NEW HD-AM Broadcast Scheme?

[ve3jf]

A few days of listening makes me pretty confident that WSCR is using the new scheme.
WSM continues to be "listenable", if I tune down a bit. I could not escape the hash before on this same radio.
The upper sideband of 650 sounds as bad as before, so it hasn't changed things much for someone with a wideband radio.
It's just a >tiny< bit narrower on the noise, but enough to make difference that I can listen to 650 almost normally.
I hear NO benefit to the audio on the host signal, no matter how I tune, or how carefully I try to center tune.
The 94% max negative mod peaks combined with the (unchanged) hiss still makes them sound flat and dull.
The change to phase modulated sidebands in summer of 2007 was a very audible improvement to the hiss level on the host.

As I said before, the "new scheme" should have no impact whatsoever on adjacent channel interference. It sounds like WSCR may have lowered the power in the lower primary digital sideband, but that's not part of the "new scheme". If they did, the reason, I'm sure, would be to reduce interference to co-owned WFAN on 660. Somebody in the Chicago area with a spectrum analyzer should be able to determine if they now have asymmetrical primary sidebands.

And what's this about a change to "phase modulated sidebands" in 2007? The primary, secondary, and tertiary sidebands use 64QAM, 16QAM, and QPSK, respectively, and there's no way they could change the modulation scheme after the system was standardized and deployed.

 

[Tom Wells]

I think the primary and secondary subchannels did indeed go from AM to PSK in August 2007, and my ears and radio
made the change evident. It reduced the hiss on host by 4-5 db for those with wideband af detector and audio radios.

This current, new change, is by comparison only of interest to those affected by a 2nd adjacent offender
who adopts the new system: they may have less interference to a preferred signal depending on the radio.

 

[ve3jf]

I think the primary and secondary subchannels did indeed go from AM to PSK in August 2007, and my ears and radio
made the change evident. It reduced the hiss on host by 4-5 db for those with wideband af detector and audio radios.

This current, new change, is by comparison only of interest to those affected by a 2nd adjacent offender
who adopts the new system: they may have less interference to a preferred signal depending on the radio.

Sorry, but this is nonsense... I don't know what caused the changes you heard in 2007, but it certainly wasn't a change in the digital modulation scheme. And as for a new change affecting 2nd adjacent interference, this simply makes no sense - unless the power of a primary sideband is lowered, as in the case of KBRT.

 

[LibertyNT]

KRLD 1080 now appears to be using this new method. Digital seems to be centered on 1065 now.

 

[briankay]

I notice WBBM Chicago cuts in and out much more than before when I go under bridges and power lines. Before it was solid for my whole 25 mile commute. Did they perhaps change from the robust hybrid mode (allowing 5 kHz analog audio) to the lest robust hybrid mode (which permits 8 kHz audio)? Or did they just lower the power of one or both of the sidebands?

Pity there is not much information on the net (that I can find) on the new AM HD (MA1 mode) scheme that allows 10 kHz analog audio. Does anyone know if the current AM HD receivers will decode the parametric stereo version of the codec proposed for this new configuration? I'm listening to see if WSCR or WBBM are implementing this but both signals right now just seem to switch between stereo and mono depending on signal conditions which would suggest the existing core and enhanced streams on the primary and secondary carriers.

One other thing I notice is that on the big Chicago HD AMs it's like the stereo stream is very fragile only being decoded a small portion of the time irregardless of whether I'm right near the transmitter site or distant. The lower power HD AMs e.g. Radio Disney 1300 go into full stereo almost as soon as you can get their HD signal. I often wondered if the big AM HD stations in town deliberately reduce the power of their secondary sidebands to reduce hiss on wideband analog radios.

 

[Savage]

Hey Brian - "how does that HD-AM thing work out for you" during thunderstorms? Have you tried that yet?

Or in the presence of any other kind of impulse noise that would cause a "pop" in your old-fashioned analog AM radio?

 

[satech]

AM IBOC does repeatedly drop out due to static crashes caused by lightning. I never had an "HD" receiver long enough to hear this first hand, but there are videos on YouTube demonstrating the phenomenon.

