen to all the top 40 or classic rock stations! Thank god for internet and satellite radio! ---
**Author:** ![salinqmind](https://avatars.discourse-cdn.com/v4/letter/s/3ec8ea/32.png) [@salinqmind](https://boards.straightdope.com/u/salinqmind)\ **Post date:** [December 16, 2009, 4:04pm UTC](https://boards.straightdope.com/t/am-vs-fm-radio-and-their-content/521178/39 "2009-12-16T16:04:05Z")
I’m probably ‘old’ to you…let’s say over 50 but under 60. Just out of curiosity, what do you think I listen to on the radio, or what YOU think I listen to on the radio? ---
**Author:** ![Kent\_Clark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kent_clark/32/105_2.png) [@Kent\_Clark](https://boards.straightdope.com/u/Kent_Clark)\ **Post date:** [December 16, 2009, 4:07pm UTC](https://boards.straightdope.com/t/am-vs-fm-radio-and-their-content/521178/40 "2009-12-16T16:07:18Z")
> [@elmwood](#): > > Interesting that you mention “old people”. I would imagine they stick with AM not because they’re all stuck with ancient cathedral radios that can’t tune FM, but rather because they’re creatures of habit. FM is a strange, mysterious land full of that rolling and rocking music these kids listen to nowadays. AM is familiar and comfortable, where they first heard about the Japs bombing Pearl Harbor. Their Buicks may boast impressive factory audio systems, but they’ll never take full advantage of it, instead sticking to the Music of Your Life and all-news stations on AM, and wondering why that slot by the stereo is too narrow to fit the sermon on tape from St. Gustavus Lutheran Church. Likewise, despite that V8 engine, they’ll never drive that Buick over 45 MPH. Oh please. People in their 80’s now were in their 50’s when FM really took off. That’s quite long enough for grammy and gramps to learn how to toggle the switch from AM to FM on their car radios. The fact is that FM is a more desirable medium for music than AM \>\> so FM stations tend to be snapped up by demographically desirable (and lucrative) formats \>\> leading to AM stations being worth less than FM \>\> which makes them more viable for niche markets, including religion, foreign language and music for old folks \>\> which means those formats tend to be “ghettoized” into the AM band. [Previous page](https://boards.straightdope.com/t/am-vs-fm-radio-and-their-content/521178.md?page=1) [Next page](https://boards.straightdope.com/t/am-vs-fm-radio-and-their-content/521178.md?page=3)