Radio World Engineering Extra 273 - June 15th, 2022

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June 15, 2022

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In-depth technology for radio engineers

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Do it yourself A purpose-built thermal sensor.

Three-phase power

Dennis Sloatman provides a useful tutorial.

Let’s get this straight

John Robinson returns to ERI as head of its Structural Engineering Group.

Vol. 46 No. 15 | June 15 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 Content Producer & SmartBrief Editor Elle Kehres, elle.kehres@futurenet.com 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, Gary Kline, Larry Langford, Mark Lapidus, Michael LeClair, Frank McCoy, Jim Peck, Mark Persons, Stephen M. Poole, James O’Neal, John Schneider, Dan Slentz, Dennis Sloatman, 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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Rolling your own

There is great satisfaction in building your own problem-solving gadgets

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n my continuous search for material for this publication, I run across all kinds of interesting people and ideas.

There are some really creative folks out there, people who think outside the box and come up Cris with innovative solutions. The history Alexander of broadcast engineering has quite the CPBE, AMD, DRB cast of such people.

Technical Editor Way back when (here he goes again!), on-air phone systems were non-existent and usually consisted of a modified speakerphone … that is until a guy named Steve Church came up with an idea for hybrid interface to the then-ubiquitous 1A2 phone system. That’s one of the best examples of smart people in broadcast engineering coming up with an innovative solution that I can think of, although there are many more.

In the decades since, a good number of niche broadcast equipment manufacturers have come out with an array of purpose-specific products. Companies like Broadcast Tools, Inovonics, Radio Design Labs, Henry Engineering and Angry Audio come to mind, although that’s nowhere near being an inclusive list.

But prior to the availability of ready-built gizmos that perform special functions, quite often we built our own; and many broadcast engineers still do that sort of thing.

In my earliest days in radio, I remember watching the chief engineer at the AM/FM combo in his shop, huddled over a smoking soldering iron and building up a gadget to do … something or other.

Time tones It wasn’t long after I moved into the technical end of things that I started doing that kind of thing myself, and with it came the deep satisfaction of creating from a pile of parts a gizmo or gadget to make someone’s life easier in the radio station.

One of the most interesting (read: weird) gizmos that I was called upon to create was a time-tone generator.

The Dallas top-40 FM where I was CE in the very early 1980s hired a programming consultant to get those extra few tenths of a point in the ratings, and in one of his first visits to the station, he told me that we had to have a tone

THIS ISSUE From the tech editor

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Robinson structures a career

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A threephase power tutorial — Part 1

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Build a customizable thermal sensor

THIS Digital audio ISSUE 22 levels review NEWS x

xxx xxx

FEATURES xxx xxx

x On the

cover

BUYERS ERI’s John GUIDE Robinson, left,

verifies xxx the lean xxx of a guyed tower during OPINION an intentionally destructive xxx x demolition. xxx

x

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From the Tech Editor

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that would come over the air at the exact top of every hour. Evidently that was somehow of critical importance to listeners.

With raised eyebrow, I nodded my understanding and I set to work building up a device that generated three distinct tones of specified frequencies that someone’s research had determined were the best attention-getters.

I used an ESE precision clock to gate the three tones into the audio mix for one second at the top of every hour, and it worked like a hose. The tone-trio blasted through the music like a train horn, and the consultant was happy.

We ran that thing for the better part of a year. I don’t recall if it helped or hurt the ratings, but I can speculate that it didn’t help. It was obnoxious!

The point is, even in today’s broadcast technical environment where we have many options and sources for every kind of gadget under the sun, once in a while, you’re going to run into a need for something that you can’t buy off the shelf. And that’s where we get to do some real engineering and show our stuff.

Affordable fix Sometimes this kind of thing takes the form of finding innovative ways of using off-the-shelf equipment to perform tasks for which it was not really intended.

In one of Crawford Broadcasting’s Midwest facilities, our engineering staff employed GPIO logic in the AoIP system to provide remote control of facility security

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Above This home-brew optical tower light status/ alarm coupler is built on a PC board designed to host either a transmitter or receiver. Just populate it with the parts for the desired function.

