AM Stereo

[Schroedingers Cat]

Most people with IQs North of 130 (The IQ of the average Ph.D. Electrical Engineer) tend to be that way, at least a little bit. But where would we be without them? Living in huts. Only Tiki torches for light. Cooking with fire. Horse drawn wagons for transportation. No radio, TV, recorded music, or computers. He was probably picked on by his peers in school. In later life, the same bullies got into legal battles with him. "Makes a fellow mean"-Burl Ives lyric.

 

[Kelly A]

Leonard Kahn tried to only seek out stations that already sounded good in Mono as I recall.

Leonard would seek out any station that would listen to his drivel. If you questioned his claims, he would hate your guts for life.

Stations that already sounded good in Mono tended to sound better in Stereo than stations that sounded bad in Mono. I seem to remember that the vast majority of Kahn stations were nondirectional or DA-N.

Some were night DA's but the audio performance suffered (even more) when phasors and ATU's were involved.

 

[Kelly A]

Sorry for moving this thread off topic a bit, but I really wish Kahn would have been more open to speaking about some of his ideas, explaining more about some of his theories and maybe even teaching younger engineers and imparting knowledge.

Leonard never held back speaking his mind, or about his ideas. It basically boiled down to: Everyone else is an idiot, and he's the only one who can fix radio. As was later discovered, most of Kahn's accomplishments were mainly smoke and mirrors. One of the reasons his ISP stereo system didn't pass muster, as compared with CQUAM systems. Truth be told; Magnavox had the superior system. Kahn, himself, just made a lot of noise and filed lawsuits. One of the many reasons why no receiver manufacturers would build a truly ISB compatible tuner: Because the actual performance of the Kahn system wasn't very good.
Companies were willing to invest in Kahn, even offering to help him tune up his design and assist with the manufacturing process. But just like someone who knew his system wasn't as good as he claimed; Kahn went all aggressive; cursing-out and threatening to sue anyone that tried to help.

Unfortunately by the time I got into the radio business, Kahn had by that time become combative, defensive (maybe he was always that way to an extent and it just became more noticeable or was reported on by industry trades more often), he had basically stopped speaking with industry publications like Radio World, was smarting from the CAM-D vs. IBOC vs. C-QUAM battles and seemed suspicious of most everyone.

Unless you agreed with everything he said and kissed his a$$, he would be your new best friend. It got to the point where he was like Nasty Edwin. Nobody wanted to play with Leonard. This started back when he was an engineer with RCA.

Sadly, he seemed like a brilliant guy, or someone who was definitely able and willing to look at things in a different way or think outside the box and had he been willing to teach others, the radio industry may have benefited.

He was a brilliant guy, but not always. ISB stereo was a flim flam project, and he knew it.

 

[Schroedingers Cat]

Call 516-222-2222. As I recall. Was it ever 212-222-2222?

It was impossible to create a truly independent sideband waveform, in my understanding. It's like FM requires an infinite number of sidebands (Fourier Analysis) to create the waveform.

 

[DavidEduardo]

Leonard would seek out any station that would listen to his drivel. If you questioned his claims, he would hate your guts for life.

I made the "mistake" of saying that he accelerated the death of AM by a decade or more when he objected through legal action to the FCC decision on AM stereo; he caused a narrow window of opportunity to be lost.

And when I had removed his Symetrapeak(dp)* from a NYC station, word got back to him and I was eternally damned.

"dp" is "dumb patent"

Some were night DA's but the audio performance suffered (even more) when phasors and ATU's were involved.

I remember the early tests of AM stereo where you would put two different radios on each side of a room and tune to the sidebands. If you don't think that such a contraption thoroughly confused the average listener, you don't understand "lowest common denominator".

 

[Kelly A]

I made the "mistake" of saying that he accelerated the death of AM by a decade or more when he objected through legal action to the FCC decision on AM stereo; he caused a narrow window of opportunity to be lost.

I don't think making that statement would be considered a mistake. Listeners were already flocking to FM in droves, but Leonard didn't do the band any favors by stalling deployment of any AM stereo system.

And when I had removed his Symetrapeak(dp)* from a NYC station, word got back to him and I was eternally damned.

I never thought the Symmetrapeak was much of an improvement either. The claim was some of the old high level plate transmitters benefited from the device being in line. I never saw it

I remember the early tests of AM stereo where you would put two different radios on each side of a room and tune to the sidebands. If you don't think that such a contraption thoroughly confused the average listener, you don't understand "lowest common denominator".

Yeah, that was part of the gimmick, but that's all it was.

 

[Schroedingers Cat]

Simplest case of Kahn System causing phase modulation of main carrier. That makes it most like the Magnavox system, which phase modulates the main carrier with L-R within one Radian.

