AM Digital NPRM

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k4om
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AM Digital NPRM

Post by k4om » Mon Nov 25, 2019 11:24 am

FCC PROPOSES TO ALLOW ALL-DIGITAL AM BROADCASTING
WASHINGTON, November 22, 2019—The Federal Communications Commission today
adopted a Notice of Proposed Rulemaking that recommends giving AM stations the flexibility to
voluntarily adopt all-digital broadcasting.
Many AM stations experience interference from electronic devices and other sources that affects
audio quality. All-digital broadcasting offers AM broadcasters the potential to improve their
signal quality and area of listenable coverage, as well as offer additional services that FM
broadcasters currently offer, such as song and artist identification. It also holds the potential to
allow AM stations to increase their programming options to include music formats.
In today’s NPRM, the Commission proposes to allow AM stations to voluntarily transition to alldigital
transmission. The Commission also proposes establishing operating parameters for alldigital
stations to minimize any risk of interference. Finally, the Commission proposes adopting
the industry-approved standard for hybrid and all-digital broadcasting.
This Notice of Proposed Rulemaking continues the Commission’s effort to revitalize AM
broadcasting by enabling it to provide a better listening experience and enhanced service
offerings.
Action by the Commission November 22, 2019 by Notice of Proposed Rulemaking (FCC 19-
123). Chairman Pai, Commissioners O’Rielly, Carr, Rosenworcel, and Starks approving.
Chairman Pai, Commissioners O’Rielly and Carr issuing separate statements.
MB Docket Nos. 19-11, 13-249
###
Media Relations: (202) 418-0500 / ASL: (844) 432-2275 / TTY: (888) 835-5322 / Twitter: @FCC / www.fcc.gov
This is an unofficial announcement of Commission action. Release of the full text of a Commission order constitutes official action.
See MCI

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Deep Thought
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Re: AM Digital NPRM

Post by Deep Thought » Mon Nov 25, 2019 7:50 pm

About f'n time.
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kkiddkkidd
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Re: AM Digital NPRM

Post by kkiddkkidd » Mon Nov 25, 2019 9:09 pm

What digical format are they proposing? The current HD IBOC or DRM or yet something new?

Later,
--
Kevin C. Kidd CSRE/AMD
WD4RAT
AM Ground Systems Company
http://www.amgroundsystems.com
KK Broadcast Engineering
http://www.kkbc.com

COMMENG
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Re: AM Digital NPRM

Post by COMMENG » Tue Nov 26, 2019 12:09 am

What digical format are they proposing? The current HD IBOC or DRM or yet something new?
It appears the Digital MA3 standard will use a 64-Quadrature Amplitude Modulation.

This means the QAM is generated at a low level and amplified by Linear Amplifiers.

...As linear amplifiers are less efficient than those that can be run in saturation, it means that techniques like Doherty amplifers and envelope tracking may be needed. ( https://www.electronics-notes.com/a...y ... 256qam.php )

I just cannot see those local mom'npop community radio stations being able to afford an expensive 64-QAM exciter and a humongous linear amplifier. Another solution looking for a problem. :roll:

If you really want to revitalize AM, increase the transmitted analog bandwidth to 30 kHz with pre-emphasis, increase transmitted power to overcome the increased noise floor, thin the herd by getting rid of deadbeat stations with 24/7 Satellite feeds, and define a hard and fast receiver bandwidth standard.

It will probably go the way as did C-QUAM. C-QUAM was a standard with a good future but, the FCC screwed the pooch by NOT specifying a definitive receiver standard AND by not selecting a stereo standard early on for stereo broadcasting.


COMMENG

Kelly
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Re: AM Digital NPRM

Post by Kelly » Tue Nov 26, 2019 5:06 am

Its the same encoding/modulation as HD, just without the analog AM component.

WWFD has been under an STA in this mode for a couple years. They've essentially found what we discovered back in the early days of testing HD on AM: That running in digital-only mode decreases the adjacent channel interference over hybrid mode, allowing the digital station to better stay inside the original NRSC Mask. Because the modulation is RMS rather than peak, the overall coverage/propagation characteristics is improved.

For AM stations with an FM translator, this might be an interesting option. Music might become viable on AM again, or at least the opportunity to gain some listeners that have long forgotten the MW band.

Last estimates I've seen put HD radio receiver penetration in major markets at around 20%, mainly attributed to vehicles sold after 2010 that came with HD tuners. This is about the only way digital-capable tuners are in the market, since consumers replaced radio purchases with smartphones years ago.

