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Wednesday, February 5, 2014

AM Revitalization

This one's a little tech and a lot of history...

It was the late 50’s.  Yes that would be the nineteen-50’s.  Living about a mile away from a set of radio towers, I ran a four- or five-foot length of wire to one end of a crystal diode, came out of the diode with a .01 to ground and into our Webcor® tape recorder. 
This rig gave me some of the best recording off-the-air that I’ve ever had.  The station happened to be “beautiful music” – yes, on AM – and I think my parents liked it more than I did.  Ah, Sinatra, Clooney, Chris Conner.  Perfection, except for the occasional dropout; you could tell when the transmitter op was reading base or common point currents.  
Alan Freed
Alan Freed
(courtesy R&R Hall of Fame)
 About that time, Alan Freed at WJW (and later, WINS), Murray “The K” Kaufmann at WINS, along with Cousin Brucie, Dick Biondi, Charlie Tuna, Robert Morgan, Larry Lujack and Wolfman Jack were driving those blowtorches up to peak power outputs of over 300 kilowatts1 as Elvis, Buddy Holly, Fats Domino, The Beatles and many, many more made their impact on America.  
Somehow, we all began to believe that louder was better.  And I participated first hand, as part of more than one rock group, in the great speaker proliferation of the ‘60’s.  If you went on a gig without at least 4 columns and double sets of speakers (one or two heads, didn’t matter) for each of Leo Fender’s Showman and Bassman and, later, Ampeg’s SVT amps in use, you were amateurs.  Nobody had enough amp power for all those speakers so they were overdriven.  

Robert W. Morgan
Robert W. Morgan
(courtesy R&R Hall of Fame)
Of course the flattopping blew a lot of voicecoils but speakers were cheap.  And, besides, it was quantity, not quality.

 Aside:  Kudos to Ampeg who did, in fact, print warnings about hearing damage. Like any of us paid attention to that.  
Well, overdriving amps became the norm.  First, for loudness but as we became accustomed to the sound, we liked it.  Witness the stomp boxes specifically designed to create distortion.  Usually a preamp, a couple of diodes across the line and a simple amp to overdrive the input of the power amp.  Who knew a 12AX7 could draw grid current.

I know, I know…AM revitalization…
Fender Showman Amp, 1960
Leo Fender's "Showman" Amp
(Fender Catalog, 1960)
The music was getting louder.  And so were radio stations.  “Better” compressors, limiters that flat-topped without too much overshoot, and positive modulation peaks up to 125 percent2 started the loudness war, I think to see which station could drive the voice coil of a Delco® speaker up out of the dash and through the windshield of that ‘56 Chevy.  Oh, and don’t forget the reverb.  There were stations with Hammond organ reverbs functioning in the signal chain full time.
One tech I know commented that if the jock ever stopped talking, he would have been sucked into the microphone and pushed out the antenna by the signal processing.
So the loudness war continued.  And, as it did, three additional things happened:
·        The Japanese 7 transistor radio debuted.  (some used 8 but the 8th was really used as the envelope detector, as such, a two-terminal diode, but the FTC didn’t police the “8” claim)
·        More AM stations came on line as a result of rules changes and better directional array design
·        FM Stereo was launched

The portable radios and additional stations worked negatively in tandem.  More stations plus the high levels of modulation, often trying to exceed 100 percent negative and creating lots of splatter, meant it was harder to avoid interference.  Because of that and the inexpensive design of the radios, the IF’s in those little 9v battery eaters were very narrow.  That meant poor high frequency response.  Of course, the 1½ inch speaker had great bass response, maybe down to around 300 Hz.
Len.  I mean it.  AM Revitalization!
OK.  Next came singles – 45’s – pressed in stereo.  Now there’s a marketing difference for a radio station.  Well, an FM station. 
Since ’61, FM had had stereo capability courtesy of Zenith and GE.  The early transmissions were more novelty than music.  A ping pong match with the ball going across the listening panorama or an orchestra but with each instrument mixed hard left or right and no center information.  But music made its way onto FM and kiddies followed.  I think it was a lot like UHF television.  Nobody would buy a converter to tune UHF but after the all-channel act, it was the kids who found it first.
And such was the case with FM.  Easy listening on the 50+ side and rock & roll for 12 to 34.  And the listenership ratio of AM to FM began to tilt to FM.  AM looked for new formats.  All news, “oldies” (though not that old at the time), and a bit of news talk.  When the Fairness Doctrine went away in 19873, it was off to the races for AM talk radio.  It was perfect.  AM listenership skewed older and the content – human voice – matched the low response medium.
Along the way, people grumbled about AM’s frequency response.  While most stations were transmitting flat well beyond 10kHz4, the receivers, totally out of control of the FCC, got worse.  With television growing, radio listening became more car-centric.  And most auto manufacturers didn’t care about AM.  Nor did the aftermarket folks.  
For car listening, AM fit well.  Low bandwidth actually allowed it to cut through the road [and screaming kid] noise better.  So did the heavy compression and limiting.  Note, though, that FM programmers weren’t far behind in signal processing.  
But there were other demons lurking out there.  Power line noise was growing.  At lower, AM frequencies, its strength was/is much greater than up in the FM band.  Besides, FM is nearly immune to impulse noise.
It doesn’t stop there.  FM portable transistor radios became available.  The FM band happens to have a quarter wave equal to about 2½ feet.  That made a telescoping antenna or an earphone cable a pretty effective antenna compared to the directional AM loopstick.
And, of course, along came AM stereo.  Well, sort of.  The commission approved the Magnavox system – one that was almost universally derided as being the worst of the systems proposed.  After years of in and outfighting, the commission threw up its arms and essentially turned it over to the marketplace, washing their hands.  Motorola’s C-QUAM and Harris’ system became de facto standards while Leonard Kahn’s ISB concept fell by the wayside.  Doesn’t matter. 
The point is that AM stereo was stalled.  C-QUAM broke into the lead when GM et. al. put the Motorola system in their automobiles.  It caused Harris to cave and embrace C-QUAM and the rest to carp about how bad C-QUAM was.    But it took from then to ’93 – a full 13 years – for the FCC to anoint C-QUAM as the standard.  “Juuuuuuuust a bit outside.” – Bob Uecker, Major League.
And, once again, with tribute to Billy May, “But wait, there’s more.”  In trying to eliminate splatter and compensate for the poor frequency response, the National Radio Systems Committee proposed two very important changes:
·         Preemphasis – boosting the high frequencies on transmission
·         Brick wall filtering to limit frequency response to 10kHz