I used an ESE precision clock to gate the three tones into the audio mix for one second at the top of every hour, and it worked like a hose.

features, such as the electric gate providing parking lot access, all without running a single wire through the ceiling.

Other times, perhaps a purposebuilt device is available but there’s no budget for that item. In those cases, we may be called on to build up a gizmo ourselves. Nothing wrong with that.

A decade ago, as we started converting to LED lighting systems on our AM towers, we needed a way to get alarm and status contacts across the tower base insulator so that they could be monitored remotely.

There were purpose-built fiberoptic devices available, but they were expensive, and we were talking about a lot of towers. So I went on www.mouser.com and found fiber-optic transmitter and receiver modules, I had some PC boards printed using one of the services featured in these pages in months past, and with a handful of resistors, capacitors, LEDs and opto-isolators, we rolled our own.

They too work like a hose, and all for about $20 per tower. Those devices are still in use all over my company.

In this issue My longtime friend and colleague Buc Fitch is an old-school home-brewer. He loves to design and build gadgets, and in this issue, he will share with you his design/build project of a thermal sensor and temperature alarm. This is a great example of what broadcast engineers do on a routine basis, and we hope that the circuit is something you can use… and modify to fit your specific application.

We’re also going to start a new educational series in this issue. Dennis Sloatman will over the next few issues teach us what we need to know about three-phase power. Most all of us use equipment that employs 208-, 240- or 480-volt three-phase power, but what do we really know about it? What do we need to know about it? I know you’ll enjoy Dennis’ approach to this topic, and I guarantee you’ll learn something.

Meanwhile, the next time you run into a special need at one of your radio stations, you might think about taking a walk on the wild side and rolling your own. You’ll get a lot of satisfaction out of creating a purpose-built device to meet that need.

radioworld.com | June 15 2022

News Maker Writer

Robinson structures a career Freshly back with ERI, he offers his views of a changing tower industry

Andy Gladding Chief Engineer, Salem Radio Network’s New York cluster.

Comment

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

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n the ever-changing world of broadcast engineering, competent tower design and structural safety remain a priority for all terrestrial operators.

Creating safe, long-lasting and effective structures can be a challenge for any broadcast solutions group.

That’s certainly true for Electronics Research Inc., a familiar name in the niche field of antenna systems design and broadcast tower construction.

Enter industry veteran John Robinson, P.E. He is a true antenna tower specialist with more than 30 years of experience in this sector.

In January, Robinson rejoined ERI as its vice president of structural engineering, coming from consulting firm Hodge Engineering, where he had been principal engineer for the tower group. In his earlier, 23-year tenure at ERI he was senior engineer of the structural division.

Prompted by the hiring announcement, Radio World caught up with him to learn about his background and thoughts on this specialized part of our specialized industry.

Safety first

Right John Robinson verifies mast deviation for a tower drop.

Robinson began his professional journey in 1977, graduating from the University of Evansville with degrees in civil and mechanical engineering. He later earned his master’s in mechanical engineering.

He started out working in the coal industry, designing conveyor systems and storage structures. Later he moved on to designing fire safety systems.

Robinson was an early user and developer of Fortran software that would later become the foundation for the widely used tnxTower tower design platform published by Tower Numerics Inc. This gave him an edge when it came to understanding how computers could help influence traditional industrial design processes when developing broadcast radial solutions.

Beginning in 1985 he started working with the late, legendary engineer Ernie Jones designing and analyzing towers. In 1994, he first joined ERI, designing and constructing broadcast towers for the company’s Structural Division.

Over the years Robinson has been directly involved in a number of major tower site projects, ranging from large AM arrays and very tall structures in the American Midwest to towers located on building rooftops such as the 4 Times Square complex in midtown New York and the Hancock Building in Chicago.

Always keeping a mindful watch on safety, Robinson said he has sought to manage projects with the same

radioworld.com | June 15 2022

News Maker

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methodical approach each time, using industrialconstruction best practices combined with cutting-edge software to achieve efficient results.

He describes walking a fine tightrope between creating long-lasting, durable structures while keeping each project ahead of schedule and under budget.

