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AM Stereo in the news

S

satech

KYET signs back on the air on a new frequency after going dark in 2000, and they're transmitting C-Quam AM Stereo...

http://www.mohavedailynews.com/articles/2012/11/15/news/local/doc50a4ac43beb11772382773.txt

Mohave Daily News said:
KYET, owned by broadcast veteran Joe Hart's Route 66 Broadcasting LLC, began operations on Oct. 14 at 1170 on the dial. "This is an AM stereo and it does generate in stereo if you've got a radio that's equipped to receive it, it will," said Hart, who also serves as Arizona's State Mine Inspector.
Click to expand...
 
satech said:
KYET signs back on the air on a new frequency after going dark in 2000, and they're transmitting C-Quam AM Stereo...

http://www.mohavedailynews.com/articles/2012/11/15/news/local/doc50a4ac43beb11772382773.txt

Mohave Daily News said:
KYET, owned by broadcast veteran Joe Hart's Route 66 Broadcasting LLC, began operations on Oct. 14 at 1170 on the dial. "This is an AM stereo and it does generate in stereo if you've got a radio that's equipped to receive it, it will," said Hart, who also serves as Arizona's State Mine Inspector.
Click to expand...
Click to expand...

There's absolutely no downside to C-QUAM for an analog operation. If you have the capabilities, and it doesn't cost more to enable them - use it. With our new digital STL going in this month, we'll also throw the switch on our transmitter and turn on C-QUAM for those with late 90's autos and the odd C-QUAM capable HD radio in the listening area. All said, C-QUAM sounds good - especially with the later model Motorola chips out there.

If it weren't an economic-political issue, HD radios using DSP code could easily support C-QUAM decoding and automatically enable 9.5 KHz bandwidth (when present). DSP could also go a long way to cleaning up impulse noise on the AM signal.

Here's a list of some modern receiver gear with C-QUAM capabilities:
http://mysite.verizon.net/tekel/amstereo/radios.htm


Brian
 
With our new digital STL going in this month, we'll also throw the switch on our transmitter and turn on C-QUAM
Click to expand...

I wish more stations (with C-Quam) sitting in the racks (disconnected) would do the same.

Anyone else on the board running AM stereo?
 
I'm my experience the C-Quam gear can have a down side to analog operation in perceived loudness due to the pilot and cutting of the total bandwidth to allow for stereo separation.
 
WPAX in Thomasville, GA is still running C-Quam. I agree, it sounds nice...for the 2 people that can hear it. It does seem to take away a bit of loudness from the mono signal, but we're running a Beautiful Music format, so loudness is not really a concern. Our Motorola C-Quam exciter died a few years ago, and I had no luck repairing it. Ended up picking up a used BE C-Quam exciter, and I think it sounds better than the Motorola ever did. We are using the 3 box CRL processing (don't recall the model numbers at the moment), into a Harris SX-1 transmitter. We have considered upgrading transmitters, but the newer 1kw boxes we looked at don't have an easy way to interface with the external exciter...so we've stuck with the SX-1.
 
I bought a stupid RS Accurian that does nothing for decoding CQUAM stereo.
It just figures I'd find one that doesn't.
 
bradgoehl said:
I'm my experience the C-Quam gear can have a down side to analog operation in perceived loudness due to the pilot and cutting of the total bandwidth to allow for stereo separation.
Click to expand...

The 25Hz C-Quam stereo pilot is part of the L-R phase modulation. It does not reduce the perceived loudness of the L+R amplitude modulation. C-Quam does not require that the audio bandwidth be reduced. Before the 10kHz NRSC high frequency limit, I ran C-Quam on a 50,000 watt AM transmitter with a full 15kHz audio bandwidth.
With C-Quam, it is important that the antenna system have a wide, flat response.
 
Tom Wells said:
I bought a stupid RS Accurian that does nothing for decoding CQUAM stereo.
It just figures I'd find one that doesn't.
Click to expand...

I was told the older runs of that radio will decode it. I have one at a station which I have yet to experiment with.
 
frankberry said:
bradgoehl said:
I'm my experience the C-Quam gear can have a down side to analog operation in perceived loudness due to the pilot and cutting of the total bandwidth to allow for stereo separation.
Click to expand...

