AM Digital NPRM

[NECRAT]

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.

You do know there are several markets in this country where there are television stations that serve as LP1s, right?
This bridge has been built already and many have already had to cross it.

[Deep Thought]

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.

We used a standard thermocouple RF ammeter along with the Delta TCA at the common point, both of which were within "spec" for this purpose.

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.

That may have been the case for this station but since MA3 requires the same modulation bandwidth as a 10 KHz-modulated standard AM signal it probably should have been re-engineered long ago if it was that bad.

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.

The transmission is in quadrature, with the same interface as C-QUAM. The content of that modulation is different but only due to the extent necessary to make the AM transmitter create the finished product at its output terminal while still operating as a standard AM transmitter. An IBOC receiver has to check to make sure the demodulated Q signal is not C-QUAM.

[Shane]

FMs are now the LP1s in some markets. Omaha is one (except that Nebraska doesn’t have LP-1s and 2s) where KFAB’s longtime FM, KGOR, is one of a few stations designated for monitoring, and KFAB is not, but can be monitored as an additional source, if desired.

in fact, the requirements are less stringent.

What Mark said.

[NECRAT]

FMs are now the LP1s in some markets. Omaha is one (except that Nebraska doesn’t have LP-1s and 2s) where KFAB’s longtime FM, KGOR, is one of a few stations designated for monitoring, and KFAB is not, but can be monitored as an additional source, if desired.

in fact, the requirements are less stringent.

What Mark said.

FMs are pretty much the normal LP1s in most markets across the country. Often times, states that have a state wide run NPR type network, the NPR network acts as the LP1, where they have a transmitter in even some remote areas. I've also seen the "big signals" in smaller states be the LP1. In Rhode Island, WWLI 105.1 is the LP1, and WHJY 94.1 is the LP2. Both are big 50kW stations that cover 100% of the state and radio market.

In Boston, 98.5 WBZ-FM is the PEP/LP1 for Mass, and 1030 WBZ is just an LP1. This changed a few years ago. (Mass has other FMs outside of 98.5's signal range that are the regional LP1s).

[TPT]

The last national EAS test was somewhat of a disaster here in WV. So much for AM primary relays.

Two of my stations got the test--but just barely. Very distorted, couldn't understand the message, presumably relayed through 3 FM's after being received off (I assume) WLW in Charleston, WV. Another station I work with had been getting tests off the same FM I monitor--but the national test didn't even decode (too distorted, I presume).

[COMMENG]

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,

Excellent point.

The majority of current receivers from the simple AM or AM/FM pocket receivers up to the table models and beyond are based on simple diode detectors (or equivalent) using analog, not digital detection circuits.

And while 64-QAM digital transmission is an interesting modulation mode and has been used as the modulation mode in cable television systems as per ANSI/SCTE 07 2018 (and other communication's systems), I find the proposed voluntary (HD Radio™ AM Transmission System Specifications) digital standard is currently monophonic, not stereo, so what does it really get us?

4.7 Analog Audio Source
The analog signal shall not exceed the modulation levels specified in Title 47 CFR §73.1570.
The HD Radio system is not compatible with existing analog AM stereophonic broadcasts. The input analog signal shall be a monophonic signal.

If there is a provision for AM stereo transmission, I have yet to see it spelled out in Doc. No.: SY_SSS_1082s.

And it appears the secondary and tertiary sub-bands for MA3 are mainly for embedding Textual/Title readouts (RDS) to make it look more "FM-like."

At least C-QUAM, using the analog Motorola system, was stereo.


COMMENG

[COMMENG]

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.

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 transmitters operate in the same class-C mode they always did...

As I stated in the post on 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.

Even the older tube-based Power Rock transmitters did not use Class C finals but rather used a Class D system with PDM modulation; only the much older tube transmitters used Class C high-level modulated finals.


COMMENG

[w9wi]

FWIW I just returned from a few days in Northern Virginia. Since my travel companion has little tolerance for radio experimentation I didn't have much time for these tests but... Using the HD Radio in a 2013 Toyota Prius, and all tests daytime...

- WWFD was decoding about 50% of the time at a point approximately 100 miles from Frederick, in west-central Virginia.
- Audio quality was near-FM. (and noticeably better than the best hybrid-mode MW station I've heard, WBAA in Indiana)
- Upon reaching my destination roughly 30 miles from Frederick, WWFD was decoding 100%. Admittedly the location is relatively quiet.
- No noticeable interference in the second-adjacent channels. There was an interference-free analog signal on 800 (didn't bother to identify it) and when listening about an hour after sunrise, a weak but interference-free analog signal on 840. (assuming Louisville)
- WWFD was transmitting artist/song data.
- Lock time seemed significantly better than hybrid mode.

[Deep Thought]

COMMENG

OK you win. I guess all that time I spent actually participating in real-world tests was just a mirage.

However, you clearly have no idea what the hell you are talking about, to wit: "And while 64-QAM digital transmission is an interesting modulation mode and has been used as the modulation mode in cable television systems as per ANSI/SCTE 07 2018 (and other communication's systems), I find the proposed voluntary (HD Radio™ AM Transmission System Specifications) digital standard is currently monophonic, not stereo, so what does it really get us? "

The amount of intentional stupidity here is stunning.

