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FCC adopts rulemaking for all digital AM broadcasting




 
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Author Topic: FCC adopts rulemaking for all digital AM broadcasting  (Read 926 times)
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W1EQX
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« on: November 22, 2019, 03:24:25 PM »

The FCC approved the adoption of a rulemaking allowing AM broadcast stations to transition to all-digital operation. The only AM station currently broadcasting all digital today under special authority is ďThe GamutĒ 820 WWFD Frederick, MD. This is full digital, no AM analog compatibility. Currently AM HD carries an analog AM component that about 10 kHz wide (5 kHz audio response) surrounded by a digital transmission. Car radios and other receivers with HD FM reception (that have AM tuners) have the capability to decode full AM digital without an analog signal. Tests conducted under all digital by WWFD indicated "HiFi" reception is possible almost down to almost the analog AM noise floor, which these days is pretty high in many areas.

The good news is there may be more older AM broadcast transmitters for sale that cannot properly transmit the all digital signal.
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« Reply #1 on: November 24, 2019, 02:01:58 PM »

well and good on the transmitters.

AM is all I listen to in the car, and the FM tuner is not HD. It's not worth the cost of a new automotive radio to me, after all I'm already paying for the broadcasts by listening to the commercials.
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« Reply #2 on: November 27, 2019, 09:29:11 AM »

As a follow up to my original all digital AM broadcasting here is the link to the technical standard below.

It appears that all digital AM is much less of a spectrum hog than the currently allowed NRSC 5 hybrid AM transmission. Currently AM stations transmitting hybrid "HD" digital take up almost 30 kHz of spectrum creating lots of adjacent splatter. All digital HD mode appears to have two modes-  standard using 20 kHz of spectrum (roughly equivalent to analog AM with a standard 10 kHz high frequency audio cutoff) and a lower bandwidth mode using a total 10 kHz of spectrum. The all digital AM HD transmission is similar to the FM HD version, allowing for program information to be displayed on the radio receiver as well as multiple individual stereo programming channels with one signal. HD1, HD2 and HD3... So one AM station could carry multiple radio formats at the same time just like in FM HD.

https://www.nrscstandards.org/standards-and-guidelines/documents/standards/nrsc-5-d/reference-docs/1012s.pdf
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« Reply #3 on: November 28, 2019, 08:13:21 AM »

Wow !  Is there a date by which stations must convert?
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kb2vxa
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« Reply #4 on: November 28, 2019, 10:18:04 AM »

One small correction, analog AM channels are spaced every 10KHz and are allowed a maximum occupied bandwidth of 10KHz. The last thing in the audio chain is a LPF with a sharp cutoff at 5KHz to keep it legal. Back in the days of tubes they didn't need filters, all those transformers, capacitors and chokes limited audio response from about 60 to 4800Hz. When I proofed out a station's two Collins and one Gates transmitter that's all I got out of them. There was one exception, phase modulated transmitters like the RCA Ampliphase units. Having no high powered modulators they had a high end surpassing 10KHz, so WOR 710 NYC using a pair of RCA 50Gs had the LPF in the processor rack at the Carteret, NJ transmitter site.

The days when we could save tube AM transmitters from the scrap yard are over. Now I wonder about the new modular solid state units that replaced them. With plug in modules that can be hot swapped they eliminated the need for backup transmitters. Frankly I have serious doubts about the newest digital transmitters being used for HD since so few stations still broadcast music. Now it's almost all Talk Radio aka Radio Ga Ga to steal one from Queen. For what its worthless, that's how Lady Ga Ga got her new stage name.
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73 de Warren KB2VXA
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« Reply #5 on: November 30, 2019, 05:22:50 AM »

... analog AM channels are spaced every 10KHz and are allowed a maximum occupied bandwidth of 10KHz ...

Clarification:  the r-f bandwidth of the transmitted signal legally can approach 20 kHz, which, when demodulated in a near-perfect AM receiver produces an audio output waveform with an upper frequency limit of about 9.5 kHz (see the clip below).

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kb2vxa
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« Reply #6 on: December 01, 2019, 11:42:00 AM »

The rules must have changed in more recent years. As I remember when most AM stations broadcast music and earlier, from 1944 to 2009 WQXR, the outgrowth of W2XR AM 1560 and FM 96.3 had special licenses. 1560 had a waiver allowing it a 20KHz occupied bandwidth as "New York's hi fi station". In the 1950s they experimented with stereo, one channel on AM and the other on FM. Those audiophiles having an AM receiver with stagger tuned or decoupled IFs, or an old TRF set and hi fi amps and speakers were in hog heaven. The transmitters employed soft knee peak limiting only allowing the classical music having a wide dynamic range to be heard as it should be. Later when the FCC mandated the AM - FM split they had a waiver allowing simulcast to continue. Today the 1560 AM is WFME and FM moved to 105.9 HD1: Classical, HD2: Contemporary Classical "New Sounds". BTW, at the time I had a rack mounted Collins broadcast station air monitor, the FM had 4 IFs, 2 limiters, and a twin diode detector. The AM was 4 tube TRF with a 10-20KC filter, remember this was before Hertz got the honor, so I heard 1560 having almost but not quite the high end response of 96.3.