The 25Hz C-Quam stereo pilot is part of the L-R phase modulation. It does not reduce the perceived loudness of the L+R amplitude modulation. C-Quam does not require that the audio bandwidth be reduced. Before the 10kHz NRSC high frequency limit, I ran C-Quam on a 50,000 watt AM transmitter with a full 15kHz audio bandwidth.
With C-Quam, it is important that the antenna system have a wide, flat response.
Click to expand...

Indeed, almost, but not quite. Loudness CAN stay, in the hands of a golden ears engineer.

"WHAM" doesn't happen ( the same) anymore with Cquam.
Or maybe it could, but it became even more elusive within the restricted range.
Or, "wham", (small letters) got lost in dim memory.
And it didn't matter anymore in the face of of world where such dynamic range was already destroyed by square wave detection to
intermediate frequency......

If I could only give everyone a "good" 1964 AM car radio, with real germanium outputs, it would be easier to understand. :)

I can squeeze a db out of a 16kc Collins magneto-restrictive 455 kc coupling can, and I sure DID hear the 2-3 db
squash on peaks when WLS ran C-Quam in the 90's and I was on the road in Avis Cadillacs with dreamy AM.

I'm not knocking this minor limitation. Good practice, rf noise reduction, and DSP could make up more than 3db of improvements.
C-Quam's not quite up to the physical limitations' practicality of the Kahn method, but at least it's more or less realtime.

Someone who really wanted to make "WHAM" happen again with C-Quam AM would read all they can about perceptual loudness.
 
Tom,

I'm glad that you brought up the 2-3dB squashing of the AM peaks.
I got around the problem (reported on the AM stereo monitor as 'high angle') by increasing the L+R amplitude modulation by a few dB.
This reduced the maximum stereo separation but it did keep the 'WHAM' in the AM signal.

Frank
 
frankberry said:
Tom,

I'm glad that you brought up the 2-3dB squashing of the AM peaks.
I got around the problem (reported on the AM stereo monitor as 'high angle') by increasing the L+R amplitude modulation by a few dB.
This reduced the maximum stereo separation but it did keep the 'WHAM' in the AM signal.

Frank
Click to expand...

It's good to know there are others who notice and do care.

At extremes, it is too easy to lose gradients and/or lose part of what could be possible maximum "variance" of volume.

It would be nice if all C-Quam users made note of this and took advantage of it.
 
C-Quam AM Stereo can handle the same +125% / -100% modulation as mono AM, so there is no loss of loudness, as long as everything is set up and performing correctly. Even old plate-modulated tube transmitters can handle C-Quam just fine, as long as you use an audio processor which includes tilt correction (CRL and Orban processors do, but not Inovonics).

The now-defunct Magnavox system demanded that the negative modulation be restricted to -95% in order to prevent a "popping" noise that would occur in a stereo receiver when the carrier pinches off, but this does not apply to C-Quam. You can drive the carrier right up to pinch-off and there is no popping noise in a C-Quam receiver. And there is no problem driving the positive peaks up to +125%, either.
 
Someone mentioned some AM Stereo discussion going on over here and I thought I'd chime in.
First off....staying on original topic...I was IN Kingman, AZ last week for Thanksgiving and did bring along my Sony SRF-A100 and got to hear KYET in beautiful AM Stereo. I recorded about 4 hours onto my laptop. Format is classic country with lots of old country classics with great separation. It sounded great! Kudos to KYET and Joe Hart for keeping AM Stereo alive.
I'm running stereo here at KEVA in Evanston, WY. I've got a Motorola 1400 exciter and the 1410 companion modulation monitor. We're running it into a McMartin BA-1K using 4-400c tubes. I've tried and can easily get 125% modulation out of it if I want to. I'm more concerned with cleanliness than loudness....so positive peaks (L+R) are about 95%. Plenty loud enough for everyone. This ain't the 70s where we need completely squashed pounded audio to sound "louder" than the other stations. I pride myself in putting out a nice clean signal and on the right radio (say the SRF-A100 or a Delco UX-1 series from the mid-90s) it rivals FM. I have a line hooked directly to the back of the modulation monitor feeding straight into a pc for our internet stream.....yes on purpose to showcase how good AM Stereo really does sound. (check it out at www.1240keva.com). I'm with the concensus that it doesn't hurt anything to run c-quam. For those listening in mono it sounds the same with or without c-quam.....and for those who DO happen to have AM Stereo capability, it's a wonderful treat. Especially if you're a music station. Even today, WLS in Chicago still runs it and they're not even a music station anymore. There are still several stations out there using it. And as mentioned previously, DSP could do a lot for the noise on the AM band these days. On another previous mention, I DO have one of the earlier Accurians and yes it DOES decode C-quam. It doesn't indicate it in any way and it's crappy 5khz but it's stereo.
I know there are still plenty of stations out there that have the c-quam equipment sitting right there in the rack...just sitting there turned off. Geez...turn it on....what's it hurt?

