Radio World Engineer Extra - Feb 9th, 2022

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Feb 9th 2022

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Taking it to the cloud

Global remote production using Ravenna/AES67 and AWS

40 kW down twisted pair?

Background photo: Arthit_Longwilai/Getty Images

Maybe it’s closer than you think

FM directional computer simulations

The rationale for authorizing the use of 3D high-frequency modeling

Vol. 46 No. 4 | February 9 2022 www.radioworld.com FOLLOW US www.twitter.com/radioworld_news www.facebook.com/RadioWorldMagazine CONTENT Managing Director, Content & Editor in Chief Paul J. McLane, paul.mclane@futurenet.com, 845-414-6105 Technical Advisors Thomas R. McGinley, Doug Irwin Technical Editor, RW Engineering Extra W.C. “Cris” Alexander Contributors: Susan Ashworth, David Bialik, John Bisset, Edwin Bukont, James Careless, Ken Deutsch, Mark Durenberger, Charles Fitch, Donna Halper, Alan Jurison, Paul Kaminski, John Kean, Larry Langford, Mark Lapidus, Michael LeClair, Jim Peck, Mark Persons, Stephen M. Poole, James O’Neal, John Schneider, Dan Slentz, Randy Stine, Tom Vernon, Jennifer Waits, Steve Walker, Chris Wygal Production Manager Nicole Schilling Managing Design Director Nicole Cobban Senior Design Directors Lisa McIntosh and Will Shum ADVERTISING SALES Senior Business Director & Publisher, Radio World John Casey, john.casey@futurenet.com, 845-678-3839 Publisher, Radio World International Raffaella Calabrese, raffaella.calabrese@futurenet.com, +39-320-891-1938 SUBSCRIBER CUSTOMER SERVICE To subscribe, change your address, or check on your current account status, go to www.radioworld.com and click on Subscribe, email futureplc@computerfulfillment.com, call 888-266-5828, or write P.O. Box 1051, Lowell, MA 01853.

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FM directional computer simulations — why not?

Computer modeling of FM antennas can save time, effort and money

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t wasn’t too long after I started fooling around with computers in the mid-1980s that antenna modeling became a thing.

NEC and MININEC were the prevalent modeling engines, and the source code was out there in the public domain.

Cris At some point, I began playing with Alexander models of medium-wave monopole CPBE, AMD, DRB antennas, simple nondirectional Tech Editor radiators. While those simple models were somewhat useful, they didn’t really do a whole lot for me. Now, if I could model a directional array Comment and get an accurate prediction of the on this or any story. Email driving point impedances, that would rweetech@ be worth something. gmail.com.

And so it was that I started playing with directional models. The challenge was not in the physical geometry of a directional array. It was coming up with a set of drive voltages and phases. I experimented but had little to no success, and I eventually gave up, moving on to other, more pressing things.

Eureka!

Fortunately, some very smart people were working on the problem, people like J.L. Smith, Ron Rackley, Jim Hatfield, Jerry Westberg, Ben Dawson and others.

They figured out that you had to compute the individual tower current moments for unity drive, then with that information and the theoretical directional parameters, solve a set of simultaneous equations to get the normalized drive voltages.

Those drive voltages, each expressed as complex numbers, could be applied as sources in the model, and the resulting tower moments would equal the theoretical directional parameters.

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THIS ISSUE NEWS From the 3

xxx Tech Editor xxx Allow 6 FEATURES computational modeling xxxof directional x FM antennas xxx

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BUYERS Ravenna takes 16 GUIDE it to the cloud xxx

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Marketplace

OPINION x 22

Readers’ xxx xxx Forum

Computer Simulations

Above This tower serves Crawford station KBRT in Los Angeles. We caught the sunset on one of our security cameras.

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After the brain trust figured that out, I was able to write some code and create a computer program that would do the whole thing, taking array geometry expressed in either X,Y,Z format or in distance/azimuth from a reference tower, then taking the theoretical directional parameters (ratios and phases) and turning that into a model that I could calibrate to real-world impedance matrix measurements and produce an output including driving point impedances, voltages and currents; element current distribution, and both near- and far-field E- and H-field values.

New FCC rules permitting “proofing” of AM directional arrays went into effect in 2008. I filed my first model-proof that summer, and I’ve never looked back.

The moment-method modeling proof option has been great for our industry. Aging arrays that needed a lot of very expensive fieldwork could be brought into adjustment very quickly in many cases, and new installations could be tuned up in days if not hours.

