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R.I.P. Leonard Kahn, father of AM Stereo

Too bad his AM stereo system was never set as the standard. No platforming at night like C-QUAM. If you've ever listened to a C-QUAM station on skywave you know what I'm talking about...
 
C-Quam did (and still does!) just fine on skywave, as this video aircheck will attest:

http://www.youtube.com/watch?v=Wm_iYK-ctiQ

Actually that was Magnavox AM Stereo hacked to use a 25 Hz pilot tone in order to trigger C-Quam receivers into stereo mode, but true C-Quam would work just as well, if not even better.

It is when a co-channel skywave signal comes in at night underneath a local signal and causes a beat between the two carriers, that C-Quam can get wobbly. The newer Motorola decoder chips detect this condition and will gracefully blend to mono.

Crawford's AM Stereo stations (before they walked the plank for HD Radio) also took the approach of purposely moving their carrier far enough off-center (but still within FCC specs) that the beat frequency between the local and distant carriers caused a fast fluttering effect, rather than a slow phase shifting, and thus effectively eliminated platform motion even on an older receiver using the original MC13020 C-Quam decoder chip.
 
The Kahn system traded potential Platform Motion for unequal noise in the two audio channels. An adjacent channel signal would produce a 10kHz whistle on the sideband which was closest to the adjacent channel. I found that more annoying than the potential for platform motion (which I never experienced).
Nonetheless, Leonard Kahn deserves a lot of respect for his dedication to the industry.
 
boiseengineer said:
I perceived the motion in the Kahn system to spin around my head where C-QUAM would go side to side.
Click to expand...

Selective sideband fading. The perceived spinning would be very annoying.
 
This is very interesting to me, because one of Kahn's many inventions, Envelope Elimination and Restoration (EER), was the subject of my Master's degree research report (thesis) in 1973. I designed, constructed, and tested an EER SSB amplifier for use on the the 2-meter ham band.

I found Kahn's seminal article on EER by looking through old copies of the Proceedings of the IRE in the library of the company where I worked at the time. He was only 23 years old when he wrote this article. I recently discovered that the university I attended has posted my Master's thesis on the Web.
 
Ermi Roos said:
This is very interesting to me, because one of Kahn's many inventions, Envelope Elimination and Restoration (EER), was the subject of my Master's degree research report (thesis) in 1973. I designed, constructed, and tested an EER SSB amplifier for use on the the 2-meter ham band.

I found Kahn's seminal article on EER by looking through old copies of the Proceedings of the IRE in the library of the company where I worked at the time. He was only 23 years old when he wrote this article. I recently discovered that the university I attended has posted my Master's thesis on the Web.
Click to expand...


Ermi,

did your ham license expire in April?


73
 
Condolences to Mr Kahn's family. There was much good he did but as someone who worked in AM radio in the eighties and early nineties I can't help to still be frustrated. It was his foot stomping and "I'm going to sue" attitude that held up AM stereo instead of just accepting that his system wasn't chosen.
 
When Kahn first proposed his AM stereo system in the early 1960s, the FCC rejected it because they wanted FM to catch on and they thought AM stereo would slow FM adoption. 20 years later when AM was already on death's doorstep, the FCC finally agreed to adopt AM stereo in an effort to allow AM to compete. Would early adoption of AM stereo have made a difference? In the long run, I really doubt it. Fidelity and noise immunity are what make FM a winner. Low fidelity AM stereo just does not sound like FM. It just sounds like AM from two speakers. Despite Kahn, plenty of AM stereo radios were available in the 80s. I had a factory installed AM stereo radio in my '86 Chevy, but the FM still sounded way better because the wideband stereo mode was only 6kHz. I still have a Sangean "Walkman" style AM stereo radio in a drawer somewhere.

The battle was lost when the public realized that FM sounded better, with or without stereo. Along about the same time, broadcasters started programming FM for the public. Previously, FM had been considered a non-starter that would never amount to anything, so broadcasters had put elevator music or something equally inane on it. As soon as good programming appeared, the medium took off and never looked back.

Kahn's ire really was more of a tempest in a teapot than a real concern for the industry. It is a shame that the FCC's social engineering delayed AM stereo for 20 years. AM might have hung in there a little longer and Kahn's life and fortunes would have been very different. In the end, though, FM would still have dominated.
 
Reply to RadioFan2J3:

My ham license was, indeed, scheduled to expire in April, but I renewed it before the expiration date. In addition, I applied for a vanity call sign in May, and it was assigned on June 12. My current license will expire June 12, 2022.

Thank you for asking.
 
AM Stereo has now entered the hobbyist arena, with a low-power Part 15 transmitter kit available:

http://www.youtube.com/watch?v=ZTUjdQBr7Cg

The kit transmits a C-Quam signal, but if you apply a 90-degree phase shift to the audio and change the pilot tone frequency to 15 Hz, you could get it to work as a Kahn/Hazeltine ISB AM stereo transmitter as well. In fact, that is basically how Kahn's later STR-84 exciter worked, by using phase modulation to produce a pseudo-ISB signal, rather than his older exciter design which directly transmitted onto the lower and upper sidebands, and was very difficult to re-tune to a different frequency than what the exciter was originally built for.
 
Ermi Roos said:
Reply to RadioFan2J3:

My ham license was, indeed, scheduled to expire in April, but I renewed it before the expiration date. In addition, I applied for a vanity call sign in May, and it was assigned on June 12. My current license will expire June 12, 2022.

Thank you for asking.
Click to expand...

Well, I was looking for your EER writings and found the ham call, and curious, and the ham call database had you with an expired license. Guess that shows that database a few months out.

Wasn't trying to snoop, but with the ten year ham licenses, sometimes the expirations can sneak up on someone.

Re Leonard Kahn, VOA Greenville had several Khan developed units which allowed the AM transmitters to generate an SSB with carrier signal, so the transmitters could be used in the utility bands as point-to-point program feeders. They were primarily used with the Gates HF-50 transmitters, but that was long ago and far away.
 
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