HD AM Occupied Bandwidth Tests

[Play Freebird]

I found an interesting comment on page 45 of the October 24 Radio World. The CE of Crawford's Denver stations sent a screen shot of a spectrum analyzer to support his belief that HD Radio fits completely within the NRSC-2 mask. However, I noticed that the analog sidebands (the portion from carrier out to 5 kHz) are about 15 dB lower than what I typically see on a compliant analog-only station. Relative to the carrier, they appear down about 40 dB, too good to be true.

No details are given about the resolution bandwidth setting of the analyzer (the NRSC standard calls for 300 Hz), or whether it was operated in peak hold mode for 10 minutes, as required by 47CFR73.44. These settings can have a big effect on the outcome of the tests. If you want to make sidebands (whether analog or digital) look lower, you simply narrow the RBW and/or defeat peak hold -- or, of course, under-modulate. This may give you a picture suitable for framing, but its an invalid test.

Those of you who own or maintain AM stations; if it's not too much trouble to review your last NRSC test, you might want to compare the 0 to +/- 5 kHz sideband amplitude against this picture and let us know your thoughts.

 

[Mike Walker]

It's possible that AM HD does fit within NRSC tolerances, AND ALSO causes increased interference, because interference from analog sidebands (cymbal crashes, trumpets blatting, "s" sounds, etc.) is transient in nature, but the HD digital sidebands are constant. An AM station that ran, say, a 7khz 100 percent sine wave around the clock may fit within NRSC tolerances, but it'd be pretty damned annoying to neighbors!

 

[ve3jf]

It's possible that AM HD does fit within NRSC tolerances, AND ALSO causes increased interference, because interference from analog sidebands (cymbal crashes, trumpets blatting, "s" sounds, etc.) is transient in nature, but the HD digital sidebands are constant. An AM station that ran, say, a 7khz 100 percent sine wave around the clock may fit within NRSC tolerances, but it'd be pretty damned annoying to neighbors!

You bet! If you want to assess the potential for interfering with adjacent channel stations, you really need to know the average power that you're dumping into the adjacent channels. Several years back, I did some measurements of the average power deposited into the 1st adjacent channels by several local AM stations (all running NRSC bandwidth), and then I calculated how much that power would increase if they started running IBOC. The answer: the increase ranged from 18 to 39 dB! The increase was least for an oldies music format, and most for talk formats, but it was huge in all cases. Details are in this 2004 FCC filing:
http://topazdesigns.com/iboc/McLarnon-ReplyComments-Jul04.pdf
As I also pointed out in that filing, if you do a real occupied bandwidth measurement (according to the generally accepted engineering definition for that term) of the AM signal, you find that adding the IBOC digital signal increases the occupied bandwidth by a factor of approximately 25! The FM IBOC system, OTOH, merely doubles the occupied bandwidth of the FM signal. If anyone is interested, the original comments referred to in that filing can be found at:
http://topazdesigns.com/iboc/McLarnon-Comments-Jun04.pdf

These and other inconvenient truths were completely ignored by the Commission in its IBOC Report and Order earlier this year. And so it goes...

Barry

 

[JohnnyElectron]

Barry, my petition on 99-325 was also singled-out and dismissed by the FCC - they don't like interpolated, extrapolated, or measured data from engineers, it would seem, along with actual over-the-air observations. So, we're in good company with Leonard Kahn, I guess.

 

[SUPERCASTER]

It's possible that AM HD does fit within NRSC tolerances, AND ALSO causes increased interference, because interference from analog sidebands (cymbal crashes, trumpets blatting, "s" sounds, etc.) is transient in nature, but the HD digital sidebands are constant. An AM station that ran, say, a 7khz 100 percent sine wave around the clock may fit within NRSC tolerances, but it'd be pretty damned annoying to neighbors!

You bet! If you want to assess the potential for interfering with adjacent channel stations, you really need to know the average power that you're dumping into the adjacent channels. Several years back, I did some measurements of the average power deposited into the 1st adjacent channels by several local AM stations (all running NRSC bandwidth), and then I calculated how much that power would increase if they started running IBOC. The answer: the increase ranged from 18 to 39 dB! The increase was least for an oldies music format, and most for talk formats, but it was huge in all cases. Details are in this 2004 FCC filing:
http://topazdesigns.com/iboc/McLarnon-ReplyComments-Jul04.pdf
As I also pointed out in that filing, if you do a real occupied bandwidth measurement (according to the generally accepted engineering definition for that term) of the AM signal, you find that adding the IBOC digital signal increases the occupied bandwidth by a factor of approximately 25! The FM IBOC system, OTOH, merely doubles the occupied bandwidth of the FM signal. If anyone is interested, the original comments referred to in that filing can be found at:
http://topazdesigns.com/iboc/McLarnon-Comments-Jun04.pdf

These and other inconvenient truths were completely ignored by the Commission in its IBOC Report and Order earlier this year. And so it goes...

