Comments on the proposed 10 db increase in digital power on the FM band.

[KB1OKL]

Interesting comments on the proposed implementation of the 10 db increase in digital power on the FM band.

COMMENTS OF H. DONALD MESSER, DR. ENG.
IN REFERENCE TO THE FCC’S PUBLIC NOTICE, DATED 10/23/08,
ON SUBMISSIONS BY INTERESTED PARTIES
ON A PROPOSAL TO PERMIT THE DIGITAL MODULATION PORTION
OF HD RADIO TO INCREASE ITS AVERAGE POWER BY A FACTOR OF 10
COMPARED TO THE CURRENT LEVEL SPECIFIED IN NRSC-5-B

OVER MORE THAN THE PAST DECADE I HAVE PLAYED A KEY ROLE
IN THE EVALUATION AND STANDARDIZATION OF DIGITAL AUDIO
BROADCASTING SYSTEMS, BOTH FOR DIRECT TERRESTRIAL AND
FOR SATELLITE DOMINATED SYSTEMS.

http://fjallfoss.fcc.gov/prod/ecfs/retrieve.cgi?native_or_pdf=pdf&id_document=6520184739

 

[radioskeptic]

Of course he's right, but that isn't enough to impress the Federal Cookie Company!

 

[RadeoEngineer]

Hell, give them the 10dB, in fact, MANDATE IT for those running the system. Then sit back and watch how many shut down from the added expense of doing over a DOA system.

 

[clouseau]

I always find stuff like this fascinating.

You know. The old... "You guys claim to have tested this and it works, but I don't like the idea so don't do it" thing. Great comments.

We in broadcasting have all had to live with more RF neighbors than we had before, at one time or another. It happened with (K)KOB and WABC on 770Kc. It happened when FM Migrated from 49KC and their new neighbor, TV. (Change to KHz and MHz) It happened with the TV drop in's of the 70's. It happened with RM 80-90. It happened when we had to refit the whole country with 2 degree compliant satellite dishes. It's happened some more when FM-HD was authorized. And you can bet your booty it will continue. We all have to cope.

I am not a party to the increased HD power tests. But as I play with the FCC "curves", I get some interesting results.

First off, If I read the proposal correctly, we are looking to have HD power be 1/10th analog power. Up from 1/100th, IIRC.

On a first adjacent analog, protecting a 60 dbu at 54 dbu, a 1 KW station 150 MTRS at 54 dbu contour is 30.838 KM. Now if we calculate the actual power of .1KW and use the CO-CHANNEL standard of 40 dbu, we get a distance of 38.251. That means, under our CURRENT standards, you would be about 7.4 KM short spaced. Is this an issue based on todays radios and the capture effect?

I don't know. It is tighter than what we have now. but I will look you in the eye and tell you we can tighten "what we have now" up, SOME, without many problems. We've already muddied the waters with our existing HD levels. (I know purists will call it exactly that, but FMHD seems to be OK so far)

The question is... How miuch tightening can we do. IIRC, some darned fool suggested we could actually do second adjacent full powers with no real problem. That whack job Clouseau, I believe.

I will not endorse this proposal because I dont know how it actually WILL work. But it strikes me it might work just fine. IIRC this is isn't an Ibiquity thing as much as broadcasters. Clearly FMHD could use a power boost. Just railing for or against without info is pointless.

They said, they said the original FM-HD wouldn't interfere, and it basicly didn't. Would they lie now? (Sorry, I'm embarrased to have even posed the question).

We'll see how it goes. FM first adjacents are "Your land or my land". I suspect the rimshots will be the only real sufferers here. Get ready to really live by your contour map.

Clouseau

 

[RadeoEngineer]

10dB more. What do you have to replace? HD transmitter? Combiner? Line? Reject load? Antenna? Modules in a low level system? How much does any of this cost? How much ROI are you getting now vs. projected with this change?

 

[Play Freebird]

Let's not forget that the majority of FM stations in some highly-populated markets, particularly in the Northeast, Midwest, and Southern California, have significant short spacings.

For example, every commercial FM station licensed to the City of Philadelphia is short-spaced to at least three other stations, including one first-adjacent. 92.5 WXTU is about 23 miles too close to 92.3 WXRK in New York; 93.3 WMMR is similarly short-spaced to 93.1 WPAT; same with 94.1 WYSP vs. 93.9 WNYC, and the list goes on and on. Between each of these pairs is the nation's most densely-populated state, New Jersey -- and millions of listeners.