Today, you can look through the FCC database and you’ll see many occurrences of the telltale file number prefix “BMM,” indicating a moment-method proofed facility. Many of those are model proofs I have filed.

Needless to say, I’m still a believer.

The trap Fast forward to 2021. Last year, a group of engineers and broadcasters (more really smart people) petitioned the FCC for a rule change that would allow model proofing of FM directional antennas. That rulemaking, at this writing, is in process.

FM directionals, which constitute a reported 20% of all full-power FM facilities, have long been a problem for engineers. I got caught in the FM directional “trap” back in the mid-1980s and had to petition the FCC for a variance to get a facility on the air.

The usual process is first to determine the maximum ERP in every direction of interest, whether a target service area or toward a protected station or border, then develop a theoretical antenna pattern based solely on the coverage and protection requirements.

That ideal or “envelope” pattern then is specified in the construction permit application. When the CP is granted, the envelope pattern is sent to the antenna manufacturer, who will do range measurements using a model based on detailed information about the mounting location provided by the permittee. The manufacturer will make tweaks, adding and moving around parasitic elements to get as close as possible with the measured pattern to the supplied ideal or envelope pattern.

The “trap” occurs in that zone between meeting all the protections and making the required RMS, which by law must be 85% of that of the authorized pattern. Sometimes the measured pattern will meet all the protection requirements but come up short on RMS. That’s what happened to me way back when.

The sure-fire way to avoid this situation is to have the antenna manufacturer develop a buildable, measured pattern and file that pattern instead of the envelope or ideal pattern with the CP application.

Then, when the time comes to file the license application, that same pattern is filed as the “proofed” pattern. All protections are met, and the RMS is 100%.

But that entails some financial risk. You have to pay the antenna manufacturer to develop and fully proof a pattern, with no assurance that the FCC will grant the application. That risk can be minimized with careful attention to detail in the application process (and leaving some white space between interfering and protected contours), but if there’s one thing I have learned from 40+ years of filing FCC applications, it’s that anything can happen.

Remember those smart people I mentioned, the ones who have petitioned for a rulemaking that will allow model-proofing of FM antennas? Their proposal will solve the problem of the “trap” as well as saving all the time, trouble and cost of FM directional antenna range measurements.

In this issue of RWEE, we feature a white paper on computer modeling of directional FM antennas by John L. Schadler of Dielectric. John provides some compelling arguments for this, and I think you’ll find it interesting.

I’m going to go out on a limb here and predict that the FCC will very shortly enact the requested rule change in some form to permit model proofing of FM directional antennas. While there are differences, the engineers at the Media Bureau have certainly seen the benefits and reliability of AM model proofing, and that undoubtedly carries some weight.

The result for broadcasters will be no more RMS/ protection traps, no more range measurements, and a reduction in time between order and delivery of custom directional antennas. Patterns can be fine-tuned to fit the application with engineering time being the only cost.

I think that’s pretty doggone cool.

radioworld.com | February 9 2022

White Paper

Alexandr Gnezdilov Light Painting/Getty Images

Writer

John L. Schadler 6

Vice President of Engineering, Dielectric LLC

Allow computational modeling of directional FM antennas The FCC should authorize the use of 3D high-frequency simulations This article is based on a paper prepared for the NAB Broadcast Engineering and IT Conference of the NAB Show and is published with permission. Proceedings of the conference are available at https://nabpilot.org/beitc-proceedings/.

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bstract: There are approximately 900 Class A directional FM stations licensed in the United States. Many reasons exist to directionalize an FM antenna, including maximizing signal coverage over a designated market area (DMA), reducing lost signal over unpopulated areas, shaping the pattern to fit within the station’s authorized footprint and conforming to the rules stated in Title 47 CFR 73.316.

Currently, applications proposing the use of directional antenna systems must include a tabulation of the antenna pattern through measurements performed on a test range of either full scale or 4.4:1 scaled model setup.

It has been requested that the FCC acknowledge that the public interest will be served by the commission accepting computational modeling of directional FM antennas in lieu of physical measurements of antenna characteristics and/ or performance for purposes of applications and licensing.

Products such as Ansys HFSS are 3D electromagnetic (EM) simulation software tools for designing, simulating and evaluating high-frequency electronic products such as antennas, antenna arrays and RF or microwave components. The use of 3D high-frequency simulation will in many ways yield results that are superior to traditional range measurement proofs, in terms of accuracy.

