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Sens. Brian Schatz (D-Hawaii) and John Thune (R-S.D.) have reintroduced the Reliable Emergency Alert Distribution Improvement (READI) Act, which is meant to improve the emergency alert system and prevent its accidental triggering.

Among other things, the bill would allow broadcasters to repeat presidential and FEMA alerts, something they can’t do now.

The bill was introduced last year — and passed the Senate — in the wake of an inadvertent missile alert triggered in Hawaii during which some people did not receive the alert. “Even though it was a false alarm, the missile alert exposed real flaws in the way people receive emergency alerts,” said Schatz, Oct. 24, ranking member of the Communications Subcommittee.

FCC Investigating Missile False Alarm

Local officials in Hawaii inadvertently issued an incoming nuclear missile alert, leading to some panic and an FCC investigation into the incident.

“South Dakotans understand how drastically the weather can change on a dime,” said Thune, chairman of the subcommittee. “For that reason, among many others, this legislation would make necessary improvements to help keep South Dakotans and communities around the country safe in times of emergency.”

The bill would:

1. “Ensure more people receive emergency alerts by eliminating the option to opt out of receiving certain federal alerts, including missile alerts, on mobile phones;”
2. “Require active alerts issued by the president or FEMA to be repeated. Currently, alerts on TV or radio may only be played once;”
3. “Explore establishing a system to offer emergency alerts to audio and video online streaming services, such as Netflix and Spotify;”
4. “Encourage State Emergency Communications Committees to periodically review and update their state Emergency Alert System plans, which are often out of date;”
5. “Compel FEMA to create best practices for state, tribal and local governments to use for issuing alerts, avoiding false alerts, and retracting false alerts if they occur, as well as for alert origination training and plans for officials to contact each other and federal officials during emergencies;” and
6. “Establish a reporting system for false alerts so the FCC can track when they occur and examine their causes.”

A House version has also been introduced by Reps. Jerry McNerney (D-Calif.), Tulsi Gabbard (D-Hawaii), Pete Olson (R-Texas) and Gus Bilirakis (R-Fla.).

“We applaud the leadership of Sens. Schatz and Thune and Reps. McNerney, Bilirakis, Gabbard and Olson for introduction of the READI Act of 2019 which develops guidance and best practices for how state and local governments can improve emergency alerts, particularly to address the issuance of false alerts,” said NCTA — The Internet & Television Association. “As participants in the nation’s emergency alert system, cable operators appreciate Congress’ efforts to improve coordination between federal and local authorities to ensure consumers receive accurate and relevant emergency and public safety information in their local communities.”

 

The post Errant Missile Alert Prevention Bill Reintroduced appeared first on Radio World.

Value engineering. What does that mean? As broadcast engineers, we typically don’t build devices, but we do build systems, often made up of equipment from multiple, disparate manufacturers. We start off by determining the goal of the project — just what is the system supposed to accomplish? We then begin drilling down to key elements of the system, their roles and how they interact with other parts of said system.

But always in the background, we’re forced to work within a framework of cost. It’s great to say, “If money were no object, this is what I would do …” but I have yet to work on a project for a radio station in which money was not an object. I’m quite sure the same goes for you. We all have budgets that need to be satisfied.

When we purchase a piece of gear, there are several aspects of it that we must consider:

• Role in the system
• Functionality
• How well it integrates with other parts of the system
• Upfront cost
• Operating cost

And let’s face it, a big part of the purchasing decision is whether we like a brand or not, and that comes mainly from prior experience. Trying a new brand, or a new technology, is often something people don’t want to do because they have no experience with it and can’t form any idea of how it will affect them negatively. “Tried and true” is something most of us want to stick with.

Value engineering comes into play when what you want to accomplish doesn’t fit within budgetary requirements. It’s as simple as that.

Say, for example, you’re moving an entire radio station cluster to a brand-new facility, and when you look at the overall cost for the entire project, you find that it’s short on budget by, say, 10%. (That’s also of concern because you’ve no contingency money at the end.)

Another cause for value engineering would be when you want to get a certain item, but it doesn’t fit within your budget parameters, so you are left figuring out what else can be removed, or otherwise made less expensive, so that your desired “thing” then does fit.