Then there are those infamous first-adjacent short spacings in the Baltimore-Washington corridor and around Chicago.

The potential for analog interference between these stations has been reduced over the years by improved IF filtering techniques. However, IBOC intentionally transmits the digital carriers directly atop neighboring analog FM channels, so how is this noise to be filtered out?

 

[dumber than a box of hair]

Looks like he has the same reservations that NPR Labs had about the proposed power increase...what effect it will have on the analog signal (lest we forget, that's where the radio business makes its money). iBiquity still seems to think this is all some sort of "free lunch"...just crank up the power and be done with it. If they were starting with a pristine, never-before-used frequency band, they might have a case...but trashing existing analog signals is like saying "the operation was successful, but the patient died."

 

[rbrucecarter5]

Time for me to submit my results, I suppose. Hopefully I can help put a stop to this madness before it ever gets started. Here is the core of what I will send:
----------------------------------------------------------
"I did a carefully controlled scientific experiment at 70 miles from the Dallas / Ft. Worth stations. My receiver was a Sangean HDT-1X. I placed a reference dipole 1 meter off of the ground, and conducted the test outdoors away from all metallic objects. The test time was 3PM, to minimize any possibility of atmospheric skip conditions. All Dallas / Ft. Worth stations locked in HD mode with no trouble, and stayed locked for the duration of the test.

I did a secondary test of FM signal strength in an office environment. No HD receiver was available, however, my tests with an Agilent 8560 spectrum analyzer showed that broadcast FM stations are attenuated by 10 dB every 6 to 8 feet. Therefore, an increase in sideband transmission power would only result in 6 to 8 feet of additional building penetration, not enough to appreciably increase HD listenership.

The same Agilent 8560, operated from an inverter in an automotive environment, showed FM signal strength in fringe areas varies by as much as 60 dB, sometimes only moving a few feet from a location of good signal strength. Given the speed of a car in a fringe situation, combined with rapidly varying signal strengths and relatively long lock times, the likelihood of a 10 dB power increase on HD sidebands improving mobile reception is remote.

The same rapidly varying signal strengths are observed in fringe areas where airplane scatter exists. Given that most metropolitan areas contain an airport and airplane scatter is a fact of life in fringe suburban areas, a 10 dB power increase on the sidebands is unlikely to mitigate reception problems there as well.

We have been in a solar sunspot minimum for the duration of the FM HD installation period, what little skip has existed will not propagate existing IBOC sidebands to any degree as it does not tend to propagate analog stations 1000W and less. However, a 10 dB power increase on sidebands will definitely put them into power levels that will skip and during periods of solar activity, broadcasters may find themselves in an untenable situation with high RF levels of noise due to IBOC sidebands hundreds or even over a thousand miles away override their signal locally. Sunspot cycles have reliably repeated every 11 years, and there is a very high likelihood we are moving into a new sunspot cycle that would correspond to this power increase. There is no way to predict when and where skip will occur, but its effects are spectacular, bring distant stations to locations with signal levels that match local stations. These events are frequent, especially during summer months. Add HD sidebands to the list of distant signals skipping, and the problem is multiplied."

------------------------------------------------------
And that is the meat of the situation - HD is plenty robust and reliable, given a stationary home listening situation away from airplanes. 70 mile HD reception - how much more do they want???? There were cows and horses, and widely scattered ranch houses 70 miles from the DFW towers. HD listenership that far from the towers is not going to be a factor in ratings, those folks won't shop in Dallas, they will shop in Sherman 15 miles up the road. So no advertisers in DFW care about them. Airplanes are a problem for HD reception - I was not on the approach path for DFW airport, but if I was I am convinced I would have had no luck with HD reception. A 10 dB power increase would have made no difference if a plane flew over.

As far as office workers - forget it. There are very few radios in offices, they don't work except near windows even in analog mode. Most people are streaming or using iPods if they listen to music at all. A 10 dB won't penetrate buildings enough to make any difference. The last thing an office worker is going to do is fool with an antenna when their boss is walking around.

Car reception has 60 dB signal variations, not 10 dB. Combined with the lock time, a 10 dB power increase is not going to do a thing.

The only thing a power increase will do is further jam first adjacents for the suburban and rural listeners who are getting first adjacents now. And it will tend to skip much more when sunspot cycle 24 begins -

 

[w9wi]

10dB more. What do you have to replace? HD transmitter? Combiner? Line? Reject load? Antenna? Modules in a low level system? How much does any of this cost? How much ROI are you getting now vs. projected with this change?