 

[briankay]

I'm sure I'll hear them like as if they were analog only (God forbid) for the 72 hours in the whole year there is an active thunderstorm. I just know during times of no thunderstorms, that the 50kW AM HD stations that use time diversity (not WBBM) on their primary carriers produce a far more consistent lock than the FM HDs when moving at highway speeds as it seamlessly switches from one sideband to the other when going under bridges and power lines to produce minimal dropout. Most of my driving is 20 to 40 miles from the AM transmitter site though I have got WMAQ HD almost rock solid out to 150 miles and I don't find AAC+ type encoding with SBR sound quality (if done properly) to be as bad as some would otherwise have you believe, especially for most of the audio material that is heard on AM nowadays. My guess is 99% of Joe Public would say the audio is an improvement over analog and I would also guess that 99% of Joe Public is not DXing a 1st or 2nd AM adjacent station in 99% of their locations that is being savagely interfered with by an adjacent HD AM station. The 1% (e.g. some people on this forum) reflects the old saying you can't please all the people all the time.

That being said, I am still looking for technical info/feedback to the questions I asked in my previous post.

 

[tomservo]

My guess is 99% of Joe Public would say the audio is an improvement over analog and I would also guess that 99% of Joe Public is not DXing a 1st or 2nd AM adjacent station in 99% of their locations that is being savagely interfered with by an adjacent HD AM station. The 1% (e.g. some people on this forum) reflects the old saying you can't please all the people all the time.

Using Joe Public as your yardstick will always net you the lowest common denominator. If I were developing a product for public consumption, I'd rather shoot for quality over Wal-Mart quantity, even though the rest of the country doesn't seem to care. But that's just me.

Your quote may be true for daytime listening, but nighttime is far different. Day OR night, there are still lots of people like me who have zero local AM stations so everything by definition is DX on that band. If I want certain types of programming, they are only available on AM stations from 80~100 miles away during the day and even further at night. Just because these listeners are in the minority doesn't mean they don't deserve the same interference protection that the FCC supposedly allegedly reportedly affords everyone.

Now, where I live there's plenty on FM. Plenty of religious yakking, plenty of oldies, plenty of country and talk. But in rural Navajo Nation? Or most of Wyoming? Or rural Texas? There is little to no FM reception 24 hours a day. They depend on far-flung but relevant AMs to provide them with information. A tiny minority they may be, but they do not deserve to be unnecessarily interfered with.

As for your other comments about AM HD, I'm sure the scheme works fine on the big 50 kW stations in Chicago. But, if we're playing the minority game, there are very few 50 kW stations in areas with excellent ground conductivity, the rest have varying degrees of "trouble" to contend with, and for them, AM HD is dead in the water.

 

[Savage]

99.99994% of "Joe Public" has'nt heard of HD Radio, doesn't care about digital vs. analog radio, or both.

And no, you won't hear (AM) stations just like they were analog (blasphemy deleted) in thunderstorms. With analog you hear the same audio somewhat marred by crackles and crashes. In the wonderful new world of HD, the signal defaults back to analog - then mutes (in many available models) until the digital stream is reacquired. It's the always present blessing of Digital World. Unlike analog, it works until it doesn't work - then you've got zilch.

In other words, thunderstorms in HD-land make AM radio LESS listenable, not more. So what's the point? HD Radio: robust, it ain't.

Glad you like the sound of the HD codec. Most people I know find it objectionable and obnoxious. But then again they're not rabid pro-HD freaks.

 

[JohnnyElectron]

Hey Zack, When in Wyoming there was actually a C-Quam AM stereo station running Classic Country - and it sounded great considering the age of the tube transmitter (after a phone call to morning man Mike who gave me the scoop), but s damn nice-sounding stereo audio chain! Actually, I think I ran across two AM's in Wyoming in analog stereo (both owned by the same owner IIRC) plus there was a 50KW Canadian station that came booming in at night as well, but you're right, slim pickin's in the 'open range' of Wyoming for the most part partner!