HOW TO FIND THAT 10 (OR MORE) PERCENT

It should be obvious that the easiest way to find savings is by studying the largest budget line items first, since they’ll have the most impact mathematically. In a studio move, for example, that will likely be consoles, followed by furniture. In a transmitter site build, that will likely be the transmitter itself.

If you’ve found out that you are over budget after completing your initial design, likely there will be some anger and frustration to get over. You could be saying to yourself, “We just can’t do it for that much!” and it’s probably true. (Although it’s putting the cart before the horse, many times budgets get set before the system design is complete. It happens that way all the time.)

The order in which I would look for savings, from the least worst to the worst, is this:

• Can I reduce some of the studios to a less complex (and less expensive) console model?
• Can I reduce the size of the routing system? Do I really need that many inputs and outputs?
• Can I defer the building of several of the studios until a different budget period comes along?
• Can I re-use one or more of the “old” studios at the new place until a different budget period comes along?

No one wants to take this approach, but it’s one of the many aspects of managing a large capital project that you must be able to do in order to succeed. Hopefully, you’ll have your project fully budgeted before the station owners say, “Just how much is this going to cost?” so that you don’t find yourself in this position. Be forewarned, though: Just because you have all the numbers added up doesn’t mean that the station owners will agree to that amount.

There’s much more on the topic of value engineering, which we’ll discuss in future editions of Best Practices. And as always, we welcome your contribution on the topic.

Doug Irwin, CPBE AMD DRB, is vice president of engineering at iHeartMedia in Los Angeles and a technical advisor to Radio World.

Comment on this or any story. Email rweetech@gmail.com with “Letter to the Editor” in the subject field.

The post What Does “Value Engineering” Mean to You? appeared first on Radio World.

NXP Semiconductors in collaboration with the Digital Radio Mondiale consortium hosted the first annual NXP Cockpit & Infotainment Forum in New Delhi on Oct. 22.

Pictured from left to right are Ron Schiffelers, NXP; Ashok Chandak, NXP; Ruxandra Obreja, DRM; Alexander Zink, Fraunhofer IIS; SK Singhal, advisor TRAI; and Yogendra Pal, DRM India Platform.

The newly created one-day event featured presentations and demonstrations of the latest trends and solutions surrounding infotainment — from radio and audio to processing and connectivity. It also provided attendees with insight into the development of DRM and the inclusion of DRM receivers in many of the new models on the roads in India.

[Read: Air Highlights DRM Ahead of Cricket Matches]

DRM says participants also received updates on the All India Radio rollout as well as information on how NXP’s latest generation of software defined radio can facilitate DRM digital radio for infotainment system architectures.

The broadcasting and manufacturing industry as well as representatives from government bodies like the Indian regulator TRAI participated in the forum, sharing their information and experience. They, in turn, received information on the latest developments in the infotainment sector.

“The NXP-DRM car event in New Delhi was a great moment where our message was that DRM, whether in AM or FM, is just one standard with the same features and benefits,” said DRM Chairman Ruxandra Obreja. The demonstrqtions of DRM for FM showed how DRM can also enhance the performance of the many cars that an increasing number of Indians will own.”

 

The post NXP and DRM Hold First India Infotainment Forum appeared first on Radio World.

Times have changed since 1945, and the FCC wants to make sure that it is keeping up with those changes, seeking to update many of its media rules that may no longer be relevant. The latest such attempt comes with rules dealing with who has access to antenna sites.

The commission announced a Notice of Proposed Rulemaking on Oct. 25, seeking comment on whether current rules originally crafted in 1945 should be eliminated or revised. Specifically, the rules prohibit the grant, or renewal, of a license for a TV or FM station if the applicant or licensee controls an antenna site that is suitable for broadcasting in the area and does not make the site available for use by other similar licensees.

The FCC says that since the rules were introduced, there has been an increase in antenna sites suitable for broadcasting, a majority of which it says are owned by non-broadcast entities. Calling them “rarely invoked,” the FCC seeks comment on whether the rules are necessary in today’s environment to promote competition and a variety of broadcast sources.

All five commissioners approved of the NPRM.

