INTERFERENCE AND PERSPECTIVE

[jhardis]

No one has ever been able to explain to me how -20 dBc is less than -25 dBc. The fact is, it's 5 dBc greater, and always will be.

Agreed on all points, Jonathan. Except don't forget that the -20 is 1/2 above the FM carrier and 1/2 below. So that makes it -23 for purposes of this measurement.

1) Show me in §73.317 where it allows -25 dBc separately in both the upper and lower first-adjacent channels.

2) Last time I checked, -20 was still a larger number than -22 (-25 + 3).

In addition some of the digital carriers are less than 120 KHz away from the assigned frequency. So if the transmitter is VERY free from intermod the original HD spec appears to be legal.

Look again.

The basic hybrid digital signal (as opposed to extended hybrid) consists of 382 subcarriers removed from the analog carrier by 129 kHz to 199 kHz. The iBiquity system specification is that each of these, individually, should be -45.8 dBc. To save you the trouble of pulling out your calculator, 10 log (382) is 25.8, and -45.8 + 25.8 = -20.0.

In extended hybrid mode there are digital subcarriers that are less than ±129 kHz from the analog, and what they do to the power calculation has been ill defined. I am aware that these questions have caught up to the NRSC in their document preparation, and that they have consulted with the FCC. I expect that one or other of them will publish something on the matter eventually. Meanwhile, if you use a spectrum analyzer to look at what broadcasters are actually putting on the air in extended hybrid mode, I suspect you will see that most if not all of them have subcarrier powers of -45.8 dBc each regardless of how many subcarriers are enabled. And to save you the trouble of pulling out your calculator again, since the subcarriers are spaced at about 2.75/kHz, and since 10 log(2.75) is 4.4, the spectrum analyzer will show subcarrier power density of about -41.4 dBc/kHz no matter what range of frequencies they span.

- Jonathan

 

[DaveBayArea]

1) Show me in §73.317 where it allows -25 dBc separately in both the upper and lower first-adjacent channels.

Hmmm... You're right. I had never thought of it that way until now.

In extended hybrid mode there are digital subcarriers that are less than ±129 kHz from the analog, and what they do to the power calculation has been ill defined. I am aware that these questions have caught up to the NRSC in their document preparation, and that they have consulted with the FCC. I expect that one or other of them will publish something on the matter eventually. Meanwhile, if you use a spectrum analyzer to look at what broadcasters are actually putting on the air in extended hybrid mode, I suspect you will see that most if not all of them have subcarrier powers of -45.8 dBc each regardless of how many subcarriers are enabled. And to save you the trouble of pulling out your calculator again, since the subcarriers are spaced at about 2.75/kHz, and since 10 log(2.75) is 4.4, the spectrum analyzer will show subcarrier power density of about -41.4 dBc/kHz no matter what range of frequencies they span.

In the installations I know of the total power of the HD carriers is set to 20 db below the analog using a power meter, so the measurement would include all of the carriers, even the ones close to the analog channel. I can't see individual carriers with my analyzer - its lowest resolution bandwidth is 10 KHz. But I can certainly see where you could be correct on their level and the actual limits would be exceeded by either 2 or 5 db, depending on interpretation. In any case, the reality is that if these signals were spurs on my transmitter in 2001 I would have received many calls about how people were hearing my signal off-frequency and we would have corrected it post-haste. It's spurious out-of-band emission by almost any standard.

Dave B.

 

[JimmyJames]

I'm confused when and where the "right" was created for people to be able to listen to fringe signals. If the market isn't the market it was licensed to serve, I fail to see how someone outside that area has some sort of "right" to interference free reception of a non local station, caused by HD or not.

 

[Tom Wells]

It's one of the inalienable rights that went unrecognized at the time of the writing of the constitution.
You would argue that you have a right to breathe clean air, right? This is no diffierent.
The right exists because that's how radio works. Physics do not respect any concept of markets.
Such a concept was created by the 'business' end radio, not the technical.
Technical people would be like Major Armstrong who liked the idea that one FM could cover several states.
The radio biz was horrified that it meant daytimes would be as "bad" as nights, with a lot of "choices" they'd rather not
that listeners have. So the FM frequency went up to 88-108 and the antennas became lower to satisfy the needs of the
business, which were different from what Armstrong thought everyone needed and wanted.
Something you've enjoyed (and was historically posssible, repeatable and even dependable) if not specifically outlawed, is something that over time becomes a "right".

