AM Stereo

[badjef]

I forgot what the issue was with the Magnavox system but its authorization was short-lived, after all the other systems complained about something specific. The FCC pulled its approval quickly in 1980.

THAT is when I knew we were in trouble!

It was not about implementing an AM Stereo system as much as it was a political move to kill the AM band as we knew it.

The cell system was being developed during that time and there was talk of Motorola wanting to either use, or investigate the possibilities of using, the AM band for cell technologies. Although, that never materialized, outside of the lab, it is my belief it was one of the contributing factors as emerging technologies such as digital was making its way into society also and marrying the technologies was still a long way off.

Jeff in Sa-ra-so-ta!

 

[Schroedingers Cat]

I never thought that any AM Stereo system created that much sideband interference. But I sure did when IBOC came on, and blotted out many formerly listenable first adjacent signals completely. That literally has made stations be unusable at Night. I have a close friend who sold one station specifically because of IBOC interference. The only reason even the Christian group owners want to buy these is for the FM translator option. Others have turned their licenses in because of IBOC. The Canadian authorities look the other way when Canadian AMs fight back by staying on Day power and/or pattern. That creates more problems even for US stations that are non IBOC innocent bystanders. It's a "One Man Wrecking Machine".

 

[oldradiotapes]

ors as emerging technologies such as digital was making

"Digital" what? Be more specific. "Digital" is not a technology or a "thing" in and of itself.

 

[Schroedingers Cat]

I think he meant IBOC.

 

[semoochie]

"Digital" what? Be more specific. "Digital" is not a technology or a "thing" in and of itself.

I think he meant "digital processing" in 1978.

 

[badjef]

"Digital" what? Be more specific. "Digital" is not a technology or a "thing" in and of itself.

I'll type slower for you.

Digital was being defined as not analogue. Something that worked on ones and zeros, had and, or, nand, nor, gates. We saw digital calculators, and music. The CD was a couple years from release but the Pioneer Video disc was already released before Magnavox system decision.

Jeff in Sa-ra-so-ta!

 

[ZantennaG1]

There are still a few dozen stations that utilize stereo, if I recall correctly, such as KCSR. They have a nasty whistler in the background whenever I tune in, but the music (they're country) sounds crisp and good. The lack of a set standard is probably why this never took off, and now we've moved onto IBOC, which is also in decline, apparently. Have to agree with Schrodinger's Cat that the sidebands are screwed up by the signal, however my nearest HD signal on AM is 97 miles away, so some room to work with. Loud sideband noise during the day, but workable signals at night. Would I like to bring back AM Stereo? Yes. Is it realistic? Meh. - ZG

 

[badjef]

There are still a few dozen stations that utilize stereo, if I recall correctly, such as KCSR. They have a nasty whistler in the background whenever I tune in, but the music (they're country) sounds crisp and good. The lack of a set standard is probably why this never took off, and now we've moved onto IBOC, which is also in decline, apparently. Have to agree with Schrodinger's Cat that the sidebands are screwed up by the signal, however my nearest HD signal on AM is 97 miles away, so some room to work with. Loud sideband noise during the day, but workable signals at night. Would I like to bring back AM Stereo? Yes. Is it realistic? Meh. - ZG

I am in a similar boat. We have two AM HDs come on the air, locally, since January. I hope it succeeds but one has the analogue component and the other doesn't.

Both sound great!

But, the one without the analogue decodes in about 3 seconds, whereas the one with, is there after 7 seconds, but the audio is there further with the analogue component. They are from the same location but completely different power and patterns.

The one thing I noticed is that there is none of the "blast you out of your seat" when the HD decodes in a fringe area.

It is a tough call.

Jeff in Sa-ra-so-ta!

 

[gr8oldies]

I may be the only person who doesn't think AM stereo would have saved top 40 radio on AM.

 

[ZantennaG1]

That's definitely an interesting take/situation, Jeff. Do you think going full digital will solve some of our woes?