Since simulations are done in a true free-space environment, any issues with the range or anechoic chamber and with the surrounding environment are eliminated, resulting in more reliable azimuth patterns and H/V ratio.

The use of software also eliminates the lengthy setup and take down time of models as well as the need for a technician to adjust the model and take data points by hand, thus removing mechanical tolerances and human error affecting the data.

Another advantage of designing in a virtual environment is that the geometry can be completely optimized and not compromised by time, materials and tolerances.

This paper will go into detail on the many benefits illustrating why the FCC should authorize the use of

radioworld.com | February 9 2022

White Paper The Commision Has a History of Accepting Computer Modeling

Above Fig. 1: DCR-Q Quadrupole FM-style antenna designed and manufactured for Channel 3 during the repack.

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3D high-frequency simulation computer modeling to demonstrate that a directional FM antenna performs as authorized.

Introduction The rule for licensing of FM directional antennas is found in §73.316(c)(2) and §73.316(c)(2)(iii) of Part 47 of the Code of Federal Regulations. It states that applications for license upon completion of the antenna construction must include a tabulation of the measured relative field pattern.

Read literally, since it asks for a tabulation of the measured relative field pattern upon completion of antenna construction, this language would seem to imply that an FM antenna must be measured after installation, through field measurements of the installed antenna, which can be quite impractical to make and would have been more so at the time that the rule was adopted in 1963.

Consequently, we assume that the rule was interpreted initially to require that FM directional antennas be measured on full-size test ranges, since such ranges were available then for characterizing both the azimuth and elevation patterns of broadcast television antennas.

In 1976, Matti Siukola, RCA scientist and unit manager of advanced development for RCA Broadcast Systems, presented his paper “Pattern Optimization of FM Antennas” at the NAB symposium.

Siukola proposed parasitic elements to be used as directors or reflectors in either horizontal or vertical positions to directionalize a simple FM antenna. In the same paper, Siukola also proposed the more economical use of scale modeling.

It has now been 45 years and basically nothing has changed regarding FM broadcast pattern verification.

Interestingly, characterization of azimuth patterns has evolved in all other broadcast services such as AM radio and television.

The procedures required or allowed by the FCC for characterization of antenna azimuth patterns vary quite markedly between broadcast services: AM radio, FM radio and television.

It is notable that, while the rules for directional antennas for FM and TV were similar at their initial publication in 1963, there were a few significant differences between them that have led to different procedures over the years.

The most significant difference between the two approaches to directional antenna rules was that the FM rules required a “means (such as a rotatable reference antenna) whereby the operational antenna pattern will be determined prior to licensed operation and maintained within proper tolerances thereafter,” while the TV rules had no such requirement.

So, while the FM rules required a method for producing a “proof of performance” on the antenna prior to its use and for its maintenance over time thereafter, the TV rules did not.

The main difference between the two sets of 1963 rules is that the FM rules require that measured pattern performance data for a directional antenna be submitted as part of the application for a license to cover the corresponding construction permit once the antenna has been installed. The current TV rules (including the DTV rules) only require pattern data for a construction permit and don’t define whether that data must be derived through measurements or can be the product of calculations. The real-world results of this rule difference are that directional TV antennas and their patterns are specified almost exclusively using calculations, which, over time, have migrated to computational modeling of the antennas.

When comparing the three fundamental broadcast services and the treatment of their directional antennas in the commission’s rules, the AM antenna rules were updated over a decade ago.

In 2008, use of the Method of Moments (MoM) computer modeling, based on the Numerical Electromagnetic Code (NEC), was permitted as pattern verification for AM services.

This approach provides considerable savings in time and cost for antenna manufacturers and ultimately for the broadcasters who purchase the antennas.

As discussed above, the TV/DTV rules already are flexible enough to permit use of computer modeling both for the design of antenna patterns and for the testing of the antenna’s performance without the need for physical models.

That leaves only directional antennas for FM broadcasting with the requirements and burdens of having to go through the steps of first building models of antennas, measuring those models and collecting the related data.

radioworld.com | February 9 2022

White Paper RF Computer Modeling Outside the Broadcast Industry Not only has the commission approved software modeling for AM directional antenna array proof of performance, but it has approved proof of performance for medical devices and RF radiation exposure evaluation of portable devices as well.

The high level of accuracy that simulation software provides has allowed a wide range of RF device manufacturers to significantly reduce the cost and time associated with proof of performance to the commission.