A large building planned that would have blocked sunlight at the Oak St beach in Chicago was stopped because the
residents and those who frequent that beach felt and successfully defended the "right" to sunlight at the beach for ALL, not just themselves.

Such a right is hard to defend once there's neighbors, pretty much like the days of the old west, with open range.
There was a really ugly battle over "fences vs no fences".
The people who wanted free range had a good argument, "Nobody owns this land right here, and these cows need to graze."
Once someone holds a deed to that property, those who used the space before, which was not property, but shared,
experience an actual loss, shared equally by those who also no longer enjoy the use of what is now "property".

Stations believe they "own" a frequency, "listeners" don't know to care, dxers believe the frequency should be utilized to their
best interests, and these are in conflict with the natural physical laws which define radio.

 

[TheBigA]

It's one of the inalienable rights that went unrecognized at the time of the writing of the constitution.
You would argue that you have a right to breathe clean air, right? This is no diffierent.
The right exists because that's how radio works. Physics do not respect any concept of markets.

The Constitution also recognizes the right of the government to create laws and establish regulations regarding interstate commerce. That is the justification for the FCC to place limits on the coverage of radio stations. The laws of physics say that two bodies can't occupy the same space at the same time. The over-licensing of the spectrum, done 25 years ago, created that problem in the radio spectrum. The only solution was to limit power and coverage of certain radio stations, and establish the concept of localism, which is part of the core agenda of the FCC. It is the law. If you believe in the Constitution, then you should respect the rules made under it.

 

[jhardis]

I'm confused when and where the "right" was created for people to be able to listen to fringe signals. If the market isn't the market it was licensed to serve, I fail to see how someone outside that area has some sort of "right" to interference free reception of a non local station, caused by HD or not.

This is a straw man that I can knock over with a feather. There is no such "right" -- and everyone know it.

The actual issue is the other way around. Under the Communications Act:

* [The] Commission from time to time, as public convenience, interest, or necessity requires shall ... Make such regulations not inconsistent with law as it may deem necessary to prevent interference between stations

* The Commission may, consistent with the public interest, convenience, and necessity, make reasonable regulations ... governing the interference potential of devices which in their operation are capable of emitting radio frequency energy by radiation, conduction, or other means in sufficient degree to cause harmful interference to radio communications

If you radiate, and if this radiation interferes with radio communications -- no matter how near or how distant -- you had better have authorization to do it.

The burden of proof is not on a listener who wants to hear a distant station. The burden is on the interferer to show that the Commission has authorized it after determining that his use of spectrum has higher priority.

- Jonathan

 

[TheBigA]

I agree. It's liberty vs. law. As Bobby Fuller once said, "I fought the law, and the law won."

 

[BRNout]

Tom described it beautifully. I couldn't do any better. And, his analogies stand up pretty well in the debate.

 

[TheBigA]

Tom described it beautifully. I couldn't do any better. And, his analogies stand up pretty well in the debate.

Except they don't stand up where it counts: In a court of law.

 

[audioguy]

Here is what I don't understand. Packing more and more stations into the same amount of spectrum, increasing the power of existing stations, and expanding the bandwidth of each station by a factor of three has only one unhappy outcome: more and more interference. The listening experience is degraded for everyone. Yet that is the experience we as an industry are supposedly trying to sell.

And just exactly what is the motivation for our industry to add more and more stations (or channels)? Aren't we all having a hard enough time making a living as it is? Why would we want (or need) to have every station carry 4 additional channels? Isn't the pie split too many ways already?

It amazes me when I read this board, which I would assume is mainly the province of radio industry professionals, that everyone is so staunchly in favor of more interference. I rarely read a post from someone like me who objects to having their radio experience further degraded.

This makes no sense to me.

 

[TheBigA]

And just exactly what is the motivation for our industry to add more and more stations (or channels)?

This "industry" isn't the motivation for more and more stations. It's the agenda of the FCC, that wants to add more stations for more revenue, and to add "diversity" to the airwaves. The industry, from the NAB, has been against adding more stations.

