AM Stereo

[Kelly A]

I never experienced that issue with asymmetrical modulation.

Just one quick clarification on the problem with running asymmetry with (RIP) AM stereo:

The problem with asymmetrical modulation wasn't a transmission problem, but in the CQUAM demodulation. IMD went through the roof when positive peaks exceeded 100%. Also, stereo separation (which wasn't good anyway) L-R reduced significantly when peaks exceeded 100% positive.

 

[Schroedingers Cat]

I think if the truth is told, all the AM Stereo systems sounded better if the antenna frequency response and hence sidebands were close to symmetrical. Since so many of us are frequent listeners in Michigan and the Great Lakes Region, the best sounding AM Stereo stations I ever heard were CKLW 800 (much higher audio frequencies allowed in Canada in addition to much better broadband DA design) and WSAM 1400 (very flat, symmetrical sidebands and nondirectional antenna). When WSM 650 used Kahn and WOWO 1190 used Magnavox, the skywaves were notably better than the other systems. WSM had/has slower ionospheric fading due to its higher wavelength, which helped a lot. Each station facility and situation was different, which also led to its falling out of favor. Then one of the worst blunders ever allowed in radio, the downgrading of WOWO to 9.8 kW Night Class B, occurred, which made AM Stereo useless at Night in its former protected skywave area.

 

[ContinuousWave]

Let's take this in order, shall we?

1. AM Stereo failed miserably. By the time Motorola was chosen, it was too late for any audience to care. Music listening had already migrated to FM by then. Leonard Kahn was a big reason AM stereo was delayed. He filed nuisance lawsuits in an attempt to force the Commission to delay a choice of something other than his system. If you want to place blame, one needs to look no further than Leonard. Combine all the aforementioned, with poor and inconsistent audio quality that couldn't come close to matching FM stereo and AM Stereo was doomed from the get-go.

2. AM Stereo has no place anymore, not that it had one to begin with. There are no new receivers being sold or provided in vehicles. No distribution=no interest. AM listeners are a dying breed, literally.

3. You're right about one thing: Consumers don't care where the data comes from to their cell phones. All they know is how to operate it. But, going back to what a consumer would want or not; if the an average consumer heard music on AM, even in stereo, it would be rejected because of the poor overall quality and excessive noise floor.

Regarding your comment about having heard AM Stereo, I absolutely have. I've installed (and removed) more systems over the years when AM stereo was sort of a thing for broadcasters, than you have, guaranteed. I was even involved in some of the original testing and evaluation of ISB and CQUAM. Compared with digital audio sources you can even store or stream via your phone these days? AM stereo sounds horrible.

Years ago I worked with Bob Carver on development of his rather high end AM/FM stereo tuner. As Bob put it, 'AM stereo was a complete waste of a year in R&D'. Much of that statement was because of the lack of consistency in stereo exciter interface to the various transmitter models. Differences in antenna systems. Program Directors insisting on running asymmetrical modulation.

So honestly, you can self-revise history all you want. AM stereo was/is a complete failure across the board.

Now, can we please return to the 21st Century and talk about AM digital? If you want to have a debate, let's at least debate something real and in current times.

AM stereo sounds horrible?? Huh???
Listen to the WION stream off their AM stereo monitor...AM sounds fuller and richer than FM stereo...also the WLS Rewind audio here, WLS REWIND audio (missing 6pm hr on 2008) - Google Drive is off the Cquam studio monitor..tell me again it sounds horrible.

 

[Kelly A]

AM stereo sounds horrible?? Huh???
Listen to the WION stream off their AM stereo monitor...AM sounds fuller and richer than FM stereo...also the WLS Rewind audio here, WLS REWIND audio (missing 6pm hr on 2008) - Google Drive is off the Cquam studio monitor..tell me again it sounds horrible.

If "fuller and richer" you mean distortion, then I'm sure it does. Let's take a look at numbers on both sides:

CQUAM AM stereo: Frequency response: 80hz-10kHz. (actually, rolls off significantly starting at 6Khz) If you can't hear frequencies above 8kHz, you have hearing loss. Stereo separation: -30dB in lab conditions, but more likely -10 to-15dB (varies with modulation) Distortion: Depending whether running asymmetrical modulation, can exceed 20% THD. IMD typically around 40%. s/n: -30dB.

Analog FM stereo: Frequency response: 50Hz-15kHz. (starts to roll off significantly around 13kHz) Stereo separation: -50 to -55db, (doesn't vary with modulation). Distortion: without aggressive audio processing, <.5% THD. IMD typically around 2%. s/n: -70dB.

And in both cases, these measurements would be read off a modulation monitor, which doesn't account for reception factors that could worsen the measurements in the field.

 

[frankberry]

If "fuller and richer" you mean distortion, then I'm sure it does. Let's take a look at numbers on both sides:

CQUAM AM stereo: Frequency response: 80hz-10kHz. (actually, rolls off significantly starting at 6Khz) If you can't hear frequencies above 8kHz, you have hearing loss. Stereo separation: -30dB in lab conditions, but more likely -10 to-15dB (varies with modulation) Distortion: Depending whether running asymmetrical modulation, can exceed 20% THD. IMD typically around 40%. s/n: -30dB.