Computer Modeling — Repack

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Below Fig. 2: Range measurement error.

The timeline of the broadcast repack created a unique situation in the industry. Since many broadcasters needed new antennas and RF systems in a short amount of time, creative engineering solutions to reduce lead time had to be found.

The adoption of 3D high-frequency simulation to gather impedance, phase and amplitude data allowed for expedient antenna design and eliminated many limitations.

This process has been successfully used at Dielectric to design more than 1,000 antennas since the beginning of the repack.

In addition, electrical design time was reduced from several weeks to less than three days. The manufacturing space needed to store physical models and house anechoic chambers has been repurposed to further accommodate manufacturing needs. This process has proven to produce more accurate designs, which is evident in the reduction of test time needed to bring the full antenna into specification.

It is safe to say that, without the use of virtual simulation, it would have been essentially impossible to design, manufacture, test and install the nearly 1,000 antennas that had to be replaced to complete the Post-Incentive

INT ERF ERE NCE

WALLS TREES STRUCTURES

REFLECTED TRANSMISSION

SOURCE ANTENNA

DIRECT TRANSMISSION

TEST ANTENNA

Auction Spectrum Repack in the minimal time allowed for the process.

It is worthy to note that, in the television spectrum repack, as some TV stations moved from UHF to Low-VHF, they needed new directional Low-VHF antennas. In several cases, the designs used were those of FM directional antennas scaled to be larger, to work at the lower frequencies of TV Channels 2.6.

Because they were to be licensed for use by TV stations, the new Low-VHF antennas could be developed and proved with all the latest computer modeling techniques for design, manufacturing and testing. Had those very same antenna designs and patterns been constructed for the purpose of use a few MHz higher, in the FM band, only because of the differences in the FCC rules, it would have been necessary to physically model them prior to building them and to physically measure them to collect data for submission to the FCC during the licensing process.

Fig. 1 shows a quadrupole ring antenna typically used for FM broadcast design for the use at TV Channel 3.

Range Measurement Accuracy An important part of range antenna pattern measurements is the alignment and reflectivity of the range. Alignment typically relies on mechanical bore sighting with the assumption that the antenna used to transmit the signal to the device under test (DUT) is perfectly electrically aligned.

Alignment accuracy is therefore limited by both mechanical and electrical constraints.

The principle reason for the pattern to deviate from what would be expected from an idealized range are reflections from the range surface, surrounding objects, the positioner and the cables used to feed the antenna. Sometimes signals from external sources also pose a problem. The field at a point in the aperture under test is the phasor sum of the test signal and the extraneous signals. The relative amplitudes and phases of the desired and extraneous signals will vary with position along the test aperture causing constructive and destructive additions, thus producing a measured pattern that will depart from the free space expected pattern. (See “National Association of Broadcasters Handbook, 11th Edition,” 2018. Chapter 10.8, “VHF and UHF Television Antenna Test Range Measurements,” John L. Schadler.)

Range measurement accuracy limitations are removed with the use of computer simulation.

Mechanical Tolerancing and Human Error With Physical Modeling REFLECTED TRANSMISSION

Software eliminates lengthy setup and take down of models as well as the need for a technician to be physically present to adjust the model and take data points by hand.

Accuracy is improved greatly using simulation as it removes mechanical tolerances and human error affecting the data.

radioworld.com | February 9 2022

White Paper BEAM WOBBLE SOURCE ANTENNA

AM MAIN BE

desired pattern is replaced by this artificial intelligence optimetric process. Criteria are set based on the desired azimuth and FCC regulation and multiple antenna configurations can be run in parallel to reduce overall study time.

Significance of Polarization Ratio

Information that is traditionally recorded by hand, such as radiator location and parasitic sizes and locations in space is replaced by a simple exportation of the computer model.

The full three-dimensional model can be sent directly to 3D CAD software for detailed component manufacturing and installation instructions, eliminating the possibility of documentation error and physical measurement inaccuracies.

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Automated Optimization Another advantage of designing in a virtual environment is that the geometry can be completely optimized and not compromised by time, materials and tolerances. Variables can be automatically adjusted, and complete data tables exported for the next step in the design process. This is done through an artificial intelligence. An optimetric setup can simultaneously solve any combination of pattern shapers, parasitics and radiators positions in space to find best fit solutions. Trial and error techniques traditionally used to develop the geometry necessary to produce a

Above Fig. 3: Antenna alignment and beam wobble.