Barry

Once again proving that the unscrupulous HD supporters will stop at nothing to inflict their new digital HD interference on the public's airwaves.

Thanks again Barry for your efforts on behalf of radio listeners and the public.

 

[calstymes]

JohnnyElectron aptly noted:

Barry, my petition on 99-325 was also singled-out and dismissed by the FCC - they don't like interpolated, extrapolated, or measured data from engineers, it would seem, along with actual over-the-air observations. So, we're in good company with Leonard Kahn, I guess.

Follow the money.

 

[clouseau]

It's possible that AM HD does fit within NRSC tolerances, AND ALSO causes increased interference, because interference from analog sidebands (cymbal crashes, trumpets blatting, "s" sounds, etc.) is transient in nature, but the HD digital sidebands are constant. An AM station that ran, say, a 7khz 100 percent sine wave around the clock may fit within NRSC tolerances, but it'd be pretty damned annoying to neighbors!

You bet! If you want to assess the potential for interfering with adjacent channel stations, you really need to know the average power that you're dumping into the adjacent channels. Several years back, I did some measurements of the average power deposited into the 1st adjacent channels by several local AM stations (all running NRSC bandwidth), and then I calculated how much that power would increase if they started running IBOC. The answer: the increase ranged from 18 to 39 dB! The increase was least for an oldies music format, and most for talk formats, but it was huge in all cases. Details are in this 2004 FCC filing:
http://topazdesigns.com/iboc/McLarnon-ReplyComments-Jul04.pdf
As I also pointed out in that filing, if you do a real occupied bandwidth measurement (according to the generally accepted engineering definition for that term) of the AM signal, you find that adding the IBOC digital signal increases the occupied bandwidth by a factor of approximately 25! The FM IBOC system, OTOH, merely doubles the occupied bandwidth of the FM signal. If anyone is interested, the original comments referred to in that filing can be found at:
http://topazdesigns.com/iboc/McLarnon-Comments-Jun04.pdf

These and other inconvenient truths were completely ignored by the Commission in its IBOC Report and Order earlier this year. And so it goes...

Barry

Barry makes a few interesting points. What I think might be different are the Conclusions.

These and other inconvenient truths were completely ignored by the Commission in its IBOC Report and Order earlier this year.

I would propose that just MAYBE Barry wasn't "Ignored". How about "In a balance of positive and negative factors, all information received was considered and a decision was rendered". (By the way, I will assert this most likely "IS" what happened) Isn't it at least possible that the FCC just thought the potential benefit outweighed what they felt was the minimal "Cost"?

And then we have the choir of Ghouls chime in...

Once again proving

Of course it's plainly evident on the surface this doesn't "Prove" anything.

that the unscrupulous HD supporters

You don't think calling this "Proof" of ANYTHING is unscrupulous? It's an out and out falsehood. While I've picked on you for your inacurracy from time to time, you seem to have the intellect to actually be able to grasp this. YOUR ARE WHAT YOU ACCUSE OTHERS OF. Sorry, dude. No proof of anything here...

Clouseau

 

[ve3jf]

I would propose that just MAYBE Barry wasn't "Ignored". How about "In a balance of positive and negative factors, all information received was considered and a decision was rendered". (By the way, I will assert this most likely "IS" what happened) Isn't it at least possible that the FCC just thought the potential benefit outweighed what they felt was the minimal "Cost"?

Fair enough, but... I think enough legitimate points of concern were raised that if the Commission were actually doing its job, it would've called for further studies of the interference concerns. Instead, they just dismissed them out of hand, without even addressing them point by point. Contrast this with the LPFM docket, where they apparently decided that the NAB was playing fast and loose with the truth concerning adjacent channel interference, so they commissioned an independent study of the matter. There was ample evidence on the IBOC docket to indicate that such a study was needed, but instead they just bailed out and bought the NAB/iBiquity party line. They never got to the heart of the essential question: "potential benefit" to whom, and what is the real "cost" to those who are not part of the iBiquity cartel?

Barry

 

[Tom Wells]

Anyone who has ever looked at an o-scope, let alone alone a frequency anaylzer, can see this is an instantaneous snapshot,
and not the prescribed duration time accumulated standard 10 min measurement.

I am shocked someone would present this as evidence. We weren't born yesterday.

It's just another example of ....whatever it is that makes them think they can sell hash as surf-n-turf.