Analog FM stereo: Frequency response: 50Hz-15kHz. (starts to roll off significantly around 13kHz) Stereo separation: -50 to -55db, (doesn't vary with modulation). Distortion: without aggressive audio processing, <.5% THD. IMD typically around 2%. s/n: -70dB.

And in both cases, these measurements would be read off a modulation monitor, which doesn't account for reception factors that could worsen the measurements in the field.

Sorry but your C-QUAM specs are incorrect. I had slightly less than 40dB separation and a L+R frequency response from 30Hz to 15kHz (before I had to add the 10kHz brick wall filter). You are also incorrect about your previous statement about asymmetrical modulation. There is absolutely nothing which prevents C-QUAM from passing it cleanly.
We know that you do not like AM Stereo. It is an antiquated system but please stop beating the same old dead horse.

 

[Kelly A]

I think if the truth is told, all the AM Stereo systems sounded better if the antenna frequency response and hence sidebands were close to symmetrical. Since so many of us are frequent listeners in Michigan and the Great Lakes Region, the best sounding AM Stereo stations I ever heard were CKLW 800 (much higher audio frequencies allowed in Canada in addition to much better broadband DA design) and WSAM 1400 (very flat, symmetrical sidebands and nondirectional antenna). When WSM 650 used Kahn and WOWO 1190 used Magnavox, the skywaves were notably better than the other systems. WSM had/has slower ionospheric fading due to its higher wavelength, which helped a lot. Each station facility and situation was different, which also led to its falling out of favor. Then one of the worst blunders ever allowed in radio, the downgrading of WOWO to 9.8 kW Night Class B, occurred, which made AM Stereo useless at Night in its former protected skywave area.

But that's the thing, we're discussing a moot point. AM as a medium is fading away. GM announced that their cars in 2035 will be all electric. Do you think other manufacturers will follow? Of course they will. The switching speed controllers emit too much RFI for AM to survive in electric cars. The best sounding AM station to modern consumers is like saying: A particular brand of cat litter tastes better to you than another brand of cat litter. In reality, very few people would eat cat litter because everyone assumes it just tastes bad. Which, I imagine, it does.

For the sake of discussion let's assume that every AM station had perfectly 50ohm J0 common point impedance across 30kHz, had no traps or phasing in their antenna system, had a transmitter which was designed for an AM stereo exciter, no asemmetrical modulation peaks (not average) not exceeding +-100%, the specifications I listed above, might be obtainable. The fact remains, very few stations would voluntarily even be able to meet those requirements. That's one of the technical reasons AM stereo was/is inferior. The other is simple: FM stereo is just better across the board.

 

[Kelly A]

Sorry but your C-QUAM specs are incorrect. I had slightly less than 40dB separation and a L+R frequency response from 30Hz to 15kHz (before I had to add the 10kHz brick wall filter). You are also incorrect about your previous statement about asymmetrical modulation. There is absolutely nothing which prevents C-QUAM from passing it cleanly.
We know that you do not like AM Stereo. It is an antiquated system but please stop beating the same old dead horse.

During my time working with Bob Carver, we visited and measured around 12 stations who were running Magnavox or Motorola systems. None of them had better specs than I posted.

The asymmetrical modulation caused the receiver chips to distort, not the transmission side. Just as in any discussion, you have different views than I do as to whether AM stereo is still a thing. Doesn't mean it is.

 

[frankberry]

During my time working with Bob Carver, we visited and measured around 12 stations who were running Magnavox or Motorola systems. None of them had better specs than I posted.

The asymmetrical modulation caused the receiver chips to distort, not the transmission side. Just as in any discussion, you have different views than I do as to whether AM stereo is still a thing. Doesn't mean it is.

Okay. Let's agree to disagree. I know how my station performed when running C-QUAM.

 

[ContinuousWave]

Okay. Let's agree to disagree. I know how my station performed when running C-QUAM.

Mine too....the DAX3 sounded damn good driven by the Motorola 1300 exciter...I had Greg Buchwald of Motorola's Cquam design team giving me advice and hints..my station beat the pants off my FM competitor in audio quality

 

[tvnut]

Do any stations in the Chicago area still broadcast in C-QUAM? I never had an AM stereo radio (was tempted to get one but was always fiddling with video during the C-QUAM rollout). I'm sure I could pick one up on eBay if there was something I could hear.

 

[fybush]

Do any stations in the Chicago area still broadcast in C-QUAM? I never had an AM stereo radio (was tempted to get one but was always fiddling with video during the C-QUAM rollout). I'm sure I could pick one up on eBay if there was something I could hear.

Nope. WLS may have been the last, when the late Warren Shulz still maintained the transmitter site, and I don't think there was actually much stereo content in the talk format even then.