The problem for AM station owners, especially ones with legacy multi-tower directionals and diplexed systems; will be the need to re-design their antenna systems to have enough system bandwidth and flat equalization. That's a potentially expensive proposition. If the new rule happens, at least it would be up to the station owner whether they want to roll the dice on the future, not mandated by the government.
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Re: AM Digital NPRM

Post by w9wi » Tue Nov 26, 2019 7:10 am

What people are saying in the DX community is there is probably a limited cohort of stations interested in all-digital.
  • The really big stations (the KFABs and WBALs and KNBRs) have enough AM audience left that they're not willing to toss most of them out by going all-digital.
    The really small stations can't afford the hardware or engineering services.
Of course, the DXers still hate anything digital:)

WWFD is a pretty good case for all-digital. All of its audience was already on the translator, but it's backed by a company large enough (Hubbard) to afford the costs of converting.
--
Doug Smith W9WI
Pleasant View, TN EM66

TPT
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Re: AM Digital NPRM

Post by TPT » Tue Nov 26, 2019 8:07 am

In other words a destructive little toy, to impress the GM's and SM's who have never seen a transmitter--and wouldn't know where their signals come from that they are flogging. "It's DIGITAL!"

When WBZ was running IBOC, the sideband hiss could easily be heard behind KDKA's signal inside the market at night. I would guess the real penetration of digital car radios may be closer to 10% (or even less) in most of the country. I have a 2015 Chevy, by business partner a 205 Accord. No HD radio in either car. And of course the home radio for most folks is...well, Alexa? Play Rock 104! "Playing Rock 104--of Tom, you need milk."

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PID_Stop
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Re: AM Digital NPRM

Post by PID_Stop » Tue Nov 26, 2019 11:42 am

And if this does come to pass, and if some of the stations that choose to go all-digital also happen to be EAS local primaries, that means everyone who is assigned to monitor them will be forced to find digital receivers suitable for continuous operation, that can be forced to wake up to the correct station and service.

Well, isn't that special.

-- Jeff

COMMENG
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Re: AM Digital NPRM

Post by COMMENG » Tue Nov 26, 2019 3:00 pm

Apparently it took quite a Kluge of supporting hardware to get this up and running:
...For analog, WWFD uses a Harris Gates Five as the main transmitter, with a Nautel AMPFET Five for auxiliary service. Re-using the AMPFET Five for MA3 wasn’t an option because it can’t support digital, so a BE AM-6A was brought in as the new main transmitter. A Nautel AM IBOC exciter and BE ASi-10 were added to generate MA3 waveforms, and for testing and demonstrating interoperability between different manufacturers’ equipment...
https://www.radioworld.com/tech-and-gea ... ns-learned


COMMENG

Kelly
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Re: AM Digital NPRM

Post by Kelly » Tue Nov 26, 2019 3:32 pm

w9wi wrote:
Tue Nov 26, 2019 7:10 am
What people are saying in the DX community is there is probably a limited cohort of stations interested in all-digital.
  • The really big stations (the KFABs and WBALs and KNBRs) have enough AM audience left that they're not willing to toss most of them out by going all-digital.
    The really small stations can't afford the hardware or engineering services.
Of course, the DXers still hate anything digital:)

WWFD is a pretty good case for all-digital. All of its audience was already on the translator, but it's backed by a company large enough (Hubbard) to afford the costs of converting.
DX'ers represent .001% of the total radio listening audience, so their opinion doesn't come close to moving the needle.
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Deep Thought
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Re: AM Digital NPRM

Post by Deep Thought » Wed Nov 27, 2019 1:34 am

One of my clients (WDGY, Hudson, WI) was a test bed station for the original MA3 testing in 2014. I had already installed the Nautel IBOC exciter and exporter, which was feeding a Nautel XR6 in hybrid mode. The only changed required to switch from hybrid MA1 to MA3 was a firmware update which Jeff Welton did on-site. There is no difference in technical requirements between "hybrid" MA1 and full digital MA3 mode; in fact, the requirements are less stringent.

If the antenna system is reasonably tuned for decent audio (+/-10 KHz) it should work fine for MA3 since that requires 33% less bandwidth than MA1 and can be set to work in +/-5 KHz if necessary at a reduced bitrate. The full transmitter power is utilized instead of being 25 dB down from carrier, which means the service area approximates analog without any of the noise.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

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Deep Thought
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Re: AM Digital NPRM

Post by Deep Thought » Wed Nov 27, 2019 1:42 am

COMMENG wrote:
Tue Nov 26, 2019 12:09 am
What digical format are they proposing? The current HD IBOC or DRM or yet something new?
It appears the Digital MA3 standard will use a 64-Quadrature Amplitude Modulation.