With the disclaimer that I'm a TV studio engineer, not a transmitter guy...

I think you're going to find most stations replacing their transmitters (both analog and HD) to achieve 10% digital power. I will not claim to be familiar with the financial consequences.

The high-level combiners commonly used for 1% HD are amazingly inefficient with regard to the HD power. In the examples I've seen, 90% of the output of the HD transmitter is lost as heat.

This is manageable with 1% HD power. Using a 20kw analog transmitter to hit an antenna system with a gain of 5 for 100kw analog ERP, the HD transmitter would have to output 2kw of which 1.8kw would be lost as heat. 1.8kw will make a building plenty warm but it's not particularly difficult to remove that much heat.

At 10% HD power you have to multiply those HD transmitter numbers by a factor of 10. You need a 20kw HD transmitter (same size as the analog) and you have to get rid of 18kw of heat. In Tennessee in July, that's a problem. Not to mention you've just doubled your utility bill. (just to run the transmitter. That doesn't count what you're going to spend running the air conditioner.)

In practice from what I'm hearing few if any stations will attempt to do 10% HD this way. They'll completely replace their existing transmitters with a single rig that generates both the analog and the HD in a single exciter and amplifies both through a common amplifier. The combiner and reject load go away altogether.

Of course you're buying a completely new transmitter. It will be generating 10% more RF - and it will be less efficient because it has to linearly amplify the HD signal. (it is not necessary to use linear amplifiers for analog FM. Linear amplifiers are less efficient than nonlinear units.) I would hope stations built their transmission systems with enough headroom that the feedline and antenna can handle the extra 10% power. (if not they're going to have to replace it)

With the economic downturn I would be surprised to see 10% HD make a whole lot of headway anytime soon.

 

[RadeoEngineer]

Exactly.

 

[ve3jf]

It's really disturbing how few comments have been filed on this important issue. Another affront to common sense about to slide in under the radar? My guess is a lot of consultants feel conflicted about it - they know it's a bad idea, but to say so in public could have a negative impact on their livelihood.

Anyway, I've put in my two cents... read all about it at http://fjallfoss.fcc.gov/prod/ecfs/retrieve.cgi?native_or_pdf=pdf&id_document=6520184871

Who knows, maybe the Reply Comments phase will bring some more folks out of the woodwork... but I'm not holding my breath.

 

[Savage]

Does it really matter? After all the Commission received scores of negative comments ca. 2002-2006 warning about the interference potential posed by the IBOC system and AM-HD in particular. They simply ignored them in a rush to adopt the system and, using Cris Alexander's picturesque phrase, "pushed past" objections to "embrace radio's digital future."

What hath Glynn and Cris and Tom Ray wrought? Listen to AM between 1000 Khz and 1220 kHz on any winter night. (Or try to.)

But, what-the-hey, "it's only AM."

Personally I'm in favor of letting the calf have ALL the rope. Give 'em their tenfold increase. It won't work - so then, give 'em 20db. Trash the whole freakin' FM band for 99 percent of listeners who depend on analog radio.

Maybe THEN the IBOC people will harvest the oblivion they so richly deserve. Hopefully some real broadcasters with integrity and common sense will still be around to pick up the pieces and lure listeners back.

Attention iBiquity, Alliance and NAB nitwits: you've sown. Now, reap and choke it down, you losers.

 

[RadeoEngineer]

I like this Savage guy.

 

[Carmine5]

Not to be missed is Mr. Savage's letter in the "Reader's Forum" in the latest issue of Radio World in which compares the stubborn determination to make IBOC work to a fly continually hitting a pane of glass (apt analogy, BTW).

As he says the 10 db increase will be bringing to the FM band what is already occurring with HD on the AM band in terms of adjacent-channel interference.

C5

 

[JohnnyElectron]

I filed 4 large comments on the 99-325 over the years, and the FCC "dismissed" my interference issues about AM IBOC; therefore, screw the FM stations and their 10dB increase. Most stations can't add it anyhow and few if any will add it, so who cares anymore?

 

[rbrucecarter5]

Not to be missed is Mr. Savage's letter in the "Reader's Forum" in the latest issue of Radio World in which compares the stubborn determination to make IBOC work to a fly continually hitting a pane of glass (apt analogy, BTW).

As he says the 10 db increase will be bringing to the FM band what is already occurring with HD on the AM band in terms of adjacent-channel interference.

C5

Adjacent channel FM interference is already horrific. 10 dB more will be ten times worse.