 

[JimmyJames]

And the listeners, well, they like that pesky thing called "choice."

 

[DaveBayArea]

I'm confused when and where the "right" was created for people to be able to listen to fringe signals. If the market isn't the market it was licensed to serve, I fail to see how someone outside that area has some sort of "right" to interference free reception of a non local station, caused by HD or not.

First of all, the average listener doesn't know the definition of a "fringe" signal. They could care less where their favorite stations' transmitter site is. If 94.5 is a button on a car radio and he/she listens to it and enjoys it, that's all they care about. Without interference, today's car radios achieve full quieting at the 40 dbu contour of an FM signal. The 1960's definition of a "fringe" area has been outpaced by low-noise front ends and ceramic filter IF's.

The 2nd problem is the means by which HD was allocated, using a fixed ratio of DB down from the main carrier. Consider the situation of two 1st adjacent FM stations. Not short spaced, but both allocated with similar coverage areas. Station one has a very high HAAT and a low transmitter power. Station two has a lower HAAT and a high transmitter power. In the analog world the station with the higher HAAT has a solid signal everywhere but a very strong signal nowhere. The station with the higher power has a very strong signal close to the transmitter site, but will typically suffer from multipath and/or the signal diminishes faster with distance. Still, the protected contours are similar.

Now add HD. Station one is still limited to -20 dbc power, maybe -14. This isn't nearly enough power to activate the HD decoder on today's radios. Even in a perfect world the thermal noise is way below the level of the digital signal. But add in self-generated noise from an HD processor along with the analog carrier of the more powerful 1st adjacent, and HD is useless. Meanwhile, station two turns on HD. His HD power is only a few DB down from the analog power of station 1. Station one becomes unlistenable in a large area, and if there are terrain issues this can easily happen within a station's FCC protected contour. The problem is that HD interference sounds just like white noise to the untrained ear, so the general public is unaware that this is why they can no longer receive their favorite station. Meanwhile, station two has way more digital power than is necessary to cover their protected contour digitally. You notice that the big complaints of dropouts are from areas of high HAAT and transmitters of 6 KW or so. Not from the 50-KW operators. HD allocations should either be specifically calculated for digital power instead of the blanket ratio, or the power derating curve for HAAT should be changed to accommodate the additional interference.

I'm probably not so good at explaining the above phenomenon, but the reality is that many stations are suffering real financial damage because of HD - especially Non-comms that rely on listener donations. I also know of many people who have just quit listening to radio because the stations they enjoy aren't receivable any more. They don't understand why, but it's just static. It wouldn't be so bad if there was some benefit. But I own 5 HD radios and all of them sound like mediocre-quality webcasts. I've given up buying more, because I'm convinced that's the way the system sounds. A good FM signal (not one that's heavily processed) sounds way better. Plus, the programming on the HD-2 channels isn't as good as the signals we lost (opinion, for sure - but I don't see any HD-2's showing up in the ratings). So what's the point? I'm sorry, but I don't see what the advantage of HD is.

Dave B.

 

[SUPERCASTER]

Here is what I don't understand. Packing more and more stations into the same amount of spectrum, increasing the power of existing stations, and expanding the bandwidth of each station by a factor of three has only one unhappy outcome: more and more interference. The listening experience is degraded for everyone. Yet that is the experience we as an industry are supposedly trying to sell.

And just exactly what is the motivation for our industry to add more and more stations (or channels)? Aren't we all having a hard enough time making a living as it is? Why would we want (or need) to have every station carry 4 additional channels? Isn't the pie split too many ways already?

It amazes me when I read this board, which I would assume is mainly the province of radio industry professionals, that everyone is so staunchly in favor of more interference. I rarely read a post from someone like me who objects to having their radio experience further degraded.

This makes no sense to me.

You have my vote!

 

[SUPERCASTER]

I'm confused when and where the "right" was created for people to be able to listen to fringe signals. If the market isn't the market it was licensed to serve, I fail to see how someone outside that area has some sort of "right" to interference free reception of a non local station, caused by HD or not.