“These rules date back to 1945,” said FCC Chairman Ajit Pai. “At the time, there was a freeze on broadcast station construction in order to conserve equipment and material needed for World War II. The commission was also concerned about developing the still-nascent FM radio and TV services at a time when broadcasters were still the predominant antenna site owners. But that was a long, long time ago; today there are abundant FM and TV stations, the tower site market is flourishing and commission staff has been unable to find a single instance where these rules were successfully invoked. What they have found are parties citing these rules without a factual basis for doing so, resulting in unnecessary delay of commission proceedings.”

“We must keep up the effort to free traditional, regulated industries from regulatory burdens where appropriate; otherwise, they will continue to fight with one, or both, of their proverbial hands tied behind their backs,” wrote commissioner Michael O’Rielly in his statement.

No deadline for comments has been given at this time.

 

The post 70-Year-Old Antenna Site Rules Up For Debate By FCC appeared first on Radio World.

Media Bureau to host a Symposium on Thursday, November 21, 2019, entitled "Current and Future Trends in the Broadcast Radio and Television Industries"

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FCC seeks comment on whether the common antenna siting rules for FM and TV broadcaster applicants and licensees are necessary given the current broadcasting marketplace

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FCC grants the petition of Charter Communications finding that Charter faces effective competition in providing cables services in franchise areas in Massachusetts and Hawaii

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Action Continues Commission's Efforts to Modernize its Media Rules

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A bipartisan quartet of House members want to force the FCC to auction C-Band spectrum rather than repurpose it via free-market deals between satellite operators and wireless carriers, as those operators prefer.

The FCC wants to free up as much of that midband (3.7–4.2 GHz) spectrum for 5G as possible, likely at least 300 MHz. Satellite carriers (most as part of the C-Band Alliance) want to be able to strike deals to free up the spectrum. But many in Congress have argued that the money for the public spectrum — to which satellite operators have licenses — should instead go to the Treasury to help fund rural broadband buildouts among other things.

[Read: C-Band Hearing Scheduled for the House]

That definitely includes the four House members who introduced the Clearing Broad Airwaves for New Deployment (C-BAND) Act Thursday (Oct. 24). They are Rep. Mike Doyle (D-Pa.), chairman of the Communications Subcommittee, Rep. Doris Matsui (D-Calif.), subcommittee vice-chair, and Reps. Bill Johnson (R-Ohio), and Greg Gianforte (R-Minn.).

“I am pleased to introduce the bipartisan C-Band Act, which would require the FCC to promptly conduct a public auction to provide more much-needed midband spectrum,” said Doyle. “This bill would ensure a transparent and fair process that would generate billions of dollars in revenue to address the urgent needs of millions of Americans such as building out broadband internet service in rural America while protecting users of incumbent services.”

The FCC would have a September 2022 deadline for auctioning the spectrum.

The act:

• “Requires the FCC to hold a public auction of C-Band spectrum;”
• “Allow for no less than 200 megahertz and no more than 300 megahertz of C-band spectrum [with 20 MHz set aside for guard bands];”
• “Ensures that incumbent C-Band users will be protected” by mandating that they get as good or better service than before. Cable operators, who are also eyeing the C-Band spectrum for 5G, have signaled they could support freeing up as much of that spectrum for 5G as is practicable, perhaps even all of it, replacing the satellite feed with fiber. Broadcasters are concerned that fiber would put their must-have programming at the mercy of an errant backhoe that failed to miss the utility, as it were.

The C-Band Alliance initially propose private sales of 200 MHz, but is likely willing to boost that to 300 MHz if they can be private sales rather than an auction.

Incumbent users include broadcasters and cable operators, who receive their programming network feeds via the satellite spectrum.

The bill will definitely be a topic of conversation at the subcommittee’s C-Band hearing next week.

“ACA Connects salutes the House subcommittee for its introduction of this bipartisan bill,” said ACA Connects President Matt Polka. “The bill appropriately recognizes that any repurposing of C-Band spectrum for 5G must ensure the same or better service for existing users of the band, including the cable operators that rely on the band to deliver video programming to millions of households across the nation. If cable operators encounter any reduction in reliability, capability or quality of that service, or any increase in costs, it is competition and consumers that will ultimately suffer, especially in rural America. To head off these concerns, it is important that any C-Band transition fully compensate cable operators for any costs they incur in opening up the band for 5G, and that receiving programming via fiber instead of satellite is an option. We applaud the subcommittee for its leadership and look forward continuing to work together on this critical public policy issue.”