Today he is a registered Professional Engineer in Indiana and 17 other states. He also is a member of the American Society of Civil Engineers and the TIA’s TR-14 Engineering Committee for Structural Standards for Communication and Small Wind Turbine Support Structures.

One major cornerstone of Robinson’s engineering methodology is designing structures that can maximize capacity while staying within safety parameters for wind load and sheer strength. He prioritizes safety over speed and said he will never compromise his fundamental training or instincts, as this can lead to tower crew injury and death.

Checking it twice Robinson recommends double and triple checking the output of the software calculations to make sure that everything is in line with the required parameters, minimizing the risk of structural failure.

This is a core component in line with his training as a structural engineer. He is also an expert on the latest telecom industry standards and recently helped shepherd companies into the latest ANSI/ASSP A10.48 and TIA-222-H standards.

“Computer software and the use of computer functions are essential to calculate a guyed tower to maintain standard,” he said, especially as the ASCE and TIA update their codes and requirements to meet the shifting terrain of the industry.

A thorough understanding of the TIA-222 Standard, specifically the checking of construction loads on towers, is critical.

According to Robinson, you must never underestimate

factors such as wind loading, guy wire tension and soil composition, as any miscalculation in these areas can lead to structural failure.

Proper antenna installation procedures also need to be followed to the exact parameter, from gin pole mounting to crane operation, or else the process can cause instability, tower failure and crew injury and death.

“Defining responsibilities for everyone on the project is key to maintaining safety,” he said. “If you’re putting up a gin pole and you’re going to lift 30,000 pounds, you need to go through all of that to make sure everyone on the team knows what their specific function is.”

We asked him how dynamic industry regulations are evolving the face and shape of the business.

He says that a variety of factors are changing the way towers are built and regulated, ranging from environmental concerns such as impacts on bird populations, usage and demand shifts.

Robinson feels that with the rapid growth and expansion of cellular technology, there is less of a need for the traditional tall tower to broadcast long-range over-the-air signals for television and FM radio.

However, these technologies remain at the forefront of communication and information during disaster and emergency situations because of their reliability compared to the cell network. And that’s due in part to high standards for tower construction, transmission system redundancy, power generators installed at the transmitter sites and the long distances at which OTA signals can travel from a single point.

“What do you do when a tornado comes through?

You look for your local TV or radio station to get the information,” he noted.

Indeed, this usage scenario is causing regulations to

“

The most important thing a broadcast station can do is maintain good records of the antennas, transmission lines and other items that are on a given tower.

radioworld.com | June 15 2022

News Maker Right At the factory, Robinson inspects a mounting flange interface that will support an ERI Lambda Optimized FM Mounting System.

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become more stringent for taller structures, as they remain the most effective line of communication in a disaster situation.

According to Robinson, a major challenge is when a company like ERI is asked to change the structural composition of a tower to accommodate hardware outside the original scope of its design.

“When you have to go in and reinforce a tower, it becomes a tedious job, especially if there are a large number of appurtenances on the structure and the site terrain requires consideration of topographic conditions.” he says.

It is important for modern structural engineers to understand how to revise loading on guyed towers. Fabrication, material quality and the demands of each location are also central components of structural reliability.

“A tower in the Midwest located in Tornado Alley will require different bracing for wind loading than a tower located on a rooftop on the East Coast.”

Finding the right balance of materials and design will assure proper structural performance, maintenance and cost.

Good records We asked if he has recommendations for engineers who may not be entirely up to speed on the latest tower safety procedures and regulations.

Robinson says be sure to have copies of your tower structural records and drawings of existing structures available at the main office or transmitter building for easy reference.

“The most important thing a broadcast station can do is maintain good records of the antennas, transmission lines and other items that are on a given tower,” he said.

“The information on file should include weight and wind area and an accurate record of each item’s location on the tower. If this information is readily available, it will save time and money when a tower needs to be analyzed for equipment that is being added, replaced or upgraded.

When it comes to engineering, the numbers don’t lie.

They tell a story.

“A tower map is key. The station engineer needs to understand what elements are physically located on the tower and what their operating parameters are.”