To some extent, preemphasis has worked.  But really, when you have IF circuits that barely pass 3kHz, you can boost your signal at 8 or 9kHz as much as you want, they're not getting through to the speakers.  So you wind up with a lot of wasted modulation.  Some chains recognized that and purposely limited their audio to as low as 5kHz, opting for more modulation in the range that receivers actually reproduced.  
And the filtering was interesting.  In the mid-90’s digital filtering was iffy at best.  Analog filtering was multi-section and with it came phase shifts, envelope distortion and any number of other anomalies.  Much of that has been eliminated now but the early NRSC boxes were scary.
So, have we screwed up the medium enough?  Well, if I’m asking the question, you know the answer.  We added IBOC – in-band-on-channel – digital transmission.  Yes. In band.  As in right on top of the analog signal.  Granted, the method is ingenious.  Flopping the phase of the carriers above and below the analog carrier “nearly” cancels the digital trash that a typical envelope detector sees.  Cool.  
Not so fast.  Go up a channel.  Take 710 WOR.  That lower sideband digital information extends into 700 – that’s WLW – territory but a receiver tuned to 700 gets only the lower sideband digital carriers of 710.  Nothing to cancel them out.  More hash than a Van de Graaff generator in winter.
Not to be outdone in the noise department, the government – yeah, those guys responsible for policing power line noise – added new regulations regarding illumination, outlawing first 100 watt incandescent lamps and progressing downward in power.  They’re supposed to be replaced by compact fluorescent or LED lamps.  In almost all of the commercial units, the power supplies use some form of switching.  You can tell the switching frequency by tuning up the AM band and counting the “buzzes.”  Regardless of the number, the interference to AM reception is horrendous.  
They’re supposed to comply with Part 15 of the rules but I don’t think any do.  In fact, it’s apparent that most computers and electrical appliances don’t.  But the rule is, by and large, ignored unless someone really forces the issue with the commission.  Even then, they have gone after small equipment manufacturers while power companies operate without oversight.
And most recently, we added the option of MDCL, Modulation Dependent Carrier Level which will save stations money on their power bills.  Fortunately, this scheme does not significantly degrade the detected audio signal.
So (finally I get to the point) we amble along to today, well, about a year ago.  FCC Commissioner Ajit Pai voiced concern for AM’s viability.  Commissioner Mignon Clyburn joins him.  Together they push for a look at revitalizing AM.  And, in October of last year (2013) the commission issues a Notice of Proposed Rulemaking aimed at revitalization.  
It asked pointed questions and put forth basic ideas, calling for comments about improving the plight of AM.  Concerns include the clear channels (does any station need that level of contour protection anymore) to the local daytimers (should they all get FM translators to improve their lot and allow them nighttime service)  IBOC.  Should it stay?  Does programming matter?  
An interesting side note to all if this is that younger demos seem intent on quantity versus quality in their music.  Ask them about their iPod or phone and they’ll tell you they have X thousand songs.  Investigate further and you’ll find that the bit rates are abysmal from a quality standpoint.  Apparently those compression artifacts are as musical to them as the distortion we all grew to love 50 years ago.  If that’s the case, maybe they’ll gravitate back to an  AM station playing their preferred music.
Comments closed about 10 days ago and the floor is open for rebuttal.  You can comment but only to the extent that it concerns already-filed comments.  Sort of like cross examination.  If it didn’t come up in direct, you can’t introduce it now.
After all of this, where will it shake out?  On one side, there is the “back to the past” group, returning AM to full analog.  The other side says wipe it all out and go 100 percent digital.  That second POV is pretty powerful when you consider the bit rates possible if one didn’t have to protect the analog signal.  It would just about put the sound on equal footing with FM. 

However, the downside is large:  it makes hundreds of millions of radios obsolete.  Further, AM can be demodulated by just about any nonlinear device – even a piece of rusty fence.  Remember that simple diode I talked about a bit ago?  In a major catastrophe, that could mean the difference between life and death for any number of people.
If you want to check it out or even file a response, start here:
or do a search for FCC 13-139 .
It’s fun riding this one out – just to see where it’s going.
1To be accurate, Wolfman for a while actually transmitted out of Cuidad Acuna, Mexico with a power of 250 kilowatts.  That’s 1 megawatt PEP. (100% modulation)
2After the FCC put a limit on positive modulation.  The action was brought about by a certain Louisville, KY station [OK, WAKY] ordering a Gates transmitter capable of 160 percent or more positive modulation.
3My opinion, the Fairness Doctrine wasn’t really fair.  Remember, it wasn’t about equal time; it was about time for opposing views.  Too often, a station would take a position, do an editorial and then immediately go out and find the most stupid, inarticulate individual to interview for the opposing view, further cementing their POV.  Go ahead.  Say it didn’t happen.
4Check 73.47 of the Rules, 1972 edition.