 

The post New Bill Would Force C-Band Auction appeared first on Radio World.

The author is membership program director of the National Federation of Community Broadcasters. NFCB commentaries are featured regularly at www.radioworld.com.

By the time you read this, Facebook will have relaunched its News tab. The Oct. 25 rollout is the social media giant’s return to aggregating journalism. It comes at one of media’s more curious moments, in a period of curiosities aplenty.

Mark Zuckerberg testified before Congress this week, as the House Financial Services Committee inquired about the company’s plans to get into the cryptocurrency business. Facebook had bowed out of news curation after being pelted with accusations of propping up misinformation in its old news feeds during the 2016 elections. Facebook promised to refocus on personal streams. Many media outlets’ fortunes plummeted in the process.

[Read: Community Broadcaster: A Cautionary Tale]

The reentry into news rekindles what has to be a love-hate relationship between journalism and Facebook. No one doubts Facebook’s power to generate audiences or conversation in news. But the power lies in Facebook’s hands and news organizations have minimal influence in what the company’s priorities may be. After Facebook changed its tools to deemphasize news stories, media organizations that had come to depend on Facebook traffic saw stock plunges and layoffs.

Will it be different this time around? Hard to know. Facebook’s newfound interest in local news is encouraging. Given the local lens, for all the criticism of Facebook receives, rightly or wrongly, the News tab could represent a benefit and opportunity to local journalism hubs like community radio.

Facebook would be wise to tap into the vast network of community radio stations providing coverage to their towns, and giving a local perspective to national stories all of us have our eyes on. Whether it’s the excellent coverage by Marfa Public Radio of the El Paso mass shooting or immigration issues, WRFI’s coverage of housing in New York state, or KZMU’s coverage of the complex environmental issues in Utah, there is no shortage of essential stories being told. They’re stories told not from the viewpoint of a parachuting journalist from the coasts, but reporters that live and work in these communities. It is authenticity that is rare in journalism. It is refreshing. And local news from community radio is needed now more than ever, by Facebook and the nation.

Beyond making community news more prominent in feeds, Facebook could build trust by investing financially in community radio journalism and by giving training and access to the slate of new features. Not every community radio station may be able to take advantage of such support, but for those willing and able, a powerful ally can only lift up local voices. Facebook has a unique power in can wield for the betterment of community media.

While details for independent publishers remain sketchy, a process for publishers to submit feeds and stories is expected. One can hope Facebook may have learned from the firestorm during its last foray into news. It launched an initiative to improve news delivered on its platform, and one can hope community radio stations are active in getting themselves listed. Facebook should also take this journalism seriously. I love the Washington Post, Fox News and the like as much as anyone, but Americans deserve the richness community media offers.

 

The post Community Broadcaster: Facebook Needs Community Radio appeared first on Radio World.

Two things have been overlooked with phasing amplitude modulation. One is the importance of pulse modulation; the other is that logic gates can be used for analog signal processing. Both of these things were new areas to explore, along with how far was it possible go with these ideas.

There are three types of pulse modulation that can be used to build other waveforms with. There are pulse width modulation (PWM), pulse phase modulation (PPM) and pulse location modulation (PLM). Whereas PPM can be used to generate the other two forms, PWM only has amplitude information and PLM only has phase information. So to be able to move from one form to the other depends on what is required: amplitude, frequency modulation or both.

By using PPM, we can do both phase and amplitude modulation, as demonstrated with this new phasing modulator amplifier design. This technique is able to work with both radio frequencies (RF) and with light at optical wavelengths.

Over the last three years during which I have been working on this phase modulation technique, it has been a test case to prove and evaluate the findings. Once this is done, the process is repeated again and again, making small improvements with each iteration.

Throughout this research process, it was not possible to go on the internet and see how this technology should work. By being first, there is no limitation on what can and cannot be done. The downside is that it takes a large amount of time to make small amounts of progress.

I also had ongoing support from Stephen Nitikman at our local college electronic labs, working through many different ideas throughout this process.