Carrier frequency 1000 kHz, 1000 watts. Vector magnitude 1.
Audio sideband for 1000 Hz at 1001 kHz, 250 watts. Vector magnitude 0.5. 100% modulation for this channel.

An audio vector spins clockwise which is one half the magnitude of the carrier. At the beginning of the full cycle, the magnitude is 1.5, the carrier phase shift is zero. At half cycle, the magnitude is 0.5, the carrier phase shift is also zero. At one quarter cycle, the magnitude is SQRT (1.25), the phase shift is Arctangent (0.5)= 26.6 degrees. At three-quarter cycle, the magnitude is SQRT (1.25), the phase shift is Minus Arctangent (0.5)=Minus 26.6 degrees. Since one radian is approximately 57.3 degrees, Kahn would seem to be very similar to Magnavox without the pilot frequency, with a slight difference in the magnitude of phase modulation.

This would be detected as 1000 Hz in one channel, no audio in the other channel.

Next simple case.

Carrier frequency 1000 kHz, 1000 watts. Vector magnitude 1.
Audio sideband for one sideband for 1000 Hz at 1001 kHz, 250 watts. Vector magnitude 0.5.
Audio sideband for other sideband for 1000 Hz at 999 kHz, 250 watts. Vector magnitude 0.5.

Audio vectors spin in opposite directions, one CW, one CCW. The perpendicular vector phase shift cancels at each point in the cycle, resulting in zero phase shift at each point in the cycle.
Vector magnitude at beginning of cycle, 2.
Vector magnitude at 1/4 cycle, 1.
Vector magnitude at 1/2 cycle, 0.
Vector magnitude at 3/4 cycle, 1
Audio vector is identical to 100% AM modulation at 1 kHz, and is in both channels equally.

 

[semoochie]

Simplest case of Kahn System causing phase modulation of main carrier. That makes it most like the Magnavox system, which phase modulates the main carrier with L-R within one Radian.

Carrier frequency 1000 kHz, 1000 watts. Vector magnitude 1.
Audio sideband for 1000 Hz at 1001 kHz, 250 watts. Vector magnitude 0.5. 100% modulation for this channel.

An audio vector spins clockwise which is one half the magnitude of the carrier. At the beginning of the full cycle, the magnitude is 1.5, the carrier phase shift is zero. At half cycle, the magnitude is 0.5, the carrier phase shift is also zero. At one quarter cycle, the magnitude is SQRT (1.25), the phase shift is Arctangent (0.5)= 26.6 degrees. At three-quarter cycle, the magnitude is SQRT (1.25), the phase shift is Minus Arctangent (0.5)=Minus 26.6 degrees. Since one radian is approximately 57.3 degrees, Kahn would seem to be very similar to Magnavox without the pilot frequency, with a slight difference in the magnitude of phase modulation.

This would be detected as 1000 Hz in one channel, no audio in the other channel.

Next simple case.

Carrier frequency 1000 kHz, 1000 watts. Vector magnitude 1.
Audio sideband for one sideband for 1000 Hz at 1001 kHz, 250 watts. Vector magnitude 0.5.
Audio sideband for other sideband for 1000 Hz at 999 kHz, 250 watts. Vector magnitude 0.5.

Audio vectors spin in opposite directions, one CW, one CCW. The perpendicular vector phase shift cancels at each point in the cycle, resulting in zero phase shift at each point in the cycle.
Vector magnitude at beginning of cycle, 2.
Vector magnitude at 1/4 cycle, 1.
Vector magnitude at 1/2 cycle, 0.
Vector magnitude at 3/4 cycle, 1
Audio vector is identical to 100% AM modulation at 1 kHz, and is in both channels equally.

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.

 

[Schroedingers Cat]

Since Magnavox was touted to phase modulate the carrier, maybe the Fourier analysis sidebands that generate the waveform went far outside the bandwidth, like FM. WOWO used Magnavox, and it sounded stable like Kahn did in the presence of fading, as opposed to the platform motion from fading and interference with Motorola, which was a real phenomena. Really, all the systems were quite good, and had immediate acceptance, didn't interfere with adjacent channels, and had the analog sound that people continue to buy vinyl records for. As practiced and configured, AM IBOC sounds harsh by comparison. I gladly give up higher audio frequencies for a mellower sound.

 

[Schroedingers Cat]

Call 516-222-2222. As I recall. Was it ever 212-222-2222?

I "missed it by that much". It was 516-222-2221. Maybe the FAX was 516-222-2222?

 

[Kelly A]

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.

