AGC Systems Key Participant in ITU-R Rapporteur Group and ATSC Planning Teams

The International Telecommunications Union (ITU) has published two new documents that support the planning and testing of ATSC 3.0 systems.  The documents are:

  • ITU-R Recommendation BT.2033-2 : Planning criteria, including protection ratios, for second generation of digital terrestrial television broadcasting systems in the VHF/UHF bands.
  • ITU-R Report BT.2495 : Methods for laboratory and field measurements for the assessment of ATSC 3.0 reception quality.

This brings the total number of new ATSC-related documents to five, which includes the Handbook on Digital Terrestrial Television Broadcasting networks and systems implementation, which was updated last year.

Several ATSC-3.0-related documents are also in the ITU-R deliberation process, which are expected to result in additional publications. AGC Systems has been involved in this process for several years, and leads several initiatives to develop these documents.

The International Telecommunication Union is the United Nations specialized agency for information and communication technologies (ICTs). Founded in 1865 to facilitate international connectivity in communications networks, ITU allocates global radio spectrum and satellite orbits, develops technical standards that ensure networks and technologies seamlessly interconnect, and strives to improve access to ICTs to underserved communities worldwide.

The Advanced Television Systems Committee, Inc. is an international, non-profit organization developing voluntary standards for digital television.  ATSC member organizations represent the broadcast, broadcast equipment, motion picture, consumer electronics, computer, cable, satellite, and semiconductor industries.  The ATSC mission is to create and foster implementation of voluntary Standards and Recommended Practices to advance terrestrial digital television broadcasting, and to facilitate interoperability with other media.

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Cugnini to Present Talk on New Audio/Video Technologies

AGC Systems’ President Aldo Cugnini will deliver an online talk, entitled “New Audio/Video/Wireless Technologies For Home Entertainment.”  Scheduled for Thursday, November 18, 2021, 6:30PM EST, and hosted by the IEEE Consultants’ Network of Northern New Jersey, the talk will explain how new technologies like UHDTV, HDR, and HEVC enable audio and video devices to efficiently deliver the latest entertainment to consumers.

The talk is free, and can be accessed by registering here.

This presentation is partly sponsored by Elecard.  Click here for more information on their video and stream analysis tools.

FCC Proposes to Reinstate Amateur Radio Service Fees

The FCC has proposed in an NPRM to impose license fees on Radio Amateurs.  I urge you to send your comments to the FCC arguing against the reinstatement of those license fees.

You may not be aware of the public good this service provides in times of emergency, as it has during the recent hurricanes.  The decrease of new applicants in recent years is not helped by this mercenary proposal.

You may also not know that amateur radio is often a leading developer of new technologies.  Just one example is the recent development of a low-cost vector network analyzer — the NanoVNA.  Originally developed by and for radio amateurs, this breakthrough device is now being used in the broadcast and other wireless industries, as written up by broadcast engineer Doug Lung in the last two issues of IEEE BTS Magazine and in TV Technology.

The NPRM can be found at FCC MD Docket No. 20-270Comments are due by November 16, 2020.

The ARRL will be filing comments, and their position can be found at this link; you may be interested to see my filed comments.


Aldo, W2AGC

Modulation 101

Modulation is the process of imparting a signal, usually audio, video, or data, onto a high-frequency carrier, for the purpose of transmitting that signal over a distance.

Let’s take a carrier signal,  cos(ω_c t) and a modulating signal,  cos(ω_m t), where ω = 2 \pi f , and f is the signal frequency.

Amplitude modulation is simply the product of the carrier signal and (1 + modulating signal):

\displaystyle AM(t) = cos(ω_c t) \times [1 + cos(ω_m t)] ,

which multiplies out as: AM(t) = cos(ω_c t) + cos(ω_c t)\times cos(ω_m t) ] . A carrier modulated by a sine wave is shown in the following example.

Note that such a signal is relatively easy to demodulate: a simple rectifier and low-pass filter will recover the modulation from this signal, as you can visualize by “erasing” the negative portion of the signal and averaging over the remaining waveform.  Such a process is called envelope detection.

To analyze the composition of this signal, we take the trig product identity, cos(x)\,cos(y) = \frac{1}{2} [ cos(x-y)+cos(x+y) ], and apply it to the product term in AM(t), producing the following:

\displaystyle AM(t) = cos(ω_c t) + \frac{1}{2} cos(ω_c t - ω_m t) + \frac{1}{2} cos(ω_c t + ω_m t) .

From this, we observe an important aspect of the process:  amplitude modulation results in a signal composed of the following three components:

    1. the carrier signal, cos(ω_c t),
    2. a lower sideband signal, \frac{1}{2} cos(ω_c t - ω_m t),
    3. and an upper sideband signal, \frac{1}{2} cos(ω_c t + ω_m t).

By the way, the reason for the “1 + ” term in the modulation equation above is that it specifically generates the carrier component in the modulated signal. Without it, we would have the following Double-Sideband-Suppressed Carrier signal, which should make it apparent that we can’t use a simple envelope detector to demodulate; note how the envelope “crosses over” itself:

An analysis of modulation is aided by using a more complex modulating signal.  A ramp signal is comprised of a fundamental sinusoid and integer harmonics of that fundamental.  For illustration purposes, we will take an approximation that uses the fundamental and the next 8 harmonics. This modulating signal is shown below, as a function of time.

The spectrum of this signal, i.e., a plot of the frequency components versus level, is shown next; it consists of a fundamental (at “1”), followed by a series of harmonics with decreasing levels.