Once everything was working in class D, this amplifier was pushed into class E and I replaced the low-pass filter with a bandpass filter. The negative was poor modulation of 65.536 kHz; it was too low to be received on an AM broadcast radio.

The next step was to increase the frequency again to go above 150 kHz, to fall within the longwave band. I found that PWM was a limiting factor to modulating the carrier, so it was time to move away from using PWM and to try again with PPM. This is how the two unknown classes of switching amplification were found. At this stage, I needed to do more research into other forms of switching amplification and could not find any match to what I was working with.

After these experiments, I added in a field-programmable gate array (FPGA) into the circuit and used its PPM waveforms as a starting point. It was then possible to modify these pulses with logic gates to build a phasing modulator.

Looking at what was done with the Tayloe mixer and taking a new approach is where the Taylor modulator came from. It is far more than a simple switching RF mixer. The Taylor modulator takes the analog building blocks and converts their analog stages into logic equivalents.

This is an interesting area of discovery that falls between both analog and digital technologies, letting us take the best parts of both to work with. Once I worked out the required logic blocks and how they would go together to build the analog digital modulator (ADM), I soon found it was possible to use it with in-phase and quadrature (I & Q) inputs.

REQUIREMENTS

There is, in my view, a need for a transmitter that has lower total harmonic distortion (THD) and higher amplifier efficiency than any broadcast transmitter that is in production. What is the best way of going about designing such a device?

With AM, there are a number of stages that present problems in reaching these aims. The way to move forward is to look at other ways to generate the desired type of modulation to eliminate many of these shortcomings.

The power amplifier would need to operate in a switching configuration for the highest level of conversion efficiency from the DC input to the RF output stage. The only way this could be done would be by using some form of phasing modulator in combination with a switching amplification process.

Let’s take a look at a couple of current I and Q mixer designs.

Phasing Modulator Version 1

Fig. 1: Basic phase modulator

The most common type of phasing modulator is made up of two balanced mixers offset by a 90° phase shift network. The oscillator is fed into this phase-shift network and each of the two inputs are driven via low pass filters. The two outputs are then combined and fed through a bandpass filter, leaving only the desired frequency. See Fig. 1.

Tayloe Mixer Version 2

Fig 2: Tayloe mixer.

The other common type of phasing modulator is the Tayloe mixer, whereby the phase offset is done in logic by a divide-by-four, generating in this case four phase angles: 0°, 90°, 180° and 270°. The mixing is done with an analog switch, rebuilding the desired output frequency and as with the other type, this is then run through a bandpass filter. See Fig. 2.

BACKGROUND

The phasing modulator has been around since the 1940s. In its early form, it was used to generate SSB as a more efficient transmission format over AM that was widely used at that time. This is when we started working with In-phase and Quadrature inputs, to represent each part of the waveform as Phase and Amplitude.

While AM radio broadcasts have been around for more than 100 years now, the basic idea remains the same, with many improvements made over time. AM radio sound quality has also changed over time. The biggest impact came about with the invention of the super heterodyne receiver and its limited bandwidth, which is a design feature to increase selectivity and reduce adjacent-channel interference, and has therefore limited the audio frequency response to below 7 kHz. This is only one of the factors that have an impact. The others are the overprocessing of modulating audio and poor linearity of modulators and RF amplifiers stages.

Up until now, we have been generating various waveforms and measuring the effects of the pulse widths to work out the minimum required bandwidth. The process described herein works the opposite way and uses pulses to generate various waveforms. This technique is able to work both ways.

This type of quadrature amplification was invented in 2017. After experimenting with an optical road safety system called the Electronic Eye Project, it was soon discovered that the same process could be modified to work at radio frequencies. This form of switching amplification is made up of two parts, one being a phasing modulator using In-phase and Quadrature inputs, the other a switching output stage that acts as the amplifier. For this process to work, it must have a minimum of four pulses: two for the In-phase components positive- and negative-going, and the same for both Quadrature components.

Classes of Amplification

From the beginning of electronic amplification devices, there was a requirement to understand how the amplification process has been done. The way this was worked out in the analog classes was by using angles to specify the on time in degrees. So you had Class A that conducts for all 360° of the cycle, Class B that conducts for 180° x 2 of a cycle, and Class C that conducts for just a few degrees of the cycle and uses an L-C tuned circuit combination to restore the full cycle. With switching amplification, classification is based on the type of switching and the way the output filtering is being done.

