Deep Thought wrote: ↑Mon Dec 02, 2019 12:34 am
COMMENG wrote: ↑Sun Dec 01, 2019 12:36 pm
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.