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Back to analog stereo AM?

It is not returning because when people replace their transmitters they are not cquam. WMBD in Peoria just dropped it because the new AM6 transmitter does not have it.
 
WLS in Chicago is a notable example of a station which dropped IBOC and returned to C-Quam.

Also, many, if not most, HD Radio receivers will decode a C-Quam signal in stereo, although almost none make any mention of it in their specifications. Apparently AM Stereo is a "surprise bonus" built into the HD Radio DSP chipset.
 
satech said:
WLS in Chicago is a notable example of a station which dropped IBOC and returned to C-Quam.

Also, many, if not most, HD Radio receivers will decode a C-Quam signal in stereo, although almost none make any mention of it in their specifications. Apparently AM Stereo is a "surprise bonus" built into the HD Radio DSP chipset.
Click to expand...

Speaking of WLS, do they actually offer any content like spots or background music in stereo? I listened to to them the other night for a break and a half and never heard any stereo content. Granted, they sounded crisp and clear (for a station 570 miles away) but they didn't seem any higher fidelity than, say, WSM.
 
I bought an Accurian and a JVC car stereo, neither one seems to do anything at all with the CQUAM on WLS. :mad:
Anyone else who has a RS Accurian that "does" CQUAM, speak up!
 
Zach said:
Speaking of WLS, do they actually offer any content like spots or background music in stereo? I listened to to them the other night for a break and a half and never heard any stereo content. Granted, they sounded crisp and clear (for a station 570 miles away) but they didn't seem any higher fidelity than, say, WSM.
Click to expand...

Zach, the spots should be running in stereo if they were produced in stereo. During the recent Dick Biondi 50th anniversary special, some of the spots were in stereo, while others were not. C-QUAM works great, but most AM stations have a talk format these days. WGN is an exception; they actually do have some musical programs (even live music occasionally) that could benefit from stereo transmission.
 
WLS's IDs, station promos, and traffic/weather beds are all in stereo, as are most of their locally originated commercials.

The Accurian does receive C-Quam, however, like most HD Radios it is rather slow to begin decoding it in stereo (usually a 5 to 10 second delay), and there is no indication on the display for analog stereo on either AM or FM. It also features a stereo blend for AM as well as FM, so on weak or unstable signals it will gradually blend to mono.
 
satech said:
WLS's IDs, station promos, and traffic/weather beds are all in stereo, as are most of their locally originated commercials.

The Accurian does receive C-Quam, however, like most HD Radios it is rather slow to begin decoding it in stereo (usually a 5 to 10 second delay), and there is no indication on the display for analog stereo on either AM or FM. It also features a stereo blend for AM as well as FM, so on weak or unstable signals it will gradually blend to mono.
Click to expand...

It also brick walls the analog to 5 kHz, even in stereo, right?

I'll have to give it a listen again some night if I can get away from all the RF at home. I've just got an old SRF-42 Walkman, it decodes everything through the stereo chip apparently when in the AM ST position. But I definitely didn't hear anything in stereo from WLS, but it was during some Wall Street Journal program.
 
Zach, you should have tuned in for the Dick Biondi 50th. Totally awesome, that was!
 
Tom Wells observed:
"I bought an Accurian and a JVC car stereo, neither one seems to do anything at all with the CQUAM on WLS."

Not all the Accurian receivers do. If I remember correctly, Ratshack got sued by Motorola a few years back and had to drop CQAM stereo support. The older pre-litigation sets support it but the ones produced since likely don't.

I have heard CQAM audio on an Accurian IBAC box and I wasn't impressed. The box was tuned to KPSU (1450) and the audio sounded quite narrow-band, kind of like the MW sections in a lot of newer car radios that roll off at about 4.5 kHz.
 
Darth_vader said:
Not all the Accurian receivers do. If I remember correctly, Ratshack got sued by Motorola a few years back and had to drop CQAM stereo support. The older pre-litigation sets support it but the ones produced since likely don't.
Click to expand...
Sounds unlikely to me. First of all, Radio Shack has nothing to do with what the HD Radio chipset used in the radio supports or does not support. I know LG in Korea makes HD Radio chipsets, but there are probably others. Probably the receiver manufacturer just switched to another HD Radio chipset which does not support C-Quam. I know Radio Shack changes components often. You can buy the same exact product twice and find completely different ICs inside.

And more importantly, the 25-year patent on C-Quam (originally filed by Motorola in the late '70s) expired in the early 2000s, and Motorola never charged licensing fees to receiver manufacturers. Motorola itself published the DSP code to receive C-Quam in the late '90s, and since then even some online "Software Defined Radios" (SDR) have been programmed to decode C-Quam signals.
 
I want to know if AM stereo improves reception of weak AM signals. Also, does AM stereo decreases the amount of interference from electronic sources (such as power lines, lightening, TV sets, etc.) on weak AM signals in comparison to mono AM signals?
 
Nope, AM Stereo C-QUAM does nothing for improvement of weak reception. Neither does the system reduce noise. It simply provides a stereo image, which is still subject to the QRM sources you list.

Some operators turned off C-QUAM because asymmetrical modulation with positive peaks in excess of 100% is not possible with the system. In the view of some, this made the AM Stereo stations sound weak in mono vis-a-vis competitors.
 
Savage said:
Nope, AM Stereo C-QUAM does nothing for improvement of weak reception. Neither does the system reduce noise. It simply provides a stereo image, which is still subject to the QRM sources you list.

Some operators turned off C-QUAM because asymmetrical modulation with positive peaks in excess of 100% is not possible with the system. In the view of some, this made the AM Stereo stations sound weak in mono vis-a-vis competitors.
Click to expand...


WLS using C-QUAM at night still sounds huge here locally, but maybe that's why they don't thunder into the boonies like used to. :-\
 
With C-QUAM, average modulation and density were down considerably compared with mono and asymmetry typical of the era. Actually, it would have been a good thing if C-QUAM had become universally accepted for AM broadcasting. Certainly the stereo image was great, but the very real improvement in audio quality could have come from not pushing transmitters to the max.
In the time of C-QUAM's rollout many stations were still using high-level modulation tube rigs from the 60s, 50s or even 40s - some handled high-density asymmetry better than others. Many a tube rig wound up eating its mod transformer or feedback ladder. Many showed considerable tilt and power-supply bounce producing carrier shift. Result: distortion and splatter.

It was the era of loudness wars, which did nothing for a perceived high quality in AM transmission. As one programmer proudly boasted to me, "man, are we loud!!" My response was, so is a locomotive air horn. Neither one will hold listeners very long.

If C-QUAM had become the norm a la FM Stereo, AM might have entered a new era of quality audio. But it was not to be.
 
Savage said:
Some operators turned off C-QUAM because asymmetrical modulation with positive peaks in excess of 100% is not possible with the system. In the view of some, this made the AM Stereo stations sound weak in mono vis-a-vis competitors.
Click to expand...
Actually, it is entirely possible to transmit C-Quam with full +125% / -100% modulation. Positive modulation above 100% does cause some crosstalk distortion for stereo listeners, but considering the levels of processing used today for AM, this would hardly be noticeable, and mono listeners would not hear any difference anyway.

It was originally the Magnavox system which was limited to -95% negative modulation, which started the common misconception that "AM Stereo causes a loss of loudness." C-Quam does not have this limitation, although many professionals recommend limiting your negative modulation to -95% even on a mono AM signal, because it provides much cleaner audio on a typical diode detector receiver than full -100% modulation.
 
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