# When Will AM RADIO Become Obsolete? **URL:** \ **Category:** Factual Questions\ **Created:** [August 23, 2003, 1:41pm UTC](https://boards.straightdope.com/t/when-will-am-radio-become-obsolete/197144 "2003-08-23T13:41:55Z")\ **Posts on this page:** 18\ **Page:** 2
**Author:** ![Tuckerfan](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@Tuckerfan](https://boards.straightdope.com/u/Tuckerfan)\ **Post date:** [August 24, 2003, 6:08am UTC](https://boards.straightdope.com/t/when-will-am-radio-become-obsolete/197144/21 "2003-08-24T06:08:19Z")
> [@](#): > > \*Originally posted by ralph124c \* > \*\*I’m asking this because I have to buy a new radio…my Grandpa’s 1935 Crosley doesn’t work anymore…so I have to break down and buy a newer one! (I’d like to keep the old Crosley going…but I can’t get tubes for it anymore). \*\* Have you checked with [these folks](http://www.vacuumtubes.net/page/indexc.html) about tubes? Or maybe [these guys](http://www.radiotubesupply.com/) could help you out. Even if they can’t a [google search](http://www.google.com/search?q=%22radio+tubes%22&sourceid=opera&num=0&ie=utf-8&oe=utf-8) turned up nearly 4,000 hits. One of them should have the tubes you’re looking for. ---
**Author:** ![wooba](https://avatars.discourse-cdn.com/v4/letter/w/aeb1de/32.png) [@wooba](https://boards.straightdope.com/u/wooba)\ **Post date:** [August 24, 2003, 6:15am UTC](https://boards.straightdope.com/t/when-will-am-radio-become-obsolete/197144/22 "2003-08-24T06:15:14Z")
> [@](#): > > \*Originally posted by Q.E.D. \* > **Aircraft use AM** Just curious as to what they use it for? Tranmissions between planes and the tower are FM. ---
**Author:** ![Walloon](https://avatars.discourse-cdn.com/v4/letter/w/fbc32d/32.png) [@Walloon](https://boards.straightdope.com/u/Walloon)\ **Post date:** [August 24, 2003, 6:39am UTC](https://boards.straightdope.com/t/when-will-am-radio-become-obsolete/197144/23 "2003-08-24T06:39:13Z")
> [@](#): > > \*Originally posted by ffolkelore \* > \*\*I wish more music was on AM, because those stations always come in stronger and clearer. Sure there’s no stereo, but few FM stations are stereo anyway. \*\* Where do you live? I have never heard of an FM station that was _not_ broadcasting in stereo. ---
**Author:** ![The\_Ryan](https://avatars.discourse-cdn.com/v4/letter/t/7feea3/32.png) [@The\_Ryan](https://boards.straightdope.com/u/The_Ryan)\ **Post date:** [August 24, 2003, 6:44am UTC](https://boards.straightdope.com/t/when-will-am-radio-become-obsolete/197144/24 "2003-08-24T06:44:35Z")
Seems to me that digital vs. analog, AM vs. FM, and frequency are all different issues. Yes, AM uses different frequencies from FM, but that’s due to human choices, not inherent properties of AM. There may be properties of AM that lend it to lower frequencies, but I know of no theoretical reasons why FM can’t work at any ffrequency. And of course from a mathematical point of view AM _is_ FM (there’s no way to modulate the amplitude without superposing two waves of different frequencies). ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [August 24, 2003, 12:00pm UTC](https://boards.straightdope.com/t/when-will-am-radio-become-obsolete/197144/25 "2003-08-24T12:00:49Z")
1. AM (just as a modulation type) is inherently noisier than FM. An FM receiver tracks a signal as it varies back and forth in frequency, which naturally rejects noise from other signals. Only when the noise gets loud enough that it causes the receiver to track the wrong signal do you hear it, which is pretty good. AM, because it modulates the signal level or amplitude, means that any noise just gets added in to the signal and there is no way to discriminate between the noise and the original signal. Hence FM radio broadcast was heavily advertised for having “no static” when it first came out. 2. The AM radio band in the US is set up for a single channel. No stereo sound. There was talk of converting it to stereo once upon a time, but that fizzled out. 3. This is where we put in the obligatory Hi Opal 4. The AM radio band in the US is defined with a maximum bandwidth of 10 KHz. The human ear can hear up to about 15 to 20 KHz depending on your age and ears, so you can definately hear the lack in quality, so to speak. All of this (except for Opal) means that AM is lesser quality than FM