Robinson recommends performing regular visual inspections of the tower and surrounding site. Some warning signs may be right in front of you: a tower out of plumb or guy wires sagging. Addressing such issues can be crucial to avoiding structural damage or failure.

Other simple but important issues to watch for include cracked foundation anchors, deteriorating brackets and corroded tower structural components. Such hazards can be identified easily through visual inspections.

“Brilliant” Looking towards his future at ERI, John Robinson is excited for the challenges that await him.

ERI’s Structural Engineering Group has four members, two of whom are Registered Professional Engineers. He hopes to expand this team, further develop the talent of its personnel and focus on departmental efficiency.

He feels that quicker turnaround of structural analysis can help increase project performance and improve the quality of customer service.

While this will be a difficult undertaking, especially as the industry faces changing regulations and staffing shortages, he has the support of senior management in this new endeavor.

“John is a brilliant and highly qualified tower design engineer,” said ERI Vice President of Marketing Bill Harland.

“His background working for a structural engineering consulting firm, experience designing antenna support spines, structural analysis, structural reinforcement design and knowledge of fabrication processes and procedures make him an excellent leader of ERI’s Structural Engineering Group.”

radioworld.com | June 15 2022

Radio Fundamentals

A three-phase power tutorial — Part 1 Dennis Sloatman CSRE, AMD, CBNT, BSEET

Engineers must have a good understanding of three-phase power

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t’s important for engineers to have a good, working knowledge of electrical power and, in particular, three-phase service to a transmitter site. I will avoid math here as much as possible and only include whatever math is necessary to increase your working knowledge.

My primary goal is to allow you to speak with confidence to your electrical vendor’s master electrician in order to get precisely what you need.

In this first installation, I’ll discuss the two primary and most-used electrical feeds: three-phase Delta and threephase Wye, zooming in on the Closed Delta.

Wye A Wye or “Y” service has several benefits. The first of these is that the center of the Wye is used as a neutral, and singlephase loads can be supplied with any phase to neutral and 208 loads can be supplied between any two phases.

Fig. 1 shows a transformer in a Wye configuration.

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Delta

Below Fig. 1: Three-Phase Wye Connection

A three-phase Delta is a 240 VAC feed with one phase center-tapped as shown in Fig. 2 to provide two 120 VAC feeds and neutral for single-phase loads.

This type of feed is fine for a transmitter site, and most transmitters can be tapped for 240 VAC use. Note in Fig. 2 that single-phase loads are connected between Phase

A and neutral or Phase C and neutral. One must be very cautious never to connect your single-phase 120 VAC equipment between Phase B and neutral — this is 208 VAC! Incidentally, Phase B is often referred to by several names: wild leg, high leg, stinger and bastard leg.

One important note here is if the number of single-phase devices and current draw of your single-phase equipment is high, the transformer winding from which the neutral is derived must be sized larger in ampacity than the other two windings.

One other note for three-phase Delta feeds: It’s possible to operate in an emergency with one winding missing (so long as it’s not the center-tap winding) and operate in an “Open Delta” configuration, shown in Fig. 3. However, such an arrangement will result in a transformer capacity of 57% (1/ ), so loads will likewise need to be reduced accordingly.

By the way, the 57% number or alternatively 1/ will be seen several times during this series so, memorize it. Its true significance will be shown in the next installation.

Transmitter manufacturers quite rightly warn that an “Open Delta” configuration by virtue of circulating thirdharmonic currents present in such a system should be avoided at all costs in order to prevent equipment damage.

There are some other variations of secondary winding configurations such as “Zig-Zag” and “Corner Grounding Delta,” but we will not be discussing these in this series.

One interesting note about the Corner Grounded Delta, about which I’ll bet you may think, “Who uses that?!” When I was in L.A., I was told immediately by the old-timers that the electrical feed at Mount Wilson was a Corner Grounded Delta. I was never able to find out why this was done, but you must remember, this is an old site.

What this meant to the broadcast engineer is that in order to run single-phase loads, an additional single-phase center-tapped stepdown transformer was required at each facility to provide 208 and 120 VAC service. The point is, always specify or at least be aware of the type of service your utility provides.