That having been said, back in my SWL daze I was an avid MW AM band DXer frustrated as all heck when a station would go into a fade on the hour or half hour station ID. Then the FCC began systematically dismantling the band, stations now use logos mostly duplicated instead of call letters. Along came IBOC and that annoying hiss atop adjacent stations and Canadians complaining mightily about getting hissed on at night. So much for my hobby.

The way radio has become a vast wasteland of commercials, talk, and general radio ga ga I haven't listened in years, so I couldn't give a damn my dear (Rhett Butler's famous last line) about it going digital. Now as previously stated I wonder what will become of those modular solid state transmitters. The old tube units that had seen better days were either given away to the AM Gangstas or scrapped, but the new units are still in their prime and worth some pretty good money. Maybe they'll be shipped overseas, maybe AM Gangstas with deep pockets will snag a few. It's all TBD..........
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73 de Warren KB2VXA
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« Reply #7 on: December 03, 2019, 06:16:38 PM »

Wow !  Is there a date by which stations must convert?

There is no date for conversion since it will be a voluntary situation in which each station will have the option of changing over to HD or staying analog.

As stated here in the NPR, https://docs.fcc.gov/public/attachments/DOC-360519A1.pdf there are many engineering issues to be worked out before it becomes viable.

This "all-digital" transmission system will be based on 64-QAM modulation with a bandwidth of 20 kHz using the NRSC's MA3 Digital 'MASK.' (see references here to 'MA3' https://www.nrscstandards.org/standards-and-guidelines/documents/archive/nrsc-5-b/1082sE.pdf )

The original MA1 "Hybrid" mask, also known as Interference Buzz on Channel (IBOC), would be replaced by the MA3 mode which deletes the combination analog/digital carrier and substitutes it for a purely digital carrier with no analog carrier whatsoever.


Phil - AC0OB

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« Reply #8 on: December 04, 2019, 03:19:15 PM »

I, along with the engineer at Hubbard Broadcasting, Dave Kolesar, put this station on the air. It's been quite an experience.

We are finding out in our testing that the enhanced carriers which convey the stereo audio and data services can be received down to the .5 mV contour and LOS is at around the .1-.2mV contour. At the .1 mV, all you would hear is the heterodyne of the analog carrier. As Phil pointed out, this is voluntary. This is to make it easier for stations to put it on without obtaining an experimental authority from the FCC. If approved, stations would only have to notify the commission by letter that they converted.
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« Reply #9 on: December 08, 2019, 02:40:02 PM »

One small correction, analog AM channels are spaced every 10KHz and are allowed a maximum occupied bandwidth of 10KHz. The last thing in the audio chain is a LPF with a sharp cutoff at 5KHz to keep it legal. Back in the days of tubes they didn't need filters, all those transformers, capacitors and chokes limited audio response from about 60 to 4800Hz. When I proofed out a station's two Collins and one Gates transmitter that's all I got out of them. There was one exception, phase modulated transmitters like the RCA Ampliphase units. Having no high powered modulators they had a high end surpassing 10KHz, so WOR 710 NYC using a pair of RCA 50Gs had the LPF in the processor rack at the Carteret, NJ transmitter site....


I have noticed that some AM broadcast stations cut off their high end at 5 kHz or below. Sounds bad, and the idea that it's required is not true now and has never been true. It seems to be gaining currency like an urban legend, with the assistance of people who know better but think 5 kHz cutoff is a "good idea" and so should be encouraged. It's actually a terrible idea.

I was engineer at both WEAM 1390 and WPGC 1580 in the Washington, DC area, among other stations, from 1976 though 1984. Full audio bandwidth was transmitted -- and could be received in wide bandwidth too if you had a good receiver/tuner, as I did with my McKay-Dymek AM5 and my Carver tx-11a and my modified Racal RA-6217.

When the (rather stupid) NRSC rules came into force in the 80s, stations were forced to limit their high end to 10 kHz. Any further restriction was voluntary, and in my opinion regrettable.

The low-bitrate digital audio stream allowed by the IBOC system is a complete turkey. Even when reception is perfect, it sounds like a 1995-era 15-kbps online Real Audio file, with egregious compression artifacts, so bad that you'd be willing to pay a subscription fee just to get them to turn it off.

IBOC has always been a scam, anyway. It was created by the big money boys in order to _prevent_ a dedicated digital band from emerging in the US. I discuss that further here: http://www.kevinalfredstrom.com/2009/12/hd-radio-doomed-from-the-start/

73,

Kevin, WB4AIO.
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KA6FZT
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« Reply #10 on: December 09, 2019, 07:48:11 PM »

One would think that the radio stations limiting their audio to 5khz would be okay as most are in an all talk mode format.  If itís music they are going to play, it would be far better to open up the audio bandwidth.