Michael
KEVA
Evanston, WY
 
Can't wait to check out the KEVA stream......and... I'll wake that Accurian back up again check WLS once more.
 
I, too, am a big AM Stereo fan. I put two on the air in the late 90's and they sounded teriffic! The best sounding AM Stereo I heard was WOKY in Milwaukee, heard in the early 2000's on a Dodge Stratus rental car radio. Even my non-technical wife remarked at how good it sounded.

Wish there was someone around here still in stereo...

EDIT: I just checked out KEVA's stream... It souns teriffic! What are you using for a processor?? Keep the fire burning, Michael!

EDIT 2: Ground buzz audible in dead air, unfortunately.
 
And for those who want to run their own little AM Stereo station at home, there is an FCC Part 15-compliant low-power C-Quam AM Stereo transmitter available, in both pre-assembled and kit form. Over 400 of these Chris Cuff transmitters have been made since the circuit board was designed in the year 2000, and they still remain in demand today:

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

I had the pleaure of testing one of these transmitters, and I was extremely pleased with its performance. It is crystal-controlled, so the RF is as solid as a rock, and the audio response is flat as a board -- when I retransmitted the audio from an FM station on it, I could see the 19 kHz pilot tone coming through on the spectrum graph of a wideband AM receiver tuned to it!
 
Ahem...yeah..you caught that, huh? The ground loop. Yeah there is a little ground hum in the signal. I haven't been able to get rid of it. It's in the line between the modulation monitor and the streaming PC. It's grounded good and that is about as quiet as I could get it. Could be in the sound card on the PC. I'm coming right out of the BNC connectors right on the back of the modulation monitor. Unbalanced L out, unbalance R out......I figured since the sound card has an unbalanced input, it would work and as you can hear, it does. I need to play with it some more to try to get rid of the ground hum but it's pretty clean.
As far as processing, 30-year old CRL boxes :) I have the CRL Stereo Matrix Processor, and the CRL Stereo Preparation Processor. Normally this set also includes the Spectral Energy Processors....which I don't have. However I have a friend in the biz that said he's got a couple sitting on a shelf and he's going to send them to me...so the sound could improve even more but the CRL's really do a nice job. AM Stereo is what they were built for and they do it well. There is a very slight buzz in the main on-air signal too and it's coming from the SMP. Most likely a filter capacitor inside the unit. I need to figure out which one it is and swap it out. Better yet maybe try to convince management to invest a little money and i could re-cap the whole thing...both processors. Anyways...for what we have I think it sounds pretty awesome!
Oh and I do have one of the Chris Cuff c-quam transmitters -- mine was 1st generation..I bought it back in the late 90s from him. It works well. It broadcasts at 1000khz. Sounds awesome. I remember back then I had AM Stereo in my car and I wired in an adaptor for power and used it IN the car to rebroadcast my laptop (and later my MP3 player) over the car radio in AM Stereo :)

Michael
 
In spite of the ground loop, the overall tonal quality and openness in the HF and bass is quite pleasing to the ear. Kudos for AM audio quality!!!!
 
If you replace capacitors on a regular basis, I would highly recommend an ESR meter Regarding the ground loop, it sounds like you may have the computer and mod monitor plugged into different legs of your AC power. Try a ground lifter on one or the other unit. And it is hard to beat CRL units for AM Stereo, although a tweaked Optimod 9100 sounds real nice, too.
 
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