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FM HD Asymmetric Power

Since it doesn't seem to be well explained in the article...

"Asymmetric" means the HD power on the upper sideband is different from that on the lower. The idea is that if there is a nearby station on the lower adjacent channel, limiting your ability to increase digital power, you could increase on the upper side only, or vice-versa.

I don't see much of a downside to this, except... on AM HD, it's my understanding the upper and lower side digital signals are 180deg out of phase. That way, on an analog radio they cancel each other out, reducing self-interference. (where the HD station interferes with its own analog signal)

I don't know whether FM HD does this. If it does... using asymmetric sidebands will prevent the cancellation from working, and could result in self-interference on some radios.
 
w9wi said:
Since it doesn't seem to be well explained in the article...

"Asymmetric" means the HD power on the upper sideband is different from that on the lower. The idea is that if there is a nearby station on the lower adjacent channel, limiting your ability to increase digital power, you could increase on the upper side only, or vice-versa.

I don't see much of a downside to this, except... on AM HD, it's my understanding the upper and lower side digital signals are 180deg out of phase. That way, on an analog radio they cancel each other out, reducing self-interference. (where the HD station interferes with its own analog signal)

I don't know whether FM HD does this. If it does... using asymmetric sidebands will prevent the
cancellation from working, and could result in self-interference on some radios.
Click to expand...
If the upper and lower side digital signals are 180* out of phase, (I'm assuming you are referring to AM) why would you still hear the "hash" on a mono radio?
It would seem that would be cancelled out, too.

Jeff in Sa-ra-so-ta!
 
badjef said:
If the upper and lower side digital signals are 180* out of phase, (I'm assuming you are referring to AM) why would you still hear the "hash" on a mono radio?
It would seem that would be cancelled out, too.
Click to expand...

To a very large degree it *is* canceled out *if* you're tuned to the HD station and there's no other HD station on an adjacent channel.

To the degree there's some left, I can think of a couple of reasons:
- Analog radio not tuned precisely to the frequency of the HD station. (some of the energy on one HD sideband is being cut off by the IF filter, so the cancellation isn't complete)
- Analog radio has asymmetric IF response. (with same results as above)
- HD station has directional antenna & its directivity isn't equal on both sides of carrier. (so the sidebands are symmetric coming out of the transmitter but not coming through the complete transmission path)
- Listener is getting some skywave & the ionospheric path is not identical on the two sides of carrier. (same selective fading effect that causes severe distortion at night on skywave analog signals)

I'm sure someone else can come up with more.

Symmetric out-of-phase sidebands do nothing to reduce digital interference to stations on *adjacent* channels, since an analog receiver tuned to an adjacent channel will only receive one of the HD sidebands.
 
badjef said:
w9wi said:
Since it doesn't seem to be well explained in the article...

"Asymmetric" means the HD power on the upper sideband is different from that on the lower. The idea is that if there is a nearby station on the lower adjacent channel, limiting your ability to increase digital power, you could increase on the upper side only, or vice-versa.

I don't see much of a downside to this, except... on AM HD, it's my understanding the upper and lower side digital signals are 180deg out of phase. That way, on an analog radio they cancel each other out, reducing self-interference. (where the HD station interferes with its own analog signal)

I don't know whether FM HD does this. If it does... using asymmetric sidebands will prevent the
cancellation from working, and could result in self-interference on some radios.
Click to expand...
If the upper and lower side digital signals are 180* out of phase, (I'm assuming you are referring to AM) why would you still hear the "hash" on a mono radio?
It would seem that would be cancelled out, too.

Jeff in Sa-ra-so-ta!
Click to expand...

It would if both signals were equal. If one of them was quieter than the other you wouldn't get total cancellation and some hash could be heard.
 
w9wi said:
I don't see much of a downside to this, except... on AM HD
Click to expand...

The proposal only affects FM, not AM.

Let me please restart the announcement at the top of the thread in another way.

There is a proposal being considered at the FCC that is intended to allow more stations to increase the power in their IBOC digital sidebands. Comments on this proposal have been filed, and may be read at: http://fjallfoss.fcc.gov/ecfs/comme...ieved.minDate=12/1/11&__checkbox_exParte=true If Radio World's short synopsis is good enough for you, then fine -- but you are entitled to read the entire set of comments for yourself, and to take advantage of the participatory Government that we enjoy.

Unless the FCC extends the deadline, Reply Comments will be due on January 3 (in less than 2 weeks).

This comment process is not a public opinion poll, it is an information gathering exercise. If you have something informative to say -- how the proposal would affect you or your station, whether or not the proposal or any of the arguments are technically sound in your professional opinion, etc. -- I encourage you to make your voice heard.

Strictly speaking, at this point, you should be addressing your "reply comments" to the "comments," rather than the original proposal. However, you can usually find a hook that would allow you to speak to both. You can argue agreement or disagreement with any of the points made thus far.

Speaking up now is preferable to merely complaining later.

- Jonathan
 
Savage said:
My understanding is that the primary function of the redundant sidebands in FM is reduction of multipath.
Click to expand...

The redundant sidebands provide spectral diversity as part of the error correction scheme. Interference or noise on only a portion of a sidebands will not cause the signal to be lost because the same information is present on other subcarriers.