There was technically nothing wrong with the Magnavox system. It was the superior system when chosen by the Commission. When Kahn started filing lawsuits, and Motorola objected to the decision, the Commission felt the fight as to their choice wasn't worth the effort. That's why they went to 'The Marketplace' to decide. By the time this all happened, Magnavox was on the ropes from overseas electronics manufacturers for products that actually made money, like TV's and appliances. It was decided the whole AM stereo thing by that time would no longer be of any consumer interest, combined with Leonard naming them in several lawsuits, Magnavox bowed out of the competition. They were smart to have done so. AM for music, and stereo in particular, was a non-event by then. There was zero chance of AM stereo changing consumers minds about where they listen to music.

 

[Schroedingers Cat]

The reason WSM sounded so good with the Kahn System was the antenna response, superior processing, and the long wavelength at 650 kHz which fades quite slowly. A well chosen station. I read about the extreme measures necessary to install Motorola on 1940s DA installations.

 

[awsherrill]

There was technically nothing wrong with the Magnavox system. It was the superior system when chosen by the Commission.

I recall reading some reports that the Magnavox system caused audible "popping" noises when negative modulation approached 99%. I don't know if that had anything to do with the Commission deciding to rescind their choice.

 

[Kelly A]

I recall reading some reports that the Magnavox system caused audible "popping" noises when negative modulation approached 99%. I don't know if that had anything to do with the Commission deciding to rescind their choice.

As I understand it, the decision had nothing to do with technical reasons. Magnavox backed out of the running because they were chosen, then when the fur started flying, the Commission decided the marketplace should decide which system. Magnavox essentially said to just forget it. Not worth the effort.

 

[semoochie]

I recall reading some reports that the Magnavox system caused audible "popping" noises when negative modulation approached 99%. I don't know if that had anything to do with the Commission deciding to rescind their choice.

Yes, that was it, pops and possibly, ticks.

 

[DavidEduardo]

Yes, that was it, pops and possibly, ticks.

Can't resist...

This is excellent for ticks. Sprinkle in the transmitter room.

 

[Schroedingers Cat]

I remember the DJ at WOWO (Magnavox AM Stereo) announcing that their engineer had gone out to sweep the mice out of the transmitter.

 

[Kelly A]

Yes, that was it, pops and possibly, ticks.

Don't close the envelope, and it wouldn't be a problem.

 

[kevtronics]

Harris had the best AM Stereo system. The synchronous detector their system required makes AM sound amazingly clean, with no "Daffy Duck" effect during selective fading and no need to limit modulation to 95% to keep it from becoming grunge city. But receiver manufacturers balked at the cost of implementing it, and the FCC threw a fit because it caused too much distortion on ordinary mono receivers, even though that distortion actually helped to brighten the sound of narrowband tuners.

Harris was also the only AM Stereo system which did not increase sideband splatter at all compared to mono. Kahn liked to blame the C-Quam system for splattering so much that it led to the NRSC audio bandwidth restriction, but in reality the Kahn system couldn't have any stereo separation above 5 kHz or its splatter would exceeds FCC limits as well.

 

[TomásEstefan]

Harris had the best AM Stereo system. The synchronous detector their system required makes AM sound amazingly clean, with no "Daffy Duck" effect during selective fading and no need to limit modulation to 95% to keep it from becoming grunge city. But receiver manufacturers balked at the cost of implementing it, and the FCC threw a fit because it caused too much distortion on ordinary mono receivers, even though that distortion actually helped to brighten the sound of narrowband tuners.

Harris was also the only AM Stereo system which did not increase sideband splatter at all compared to mono. Kahn liked to blame the C-Quam system for splattering so much that it led to the NRSC audio bandwidth restriction, but in reality the Kahn system couldn't have any stereo separation above 5 kHz or its splatter would exceeds FCC limits as well.

Back in the 80's I had a Sansui AM stereo/FM stereo home tuner that had a synchronous detector for the purpose you describe. This tuner received and decoded all the systems, with a couple of significant problems, one of which was inexplicable. Both the AM and FM sections had a muting circuit. This worked beautifully on the FM side, if you activated it there was no hiss/noise as you tuned across the FM band looking for a station. On the AM side, however, it was always on, (the muting button would not turn it off) the big problem with this is that if you were listening to a station that would go into selective fading - instead of getting a nice clear signal your audio would mute off. Many times when there is selective fading only the carrier is lost so the signal is still very strong, but very distorted since there is no carrier to demodulate. So the muting circuit thinks there's no signal so it mutes off - entirely defeating the purpose of the synchronous detector. It asked Sansui about this but they had no answer. Moreover, the AM band audio's bass response was rolled off at probably 200 Hz (for this they said it was to avoid interference with the stereo pilot signals, certainly there was another way around this...