 

[drt]

I am in a similar boat. We have two AM HDs come on the air, locally, since January. I hope it succeeds but one has the analogue component and the other doesn't.

Both sound great!

But, the one without the analogue decodes in about 3 seconds, whereas the one with, is there after 7 seconds, but the audio is there further with the analogue component. They are from the same location but completely different power and patterns.

The one thing I noticed is that there is none of the "blast you out of your seat" when the HD decodes in a fringe area.

It is a tough call.

Jeff in Sa-ra-so-ta!

Jeff, I had noticed the same thing on my Sangean HD radio; 1470 decodes faster than 1150; both sound in IMO as well. Unfortunately I’ve not been able to receive either on after the sunset power changes from my location; will have to get closer to “Egypt Lake” (Tampa) sometime after dark to check out the nighttime HD.

 

[Kelly A]

I may be the only person who doesn't think AM stereo would have saved top 40 radio on AM.

Trust me, you aren't the only one. Some folks here just suffer from cases of revisionist history.

Majority of the music audience had already left for superior sounding FM stereo by the time AM stereo was being fooled around with. No matter what AM stereo system, FM stereo was/is technically superior. The time to have done AM stereo, would have been in the 50's, to allow for adoption by receiver manufacturers and the general public. Even then, FM would have been superior for reduced noise and fading in a mobile environment, not to mention much better stereo superior separation, frequency response, and lower distortion.

 

[kevtronics]

With Sansui's synchronous detector the muting is reduced if you switch it into mono mode. (Even if it isn't receiving a stereo signal, it still mutes at a higher threshold if you leave it in stereo mode.)

Many 1980s AM Stereo tuners had weak bass response due to the subaudible pilot tone filtering. They should've only filtered the L-R (stereo difference) component instead of L+R as well, but that would've added extra circuitry. With my Realistic TM-152 I bypassed its filtering and connected the output of the C-Quam chip directly to the RCA jacks. With small speakers you don't hear the 25 Hz pilot tone anyway, and with larger speakers, you can use the turntable rumble filter on your amplifier to filter it out without reducing the bass so much.

The Magnavox AM Stereo system was also designed to use the pilot tone to transmit data, like an early form of RDS, but only a handful of stations ever used that system.

 

[gr8oldies]

Trust me, you aren't the only one. Some folks here just suffer from cases of revisionist history.

Majority of the music audience had already left for superior sounding FM stereo by the time AM stereo was being fooled around with. No matter what AM stereo system, FM stereo was/is technically superior. The time to have done AM stereo, would have been in the 50's, to allow for adoption by receiver manufacturers and the general public. Even then, FM would have been superior for reduced noise and fading in a mobile environment, not to mention much better stereo superior separation, frequency response, and lower distortion.

I remember doing a car dealer remote for a dominant FM station. Our AM competitor was touting its AM stereo. I had the keys to one of the cars in the showroom and turned on the AM station. Basically, it sounded like AM with 2 channels.

 

[Kelly A]

I remember doing a car dealer remote for a dominant FM station. Our AM competitor was touting its AM stereo. I had the keys to one of the cars in the showroom and turned on the AM station. Basically, it sounded like AM with 2 channels.

That's the thing. Back when AM stereo was being experimented-with, the bottom line was it sounded different. Some would claim it sounded better, but considering the few receivers on the market amounted to compromise. Unlike FM stereo, AM never stood a comparative chance.
I remember back in the early 2000's, the AM stereo radio in my 1999 Jeep Cherokee used to mistake hetrodyne as an AM stereo pilot, and try to decode AM stereo on a station that wasn't. Ironically, the audio on an AM mono station being decoded by my car radio sounded wider and different, but not much different than the few remaining AM stereo stations within range.