Types of Pulse Modulation

Fig 3: Basic pulse waveforms.

PWM has the same information on both sides of the pulse but is mirrored or 180° out of phase, and the phase information is canceled out, leaving just amplitude information. By converting PWM to PPM by removing one side, we keep all the encoded information as well as the all-important phase information. This is, in a way, like what you would get with amplitude modulation with the sidebands on each side of the carrier when all that is needed is just one of the side bands to convey the information.

PWM Amplification

Class D and I are switching amplifiers. Class D uses PWM. This process chops the sine wave into wide or narrow pulses. The widest point of the pulse is at the peak of the sine wave and the opposite at the minimum point. With Class I, there are two in-phase PWM carriers that are connected to a common clock, using a differential process where one input is offset to the other by 180°. This means the audio input needs to be phase-shifted by 0° and 180° to drive each PWM input.

Both classes of amplification, therefore, are linear. What goes in comes out with very good efficiency. These are known as switching classes, and all require filtering after their output stages to remove unwanted harmonics. In class D and I, a low-pass filter is used.

The efficiency of these classes comes from the output device being turned hard on and off, minimizing power being dissipated within the switching device.

Quadrature Amplification

Quadrature amplification starts out with two signals that have the same frequency and are offset by 90°, which is expanded out to four phase angles that have an offset of 90° (0°, 90°, 180° and  270°). Unlike Class D, quadrature amplification works at minimum of four times the highest frequency, where Class D works at a minimum of two times the highest frequency.

Another difference between the other switching classes is that quadrature amplification uses PPM and not PWM. The latter has no phase information and is therefore used to vary only the amplitude. However, if you remove one side, you end up with both the phase and amplitude components. In quadrature amplification, the amplitude part is not used.

Phase information is processed within logic gates and by adding I and Q pulses together, and with that, it is possible to rebuild any type of analog waveform. This is where Nyquist is very misleading, stating you only need two pulses to regenerate a sine wave. This is not true for phase integrity, where you need a minimum of four. This is the key difference between quadrature amplification and what happens in Class D and many other switching classes.

Class P and Q

Fig. 4: Class Q on the left with class P on the right, where the sine and cosine swap based on what sideband information is required. Both of these classes are based on pulse phase modulation.

Class P and Q are unique due to the way that they are based on phasing principles, so you will have sine and cosine parts to the step waveform. These amplifiers employ four pulses as parts of the generated analog waveform: two positive-going and two negative-going. This approach is used in these new forms of amplification, moving on from the limitations of class D and the two-times-clock technique.

There are two forms of quadrature amplification, which I will call Class P and Class Q. In Class P (pulse), you have four PPM pulses that are offset by 90° from each other. In Class Q (quadrature), each side of the pulse has the in-phase and quadrature information.

Fig. 5: Prototype testing with an oscilloscope.

In Class P, each pulse must have less than 25% on time, and you have a gating window that the pulse must fall within. The PPM, therefore, is between 0% and a maximum of 25%. It must be triggered to start at 0°, 90°, 180° and 270°. With PLM, the pulse just needs to be within the gating window. The output waveform, therefore, has 0° and 90° positive-going, and 180° and 270° are negative-going pulses. Possible uses for Class P would be in applications where you need an extra level of processing between input and output stages, whereas Class Q has the higher efficiency of the two.

With Class Q, the maximum on time is 50%, where you will end up moving into Class E (square wave). Therefore, when amplifying a modulated signal, you always will be less than the maximum of 50% on the positive- and negative-going cycles to provide room for modulation. Where there is a sharp cutoff between the linear and nonlinear zones, this starts to have an impact above 25% pulse average until you reach 30%, where it mostly becomes nonlinear. Another way to look at Class Q is that it provides the linearity of class A with the efficiency of Class E, making it ideal for many forms of analog and digital modulation systems.

With quadrature amplification, it can also be used for audio applications, but there is no real advantage over existing classes like D and I, so my focus has been on RF applications where I and Q inputs are used.