Below left Fig. 4: A 4.4:1 scaled model antenna test.

Below right Fig. 5: HFSS model used for simulation.

The rules under 47 C.F.R. §73.316 state that the supplemental vertically polarized effective radiated power (ERP) required for circular or elliptical polarization shall in no event exceed the effective radiated power authorized.

Since in most cases, broadcasters consider the vertically polarized component more important than the horizontal and tend to maximize their vertical signal, accurate polarization measurements are important.

Range measuring the polarization ratio at any point in space with accuracy is difficult. Since no range is completely free of reflection and the fact that horizontal and vertically polarized waves reflect differently, the accuracy in the ratio is limited by the range reflectivity. Polarization ratio range measurement accuracy is also limited by the transmit antennas horizontal and vertical polarization pattern congruency.

If the transmit antenna is linearly polarized and is spun from horizontal to vertical for polarization tests on the DUT, the assumption is that the beam is perfectly straight and has no wobble. If separate radiation paths are used to measure the polarizations, such as switching between crossed dipoles, the assumption is that each of the patterns and gains of the two paths are identical.

Each of these sources for error is eliminated with the use of 3D high-frequency simulation.

Comparison of Physical Model Measurements and Computational Simulation To show the validity of computer modeling in place of physical modeling of FM directional antennas, an example design using both methods, i.e., physical modeling

radioworld.com | February 9 2022

White Paper and computational modeling of the same antenna, are compared.

In the example design, a directional pattern study for Station WHEM, 91.3 MHz, Eau Clair, Wis., was performed on a scale model FM test range using a scaling factor of 4.4:1 for all elements involved in the study.

The scaled elements included a model of an antenna bay and identically scaled models of parasitic elements and the mounting pipe to be used by the station. All the scaled model components were rotated through 360 degrees while receiving a signal at the appropriately-scaled frequency from a linear cavity-backed source antenna.

The horizontally and vertically polarized azimuth patterns were measured in an anechoic chamber test range. The signal source and scale-model antennas were mounted at identical elevations and at opposite ends of the test chamber. A network analyzer was used to supply the RF signal to the source antenna at 4.4 times the fundamental FM frequency (i.e., at 401.72 MHz) and to receive the signal intercepted by the antenna under test.

A photograph of the scale-model pattern study configuration is shown in Fig. 4.

This directional pattern study was replicated in the Ansys HFSS environment using the full-scale CAD model of this antenna bay, mounting pipe and parasitics at the fundamental frequency of 91.3 MHz six years later.

See Fig. 5.

The original results of the scaled model directional pattern study were accepted by the customer and demonstrated both proof of performance and FCC pattern envelope compliance in both the horizontal and vertical planes. A statistical measure of the relationship between two sets of data can be analyzed using the correlation coefficient (r). A correlation coefficient of r = 1.0 represents a perfect match. It can be used as the figure of merit to determine how closely the range measurements match the HFSS calculations.

∑(x i—x)(y i—y)

Thank you A special thank you to S. Merrill Weiss, president of Merrill Weiss Group LLC, for his contributions to this topic. He is responsible for the writing and submission of the Petition for Rule Making to the FCC, “Computational Modeling of FM Directional Antennas.”

Portions of this paper are based on that work.

∑(x i—x) 2 ∑(y i—y) 2

Where: x i = x Values in sample x = mean of the x value samples y i = y values in sample y = mean of the y value samples Fig. 6 displays the overlaid horizontal and vertical polarization patterns and the FCC pattern mask. As can be seen, the results of the Ansys HFSS directional pattern study very closely match the results of the scaled model study.

The horizontal polarization azimuth pattern for both the scaled model study and the simulated pattern study have a maximum deviation of 1.67 dB and a minimum deviation of –1.39 dB compared to the scaled model study.

The correlation coefficient for the horizontal polarization is .986 and .960 for the vertical polarization. The figure also shows that the computationally simulated antenna exceeds the FCC pattern mask in the vertical polarization pattern by a minimal amount. It must be noted that if computer modeling was used in 2015 at the time of this study, modifications would have been made to bring the vertical component inside the FCC protect.

Conclusion

Below Fig. 6: A 4.4:1 scale model physical testing vs. HFSS simulation.

The tools that were available when the current rules for FM directional antennas were developed in 1963 only included full-size or scaled modeling of antennas, combined with physical measurements, to approximate the characteristics that would be obtained when an antenna was installed.

