Ok I am not in the radio business, so I have always wondered why it is that AM radio has to sound like crap. In this day and age why cant AM radio sound like FM radio?

Please to inform me on this.

AM radio is basically noise and any other source of noise tends to interfere with it. On top of that, additional stations were added, creating more interference, hence noise. To make the noise tolerable, receiver manufacturers began limiting the frequency response of the radios. Technology has improved but not until too few cared about the sound for the expense to be worthwhile. As best I can tell, HD seems to be on the way to solving this problem at least close in. You don't have the noise and properly executed, it pretty much sounds like FM.

Analog AM is based on hundred-year-old technology, while FM is newer, 70 year-old technology.

The key reasons for the difference in quality is technical. Amplitude modulation is more susceptable to interference and noise than frequency modulation.

I understand the basic technical differences but cannot explain them. Wikipedia helps if you understand basic radio theory. Here is an animated diagram that illustrates the difference between the two systems:

http://en.wikipedia.org/wiki/Image:Amfm2.gif

My take:

AM is an additive system. Any change in the spectrum shows up, on an AM radio, given it's within the frequency being used for programming. Essentially, AM stations need to be several times louder than their electromagnetic surroundings, or excessive noise will be heard in the program stream.

(some noise is always heard because everything adds together on AM)

The more bandwidth (wider the station is) a given AM station has, the better it's sound quality to the listener. However, wider bandwidths require more power than narrow ones, and there are lots of other factors that contribute to this. My explanation is simple. Probably too simple.

For a given power output, there is a tradeoff between how wide a station signal is, and it's effective (low noise coverage area) coverage is. More bandwidth = generally less acceptable coverage.

One fly in the ointment is the spacing between channels too. AM stations are placed too closely together to allow for more than 5Khz of solid bandwidth, known to be free of other stations signal noise. Because AM propagates long distances, wider bandwidths are problematic, particularly at night.

The result is narrow radios to keep issues to a minimum. Most listeners prefer narrow to wider plus noise or fickle tuning, complexity in operation, spotty performance, etc...

Up until very recently, most AM signals were quite a bit better than nearly all the receivers used to listen to them. The consistency and noise issues are why.

FM systems are quite different in that they encode (modulate) the program material on a carrier that varies in frequency. Small variations in carrier strength, normally heard as noise on AM systems, do not impact the program material as they are outside the frequency domain.

Essentially there is still noise (always is), but it's sharply diminished compared to AM, due to frequency being the primary means by which a signal is conveyed to the listener. Mono FM is extremely clean and quiet and clear. Stereo FM, is somewhat more noisy (and has other problems) because the stereo portion of the signal is actually an AM signal added to the FM one.

I'll let the real engineers carry it from there.

FM also has a property known as capture effect, which means that you will hear only one station at a time, even if two or more are transmitting on the same frequency:

http://en.wikipedia.org/wiki/Capture_effect

AM has no capture effect, so on some channels you may hear an awful jumble of stations, particularly at night when distant stations are being received.

If one applies Occum's Razor, Randy's explaination is the correct one: "Analog AM is based on hundred-year-old technology, while FM is newer, 70 year-old technology."

How is HD going to make AMs sound better?

> How is HD going to make AMs sound better?

The main thing that HD is supposed to do is to prevent the listener from hearing interference. Some types of digital systems, like HD radio, CDs, the transmission protocols used by space probes, etc. have something called "error correction" built in that allows for some amount of signal corruption to be tolerated. This is accomplished by building in some redundancy in the way that the digital data is encoded. In the case of CDs, this means that small specks of dust or small scratches on the disc won't cause disruptions or clicks in the audio. In the case of the space probe, it means that clear pictures and data without errors can be received from the probe, even though the signal picked up by NASA's antennas is very weak. In the case of HD radio, it means that even though the radio is still receiving a signal with interference, there is circuitry in the radio that is able to reconstruct what the digital data is "supposed to be" so that the audio played back by the radio doesn't break up.

>...I have always wondered why it is that AM radio
> has to sound like crap

My answer to this is that it doesn't HAVE to sound like crap. Subjectively speaking, you can get relatively good sound from AM with certain radios, on certain stations, and in noise-free conditions. It is very hit-or-miss. If you can get the combination of radio, station, and conditions listed below, I think that you will might be pleasantly surprised:

Radios--Wide bandwidth, low distortion radios, such as:
* Tube Hi-Fi tuners from the 1950s and early 1960s.
* Some table radios and stereos from the early 1970s (when there still was a lot of music programming that could only be found on AM).
* Some deluxe factory car radios from the late 1980s and 1990s, such as those in Cadillacs (look for one that has a button labelled "AM ST").
* Radios that have a logo that says "AMax" or "AMax Stereo."

Stations--Stay away from Clear Channel and Crawford Broadcasting stations. Instead, try:
* KXL
* KPDQ
* KBND (if you are in Bend)
* KXMG
* KLYC
* KUIK
* KBPS
* KBMS
* KKAD

Conditions-Preferably during the day (when the dial is not as crowded), away from utility lines and electronic equipment, and not during a thunderstorm.