Closed Delta Secondary Feed Zooming in on the closed delta secondary feed, refer again to Fig. 2.

radioworld.com | June 15 2022

Radio Fundamentals Each phase-to-phase voltage such as, B to A, A to C and C to B, are all 240 VAC. We derive a neutral which is joined to ground in the main distribution panel (but NOT in subpanels!) by means of a center tap of the Phase A-C winding, and Phase B is the “high leg” as is dictated by North American Code (at least, generally).

Recall that neutral to the high leg to B phase is 120 VAC x 1.732 (1.732 is ), or 208 VAC. You and your electrician must be extremely careful not to introduce Phase B to neutral into your single-phase loads (it has happened and that is no balderdash). Most electricians are well aware of this and will not make that error, but to invoke the Russian proverb, “Trust but verify” (Ronald Reagan wasn’t the progenitor of that phrase).

TIP: The best way to deal with avoiding a high-leg concern is to have a three-phase distribution panel feeding a singlephase distribution fed from winding A-C-N (not B) for the 240/120 distribution panel. This eliminates the “High Leg” concern for single-phase loads.

When using such a service, the electrician must be made aware by you of the ampacity required by your singlephase loads (generally you’ll mention this to the master electrician during the bid process). This isn’t just 120 VAC loads, which can be load-balanced between A-neutral and C-neutral, but also consider your 240 VAC single-phase loads such as dummy loads, smaller backup transmitters

and blower/circulating fans in your transmitter plant. If these are significant, the A-C winding will need to be sized accordingly or the entire three-phase transformer will need to be sized for worst-case.

Above Fig. 2: Closed Delta Secondary Feed

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Radio Fundamentals Right Fig. 3: Three-Phase Open Delta

As I mentioned, one benefit of the Closed Delta secondary is that if a winding fails, so long as it isn’t the one used for the singlephase loads, you can continue to operate in an emergency mode with a phase missing, which makes this an Open Delta, but at only 57% ((1/ ) x 100%). If all three phase windings are center-tapped, you can reconfigure but have the electrician on-site.

Also, the transmitter may have issues due to odd-order harmonic distortion from the Open Delta service — not recommended! As a matter of fact, most transmitter manufacturers will not sell you a transmitter for an Open Delta service, and with good reason!

Current affairs

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Now, having discussed three-phase Closed Delta voltages, let’s have a look at currents, both line and phase. This is an interesting topic. Let us discuss in some detail.

First understand that each phase is 120 degrees in phase apart from the other two phases. If Phase A is the reference, then Phase B is lagging by 120 degrees and Phase C is lagging by 240 degrees (or alternatively, +120 degrees versus phase A).

When the circuit is analyzed with trigonometry — which I promised to avoid — the following can be shown. You’ve seen the irrational number mentioned a few times here, which is approximately 1.732 (check this on your calculator). Recall from Kirchhoff’s current laws that the current leaving a node (such as A to B in a delta), is the sum of the currents flowing into the node. In the case of a Delta by virtue of the phase difference, the sum of these currents is not algebraic, but vector addition.

Now, let us say we place our clamp-on ammeter on a line A (junction of phases A-B and A-C) and observe 100 amps. Is this the amperage in the windings? No! The phase A current is the vector sum of windings A-C and A-B. So, not getting into vector analysis, the 100-amp current read by your ammeter in line A is the vector sum of Phase A-B and Phase A-C currents.

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My primary goal is to allow you to speak with confidence to your electrical vendor’s master electrician in order to get precisely what you need.

Each of these currents is 100 amps / , or 57.73 amps.

Algebraically, this would be 57.73 amps + 57.73 amps summing to 115.5 amps … but that is not correct. So, in order to be clear, winding A to C is contributing 57.73 amps and so is winding A to B. This will lead to a line current in line A of 100 amps. If the three-phase load is balanced (each line having 100 amps flowing), then 57.73 amps will be flowing in each winding. Note that this condition (balanced loads) is highly unlikely — especially due to the single-phase loads from winding A-C.

Why three-phase power?

At this point, I’d like to deviate momentarily for those new to engineering or new to working with three-phase power. There a few very good reasons for having a threephase service.