This means the QAM is generated at a low level and amplified by Linear Amplifiers.

...As linear amplifiers are less efficient than those that can be run in saturation, it means that techniques like Doherty amplifers and envelope tracking may be needed. ( https://www.electronics-notes.com/a...y ... 256qam.php )

I just cannot see those local mom'npop community radio stations being able to afford an expensive 64-QAM exciter and a humongous linear amplifier. Another solution looking for a problem. :roll:

If you really want to revitalize AM, increase the transmitted analog bandwidth to 30 kHz with pre-emphasis, increase transmitted power to overcome the increased noise floor, thin the herd by getting rid of deadbeat stations with 24/7 Satellite feeds, and define a hard and fast receiver bandwidth standard.

It will probably go the way as did C-QUAM. C-QUAM was a standard with a good future but, the FCC screwed the pooch by NOT specifying a definitive receiver standard AND by not selecting a stereo standard early on for stereo broadcasting.


COMMENG
The above analysis is pretty much 100% inaccurate. The transmitter interface is identical to the C-QUAM connections and modulation scheme, sending I and Q via the audio and external oscillator drive inputs on the transmitter. Some like the Nautel XR series have digital inputs for this and connect directly to their exciter using Cat5 cable. The transmitters operate in the same class-C mode they always did. This is not like the situation for FM where linear amplification is required since the signal is created at a high level in the transmitter itself. This is one of the reasons the AM IBOC decoders have to "check" for CQUAM encoding before they switch since the quadrature modulation and demodulation process is identical.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

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Re: AM Digital NPRM

Post by Kelly » Wed Nov 27, 2019 10:44 am

So with measuring power when operating MA3, just standard common point (directional) or base current Non-D is all one needs to maintain?
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COMMENG
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Re: AM Digital NPRM

Post by COMMENG » Wed Nov 27, 2019 11:42 am

Assuming the article in https://www.radioworld.com/tech-and-gea ... ns-learned was correct, they were using the https://www.bdcast.com/products/details/a-series/am-6a as the main digital platform which has Class E output circuitry, not Class C.

If memory serves correctly, the Harris transmitter used four bridge (H-configuration) Class D amplifiers with four power MOS-FETS in a bridge or quad.

The early data about having to use a Linear Amplifier only is the only information that may not have been entirely correct as it appears a reprogramming of the Nautel IBOC exciter feeding the BE-6A was sufficient, therefore, a linear amplifier could be used but was found not to be necessary in this case.
...But because the MA3 mode is an OFDM method of transmission, all-digital power can’t be measured using the traditional analog AM practices.

For example, MA3’s peak-to-average ratio is significantly higher than that of analog AM, so the transmitter’s power level meter may read inaccurately. Also, if the transmitter isn’t optimized for MA3 mode, the peak-to-average ratio may be reduced, and a different power level reading may result than if the transmitter been optimally adjusted.

Thus, a new procedure is necessary to verify that transmitters are operating at licensed power when in MA3 mode...
So a new power output monitoring method has to be established as well.

It also appears from the article that since this station's ATU had a narrow bandwidth it had to be highly modified as well since they had formerly been running analog only.

So a lot of re-engineering went into converting from analog to digital operation in this case.
This is one of the reasons the AM IBOC decoders have to "check" for CQUAM encoding before they switch since the quadrature modulation and demodulation process is identical.
In 64-QAM, you have 8 bits modulating the I-channel (cosine channel) and 8 bits modulating the (sine) Q-channel so I don't see how the process is identical.


COMMENG

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Re: AM Digital NPRM

Post by jthorusen » Thu Nov 28, 2019 1:28 am

As Jeff points out, there is a real problem with EAS. But I will take that problem a step further. Suppose the fecal matter really does impact the rotary air impeller and we have a real emergency? I can wind some wire on a Quaker Oats box, throw some more over a tree limb, add a 1N34 and some headphones and I can hear emergency notifications transmitted in good ol' AM. Digital? Forget it!

Therefore, I propose that all AM band stations have to retain real AM capability, that all EAS messages be transmitted in that format, and in the event of a real emergency, AM be used exclusively in that band until the emergency passes.

If things get bad enough, that is the only way that general communication can continue.

Regards,
James K. (Jim) Thorusen
KB6GM
Central Coast Electronics
www.centcoast.com
NW Oregon Consulting Bdcst Eng.

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