- Jonathan
 
I am wondering if HD on AM or FM is being incrementally installed.
1.) Put it on at a low power in the real world environment.
2.) Have people complain it doesn't have the range and allow higher powers and heights on a case by case basis.
3.) Turn off the analogues as the HD radios are installed in more cars over the next ten years.

Anybody see the same? Or do I need to readjust my tin foil hat?

Jeff in Sa-ra-so-ta!
 
The tin foil hat needs adjustment. There are thousands of FM's that simply can't afford to do IBOC, much less have any desire to so with no ROI.
 
Instead of spending so much to eliminate one sideband, why not just save a lot of money by eliminating both sidebands?

Why would a station want to increase their HD power unevenly if that requires a new expensive transmitter? The ROI has been zero with the lower power, and will still be zero with the higher power. Nobody has the HD radios. I'm sure a station can ask its employees if they even know what an HD radio is and they won't. HD2s have been allowed to air commercials for years, yet they aren't unless they're feeding a translator or simulcasting an AM.
 
Nick said:
Why would a station want to increase their HD power unevenly if that requires a new expensive transmitter?
Click to expand...

Well, maybe you just want to occupy spectrum so someone else can't use it.

Or maybe you'd take that expensive new transmitter if the Government gave you money to buy it.

(Read the comments on the FCC docket.)

- Jonathan
 
RadeoEngineer said:
The tin foil hat needs adjustment. There are thousands of FM's that simply can't afford to do IBOC, much less have any desire to so with no ROI.
Click to expand...
Well, I remember hearing something similar about FM. Of course, FM was a system that worked. On the other hand, we are dealing with an FCC as it is now, that doesn't seem to matter if it works, the word digital is a buzz word that they want to make work and the ROI will come later.

But then, why would the FCC have authorized a system that would rely on thousands on radio stations not able to use/justify it?

It makes no sense.

Jeff in Sa-ra-so-ta!
 
So now FM iboc, which doesn't make noise on the host any more than AM iboc doesn't make noise on the host signal,
is being allowerd to be non-symmetric in response so it can.....choose better which neighbor(s) they prefer to
splatter into oblivion.

There is an of odd parsing of "is" occuring when anyone able to say that 180 degree relataionship
means the sidebands cancel each other.

We're talking the laws physics here, not making excuses about what is and isn't "presidential" or "sexual.".

I'd love to hear ANY acccount of how any operation of the present AM iboc did not create noise.

If cancellation did occur in a meaningful way, then lightning would make no static either.

However, instantaneous imbalances between frequencies ensures that there is product in the differences and balance between them.
The modulation itself creates inter-harmonics NOT acknowledged in the design, and pretends the sidebands behave as
independent agents.
They must, as far as the capturing of data, but each new sidepair is relative to all the other info "nearby" in bw,
meaning 50 khz each way.

It's bad enough to pretend the interaction between the sine wave wave signal and sideband data bits is not noise,
it's worse to pretend that the same thing isn't happening as the data modulates bits.

Information must make some imbalance to radiate.
At least in analog AM, all the harmonics are or should be real audio range info, and useful to contribute to decoding.
In data modes there is nothing intuitive or related about the data pairs or their harmonics to contribute to the
decoding of the info.

George Carlin I think, said it best.

"If there are only 2 people on an elevator, and one of them farts, everyone knows who did it."

Just don't publish a paper about how no actual smell is created and then try to pass that off as some kind of engineering.
 
Even a "Fart" was designed and executed with a useful purpose.

Jeff in Sa-ra-so-ta!
 
Not only do most stations not have the funds or interest to install IBOC, if every station on the AM or FM dials (or any implementation approaching "every station") did so the radio broadcast bands would become unusable oceans of interference.

Some would argue that's already happened on AM. :-\
 
Savage said:
Not only do most stations not have the funds or interest to install IBOC, if every station on the AM or FM dials (or any implementation approaching "every station") did so the radio broadcast bands would become unusable oceans of interference.

Some would argue that's already happened on AM. :-\
Click to expand...
...and nobody brought that up in the discussions on the viability and implementation of the iBoc system?
Either incompetence, or a systematic plan to expedite the elimination of the AM broadcast dial.

Jeff in Sa-ra-so-ta!
 
badjef said:
...and nobody brought that up in the discussions on the viability and implementation of the iBoc system?
Either incompetence, or a systematic plan to expedite the elimination of the AM broadcast dial.

Jeff in Sa-ra-so-ta!
Click to expand...

There were lots of critics before the FCC approved IBOC. I was at a Texas Association of Broadcasters convention several years ago where Ibiquity made a demonstration of their system. I stood up and asked them in public how they intended to deal with the interference issues? The reply I got was "They won't be a problem." Even the rep from Nautel agreed with me, saying "How could there not?"

So why was it approved? Your imagination is as good as mine....
 
Today, the FCC extended the comment period on this proposal, from last Monday (December 19) to the first business day of the new year (Tuesday, January 3). The reply comment period has been extended until Tuesday, January 24.

I encourage you to become familiar with the issues, by reading the proposal, http://hraunfoss.fcc.gov/edocs_public/attachmatch/DA-11-1832A1.pdf , and the comments to date http://fjallfoss.fcc.gov/ecfs/comme...ieved.minDate=12/1/11&__checkbox_exParte=true .

Additional informational comments, or reply comments, would be appreciated.

- Jonathan
 
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