 

[Savage]

Yep, no doubt about it. I looked at that SA display photo, laughed, and tossed the magazine in the trash. I couldn't believe they bothered to print it. It was like publishing a picture of some guy furiously pedaling a bike, with an accompanying caption: Local Cyclist Breaks Sound Barrier!

You can make an instantaneous display look like anything you want. Around here we'd call Cris Alexander's "creative" NRSC mask measurements "AAM" (analyzer-aided masturbation.)

Once again: HD boosters declare victory and march home.

 

[clouseau]

Fair enough, but... I think enough legitimate points of concern were raised that if the Commission were actually doing its job, it would've called for further studies of the interference concerns. Instead, they just dismissed them out of hand, without even addressing them point by point.

I was under the impression there was a significant delay in authorizing nightime Am for just this reason. I wasn't involved , but that was my impressin.

Contrast this with the LPFM docket, where they apparently decided that the NAB was playing fast and loose with the truth concerning adjacent channel interference, so they commissioned an independent study of the matter.

Ahhh the Mitre study. Commissioned to prove 3rd adjacent 100 watt stations don't interfere more than second adhacent 250 watt stations. Shockingly, they don't.

But seriously you may be right here political-wise. There was a lot of fervor over getting something up and running.

There was ample evidence on the IBOC docket to indicate that such a study was needed, but instead they just bailed out and bought the NAB/iBiquity party line. They never got to the heart of the essential question: "potential benefit" to whom, and what is the real "cost" to those who are not part of the iBiquity cartel?

From what I have seen of Mitre, I would bet such similar research was done. Obviously much was theoretical such as you have presented on your site, but IIRC there was extensive real world testing as well. I'm not sure I'd charactaize the FCC's reaction as "Bailed Out", but I see where you're coming from.

Clouseau

 

[ve3jf]

I was under the impression there was a significant delay in authorizing nightime Am for just this reason. I wasn't involved , but that was my impressin.

Well, the delay in authorizing nighttime AM was close to 5 years. There are two possible explanations:

(1) More extensive studies, and especially field tests, were needed to look at the interference problems.

(2) Those "in the know" in the IBOC camp knew that nighttime AM would be a huge mess, and the negative publicity that it generated could stall the IBOC rollout, or even kill it dead.

Now, if (1) were the correct answer, it stands to reason that there would've been extensive nighttime field tests involving a considerable number of stations, with numerous reception locations and a large collection of different receivers, over time periods long enough to coverage different propagation conditions, and so on. But no such measurement campaign took place. In fact, the only documented field test during those 5 years involved exactly two stations, and lasted two or three nights. That's it. And, if you read past the executive summary of the report and actually looked at the data, it was apparent that there were enough interference issues to merit further field tests. But they never happened. Why? Because the real answer is (2).

Barry

 

[JohnnyElectron]

The only night time HD-AM testing that I'm aware of was done from Cincinnati a few years back.

 

[clouseau]

I recall reading a release from a comissioner stating something like "We have approved AM at night based on extensive testing my Ibiquity and Blah Blah Blah..."

I could look it up, but I don't have an index. Strikes me it was in March 07...

Did it happen? I would assume so, but haven't seen any research published.

Barry raises some interestng issues. Clearly there are differeing sides to these issues. I'd ask... "Is AM ruined after the introduction of IBOC?"

From my perspective... NO.

I do understand others may disagree. I don't. YMMV

Clouseau

 

[JohnnyElectron]

Night Time HD-AM Testing

Was HD-AM tested on any station other than the 1 minute on - 1 minute off BUZZ from Cincinnati 1530 a few years back?

And interestingly enough, I notice that they don't run IBOC on 1530 at night at all now?

 

[dumber than a box of hair]

Re: Night Time HD-AM Testing

Was HD-AM tested on any station other than the 1 minute on - 1 minute off BUZZ from Cincinnati 1530 a few years back?

And interestingly enough, I notice that they don't run IBOC on 1530 at night at all now?

WOR and WLW ran many coordinated nighttime tests of HD-AM, long before it was approved. Tom Ray should be able to enlighten us as to the results of those tests.

 

[ve3jf]

Re: Night Time HD-AM Testing

Was HD-AM tested on any station other than the 1 minute on - 1 minute off BUZZ from Cincinnati 1530 a few years back?

And interestingly enough, I notice that they don't run IBOC on 1530 at night at all now?

WOR and WLW ran many coordinated nighttime tests of HD-AM, long before it was approved. Tom Ray should be able to enlighten us as to the results of those tests.

I always look forward to enlightenment, but I think "many" nighttime tests is a gross exaggeration. In any case, what counts is the tests whose results were documented, and disclosed to the public. The documented tests only covered a couple of nights. Even if there were many such tests between WOR and WLW, looking at only two stations is a woefully inadequate sample size for studying such an important issue.

Barry