In the decades since then, computational methods have evolved to enable more accurate and precise predictions of the antenna performance. The FCC has for decades relied upon manufacturers of FM directional antennas with engineering personnel who can apply the necessary skills to design and test broadcast antennas. The basic knowledge, experience and expertise requirements with respect to antenna design and modeling remain the same when the newer computational modeling techniques are applied as was the case prior to their availability.

It therefore stands to reason that the manufacturers of FM directional antennas should be permitted to apply the new tools at their discretion and that the FCC should accept the results of computational modeling as being just as valid as the results from physical construction and measurement of either full-size or scaled models of antennas.

radioworld.com | February 9 2022

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White Paper

MR.Cole_Photographer/Getty Images

Ravenna takes it to the cloud Global remote production using Ravenna/AES67 and AWS

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R

emote production is clearly a hot topic today, as companies around the world race to maintain their existing workflows with their talent dispersed in many off-site locations.

Such production is the new normal and — now that we have experienced its potential — is likely to continue to be a focus in the future.

While many solutions have been hastily cobbled together, there is a need for higher-quality productions with lower latency that integrate easily with existing equipment.

Starting Point We started with a basic question: Can we send Ravenna/ AES67 traffic over the public infrastructure and over long distances?

Then we wondered, would we be able to listen to something resembling audio? Would it be good quality?

It is one thing for a single company with their own equipment to do it, but could we also interoperate with equipment from other companies? After all, this is the whole point behind Ravenna and AES67.

Finally, we also wondered how we would do it and what challenges would we face.

Before digging into the setup and challenges that needed to be overcome, it is important to understand that Ravenna and AES67, even though they use IP, are designed to be used in local-area networks (LANs).

Despite this, Ravenna and AES67 have been proven and are being used commercially in wide-area network

Writers

Andreas Hildebrand Senior Product Manager and Evangelist, ALC NetworX

applications across private networks, even though their use in WANs was never contemplated by the standards.

Private dedicated networks, whether owned or leased, are well-architected, have predictable behavior and come with performance guarantees.

Public networks, on the other hand, are the equivalent of the “wild west.” You can’t control them. They are congested and unpredictable. Public networks suffer from packet loss due to link failures and have large, sometimes dramatic, latency due to packet retransmissions.

This makes the public environment hostile for Ravenna and AES67!

Challenges

Bill Rounopoulos Business Development Manager, OEM & Partnerships, Ross Video

There are three main challenges: latency and packet jitter; packet loss; timing and synchronization.

Fortunately, the increased latency and packet jitter of the public network is handled by Ravenna by design, through the use of large receiver buffers that must be able to handle a minimum of 20 mS. AES67 only requires 3 mS but also recommends 20 mS. Most well-designed Ravenna solutions, like all the equipment used in this experiment, have even bigger buffers and other associated techniques that can compensate for the added delay.

The AES Standard Committee working group SC-02-12-M is working on guidelines for AES67 over WAN applications, and a key recommendation is to increase the buffer size within devices.

radioworld.com | February 9 2022

White Paper

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Packet loss is another important challenge.

Ravenna and AES67 are not designed to cope with dropped packets.

Fortunately, there are other transport protocols that are architected to deal with dropped packets without introducing a lot of extra latency. These include Secure Reliable Transport (SRT), Zixi and Reliable Internet Stream Transport (RIST), but there are many others.

We solved the challenge of packet loss by using SRT encapsulating Ravenna traffic within SRT. The final but significant challenge is timing and synchronization. We start by having a separate Precision Time Protocol (PTP) Grandmaster (GM) at each site that is synchronized to GPS. All equipment at each location is locked to PTP locally in order to maintain synchronization among all participating devices. No PTP packets are sent across the WAN or through the cloud, which would simply not be practical as packet jitter is too high to achieve adequate synchronization precision.

The Demo Setup These musings resulted in an ambitious proof-of-concept demo involving equipment from three Ravenna partners — Ross, Merging Technologies and DirectOut — across four sites over two continents, North America and Europe, that leverages the public cloud infrastructure from Amazon Web Services, or AWS. The graphic gives a generalized view of the demo setup. Ross equipment in Ottawa, Canada, interfaced with

“

We solved the challenge of packet loss by using SRT encapsulating Ravenna traffic within SRT.