A few months ago, I was driving out towards the Bend area. There are really long stretches of highway out there where there is ZERO interference from utility lines. I could hear some of the Portland stations almost all of the way into Bend. I also noted that KBND has a sound that is much easier on the ears than that of the Portland stations (due to less processing), and because of the lower interference levels out there, there was not an issue with that station's sound not being able to "punch through."

JayZie, if you are able to hear KEX in HD when they play music, as I did recently, you will hear noise free sound very close to FM stereo. The local Radio Disney affiliate should be up and running with HD in the near future and hopefully, they will understand the technology enough to sound as good. It should continue to get better as codecs improve. It already has.

I haven't heard any music on KEX.

1330 plays music in the evenings, which is a good test of AM HD.

Where is Eric Norberg when you need him? I remember attending various seminars where Eric would extoll the virtues of AM stereo. He said that AM had the "potential" to sound as good as FM but was restricted by various factors such as transmitted frequency response and the frequency response of AM receivers (which is poor) and interference problems. I just bought a new JVC HD car radio from CC and the Am analog sound is worse than awful. And, there are no HD AM stations in Eugene. Eric, do you monitor these posts? If so, hello to you.

Thinking about KBBT AM 970 "The BEAT" right now. Great sounding AMS station. Kent worked that one over, and I got to enjoy pretty damn good AM for a few years.

I got solid, very listenable reception on drives to the coast to where Spirit Mountain is, regularly.

In the car, the most notable differences were:

-reduced bandwidth

-no multi-path

-great seperation

-electrical noise at times

-good fringe area listening, just a smooth fade to noise, with stereo there nearly the entire time. Most changes were this way, but for electrical noise.

Somebody should have done an AMS with DSP. Adding some harmonic content to open up the bandwidth would not have been a big crime and would have significantly improved some material. I would have done this, keyed to the treble or tone control. On most radios, the utility of this control is limited due to it having most of it's effect on the audio above the broadcast. So apply the DSP in stages, past the point where the control does nothing. User either likes it or does not, and that's it.

Most of the electrical noise would have been reduced significantly as well. Oh well...

Ended up liking the reduced bandwidth. The radio I used was somewhere about 6-8Khz. For some tunes, this was not enough. For a lot of them, it was just fine. Extended listening sessions were pleasant.

If you've ever listened to an AM Stereo talk broadcast, where the talk program was stereo, it's the best! I don't know what it is about AM processing that brings out the best in voices, but it would be nice to have it on the FM talkers, when they appear.

IMHO, an FM mono talk station, with the AM processing done, would be very good for extended listening sessions as well.

Thinking about KBBT AM 970 "The BEAT" right now. Great sounding AMS station.
(sigh) After all these years, I still miss that station. Didn't have anything capable of AM Stereo at the time, but they played a ton of stuff that wasn't played anywhere else - even NRK. A definite issue of program quality vs. anything else, even which band (AM or FM) sounds better.

I once ran into Dave Numme, and asked him if we asked very nicely, and didn't ask for anything else if The Beat could come back. The answer was: "No - you'd have to like Merle Haggard to listen to 970 now." (The station was Classic Country at the time.)

Although I don't think the programming was in stereo, the station that played Blazer games in Salem about 10 years ago (thinking it was 1430 KYKN) seemed to run AM stereo - the radio in my family's vehicle picked up AM stereo and there went a lot of the noise that normally crept through AM stations.

Where is Eric Norberg when you need him?
In Sellwood, running The Bee newspaper.

High definition AM eh? Could this be the return of some good ole' music formats to the AM dial ?

Call me old fashioned but there are some songs from the 60s and early 70s that just dont sound right unless they are run through an Optimod processor with the compression set to the tune of 120 % modulation on Positive peaks hooked up to a Harris MW 50 transmitter on 1190 KHZ. A Harris MW 5 would be ok on 620 KHZ too, but only if the antenna was located in the Janzen Beach duck blind with a new copper mesh 1200 foot radius ground system and 2 (5/8) wave towers.

NOW THAT WAS AM RADIO..........................

Did you know there was a horrid whine that went all through SE Portland and Clackamas when the station was at Delta Park? This is much better!

newflyer: I don't believe kykn was ever am stereo but KWIP with Eric Norberg at the helm was AM Stereo in 1986, I was there and yes I was at a few of his "seminars" too!
He and the owner had am stereos in their cars and man it sounded great!

KSLM had a new Harris 5kw and went AM stereo for a short time till the station was sold to Doc Nelson and Co. and part of the deal was that the TX and exciter went to a station in Portland thus the station reverted back to it's old Gates.

Which Portland station got the Harris transmitter from KSLM?

My guess would be am 1010.

"A definite issue of program quality vs. anything else, even which band (AM or FM) sounds better. "

Totally.

Anyone who says analog AM is dead, dying, not appropriate, can't compete, etc..., needs to only look back at "The BEAT" on AM (I still see stickers, BTW), talkers, or the Latino stations that see plenty of listeners.

Better quality AM will make cheaper, less compelling content forms viable, but that's it really.