First of all, the average listener doesn't know the definition of a "fringe" signal. They could care less where their favorite stations' transmitter site is. If 94.5 is a button on a car radio and he/she listens to it and enjoys it, that's all they care about. Without interference, today's car radios achieve full quieting at the 40 dbu contour of an FM signal. The 1960's definition of a "fringe" area has been outpaced by low-noise front ends and ceramic filter IF's.

The 2nd problem is the means by which HD was allocated, using a fixed ratio of DB down from the main carrier. Consider the situation of two 1st adjacent FM stations. Not short spaced, but both allocated with similar coverage areas. Station one has a very high HAAT and a low transmitter power. Station two has a lower HAAT and a high transmitter power. In the analog world the station with the higher HAAT has a solid signal everywhere but a very strong signal nowhere. The station with the higher power has a very strong signal close to the transmitter site, but will typically suffer from multipath and/or the signal diminishes faster with distance. Still, the protected contours are similar.

Now add HD. Station one is still limited to -20 dbc power, maybe -14. This isn't nearly enough power to activate the HD decoder on today's radios. Even in a perfect world the thermal noise is way below the level of the digital signal. But add in self-generated noise from an HD processor along with the analog carrier of the more powerful 1st adjacent, and HD is useless. Meanwhile, station two turns on HD. His HD power is only a few DB down from the analog power of station 1. Station one becomes unlistenable in a large area, and if there are terrain issues this can easily happen within a station's FCC protected contour. The problem is that HD interference sounds just like white noise to the untrained ear, so the general public is unaware that this is why they can no longer receive their favorite station. Meanwhile, station two has way more digital power than is necessary to cover their protected contour digitally. You notice that the big complaints of dropouts are from areas of high HAAT and transmitters of 6 KW or so. Not from the 50-KW operators. HD allocations should either be specifically calculated for digital power instead of the blanket ratio, or the power derating curve for HAAT should be changed to accommodate the additional interference.

I'm probably not so good at explaining the above phenomenon, but the reality is that many stations are suffering real financial damage because of HD - especially Non-comms that rely on listener donations. I also know of many people who have just quit listening to radio because the stations they enjoy aren't receivable any more. They don't understand why, but it's just static. It wouldn't be so bad if there was some benefit. But I own 5 HD radios and all of them sound like mediocre-quality webcasts. I've given up buying more, because I'm convinced that's the way the system sounds. A good FM signal (not one that's heavily processed) sounds way better. Plus, the programming on the HD-2 channels isn't as good as the signals we lost (opinion, for sure - but I don't see any HD-2's showing up in the ratings). So what's the point? I'm sorry, but I don't see what the advantage of HD is.

Dave B.

Good points. Unfortunately HD radio was "sold" by claiming total immunity from all forms of noise and interference and pristine fidelity simply because it's "digital"

Some of us knew better even before the crap hit the airwaves.

 

[BRNout]

Tom described it beautifully. I couldn't do any better. And, his analogies stand up pretty well in the debate.

Except they don't stand up where it counts: In a court of law.

In case you haven't noticed, the law is only important now when it's convenient. And, it can be surprisingly elastic. Just ask the folks in Washington about their plans this weekend. :

At least Tom makes a clear statement with regard to what's right, what's wrong and what's common sense.

 

[Tom Wells]

I was offering perspective and considerations, recognizing historic common law as applied to this matter.
I think we all know I favor a well-managed band plan for MW that permits the most choice for listeners.
Such as was dismantled by the FCC and enforced by ever increasing noise from devices with little or no RF noise supression.
I can't begin to make any legal argument, but I have studied RF and its behavior since I was aware,
as many others here have. I'm doing my best to see all sides here.
Monkey chatter is something I can live with, iboc just makes me want to ....Arghhh.
And I have no problems with digital. It is what is it is. It needs its own spectrum.
And existing stations ought to be able to stay where they are if they want, AND be on the new band.
Medium wave's peculiar advantages are being foolishly wasted with multiple redundancy duplications where original regional content is badly needed.

 

[TheBigA]

In case you haven't noticed, the law is only important now when it's convenient.

And in case you haven't noticed, the reaction to that kind of behavior is pretty loud.

What Tom says is only common sense in the world of 1912, ignoring everything that happened since. Common law doesn't apply here, since there is more recent precedent.