when it comes to sound reproduction. This is why all of the music stations moved to FM and now AM is mostly the domain of the talk radio crowd. Everyone said AM was dead, then there was this resurgance of talk radio, and now it’s far from dead, so you can never say that it’s obsolete. Digital radio has the potential to do to FM what FM did to AM. There’s a good chance it could fizzle out like HDTV though for basically the same reason. FM is good enough for most people, just like regular TV is good enough for most people. We’ll have to see how it goes. If the current radio stations all decide to broadcast in digital and the digital band gets picked up as a new feature on most automobiles, then it will likely take over. If not, then it will be yet another passing novelty. Also, all other things being equal, digital signals propogate better than analog signals. A digital signal just has 2 states, on and off, which can be represented by signal or lack of signal. This can tolerate a huge amount of noise and signal deterioration. Analog signals, by comparison, can’t tolerate anywhere near as much noise and signal loss. When broadcasting though, all things are definately not equal, since the frequency your broadcasting at makes a huge difference on how the radio waves will propogate through the atmosphere. Polarization also makes a difference. AM radio signals are polarized vertically, which helps them bounce through the atmosphere. FM radio signals are polarized horizontally, which helps them to not bounce. This, combined with the frequencies used, helps signals on the AM band go a lot farther than signals on the FM band. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [August 24, 2003, 12:11pm UTC](https://boards.straightdope.com/t/when-will-am-radio-become-obsolete/197144/26 "2003-08-24T12:11:56Z")
> [@](#): > > \*Originally posted by The Ryan \* > **There may be properties of AM that lend it to lower frequencies, but I know of no theoretical reasons why FM can’t work at any ffrequency.** AM is basically sampling the sound on a carrier wave, so you’re dealing with Nyquist’s theorum. The max frequency you can pass is half of the sampling frequency, which is the frequency of the carrier wave. FM won’t work at quite as low of frequencies due to the fact that you’d have to make a frequency discriminator that was extremely sensitive for it to be practical. Also, FM is going to require more bandwidth, since the range that the frequencies can vary determines the overall dynamic range of the signal you can pass through it. Slow scan television (a method of sending pictures using a format that is similar to the way television frames are sent) uses frequency modulation on audio frequencies, so you are definately correct that FM can be used with virtually any frequency. ---
**Author:** ![AWB](https://avatars.discourse-cdn.com/v4/letter/a/bb73d2/32.png) [@AWB](https://boards.straightdope.com/u/AWB)\ **Post date:** [August 24, 2003, 12:43pm UTC](https://boards.straightdope.com/t/when-will-am-radio-become-obsolete/197144/27 "2003-08-24T12:43:55Z")
> [@](#): > > \*Originally posted by Bob55 \* > \*\*This is one of the reasons I don’t think AM will ever be obsolete. The larger stations bounce off the ionosphere and travel very far at night - I can hear AM 750 our of Atlanta once the sun sets, over 400 miles away. The best FM, to my knowledge, reaches ~120 miles. Now XM radio might be worth looking into since it uses satellites. \*\* I used to listen to KFI Los Angeles from the middle of the Colorado Rockies. I couldn’t get the stations nearby because of the mountains, but the angle that KFI was bouncing in on was unimpeded. ---
**Author:** ![AV8R](https://avatars.discourse-cdn.com/v4/letter/a/898d66/32.png) [@AV8R](https://boards.straightdope.com/u/AV8R)\ **Post date:** [August 24, 2003, 12:45pm UTC](https://boards.straightdope.com/t/when-will-am-radio-become-obsolete/197144/28 "2003-08-24T12:45:11Z")
> [@](#): > > ## quote: > > ## Originally posted by Q.E.D. Aircraft use AM > > **Just curious as to what they use it for? Tranmissions between planes and the tower are FM.