First, by having electrical service delivered in three phases, more power can be delivered to a load with smaller conductors (because each conductor will carry 1/3 of the total load). Also, three-phase blower motors in air conditioners and transmitter cooling induction motors are simpler to start than single-phase induction motors. Single-phase motors require a starting capacitor and a centrifugal capacitor cutout switch in order to start, while three-phase motors generally start with a Wye-Delta starting system (for surge reduction) by virtue of the three-phase rotation. So, if a three-phase motor blows in the opposite direction, you only need to switch two wires of the three-phase feed to correct the blower direction.

In summary, a three-phase Closed Delta is a perfectly fine feed to a transmitter site and has the advantage of pseudo redundancy if a coil or winding is defective and has some advantages for balanced voltages so long as single-phase loads are carefully considered.

In the next installment, we’ll examine the Wye or “Y” configuration and its characteristics.

radioworld.com | June 15 2022

Project Journal Writer

Build a customizable thermal sensor I used it for a purpose-built low-power FM transmitter

Charles S. Fitch P.E. The author is a longtime contributor whose articles about engineering and radio history are a popular recurring feature.

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roadcast engineers love to talk. Recently, over a pleasant long lunch, between being handed the menu and the final credit card receipt, the conversation was all about equipment and its manufacturers.

Somewhat surprising was that we cohorts all shared a sort of uniform appraisal of one particular purveyor that has the knack of supplying gear which, no matter how challenging the task, seems to have that highly desirable perfection of elegant simplicity of design.

These folks just seem to be able to choose the ideal circuit solution, select the optimal devices, somehow minimize the

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The most often-used, cost-effective sensing device for this application is the venerable LM-34.

parts count as well as achieve exceptional feature flexibility with an intuitive operating ergometric control panel. No wonder the firm has had a longevity of success and a sterling reputation to match.

On the drive home, I pondered my own design work over these last nearly 60 years. What was my design record and how would my own work stand up?

In the rearview mirror review, I seemed to have toggled between mostly the near obscenely overly complex and a small handful of well-realized, durable, slick circuit solutions.

Out of this rumination, one simple yet highly useful device with a Spartan simplicity came to mind that has

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Project Journal

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The LM-34 comes in three formats but most often looks like a plastic TO-92 transistor.

Above left The project is in its nascent stage with components roughly positioned on the proto PCB to make certain that all will fit and optimal, uncomplicated interconnection can be made.

Above right The finished PCB assembly in initial test. After hightemp trip setting, the board will go to its final home position inside an LPFM transmitter.

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been optimized on my drawing board over a dozen reincarnations.

An old friend

Most recently, a need has appeared for small translator transmitters to deliver the low-power FM signals assigned to AM stations.

Like many laboring on these projects, I fabricated a purpose-built unit in the 200-watt class, and as on past similar efforts, I found that I needed an accurate operating internal thermometer with digital readout.

To that point of simplicity ... the most often-used, costeffective sensing device for this application is an old friend, the venerable LM-34, which outputs a linear voltage analog of the ambient temperature.

From this starting point of an accurate proportional value, this particular version of my classic design can accomplish many tasks and provide an important measurement.

Please review the schematic shown at the top of this article,

as it will help you follow along with the circuit explanation.

The LM-34 provides 10 mV of output per degree Fahrenheit from 5° F to 300° F if no offset compensation is used to allow reading temps below 5° F. As such, typical room temperature (72° F) would produce 0.72 volts at the output.

This device comes in three formats but most often looks like a plastic TO-92 transistor. It is quite amazing as it has all the circuitry to generate this analog output as well as an internal regulator, so you can impress any supply voltage from 5 to 20 volts … all inside this tiny device.

(The metal can TO-46 format, pricy and often hard to find in one quantity, is available as a help in horrendous RF environments as the ground/common lead grounds the can.)

Many people use this voltage output directly, but in an RF environment, it’s good engineering practice to amplify the output so that it is above the residual noise level as much as possible. The 0.01 uF ceramic capacitors on the LM-34’s voltage supply input and the analog output to ground are attached as close as possible to the device and are for RF decoupling. The specification of Belden 8451 or equivalent wire shields the signal flow of this low-level data as it travels.