 

[Schroedingers Cat]

Leonard Kahn wrote a lot about stations that were Mono or Kahn AM Stereo "Falsing" into Motorola Stereo when an interference caused audio signal the same frequency as the Pilot was present. He tried putting the pilot in the exciters, but Motorola and the FCC outlawed it. High hat cymbals have enough harmonics at 19 kHz to cause a FM Mono signal to be detected as Stereo. Overmodulation could also do it, as it would throw extra strong harmonics into the audio.

 

[Kelly A]

Leonard Kahn wrote a lot about stations that were Mono or Kahn AM Stereo "Falsing" into Motorola Stereo when an interference caused audio signal the same frequency as the Pilot was present. He tried putting the pilot in the exciters, but Motorola and the FCC outlawed it. High hat cymbals have enough harmonics at 19 kHz to cause a FM Mono signal to be detected as Stereo. Overmodulation could also do it, as it would throw extra strong harmonics into the audio.

Since the pilot tone for AM stereo was 25Hz., it was pretty common for distant stations beating against each other to trick a tuner into hearing a pilot. Sibilant audio or crashing cymbals splattering into an FM stereo 19Khz pilot tone stopped being a problem for FM stereo stations as modern stereo generators were being produced with filters that didn't ring with modern (1970's) audio limiters. FM pilot filters start rolling off a couple db around 13kHz, dropping off over 30db at around 15kHz. As I recall, AM stereo pilot filters started rolling off at 50Hz, and was down around 30db at 30Hz.

 

[kevtronics]

Leonard Kahn wrote a lot about stations that were Mono or Kahn AM Stereo "Falsing" into Motorola Stereo when an interference caused audio signal the same frequency as the Pilot was present. He tried putting the pilot in the exciters, but Motorola and the FCC outlawed it.

The pot calling the kettle black -- Kahn's system suffered from "falsing" too. And the FCC never outlawed transmitting the 15 Hz Kahn pilot tone. After C-Quam became the single standard for AM Stereo, it was still legal to use the Kahn AM Stereo exciter to transmit his "POWER-Side" system (pseudo-single-sideband), and many POWER-Side stations transmitted the 15 Hz pilot tone even though it no longer served any purpose, except to trigger multi-system receivers into Kahn mode, and then the listener would hear one channel much louder than the other.

At 10:09 this video has a sample of 1600 WWRL in New York City transmitting Kahn POWER-Side with the 15 Hz pilot tone in 2012:

p.s. Or maybe you're referring to Kahn's last-ditch plea to make his system the standard, and to transmit both 15 Hz and 25 Hz pilot tones, so that C-Quam receivers would also switch into stereo mode when receiving a Kahn signal? The FCC rejected that idea, because it would not provide a correct stereo image.

 

[192khz]

Back in 1987, I installed C-QUAM in the WQYK-AM (Tampa Bay) transmitters. It really sounded great before we were required to install a 10kHz brick wall audio filter. At the time, the AM station was simulcasting WQYK-FM. The jocks actually liked to listen to the AM station on their headphones because it sounded "bigger." I cheated somewhat by increasing the L+R amplitude modulation so that the station could hit 125% positive modulation without causing too much C-QUAM splatter. Of course, this reduced the stereo channel separation by several dB but the station sounded great!

Maybe a little off topic, but how do you increase the positive modulation on FM?

 

[kfbkfb]

Although Quad (matrix encoded) stereo radio fell out of favor over 40 years ago, one simple way to get surround sound from stereo content is the DynaQuad/Hafler (passive) speaker matrix:

Brian Eno 3 speaker setup, Hafler circuit, etc.

I just watched a new video from Paul/PS Audio () regarding Brian Eno's suggestion to use a 3rd speaker connected to the positive terminals of your amp, placed behind, to play the uncommon audio from both channels, potentially playing audio not heard with a standard 2-speaker setup. Does anyone...

www.audiosciencereview.com

My car has double stereo (L/R front, L/R back), I'm considering rewiring the L/R back to DynaQuad, has anyone done this to get surround sound in their vehicle?


Kirk Bayne