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AWS Virginia, while the Merging and DirectOut setups in Grenoble, France, Lausanne, Switzerland and Mittweida, Germany communicated with AWS Frankfurt.

On-site in Ottawa, Mittweida, Lausanne and Grenoble, various Ravenna/AES67 gear from Ross Video, DirectOut and Merging was used to create and receive standard AES67 streams. Gateways on the local networks were used to wrap these AES67 streams into SRT flows, which in turn were handed off to the AWS cloud access points using the public internet.

The flows were then transported within the AWS cloud between the access points, from where they were handed off (secured by SRT) to the local SRT gateways via public internet again. The gateways unwrapped the AES67 streams so that they appeared unchanged in the

radioworld.com | February 9 2022

White Paper

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local destination networks and could be received by the Ravenna devices.

All SRT gateways were built from Haivision’s open-source SRT implementation. While Ross Video and Merging used separate host machines to run the SRT gateways, DirectOut was able to include the gateway functionality into their Prodigy.MP Multi-I/O converter.

Since all Ravenna devices were synchronized to the same time source via GPS, the generated streams received exact RTP timestamps that were transparently transported through the cloud, so that a deterministic and stable playout latency and inter-stream alignment could be configured at the receiving ends. Since streams were not processed or altered in the cloud or by the SRT gateways, the audio data was bit-transparently passed through with full quality.

Since any packet loss was coped with by the SRT protocol, a higher latency setting needed to be configured to accommodate the larger packet delay variation (PDV) due to occasional packet retransmission.

Thankfully, the Ravenna receiver devices used in this demo provided ample buffering capacity to allow adequate configuration. In practice, buffer settings (= overall latency setting) ranged from 200–600 mS, depending on quality and bandwidth of the local Internet connection.

A monitoring web page connected to a local loopback server hosted on AWS enabled listening to the live streams

“

Thank you

Thanks to Angelo Santos of Ross Video for providing the drawing of the proof of concept setup; Nicolas Sturmel of Merging Technologies for programming the monitoring website and setting up the AWS cloud access; and Claudio Becker-Foss of DirectOut Technologies for providing thoughts on gateway programming.

Latency, at significantly less than 1 second, is lower than what we expected, but still substantial.

To manage increased network delay, manual tuning of the link offset at each location was required, as expected, but the deep buffers of the receivers were able to compensate for it.

Future Considerations There are a few items that require further study to make it a more practical and usable solution: A big one is how to transport timing through the cloud.

We consciously decided on manual connections using session description protocol (SDP) files to keep things simple. It would be valuable to be able to use Ravenna or NMOS registration and discovery over the cloud to automate the connection process.

Ease of use would be greatly enhanced if the linkoffset could be handled automatically to compensate for network delay.

To manage packet loss, it would be interesting to learn if ST2022-7 redundancy would work.

Although SRT worked great, it would be good to experiment with RIST to understand if there are any performance or reliability benefits.

The proof of concept showed there is a lot of promise for Ravenna in the cloud and we are excited and motivated to tackle these items soon.

To manage increased network delay, manual tuning of the link offset at each location was required, but the deep buffers of the receivers were able to compensate.

via http within any browser, including display of live VU metering and accumulated (unrecoverable) packet loss per stream.

More information and the live demo page are available on a dedicated page at www.ravenna-network.com/remoteproduction/.

Trends in Transmitters 2022

The quality of professional broadcast transmitters available today is unquestionably high. That’s good news for radio engineers and managers who are in the market for a new one.

If someone hasn’t purchased a transmitter in a while, what should they know? What are the most important recent developments in how they are designed and manufactured? That’s the subject of a free ebook that you can read and download at radioworld. com/ebooks.

Lessons Learned

The proof-of-concept demo worked well, and we are very pleased with the results. It required some expertise and fiddling with manual settings to get it to work.

Many lessons were learned from the proof of concept.

Here are a few: “Local only” PTP synchronization locked to GPS works fine.

There is packet loss, but this can be managed via SRT.

radioworld.com | February 9 2022

”

Marketplace Shure Podcast Mic Looks Familiar

Future support is planned for WheatNet-IP. Intraplex Ascent is described as a nextgeneration audio over IP platform built to transport broadcast and media content at scale, “leveraging common off-the-shelf hardware to reduce the costs of multichannel contribution and distribution between many locations.”

Shure recently introduced the MV7X. While it has the readily recognizable shape of its wellknown broadcast veteran cousin the SM7B, the MV7X is aimed at the podcaster market, though broadcasters, streamers and musicians would also find it of interest.