The phasing technique used is the same for both classes. The only difference is in pulse processing stage of the modulator. In Class P, you have four time slots for each of the angles, where one side of each pulse is modulated (PPM). The location within that time slot can also vary, using pulse position modulation. In Class Q, each side is modulated. The positive side has two parts of the information and the negative side has the other two. With Class Q, the 0° and 90° phases are set in the pulse processing stage, but are not so important in the pulse converter stage.

As with Class D and all the other switching classes, output filtering becomes very important to rebuild the analog waveform. Both Class P and Q use low-pass, bandpass or a combination of both.

The table shows amplifier grouping types.

Table 1: Amplifier Grouping Types

A Class Q AM Broadcast Transmitter

By using one dual device and doubling the frequency, in logic I then did a divide by two, bringing the operating frequency back down to 660 kHz from 1.32 MHz. With this version, it modulated both digital and analog waveforms with very good linearity. For analog testing, I used AM Stereo (C-QUAM), and for digital, Digital Radio Mondiale (DRM) was used at 64QAM.

Fig. 6: ADM design version 4, modulating QPSK. Fig. 7: ADM design version 4, modulating 16QAM.

The current prototype has elements of all the other versions as well as new ideas for the first fully-working AM transmitter. Whereby in this configuration you are able to operate up to the maximum frequency of 10 MHz, this is well within the range of the AM broadcast band from 540 to 1700 kHz. All the testing was done over three frequencies, 660, 1110 and 1500 kHz, where there were gaps found between local radio stations. For the output power, I was getting a maximum of 200 watts at 100% modulation, using an LDMOS switching device.

Operating in I and Q Mode

Operating in I and Q mode with DRM using an offset of 12 kHz, there is no issue generating any waveform type, regardless of the type of information been sent analog or digital. A waveform as complex as COFDM can easily be modulated. The only limitation is the linearity of the phase modulators used. This is why the THD is so important.

Fig. 8: ADM design version 5, modulating QPSK. Fig. 9: ADM design version 5, modulating 16QAM.

Unlike other types of analog RF amplifiers, this configuration uses very nonlinear amplification, just two states: on and off. So phase noise and phase distortion effects need to be minimized wherever possible. This is why so much negative feedback was used in various parts of this circuit.

Fig. 10: Two-tone test.

From Fig. 10, you can see the version using two phase modulators with better switching output devices made an improvement over Version 4 using the four-phase modulator design. This was due the switching power MOSFETs that had a higher amount of phase distortion.

In version 5, a newer design was used for the negative feedback path, using two PWM signals through a low-pass filter driving back into each of the inputs of the phase modulators. With quadrature amplification, it is an ultralinear process, where most of the distortion takes place in the phase modulator stages (converting the analog inputs to PPM or PWM). With ongoing improvements, I am sure it is possible to bring this level of distortion down, closer to 0.5% at 100% modulation.

NEXT VERSION

Fig. 11: Two-tone test at 750 Hz and 1 kHz.

I now have my first working product based on the experimental work done with all the previous versions. The next version is a 100-watt model that operates in Class Q with a small number of improvements, such as using a new type of phase modulator design, providing a wider frequency range from LF all the way up to HF. It also has an in-built audio compander stage just before the preemphasis to provide improved signal-to-noise performance on the receive side. The plan is to go with this design for on-air testing here in Toronto this year.

Fig. 12: 99% modulation at 1 kHz.

The 1 kW model uses the NXP MRFX1K80H device. For higher efficiency, I am working with a switching DC power supply rail to operate in class G and Q using a combination of techniques from the older versions with flexibility from a common hardware layout. Quadrature amplification is a fully scalable process, making for much higher power levels above 1 kW possible with minimal design changes.

This transmitter design is lost on your average AM receiver. I am using a Denon TU-680NAB receiver connected to a Pioneer EX-9000 expander, and this is providing good off-air performance with this setup. With renewed interest in AM stereo, I hope manufacturers will soon get the message and start making receivers again — it is not that hard to do in a single DSP chip these days.

Grant Taylor started experimenting with a simple FM transmitter in high school. He spent the next few years experimenting with home-made television equipment within amateur radio. From there, he worked repairing and installing outside broadcast links in New Zealand, which led to working on local radio and television infrastructure projects. He experiments with new technologies that have applications in broadcasting.

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