This past summer while bored driving home from work at night, I rediscovered XEPRS 1090 (Mighty 1090) whose transmitter is south of San Diego (Rosarito, Baja) and is simulcasting from its family owned FM station which is out of Alamo, Texas (KJAV 104.9, Ultimate 104).  The sound coming out of my cars radio in the AM mode sucks--telephone audio.  Gone are the days of the permeability tuned car radios feeding a 6x9 or 5x7 speaker in the dash plus those highly extendable antennas.  However, listening to XEPRS at home using the RSP-1, one can see the stationís overall bandwidth is a respectable 20Khz wide.  In fact, the lower sideband wipes out Los Angelesís KNX 1070 upper IBOC signal and KNX is much closer to where I live.  Almost all of the stations I can see across the band with the RSP are definitely restricting themselves to the 5kz audio limit and very few running IBOC.

My issue with going all digital is getting and maintaining lock.  Look what happened with digital TV.  If you get a signal, itís an awesome picture but to get it requires a minimum S/N ratio.  What was a clear signal analog with a tv antenna at 15ft almost cannot be done in digital with the antenna at 30ft.  How would that work with AM with signal fade especially at night or even just driving around?  I suppose that if the signal drops out, you are not considered in the area of coverage in the first place?  How about the millions of analog AM radioís still out there?  How many are really being used these days?  I understand the advantages with digital such as multi channeling, etc., using the same frequency but I wonder if going full digital would be the end of the AM broadcast as we once knew it, killing it off completely?  Maybe we amateurs can take it over, making it the new ď320 meterĒ band?
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« Reply #11 on: December 10, 2019, 02:08:42 AM »

Quote
...When the (rather stupid) NRSC rules came into force in the 80s, stations were forced to limit their high end to 10 kHz. Any further restriction was voluntary, and in my opinion regrettable...

For sure.

The artificial 20kHz bandwidth limitation came about because of shoehorning by large corporate stations wanting to put as many stations on the air as possible; i.e, pure and simple greed.

If the FCC had truly wanted even competition between AM and FM they would have allowed an AM audio bandpass of 15 kHz  (same as FM) with pre-emphasis and a power increase to overcome the increased noise floor, and more importantly, specified a hard receiver IF bandwidth of 30kHz as well.

Kintronics offered a similar solution back in October 2014 (PDF below) which is still viable today, but the FCC and the industry fell into the hands of the IBOC and new equipment lobbyists.

Currently, the IBUZZONCHANNEL IBOC MA1 mask (the combined Hybrid analog and digital system) occupies a 30 kHz bandwidth. Had the FCC given analog AM the same 30kHz analog bandwidth with C-QUAM, a currently available technology, you would already have FM quality stereo.

Thankfully, the newly proposed AM 64-QAM system is voluntary and would only occupy a 20kHz bandwidth, the current AM bandwidth standard.

* AM Revitalization 2 by Kintronics.pdf (1106.6 KB - downloaded 11 times.)
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« Reply #12 on: December 10, 2019, 03:56:54 PM »

Wow, IBOC all digital AM. Imagine they would have to drop the D from the HD logo? Always surprised how many think HD FM is somehow superior to regular analog, or realize that HD in FM stands for Hybrid Digital and not High Definition like in TV.
As long as IBOC keeps tight monetary control of the licenses and decoder chips that will be an issue. I thought it was dying but I had to install a couple systems on FM stations this last year.
The big thing out here in the wilderness with our AM broadcasters is now installing FM translators within the coverage of their AM stations so they can be on the FM band.
Hardly ever see a FM IBOC radio canít imagine an AM one.  Having to maintain linearity and phase across the channel on a directional system looks like it would be fun.
Analog TV is now a thing of the past, the analog television transmitters, exciters and all the analog video equipment have no resale value and tons of this stuff has been scrapped. The new solid state lower power digital transmitters are almost as useless when removed from service. Just recently scraped three digital TV transmitters that did not make the last channel migration. Most of the modern stuff is difficult to do anything with. Have sold several PA panels for people to build amplifiers but unless you are doing strip line surface mount relatively hard to do anything with.
Somehow imagine the transition from broadcast to Ham is going to be less and less with the old broadcast stuff providing parts if anything at all. Unfortunately almost all AM broadcasters have done away with their tube transmitters years ago and are now running solid state multi parallel PA deck stuff and anything thatís coming out from broadcasting today would be that type design, but can see where some of the smaller 1kW AM transmitters can be reworked for 160 or 80 with some changes to their tanks.  The trick would be a modern PDM transmitter may be a lot less tolerant of mistakes when doing the work then the old tube stuff.


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« Reply #13 on: December 10, 2019, 05:41:28 PM »

And if any AM station goes with all-digital MA3 system they should forfeit any FM translator channel license they hold.

Note: if anyone here has any interest in the 64-QAM transmission system, I will gladly share my class notes here on AMPHONE in which the class notes have a block diagram and an actual waveform.


  
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« Reply #14 on: December 10, 2019, 05:48:25 PM »

...Wow, IBOC all digital AM...Having to maintain linearity and phase across the channel on a directional system looks like it would be fun...

It took quite a few upgrades to get WWFD up and running.

https://www.radioworld.com/tech-and-gear/upgrading-an-am-to-all-digital-why-how-and-lessons-learned
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