[COMMENG]

COMMENG

OK you win. I guess all that time I spent actually participating in real-world tests was just a mirage.

However, you clearly have no idea what the hell you are talking about, to wit: "And while 64-QAM digital transmission is an interesting modulation mode and has been used as the modulation mode in cable television systems as per ANSI/SCTE 07 2018 (and other communication's systems), I find the proposed voluntary (HD Radio™ AM Transmission System Specifications) digital standard is currently monophonic, not stereo, so what does it really get us? "

The amount of intentional stupidity here is stunning.

I don't think those kinds of insinuations are necessary as I was merely pointing out earlier that modern AM solid state transmitter Final stages (Power Amplifiers) now operate in either Class E or Class D modes and not Class C.

From the FCC-CIRC1911-05:

B. Auxiliary data.

12. We tentatively conclude that all-digital operation would provide AM broadcasters the opportunity to provide additional services such as stereo audio, song and artist identification, as well as emergency notifications that include text and images (such as missing person photos or emergency evacuation maps)...

So where in the WWFD report that stereo operation was part of the test?

D. Operating Rules

24. Emissions mask compliance. As stated above, we propose to require all-digital AM stations to comply with the relevant emissions masks set out in the Commission’s rules and the NRSC-5-D standard.87 We seek comment on the ability of all-digital stations to comply with these requirements. The HD Radio Emissions Mask was originally developed prior to the widespread development and deployment of AM HD Radio transmission equipment and is based on a theoretical analysis designed to minimize out-of-band emissions while not “overly constraining the signal.”88 The NRSC has not tested or evaluated the MA3 mode, including the emissions mask, although the all-digital specifications are included in the NRSC-5 standard.89 In its NRSC RF Mask Compliance Guide, the NRSC explains that it will incorporate guidelines for all-digital MA3 emissions mask compliance “when such transmissions are authorized by the Commission.”90 The nine radio stations that underwent field testing as part of the NAB Labs All-Digital AM Test Project had some difficulty meeting the HD Radio Emissions Mask limits.91 For this reason, NAB Labs suggests that a possible future study regarding emissions compliance could be appropriate.92 We seek comment on whether these compliance issues also implicate the test stations’ ability to comply with section 73.44 of the rules. In general, are there specific characteristics of all-digital AM operation, particularly using existing AM facilities, that pose challenges to emissions mask compliance, and if so, how should these issues be approached?93

Apparently many of the nine test stations had problems meeting the Mask requirement so the FCC is asking for more input. In addition, "...The NRSC has not tested or evaluated the MA3 mode, including the emissions mask, although the all-digital specifications are included in the NRSC-5 standard...," as they have only simulated the Mask and thus no real-world testing has been done to validate the MA3 Mask.

26. Finally, we seek comment on how signal power should best be measured in all-digital
broadcasting mode, for the purposes of compliance with sections 73.44, 73.51, 73.1590, and the HD
Radio Emissions Mask.95 What procedures and equipment would give the most accurate results?96 The
NRSC states that it anticipates that “instrument manufacturers may develop innovative methods for
evaluating signals and achieving compliance.”97 Should the Commission specify what types of
measurements will be acceptable to demonstrate compliance with the Commission’s rules? Due to the
peak-to-average ratio of the MA3 mode, which is significantly higher than that of standard amplitude
modulation, the power level meter on some transmitters may not read accurately.98 Do the majority of digital transmitters include measurement tools capable of accurately monitoring compliance with the
operating power and emissions mask limitations proposed herein?

So the present power measurement methodologies may not be sufficient since the peak-to-average power ratio (PAR) may be different. Here the FCC is asking for comments on how best to measure the transmitter output power of this 64-QAM waveform.

Apparently there are many engineering questions the FCC would like to have clarified to make this a viable all-digital voluntary standard.

COMMENG

[COMMENG]

FWIW I just returned from a few days in Northern Virginia. Since my travel companion has little tolerance for radio experimentation I didn't have much time for these tests but... Using the HD Radio in a 2013 Toyota Prius, and all tests daytime...

- WWFD was transmitting artist/song data.
- Lock time seemed significantly better than hybrid mode...

Again from the FCC CIRC1911-05:

B. 12 Auxiliary Data

...However, we note that NAB Labs did not report on auxiliary data transmission and that the WWFD secondary and tertiary carriers—which transmit program metadata such as song and artist information—are reportedly not always reliable.49 Therefore, we seek comment on whether all-digital operation, as a practical matter, would put AM stations on a more level playing field with other broadcast services that have the ability to broadcast music formats complete with program metadata. We also seek comment on how broadcasters might use their additional digital capacity in other ways. According to Xperi, the all-digital MA3 mode provides flexibility in allowing tradeoffs between audio quality and the amount of data devoted to auxiliary services...

In practical terms, the last sentence means that as you add more "metadata" or RDS content the audio quality by necessity decreases to attain the same bandwidth in order to stay within the "Mask."

If the true intent of the NPR is to improve the audio quality, using an all-digital transmission mode, then the emphasis should be on audio quality and stereo audio capabilities and less on "metadata."