This layout does use the output directly as a selected input for a typical 200 mV front-panel digital meter. The parallel 20-turn 100 kΩ potentiometers are a trifling and stabilizing load at 50 kΩ for the LM-34. The pot, when properly adjusted, allowed a direct temperature display on the meter. Not drawn but a nice touch was for that same switch that selects this metering input choice also properly positions the decimal point on the meter.

radioworld.com | June 15 2022

Project Journal

The ubiquitous LM-392, one of the oldest and most useful of the DIP-type linear ICs, conveniently has two distinct sections perfect for this project. The first works well as an op-amp, and the second as a very nice comparator.

We’ll ask this IC to perform both these tasks for us. The former section provide gain for easier signal handling and a more definite decision point, and the latter is used

Above The author inspects his solder work under the magnifier. Notice the 1N914s under board, placed there as back voltage protection for the relay coils.

as a comparator to generate a temperature extreme alarm.

In the case of my unattended LPFMs, I used the overtempt, as shown in the schematic, to latch off the RF power amplifier for attention to the problem’s cause at a later time, preventing self-generated damage in the meantime.

The gain of this little op-amp as drawn is a nominal 3, which raises the 72° F (0.72 volts) previously mentioned to about 2.2 volts. You’ll also notice an optional branching resistor from this stage output which allows one to take a healthy voltage sample to a remote control system’s telemetry input, which can be used as an analog value to display the temperature sensed by the LM-34. This resistor is shown as 10 kΩ, but you can lower this value some if your remote control system requires more sink current.

The comparator has a fixed trip point of 3.3 volts, which when finally adjusted I made correspond to 122° F, sort of the universal maximum high temperature to which most broadcast gear is intended to operate properly.

Since the LM-34 conveniently outputs a linear voltage, substituting 1.22 volts in place of the LM-34’s output allows you to set the 122° F trip point by adjusting R1 to

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Project Journal

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activate the trip. The latch relay that I used was a 4.5-volt type intended to work in TTL circuits. The latch coil draws about 16 mA to operate, and that is within the range of the comparator section’s independent output pass transistor’s 40 mA limit. This transistor conducts to IC ground (open collector) when “high,” and hence is in the negative return of the latch coil.

The first insert is a following high-current control for sinking more current if needed. If you need to change voltage levels, such as controlling 24 volts, a 4N33 optical Darlington isolator works really well.

The reset push button is mounted front-panel on my LPFM amp, and this sends a voltage to the high side of the “unlatch” coil through electrolytic capacitor C1, which allows current to flow into the unlatch coil for about one second. The 3.3 kΩ resistor will discharge the capacitor in less than five seconds unless you continue to push the button.

If voltage is present on the latch coil, the relay can’t move. If the temperature has dropped below the trip point, the relay will reset, allowing overtemp operation once again.

Above The end of the multiturn pot — blackened to avoid orientation errors.

Below Substituting an LM-35 for the temperature sensor allows display of centigrade such as this 16.2C, which is about 62 degrees Fahrenheit in the basement shop this winter morn.

Qty. 1

Description LM34

1

PCB board

1

DPDT latch type relay

1

DPDT switch on-on type

1

Digital 200 mV meter

1

LED 20 mA

1

LM-392

3

100 B18k 20turn trim pots

1

5 volt 7805 regulator

1

100 uF 16 volt electrolytic capacitor

1 2

680 uF 6.3 volts 1N914 or 1N4001 diodes 47 uF 16 volt electrolytic capacitor 150 ohm resistor 3.3 k resistor 10 k resistors 33 k resistor 1 k resistor 1.8 k resistor

1 1 1 3 1 1 1 1

radioworld.com | June 15 2022

SPST momentary push button switch NO

Notes The LM35 series is directly calibrated in Celsius for our metric readers at 10 mV per 1 degree centigrade Buc prefers the DIP style protoboards from Newark models 21-4575 and the slightly larger 21-4580 shown in the article Latch relay in Buc’s version is an Omron G6AX-234P-ST410US which is a 5 volt relay but is sensitive enough to function at 4.5 volts. Possible alternatives are Panasonic TXS2-L2-4.5V or a KEMET EC2-4.5TNU in the $4 to $5 range.