It is a dynamic cardioid mic with an XLR connector mounted on the rear. Its output is analog thus requiring a preamp or digital audio converter.

It ships with an adjustable yoke.

Price: $179.

Info: gatesair.com

Info: www.shure.com

GatesAir Adds Native Livewire Support to Intraplex Ascent GatesAir added native Livewire+ IP audio networking to its Intraplex Ascent cloud transport platform.

This means Intraplex Ascent can ingest and output multiple audio channels via IP without the need for conversion equipment, which the company said adds scale and efficiency for broadcasters that manage many digital audio channels between studios.

21

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Readers’ Forum pattern replication with improved audio quality and possibly a lower capital and operating cost, some of which could even be a shared burden.

I am not even thinking of SFN per se. We can achieve 50 kW or more ERP in a managed wireless network just by making good technology decisions. We have video ingested on mesh networks where selected channels are then broadcast over the same mesh to connectionless receivers.

If we can do that citywide for video, it’s only vision and money that prevent the use of such for audio networks.

I suggest that Cris’s 40 kW goal is way closer than we think, and may already be happening. Let’s get that puppy in the dashboard first and work from there.

40 kW down twisted pair

22

I have read many of Cris Alexander’s articles over time, but as a practitioner of broadcast engineering arts for 40 years, mostly in the large markets and networks, his article on air chains was an enjoyable must-read, a memory train ride.

I’ve been building stations since the days of deregulation and divestiture in analog, through AES, T-1 and ISDN, then cellular as a viable technology, to where we are with Livewire and the birth of AES67.

For me, AM was already in the past by the early 1970s. We listened to it for school closings and some country music, but by 1973, FM was king, and New York’s WPLJ was where I learned about rock and roll.

Cris drove us along a multi-lane highway, through tech corridors that divided, converged, intersected, over/underpassed and cloverleafed, via on-ramps and off-ramps of various construction and at various speeds.

Having never been happy to be Yesterday’s Man, I’ve tried to push the envelope on development and use of technology, pursuing what Steve Church referred to as the “artful application of science.”

Which brings me to the closing comment Cris made about sending 40 kW down twisted pairs. Why not? Maybe we are already there? The Holy Grail of digital broadcasting has always been pattern replication with audio improvement.

We have at least two technologies that push MPX over twisted pairs or UDP paths on wired and wireless networks. Those cabling standards work at 350 MHz or higher.

In the AV world, twisted pair to coax baluns are already being used for wireless mic, intercom and IFB, usually in fixed installations.

HDBaseT carries A/V and internet and has an extrapolation to carry 100 watts similar to POE. We stream media over wireless devices. We have a few brands of radiating cable.

I like to say that my imagination is limited only by my budget. While not as efficient as a 40 kW SCPC “broadcast” signal, the technology to broadcast down the wire rather than up a tower is there but stifled by the regulatory climate.

We can build modern networks that feed localized transmitters, powered on POE, that broadcast transmitter location and content identification to receivers that could be directed to what channels are “subscribed” to an “edge recipient” in a given market, and thus achieve

Above Ed Bukont’s letter at left refers to a commentary about air chains

by Cris Alexander that appeared in the June 16 issue of RWEE. Find it at radioworld.com/ digital-editions.

Tell Us What You Think

Radio World welcomes letters to the editor about any article or relevant radio industry issue. Email radioworld@ futurenet.com with “Letter to the Editor” in the subject line.

Ed Bukont, M.Sc., CTS, CSRE E2 Technical Services & Solutions Gallatin, Tenn.

Stations in the stream, that is what we are I liked Cris Alexander’s “A Stream of Thought … on Streaming” article in the Dec. 15 issue.

It brought back memories of my first streaming of a radio station. In many ways, how bad it was, yet it was better the 90% of the others, and I made it work.

I like pushing the edge of technology, seeing it as the future.

However, it took some training for the host to understand that even if the local transmitter had issues, they needed to keep playing the hits since they were still streaming.

Thank you for touching on Nielsen and the watermark.

I find that stations don’t think a watermark is needed to know how the stream is doing compared to the air. The listener information became vital in 2020 with the lockdown, when people were not listening to the radio on the way to work. Management wanted to know if people were listening to the stream.

I hope people read your article and will implement the improvements.

radioworld.com | February 9 2022

David Shantz Product Manager Burk Technology

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