 

[tomservo]

Now you're making me jealous, Johnny. Wyoming is one of my favorite places to visit, and AM stereo is one of my favorite geek out things. That's a double whammy for me.

 

[stacker]

My guess is 99% of Joe Public would say the audio is an improvement over analog and I would also guess that 99% of Joe Public is not DXing a 1st or 2nd AM adjacent station in 99% of their locations that is being savagely interfered with by an adjacent HD AM station.

There are many instances of 2nd adjacents serving the same market. Imagine an instance where you have, say, a 1330, 1350 and 1370. None of the station's 5mV contours can overlap, but their metro grade 2mV signals can and do. The listeners of these stations are not DXer's. Can you imagine what would happen if the middle station began transmitting an HD signal? What about all three? Mutually Assured Destruction. By the way, under the rules each of these stations are protected from interference, during the daytime, out to their 0.5 mV contours. Yet, under the HD scheme, they'll receive much more interference because of the fiction that you can fill the mask with an always on/off digital signal and still comply within the present allocation scheme.

 

[tomservo]

As far as AM goes, I'm in a pretty dead area. But that doesn't mean the band is dead, just that there isn't anything really local. Thanks to outstanding ground conductivity, the Mississippi Delta is fertile ground for distant AM signals.

Three of the stronger stations on the dial here are all just 10 kHz apart. When it's cloudy they already slop over one another. I can't imagine one of them going HD.

This may not sound like much:

940 - 50 kW due east @ 47 miles
950 - 5 kW NNW @ 102 miles
960 - 1 kW SSW @ 28 miles

But they are all very much listenable on a decent radio, moreso on cloudy days. They all claim all or part of the Delta in their coverage areas, so one going HD would cause a loss of coverage for the others.

Just because some of us are outside the 2.0mV line doesn't mean we don't hear and respond to the advertisements.

 

[Play Freebird]

Just because some of us are outside the 2.0mV line doesn't mean we don't hear and respond to the advertisements.

This is where I have a problem with the position taken by the larger group owners which are leading AM IBOC proponents. They would have us believe that fringe coverage (< 2 mV/m) doesn't matter any more, nighttime skywave service no longer serves a significant audience, and if a local station get clobbered outside its NIF groundwave contour (or even inside), tough luck. That's how they justify the adjacent-channel interference caused by IBOC operation.

But when the fringe coverage of one of their Class A stations is threatened by a small local broadcaster who isn't a member of the "club", then it become a big deal. For example, CBS recently contested the proposal of WOAP, a Michigan station, to operate at night on 1080 because it would affect WTIC's skywave service provided by extended use of the day pattern. In this case, the FCC wisely rejected those arguments:

http://hraunfoss.fcc.gov/edocs_public/attachmatch/DA-08-2455A1.pdf

Many of us are required to reduce power substantially during "critical hours" to protect 0.1 mV/m service contours of co-channel Class A stations. Although the service area between 2 and 0.5 mV/m is still quite listenable in some rural areas, I question whether the zone from 0.5 to 0.1 still deserves protection, due to the ever-increasing noise floor in the mediumwave band. But if we "little guys" decided to petition the FCC to relax our critical hours power limitations, I guarantee that the big owners of these Class A stations would fight our efforts with tooth and nail, as they continue to spill their digital interference into adjacent channels with impunity.

 

[stacker]

This is where I have a problem with the position taken by the larger group owners which are leading AM IBOC proponents. They would have us believe that fringe coverage (< 2 mV/m) doesn't matter any more, nighttime skywave service no longer serves a significant audience, and if a local station get clobbered outside its NIF groundwave contour (or even inside), tough luck.

Fbird...couldn't agree with you more. No matter where your "fringe" coverage occurs, 2 mV, 1 mV or less, the daytime coverage is protected out to the 0.5 mV contour.

I know of an instance where a heavily modulated IBOC signal throws spikes into the 10 mV contour of a third adjacent.

The AM headache has gone on long enough. Turn it off, AM IBOC-er's. No one is at home. No lights on. No creatures stirring....most of all, no receivers jumping off the shelf.