NO center off for selecting between relative RF output level and the temperature. The second section is for switching the decimal point on the meter if desired.

IMPORTANT: Make certain whatever meter you use can measure common ground inputs.

Buc prefers red for alarm.

The L series from the Visual Communications Company shown in the article conveniently slip directly into a ¼ inch chassis hole. Also available in the L series are 5 volt LEDs with built in resistors.

Order socket to match format you chose Select the adjustment orientation, side or top that suits your design scheme.

Shown in the article but not on the schematic as the finished unit was intended for a 12 volt regulator source – use if needed – fender washer heatsink optional Used on the output side of the 7805

If you cannot readily locate this value, 2 k will work but will move the adjust point Can be paralleled with other NO switches Such as a remote control momentary relay closure

Project Journal

Top Tips As the Brits say, here are some “top tips” to help your project come together successfully.

•M ulti-turn PCB pots as appear in this project, usually in very tiny print, are marked for rotation direction with the related change in resistance value. I find that marking the pot arm that is furthest from the center arm when the pot is fully clockwise (CW) that in most circuits is connected to ground with a black sharpie reduces orientation mistakes.

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As noted, you can customize this circuit in whole or in part for your own applications. You can use the latch feature to latch a status alarm on your remote control. As noted, you can simultaneously grab the op-amp output for a low-noise temperature value for the remote control.

You can bring out the reset (unlatch coil) control to your remote control to test if the alarm is ongoing or past.

You can eliminate the latch section and thermostatically operate the AC or a fan.

In smart remote control systems, you can even use the overtemp to summon the HVAC repair people on high temperature alarm.

Elegant, simple, flexible, useful. As was said at the end of the original “Outer Limits,” we now turn control over to you.

Above After the trip point has been set for 122 degrees, the meter display pot is then adjusted to 122.

• Working on small prototype PCBs I have the best results using ultra-thin solder and running my Weller WESD51 soldering station at 567 degrees F. In that series the ETA-1/16 1.6 mm screwdriver tip, for me, matches the DIP spaced solder pads best avoiding solder bridges between sections.

•W ith prototype PCBs, you achieve your best results if you really plan your layout ahead. Temporarily mount/position your components and then make an accurate drawing to any needed connection pads or wire jumpers. Yes, this is tedious but winging as you go quite often boxes you in such that you have to trash what you’ve done to that point.

• Always inspect your work as you go and especially before any periodic testing. With proto PCB DIP-type construction, look carefully at the solder traces and if possible with either a jeweler’s eye or magniscope. Catching errors at an early stage will save you a lot of grief and troubleshooting time later on.

Digital Audio Levels Review And to conclude this issue of RWEE, the following is one of a series of audio tips by Larry Wilkins that have appeared in the Alabama Broadcasters Association “Monday Morning Coffee and Technical Notes” e-newsletter.

It’s easy to understand a correlation of the analog signal level to the digital signal level by going number-by-number or level-by-level.

Decibel full-scale (dBFS) is a unit of measure for the amplitude of digital audio signals. It is critical to understand that though digital and analog signals have similarities, their characteristics differ significantly. Zero dBFS occurs when all the binary digits (bits) making up the digital signal are on or read as 1s and not 0s in computer talk.

All the bits available to make up the signal have been used at this finite point and no additional headroom exists.

Trying to increase the level simply doesn’t work and causes immediate distortion.

Another major difference that should be noted is at the point of digital signal overload at the 0 dBFS level. Should

an analog signal reach its maximum amplitude capacity, distortion will creep into the signal, most likely at a gradual and perhaps indistinguishable rate, until the distortion is audible after initial overload is reached and then exceeded. This process is different and more forgiving to the ear than reaching digital overload at 0 dBFS. When an unprocessed digital signal clips at this level, distortion is immediately apparent. The encoder has no more bits to use for the “digital word” and you end up with digital distortion, which can be much more distracting than analog distortion.

Larry Wilkins is director of engineering services for the Alabama Broadcasters Association and a past recipient of the Radio World Excellence in Engineering Award.

radioworld.com | June 15 2022

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