If we amplitude modulate a carrier with this ramp signal, we get the following time-varying signal; note again that this signal can be demodulated by an envelope detector:

The spectrum of the modulated ramp signal follows; note that there is a carrier at “0” and sidebands extending in both the positive and negative frequency directions. (In practice, this zero point would actually be at some high frequency, such as at 7 MHz for example. The spacing of the individual components in this example would be exactly that of the frequency of the fundamental component of the ramp signal.)

Recall from our earlier discussion that amplitude modulation results in a signal composed of the three components, the carrier signal, a lower sideband signal, and an upper sideband signal. Note the following as well: because the lower sideband component has a negative modulating-frequency term (cos(ω_c t - ω_m t), for a sine wave) the spectrum of the lower sideband is reversed compared with that of the upper sideband (and that of the baseband modulating signal).

We can also see from this example that amplitude modulation is rather wasteful of spectrum space, if our goal is to take up as little bandwidth as possible.  For one, the two sidebands are merely reflections of each other, i.e., each one carries the same information content.  For another, the carrier itself is unnecessary for the communication of the modulating signal as well — something that wastes power on the transmission side.

Taking that into account, we can choose to transmit only one sideband, resulting in a Single Sideband (SSB) Transmission. If we transmit only the lower sideband, its spectrum will look like this (note that the carrier is also absent):

SSB modulation can be implemented using a variety of methods, including an analog filter, or phase-shift network (PSN) quadrature modulation.  (For a clue as to how PSN works, look up and calculate the result of adding cos(x) cos(y) + sin(x) sin(y).)

The challenge in receiving this signal is how to demodulate it, as we can see from its time-domain plot:

As compared with amplitude modulation, a SSB signal cannot be demodulated with an envelope detector, because the envelope is no longer a faithful representation of the original signal.  One way to demodulate it is to frequency-shift the signal down to its original range of baseband frequencies, by using a product detector which mixes it with the output of a beat frequency oscillator (BFO).

One can appreciate that, if the demodulator BFO is not exactly at the original carrier frequency, the resulting demodulated signal will be frequency-shifted up or down by the amount of the error, resulting in a kind of “Donald Duck”-sounding voice signal.  While this was often an issue with analog transmitters and receivers, whose carrier frequencies were imprecise, and would drift over time, modern digital equipment is so accurate that a near-perfect re-synchronization is not difficult to achieve.

— agc

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Video Pioneers Remember Historic HDTV Debut

Grand Alliance Prototype

Twenty-five years ago this week, the world’s first HDTV broadcast system was unveiled in Las Vegas at the 1995 NAB Show.  AGC Systems’ Aldo Cugnini was there, as one of the many engineers who developed the “Grand Alliance” digital HDTV system.  Then at Philips, Aldo had a leadership role in the system’s development, which went on to become the ATSC digital television system.

Click here to see historic videos of the debut of HDTV.

Selected Papers

  • The Promise of Mobile DTV, NAB Broadcast Engineering Conference Proceedings, 2011.
  • A Revenue Model for Mobile DTV Service, NAB Broadcast Engineering Conference Proceedings, 2010.
  • Considerations for Digital Program Insertion of Multiple-Video Programs, NCTA Fall Technical Forum, 2002.
  • Digital Video and the National Information Infrastructure, Philips Journal of Research, Volume 50, Issues 1–2, 1996.
  • MPEG-2 video decoder for the digital HDTV Grand Alliance system, IEEE Transactions on Consumer Electronics, Vol. 41, Aug 1995.
  • Grand Alliance MPEG-2-based video decoder with parallel processing architecture, Intl. J. of Imaging Systems and Technology Vol. 5, No. 4, 1994.
  • The ISO/MPEG Audio Coding Standard, Widescreen Review, June/July, 1994.

NAB 2019 Conference Widely Featuring ATSC 3.0

More than 100 NAB Show sessions and more than 50 exhibitors will feature Next Gen TV technology that is now voluntarily spreading to cities throughout the country. Powered by the ATSC 3.0 next-generation broadcast standard, Next Gen TV promises to deliver sharper, more detailed pictures and lifelike multichannel audio with upgraded broadcasts that will be transmitted and received in the same Internet Protocol language as Internet-delivered content.

Jointly sponsored by the Advanced Television Systems Committee, the Consumer Technology Association and NAB, the “Ride the Road to ATSC 3.0” exhibit will be featuring a series of free presentations about all facets of the ATSC 3.0 standard. And attendees can pick up a free Guide to 3.0 at the Show in the Central Lobby of the Las Vegas Convention Center during the show.

Single Frequency Network Demonstrations

The NAB, with support from a number of technology companies, will demonstrate the Single Frequency Network (SFN) capabilities of the Next-Gen TV standard, showing how reception can be improved in difficult locations and in moving vehicles by deploying multiple broadcast towers transmitting the broadcast signal on the same channel.

Using several local transmissions, special SFN viewing kiosks will showcase the flexibility of the ATSC 3.0 standard. Dozens of sessions planned in the exhibit will include updates on the Dallas, Phoenix, Santa Barbara, East Lansing, Cleveland, and Korea ATSC 3.0 deployments.

Scores of papers and sessions will be presented about Next-Gen TV during the 2019 NAB Show, with session topics that will cover consumer research, consumer device plans, conformance testing, audio enhancements, station build-out advice, watermarking, advanced emergency information, channel security, advanced advertising and interactivity. In addition to ATSC, CTA and NAB, exhibit sponsors include Pearl TV, Sinclair Broadcast Group, LG Electronics, Dolby, Sony, Samsung and the AWARN Alliance. The centerpiece of the Ride the Road stage is a giant new LED videowall optimized for broadcast applications, provided by LG Business Solutions.

AGC Systems president Aldo Cugnini will be at the show, and available for discussions regarding support for ATSC and other related ventures. If you’d like to meet up, please contact us.