Let's see how long the Latino stations continue to have listeners. One more FM ought to about do it! It may not even take that many. 970 KBBT was wiped out by KNRK and it didn't even take very long!

No disagreement there.

However, there are always niches.

IMO, having 970 around made 94-7 a better station, and vice versa. Each would add different tracks from different bands at different times, I remember 94-7 added The Refreshments (I forget the name of the song, it was their first one that went "everybody knows that the world is full of stupid people, so meet me at the mission at midnight...") much quicker than 970 did, and 970 added the song "Honky's Ladder" (forget the name of the band at the moment... wow, I'm doing great tonight! LOL!), additionally I don't think I ever heard the Josh Clayton Felt song on 94-7 or any other station for that matter, and the only other person who'd ever heard of Babylon Zoo (another song only 970 played) was a guest on Jaime Cooley's "Something Cool" when that was on at midnight.
Besides, when you got tired of one station or didn't like the song they were playing, you could always flip to the other. Was possible for me to listen to the radio for hours back then. Throw in KUFO and, looking back, I think it's amazing that I only used to listen to 3 radio stations.

"Did you know there was a horrid whine that went all through SE Portland and Clackamas when the station was at Delta Park? "

Maybe only when driving by the KEX transmitter.
I never noticed a whine or other problems with KGW when they were at Delta Park. In fact, it sounded better than most other stations on AM. I have no idea how they sound from Harmony site since I have not tuned in since they stopped playing music.

KISN on 910, however, always had a whine or noise. Not because of where they were but because radios in that era normally had 455 kHz as the IF which created the whistle on 910 (2X)

Most radios picked up a second version of 1520 right next to 620, creating a high pitched whine on the latter because of it being overpowered, some worse than others. Since it's now down the street from the other one, it doesn't do that anymore.

1520 - (455 x 2) = 610

Yes, in Oak Grove we suffered receiver images of both KYXI and KEX on the low end.

The KISN whine was atrocious, making the station almost unlistenable, though I'd long believed it was 920 in Spokane vs. KISN's weak signal our way, being unaware it was a receiver defect.

Interestingly, the only station outside north Clackamas County (KYXI, KEX, KPOJ/Mount Scott and KXL/Harmony) that put enough signal into the neighborhood to be picked up on the crystal-diode sets we had as kids was KGW/Delta Park (faintly).

Calhoun once told me of friends who lived near (I'm almost certain it was) KISN's xmtr who received it on their fireplace screen. He thought this was very funny.

The KISN 910 whine on most radios was because of the internal circuitry. The standard internal conversion frequency was 456 khz, the first harmonic of that is 912 khz (2x 456), resulting in that whine.

Perhaps that's why the recent revivals failed; maybe they shoulda injected a 2kHz sine.

(Ducking with tongue in cheek.)

I don't think I would consider it a defect because that's what happens with radios that aren't digitally tuned. I understand Delco got around it by moving the IF to a different frequency. I don't know why others didn't. KEWB in San Francisco was a pretty major Top 40 that must have had the same problem and there are many others.

When I had my high school electronics class in Oregon City, pretty much any circuit anyone built that included a capacitor and speaker would receive KEX.

The 910 kHz interference is indeed a receiver defect because there is some kind of unintentional feedback path from the diode detector back to the front end of the radio. In the case of a transistor radio, this very well could have been magnetic coupling from the board traces (or in some cases wiring) of the diode detector circuitry back to the antenna.

Some automotive radios eliminated this problem by making the IF 262.5 kHz so that the 2nd harmonic is 525 kHz. This is OK in a car radio because it has a dual-tuned front end. If a 262.5 kHz IF were used in a portable radio (with only a single-tuned front end), then the image rejection wouldn't be as good as if a 455 kHz IF were used.

When single-chip AM receivers came on the scene, the problem was largely mitigated because the current paths in the detector circuit which could radiate harmonics of the IF back to the antenna became physically small.

As is the case with portable electronics today, the engineering decisions made in those old transistor radios were all about manufacturing costs. There were a some transistor radios made with dual-tuned front ends, but most only had a single-tuned front end (the ferrite rod antenna was the tuned element).

Here's a post-script for the 910kHz whine issue: the diode detectors in transistor radios had to operate at signal levels of hundreds of millivolts in order produce enough output to drive the automatic volume control circutry in the radio and to keep the audio distortion down. The signals coming from the antenna, on the other hand, could easily have been in the hundreds of microvolts range. It would take just a little bit of unintentional feedback from the detector to the antenna to really muck things up with an annoying whine.

Every old radio I ever had experienced a heterodyne squeal on 910! I don't consider it a defect because usually, when you replace something with a defect, you get rid of the defect but if all the radios were made that way, you couldn't do that!

Alfredo can go through all that gobbledygook and explanation but the bottom line is that it was not a defect. That is the way radios were made back then just as Semoochie just said. All radios had that squeal on 910 because they all used 455kHz as their IF frequency and that is the way those radios worked. It is just that simple. Even the higher end models were that way. Same thing in car radios.

Even my dad's ham receivers (Hammarlund, NC...) that tuned that band had it.

i wonder that to