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Kahn Power-Side really does work!

S

satech

1600 WWRL in NYC just recently turned off their Kahn Power-Side, and as a result, here in central NJ I am now hearing nasty sideband phase cancellation that I never heard before. Yay.

And now that Leonard Kahn has passed away and has no heirs (his wife predeceased him, and they had no children), what will become of his patents? Are Symmetra-Peak and Power-Side in the public domain now? I would love to see AM transmitters start coming with built-in Power-Side, or some other equivalent form of SSB AM.
 
I was a firm believer of Leonard's AM Stereo and Powerside technology. I remember back in the late 1980's I ran an overnight test for the National Radio Club on the AM I engineered. I didn't have his fancy Powerside unit connected to our STR-77 but had a split CRL AM Stereo system he gave me instructions on how to adjust the EQ separately on the left and right processors to simulate it. Got some nice comments for the respondents.

I really thought his AM Stereo was technically better than C-QUAM but sadly he lost the battle.
 
The worst thing, unfortunately, was that he was a sore loser.
 
Yes, Powerside does work. It worked especially well under certain conditions. If most of your desired audience was located between the station's 5 and 2 mV contour, it worked wonders by decreasing fading due to re-radiation, because it tended to lessen cancellation of the sidebands being reflected back to the receiver at the same amplitude. One sideband was always stronger. So, it tended to punch through in those areas. Same with improving coverage in directional nulls.

On the downside, back in the days of a tube transmitter, it required readjustment as the tubes in the modulator stage aged. Not a big deal for the increased coverage the Powerside provided. In the solid state days, it became easier to maintain, but less of an advantage, because of the higher modulation density capability of the newer transmitters. In addition, I found that during critical hours, the unbalanced sideband actually seemed to increase the fading effect from a co-channel station (note this was a co channel station running IBOC.) I turned off the power side and let the Optimod do it's work and the co channel effect was reduced significantly.
 
Sometime around the late 80s or early 90s, the loudest AM in Denver was the little known 5 KW daytimer on 1390. Not only was it loud, it was clean. I was so impressed by the sound, I asked an engineer what they were using. It was Power-Side. I wish I had airchecked them when they were using it.
 
You could put an attenuator on it and get it down to 100mW...
 
WNTIRadio said:
You could put an attenuator on it and get it down to 100mW...
Click to expand...

But from what I recall you would still need to modulate it in a traditional sense to get your mono audio. You would use the exciter in place of the transmitter's own oscillator.

When I worked with it in Westport there was an attenuator to interface the Kahn STR-77 with our Harris MW-1 transmitter.
 
WNTIRadio said:
You could put an attenuator on it and get it down to 100mW...
Click to expand...
Technically that wouldn't fly. The DC input to the final amplifier must not exceed 100 milliwatts. A 5 watt final throttled down to 80 milliwatts would produce the same signal level as an efficient part 15 box but would not meet the letter of the law. FWIW, decades ago I had a part 15 AM running 2 ma @ 50V with a 5763 "final" and it lit a #47 pilot lamp hooked to the output. You couldn't read the newspaper with the light but it did illuminate.
 
A curiosity about legal Part 15 AM is that under §15.209, neither the d-c input power to the final r-f stage, nor the radiating length of the antenna matters.

The only thing that does matter under §15.209 setup is that the field intensity it generates 30 meters from its antenna system cannot exceed 24,000/F µV/m, where F = frequency in kHz. So the legal field at 30 meters from such a system operating on 1700 kHz would be about 14 µV/m, which is below the ambient r-f noise floor in most locations outside a screen room. Not much of a "coverage area."

OTOH a system operating in strict compliance with §15.219 must restrict its (unmodulated) d-c input power of the final r-f amplifier to 100 mW, and limit the radiating length of its antenna - including the complete path to an r-f ground - to a maximum of 3 meters.

However an average system operating legally under §15.219 on 1700 kHz can produce a field of about 3 mV/m at a distance of 30 meters, which field is over 200 times greater than permitted by §15.209.
 
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