** The ADF (Automatic Direction Finder) in an airplane is a navigation instrument that receives signals from AM radio stations and from NDBs (Non-Directional Beacons) on the ground. In the old days, pilots were able to navigate cross country by tuning the ADF to commercial AM radio stations. ADFs are not used much anymore, because of the superior technology of VORs and GPS. (By the way, in the movie **Die Hard 2** , the airport’s Main Transmitter™ was blow’d up by the bad guys, so the good guys finally figured that they could talk to the circling airplanes by broadcasting on the NDB frequency. Of course, the movie never explained why they just didn’t walk out to any airplane sitting on the airport and use the normal frequencies (or even the emergency frequency 121.5 MHz) to tell all planes to divert to their alternate, but this kind of discussion is for another post at another time…….) ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [August 24, 2003, 12:45pm UTC](https://boards.straightdope.com/t/when-will-am-radio-become-obsolete/197144/29 "2003-08-24T12:45:23Z")
> [@](#): > > \*Originally posted by wooba \* > \*\*Just curious as to what they use it for? Tranmissions between planes and the tower are FM. \*\* No, they are not. Aircraft use the 118-136 MHz band in AM mode. ---
**Author:** ![Broomstick](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/broomstick/32/246_2.png) [@Broomstick](https://boards.straightdope.com/u/Broomstick)\ **Post date:** [August 24, 2003, 1:13pm UTC](https://boards.straightdope.com/t/when-will-am-radio-become-obsolete/197144/30 "2003-08-24T13:13:54Z")
> [@](#): > > \*Originally posted by AV8R \* > \*\*The ADF (Automatic Direction Finder) in an airplane is a navigation instrument that receives signals from AM radio stations and from NDBs (Non-Directional Beacons) on the ground. In the old days, pilots were able to navigate cross country by tuning the ADF to commercial AM radio stations. ADFs are not used much anymore, because of the superior technology of VORs and GPS. Well, yes and no. ADF navigation is still covered on the written test for the private (and maybe others, it’s just that the private is the only one I’ve taken), and if there’s one mounted in your airplane and an examiner asks you to use it you’d better know how. I would expect it’s covered on the instrument tests, too, since NDB’s can be used for instrument approaches. While GPS and VOR are superior in many ways, they do fail from time to time. You still can navigate cross country on ADF. You can listen to AM radio stations to aleviate the tedium of a long, uneventful cross country (yes, really, long distance travel in small planes can get boring). And, at least on my end of the aviation spectrum, I still see ADF’s more often than not on rental planes, even those with dual VOR’s and a GPS installed. I mean, why not? I carry a map and compass, too. Belt AND suspenders. ---
**Author:** ![MsRobyn](https://avatars.discourse-cdn.com/v4/letter/m/90ced4/32.png) [@MsRobyn](https://boards.straightdope.com/u/MsRobyn)\ **Post date:** [August 24, 2003, 2:31pm UTC](https://boards.straightdope.com/t/when-will-am-radio-become-obsolete/197144/31 "2003-08-24T14:31:19Z")
> [@](#): > > \*Originally posted by Q.E.D. \* > \*\*IAircraft use AM, as does the audio portion of an analog TV channel. \*\* Actually, with the M monochrome standard, the audio is FM. The picture carrier is AM. ---
**Author:** ![Airman\_Doors\_USAF](https://avatars.discourse-cdn.com/v4/letter/a/e36b37/32.png) [@Airman\_Doors\_USAF](https://boards.straightdope.com/u/Airman_Doors_USAF)\ **Post date:** [August 24, 2003, 2:32pm UTC](https://boards.straightdope.com/t/when-will-am-radio-become-obsolete/197144/32 "2003-08-24T14:32:18Z")
And, of course, that was me, not Robin. ---
**Author:** ![wooba](https://avatars.discourse-cdn.com/v4/letter/w/aeb1de/32.png) [@wooba](https://boards.straightdope.com/u/wooba)\ **Post date:** [August 24, 2003, 3:01pm UTC](https://boards.straightdope.com/t/when-will-am-radio-become-obsolete/197144/33 "2003-08-24T15:01:37Z")
> [@](#): > > \*Originally posted by Q.E.D. \* > \*\*No, they are not. Aircraft use the 118-136 MHz band in AM mode. \*\* Then I’m confused. I have a portable radio that says right on the back “FM AIR 88 - 135 MHz” Does it magically change to AM once I reach 108? Not trying to be a smart ass, I really don’t know. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [August 24, 2003, 3:22pm UTC](https://boards.straightdope.com/t/when-will-am-radio-become-obsolete/197144/34 "2003-08-24T15:22:59Z")