If any of my clients ask about AM stereo, I tell them there's no business model in it. Want to do it as a science experiment or a weekend project? Go and have fun - but unless most of your audience is tooling around in 1986 Chrysler and GM high-end models, nobody's going to be able to hear it. The HD tuners that supposedly decode C-QUAM don't do it very well, with channels reversed and very limited audio bandwidth. And while some modern transmission chains can encode C-QUAM, I don't know how well they do it, either, compared to the classic gear from the 80s (which I wouldn't want to put in any sort of mission-critical use now that they're over 30 years old.)

 

[tvnut]

Scott, thanks. Interesting that all the gear in the WLS transmitter building is as modern as can be, but the Prairie Farmer-era WLS logo with the lightning-bolt typeface (for lack of a better term) remains above the door. Old-school.

 

[badjef]

Scott, thanks. Interesting that all the gear in the WLS transmitter building is as modern as can be, but the Prairie Farmer-era WLS logo with the lightning-bolt typeface (for lack of a better term) remains above the door. Old-school.

It is a tie to the past.

"Learn and remember how you got here, you will appreciate being here much more!" - me

Jeff in Sa-ra-so-ta!

 

[kevtronics]

Not under FCC rules...only Cquam is legal...and it's better than Kahn ever was..

Actually all of the systems are still legal to use, just as long as they are not transmitting stereo audio. That's how Kahn Power-Side remained legal to use, because although it is based on the Kahn AM Stereo system (even including the 15 Hz pilot tone), the content of the two audio channels is the same, just with differences in modulation level and frequency response, to focus most of the station's power on one of the sidebands (hence the name).

Speaking of which... are there any stations still using Power-Side? Anyone doing so would need to be really dedicated to keep the equipment on the air, because Mr. Kahn never published any schematics or service manuals, as he was paranoid about competitors copying his inventions. He kept Motorola in court well into the late 1990s, accusing the C-Quam system of violating his patents. In his dying days, he even sued iBiquity, also accusing the IBOC/HD Radio system of patent violation.

 

[Kelly A]

Speaking of which... are there any stations still using Power-Side? A

Far as I know, KSL was the last station to have Powerside on the air. Since radios went to one-chip software defined center-tuned receivers, a station putting more energy into one side band or the other, would have no tangible benefit.

 

[kenglish]

KSL scrapped PowerSide years ago, probably about the time they got rid of the Dougherty.
IIRC, the main reason it was used at KSL was to overcome interference from some of the new stations that started popping up on 1160.

 

[ContinuousWave]

Actually all of the systems are still legal to use, just as long as they are not transmitting stereo audio. That's how Kahn Power-Side remained legal to use, because although it is based on the Kahn AM Stereo system (even including the 15 Hz pilot tone), the content of the two audio channels is the same, just with differences in modulation level and frequency response, to focus most of the station's power on one of the sidebands (hence the name).

Speaking of which... are there any stations still using Power-Side? Anyone doing so would need to be really dedicated to keep the equipment on the air, because Mr. Kahn never published any schematics or service manuals, as he was paranoid about competitors copying his inventions. He kept Motorola in court well into the late 1990s, accusing the C-Quam system of violating his patents. In his dying days, he even sued iBiquity, also accusing the IBOC/HD Radio system of patent violation.

Incorrect...use of any stereo system,including the pilot, but even with mono audio,is illegal. Powerside did not use the pilot but transmitted L+R in both sidebands. Thus it was not stereo. Use of Magnavox, Harris or Kahn in the stereo mode is illegal period, or with mono audio but the pilot still present is also Illegal.

KCRM in Beaumont TX ran Powerside...what a waste of money...since radios are primarily envelope detectors with no selection of sideband rejection, noone could use Powerside as designed. It taken off after a year...no range increase, etc...it wasn't needed on 1380 as there was no adj channel issues with it anyway. Kahn even conned KCRM into running Cam-D...another waste of money...

 

[Kelly A]

Incorrect...use of any stereo system,including the pilot, but even with mono audio,is illegal. Powerside did not use the pilot but transmitted L+R in both sidebands. Thus it was not stereo. Use of Magnavox, Harris or Kahn in the stereo mode is illegal period, or with mono audio but the pilot still present is also Illegal.

KCRM in Beaumont TX ran Powerside...what a waste of money...since radios are primarily envelope detectors with no selection of sideband rejection, noone could use Powerside as designed. It taken off after a year...no range increase, etc...it wasn't needed on 1380 as there was no adj channel issues with it anyway. Kahn even conned KCRM into running Cam-D...another waste of money...

Yep, technically same goes with FM stereo. If you broadcast mono audio, you're supposed to turn off the pilot.

One can still broadcast in Motorola CQUAM AM stereo, but the audio must be stereo. The other systems, including Kahn and Magnavox, were tested under a special STA back in the day. Stations can no longer use those systems on the air without filing, and getting approval, for an STA to test a system on the air. Not that there would ever be a reason to....

 

[ncradioeng]

WPIP 880 in Winston-Salem, NC still runs the Powerside.

 

[Kelly A]

WPIP 880 in Winston-Salem, NC still runs the Powerside.

Guess the question is: why?