COMMENG

[Kelly]

Apparently many of the nine test stations had problems meeting the Mask requirement so the FCC is asking for more input. In addition, "...The NRSC has not tested or evaluated the MA3 mode, including the emissions mask, although the all-digital specifications are included in the NRSC-5 standard...," as they have only simulated the Mask and thus no real-world testing has been done to validate the MA3 Mask.

Not sure where you heard that. Stations that tested with the full MA3 tests run over the past few years, was measured well within the existing NRSC Mask. Mark could probably elaborate. That's the thing about running digital only. If the installation and interface is all correct, it meets the existing mask. Sure, I get the whole grumbling about stations that were running hybrid mode, but that isn't what we're talking about.

[COMMENG]

Apparently many of the nine test stations had problems meeting the Mask requirement so the FCC is asking for more input. In addition, "...The NRSC has not tested or evaluated the MA3 mode, including the emissions mask, although the all-digital specifications are included in the NRSC-5 standard...," as they have only simulated the Mask and thus no real-world testing has been done to validate the MA3 Mask.

Not sure where you heard that....Sure, I get the whole grumbling about stations that were running hybrid mode, but that isn't what we're talking about.

Hi Kelly. Right. We're not talking about the Hybrid MA1 mask but we're talking about the MA3 all-digital Mask. I didn't hear that. It was a direct quote from the actual FCC document I referenced, FCC-CIRC1911-05:

https://docs.fcc.gov/public/attachments ... 0519A1.pdf Pages 13 and 14.

D. Operating Rules

24. Emissions mask compliance. As stated above, we propose to require all-digital AM stations to comply with the relevant emissions masks set out in the Commission’s rules and the NRSC-5-D standard.87 We seek comment on the ability of all-digital stations to comply with these requirements. The HD Radio Emissions Mask was originally developed prior to the widespread development and deployment of AM HD Radio transmission equipment and is based on a theoretical analysis designed to minimize out-of-band emissions while not “overly constraining the signal.”88The NRSC has not tested or evaluated the MA3 mode, including the emissions mask, although the all-digital specifications are included in the NRSC-5 standard.89 In its NRSC RF Mask Compliance Guide, the NRSC explains that it will incorporate guidelines for all-digital MA3 emissions mask compliance “when such transmissions are authorized by the Commission.”90 The nine radio stations that underwent field testing as part of the NAB Labs All-Digital AM Test Project had some difficulty meeting the HD Radio Emissions Mask limits.91

For this reason, NAB Labs suggests that a possible future study regarding emissions compliance could be
appropriate.92 We seek comment on whether these compliance issues also implicate the test stations’
ability to comply with section 73.44 of the rules. In general, are there specific characteristics of all-digital
AM operation, particularly using existing AM facilities, that pose challenges to emissions mask
compliance, and if so, how should these issues be approached?93


25. We seek comment on the advisability of mandating compliance with the HD Radio
Emissions Mask, given that the NRSC has not evaluated it and the NAB Labs testing indicated that alldigital
stations might have difficulty complying with it. NAB Labs states that the HD Radio Emission
Mask is “likely to be re-evaluated to take into account operational information and an assessment of the
realizable performance of AM facilities.”94 Should the Commission wait to approve all-digital operation
until the HD Radio Emissions Mask as it relates to MA3 all-digital operation has been evaluated and/or
formally endorsed by the NRSC?...

It appears the FCC is asking for more input on some serious engineering issues that came up during the testing of the nine stations. The Mask compliance issue was only one of the many issues identified by the FCC.

COMMENG

[PID_Stop]

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.

You do know there are several markets in this country where there are television stations that serve as LP1s, right?
This bridge has been built already and many have already had to cross it.

Sure... but it's a trivial exercise to get a DTV demod that stays on whatever channel and service you need even when it is powered down and back up. I haven't encountered a receiver for digital AM that does this. The other challenge (which might be more difficult) is getting New York to update its EAS plan.

[COMMENG]

Maybe the Xperi reps can explain this:

Digging down into the technical bowels of the internal/operational details:

HD Radio™ Air Interface
Design Description
Layer 1 AM
Rev. G
December 14, 2016
[IBOC HD Document] SY_IDD_1012s

11.2.4 Analog Audio Bandwidth Indicator (AABI)
The analog audio bandwidth indicator (AABI) is a one-bit flag used to indicate the maximum bandwidth of the analog audio signal when transmitting a Hybrid waveform. If the flag is cleared, the maximum analog audio bandwidth is 5 kHz; if the flag is set, the maximum analog audio bandwidth is 8 kHz.The AABI flag is always 0 when an All Digital waveform is being transmitted.


So in the all-digital (MA3) mode the AAB1 flag, the audio bandwidth flag appears to be defaulted to 0 which means that the transmitted audio bandwidth will be limited to 5 kHz in the All-Digital Mode?

If one of the reasons for this system is to help "Revitalize" AM, to improve the audio, and to bring more listeners to it by encouraging stations to transmit (more) music, how can one do this if the audio bandpass is limited to 5 kHz?

COMMENG