> [@](#): > > \*Originally posted by wooba \* > \*\*Then I’m confused. I have a portable radio that says right on the back > “FM AIR 88 - 135 MHz” > > Does it magically change to AM once I reach 108? > Not trying to be a smart ass, I really don’t know. \*\* Yes, it does. Well, not magically. If it’s digitally tuned, it’s trivial to change the mode when the 113-136 MHz band is tuned in. If it’s analog, either you have to switch to “aircraft band” or some such, or if it’s continuously tuning analog, there must be some circuitry to determine when the aircraft band is in tune, and switch the mode. > [@](#): > > \*Originally posted by Airman Doors, USAF \* > **Actually, with the M monochrome standard, the audio is FM. The picture carrier is AM.** I know…I corrected myself later: > [@](#): > > _Originally posted by Q.E.D._ > \*\* haven’t read your links, but my memory did just kick in, and I had that backwards: it’s the video portion of the signal that is AM, not the audio, as you correctly pointed out.\*\* ---
**Author:** ![Rayne\_Man](https://avatars.discourse-cdn.com/v4/letter/r/df705f/32.png) [@Rayne\_Man](https://boards.straightdope.com/u/Rayne_Man)\ **Post date:** [August 24, 2003, 3:36pm UTC](https://boards.straightdope.com/t/when-will-am-radio-become-obsolete/197144/35 "2003-08-24T15:36:46Z")
As I stated above one advantage of digital radio is the ability to transmit more radio stations on a given frequency band. This is because the stations are digitally time shared. We now have the situation in the UK where , as well as all the analogue stations also broadcasting digitally, there are now digital only stations that could not get a slot on the old FM analogue band. These stations are also broadcast via digital satellite and terrestrial TV which means that many people now listen to digital radio via their TV. The digital boxes all have the ability to connect to a HI-Fi so you do not have to have your TV actually switched on to listen to the station. I do not think digital radio will be a passing fad. Prices of digital radio sets are reducing and I can see a time when they cost the same as analoque sets. Look what happend to the price of CD players compared to cassete players. ---
**Author:** ![Airman\_Doors\_USAF](https://avatars.discourse-cdn.com/v4/letter/a/e36b37/32.png) [@Airman\_Doors\_USAF](https://boards.straightdope.com/u/Airman_Doors_USAF)\ **Post date:** [August 24, 2003, 4:01pm UTC](https://boards.straightdope.com/t/when-will-am-radio-become-obsolete/197144/36 "2003-08-24T16:01:09Z")
My bad, **Q.E.D.** ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [August 24, 2003, 4:16pm UTC](https://boards.straightdope.com/t/when-will-am-radio-become-obsolete/197144/37 "2003-08-24T16:16:14Z")
> [@](#): > > \*Originally posted by Q.E.D. \* > **…the 113-136 MHz band…** Errrm…that’s 11 **8** , of course. I need more coffee this morning. Incidentally, the labelling on your radio is what may be leading to your confusion, and I can see why. It really should say FM\*\*/\*\*Air, to distinguish the two bands. In this case, FM refers to the FM broadcast band, not the mode of modulation. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [August 25, 2003, 12:16am UTC](https://boards.straightdope.com/t/when-will-am-radio-become-obsolete/197144/38 "2003-08-25T00:16:08Z")
> [@](#): > > Also, all other things being equal, digital signals propogate better than analog signals. A digital signal just has 2 states, on and off, which can be represented by signal or lack of signal. This can tolerate a huge amount of noise and signal deterioration. Analog signals, by comparison, can’t tolerate anywhere near as much noise and signal loss. But then again when a digital signal degrades enought you get no useful information at all while an analog signal eually degraded could still be decernable (though not pleasant to listen to). So I’m not sure of your statement, and tend to beleive that the absolute range where a signal can still be audiable would be further w/ analog then digital. Also another problem w/ digital stations. The RIAA is having a cow over digital music, I think they would not like music brodcast this way as well. [Previous page](https://boards.straightdope.com/t/when-will-am-radio-become-obsolete/197144.md?page=1)