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Troubles up High

Posted by Kirk Harnack [TWiRT] on Nov 20, 2014 12:12:00 PM

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TWiRT 235Fixing broadcast gear is difficult enough at ground level. What’s it like to troubleshoot, diagnose, and repair broadcast systems 300, 600, or 1200 feet above ground? Chris Tobin advises about what can go wrong and some common remedies, and we analyze an antenna repair by tower pro, John Hettish, while he’s 925 feet above ground.

 

 

 

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Kirk: "This Week in Radio Tech: Episode 235" is brought to you by Lawo and the new crystalCLEAR Virtual Radio Console-crystalCLEAR is the radio console with a multi-touch touchscreen interface; by Telos and the Telox VX VoIP Broadcast Phone System-powerful, flexible and scalable, phones never sounded this good; and by Axia Audio and the Axia Radius Networked IP Audio console. Throw your budget a curve and meet Radius.

Hey, fixing broadcast gear is difficult enough at ground-level. What's it like to troubleshoot, diagnose and repair broadcast systems 300, 600 or 1,200 feet above ground? Well, Chris Tobin advises about what can go wrong and some common remedies and we analyze an antenna repair by tower pro John Hettish while he's 920 feet above the ground.

Hey, welcome in to "This Week in Radio Tech." I'm Kirk Harnack. Glad that you're here. This is the show we talk about everything to do with radio technology-audio, RF, sometimes mechanical stuff like this show, stuff that's up high, made of metal and Teflon and brass and stainless steel up on a tower. Sometimes, we've got to take really expensive gear up there and try to fix it. That's going to be interesting.

Our co-host on the show Chris Tobin joins us, the best-dressed engineer in radio from Manhattan, New York. Chris, thanks for coming in. How are you, buddy?

Chris: I'm doing well. I just got back from the CCW+SATCON show, the expo here in New York City.

Kirk: For those of you who don't know, that means counterclockwise.

Chris: Counterclockwise for some and to others it actually means the Content & Communications World, the Satellite Communications Conference and Expo, held at the Jacob Javits Center here in New York City.

Kirk: Hey, satellite communications-now, before the internet came along, satellite was hot. If you wanted to get audio, video, telephone calls, data, stock market out to a bunch of people and even return data, satellite is what you used. In the 80s especially, we were hot to trot on satellite. The 90s came along, we were still hot to trot on satellite because internet sucked. What's the prospect for satellite over the next 10, 15, 20 years? What do you think?

Chris: Actually, satellite is doing very well depending on the business sector you're in. It's still, in some cases depending on your industry, still the most economical cost/benefit way of distributing from a single point to many points. It's used a lot in emergency operations where landlines or terrestrial connectivity is decimated so the only way you're going to hear or talk is through the satellite, through the sky. So, in places like Haiti where there were terrible conditions there or earthquake zones or things like that.

Kirk: Oh, yeah.

Chris: The satellite industry continues to grow and shift. So, the latest now is Ka-satellite. That's really high-frequency, super high-frequency. I was looking at some stuff today. It's the funniest thing. If you can picture the size of a shoebox and a small pie plate in front of it at a 45-degree angle, at Ka-band, you can now put yourself on a satellite from outside.

Kirk: Wow.

Chris: That's how the technology has shifted from the days of C-band, where it would take a pie plate the size of a car.

Kirk: Yeah. The antenna, the size of a car, sure.

Chris: The antenna, and then the actual transmission device would be the size of a coffin. That's basically what you've got, a car and a coffin.

Kirk: Well, the times they are a-changing.

Chris: They are indeed.

Kirk: In fact, we may touch on a satellite a bit during the show. We've done some shows about satellite and we can probably have another one to catch us up on the technology. We had a guest, a guy from a company, I believe it was called [Kayu]. They were doing installations out in Papua, New Guinea and places like that, crazy places that the only way you could get there was with satellite. So, I guess that's a good point.

Hey, our show is brought to you in part by the folks at Lawo. Lawo, maker of this really cool audio console. If you have ever dreamed of controlling an audio console from a touchscreen, well, you need to look into the Lawo crystalCLEAR Virtual Radio Mixing Console.

Why is it called virtual? Because there's no actual piece of hardware with faders that you move and buttons that you actually need to press and nobs that you actually turn. It's all represented to you in a gorgeous, gorgeous multi-touch touchscreen interface. That interface is simply an off-the-shelf HP multi-touch PC. It's running Windows 8. The application takes the whole screen so it doesn't look like Windows. It looks like an audio console.

I've got to tell you, those guys at Lawo, they've been designing consoles for a long, long time. They do big consoles. They do consoles that do surround sound and multi-channel stuff for big television productions and symphony halls and TV stations, remote trucks and all that. Now they're doing consoles that are smaller, more appropriate for smaller venues, like radio stations.

This crystalCLEAR console is pretty interesting. It consists of a 1RU, one rack unit, box that goes in a rack. It doesn't have to be close to the multi-touch PC. It can be off somewhere else. Although, it does have inputs and outputs on it for your local source, like your microphones. It's got a couple of mic inputs. It has some line-level analog inputs and some AES inputs, as well as some line level analog outputs and AES outputs. Of course it has some GPIO, so you can turn on your on-air light, your tally light, let folks know not to come in the room. It's got the other outputs you need, like your speaker outputs, your headphone outputs.

So, that is a 1RU box that has the entire mixing engine in there. And that is where also there's an Ethernet connection. That's where you can connect to your other studios, to other gear using the Ravenna AoIP standard which, by its nature, contains AES67, the AoIP standard that you've heard a lot about that's now an actual year old-it's a little over a year old now-standard from the Audio Engineering Society.

There's power supply redundancy also. The mic preamps are fantastic low-noise preamps. There are two separate amplified headphone outputs. The virtual console features three stereo mixing groups-program one, two and a record bus-plus all the things you'd expect, a q-bus pre-fader level, if you will, precision stereo meters, programmable scene presets that can recall every detail.

One of the cool things, when you design a console completely in software, you can have the buttons be entirely contact sensitive. So, if you touch an options button above the mic fader, what you get are options that have to do with a microphone, like presetting the level for a particular mic or a particular guest, get their audio arranged just right so your fader is sitting in the right range. That kind of thinking has gone into the design of this console.

If you're interested in a multi-touch touchscreen console, someday everything I think will be like this. It's really cool. I can't wait until some day we have haptic feedback on the screen itself. I think the military has that. But Lawo is letting you just look at it and run the faders up and down yourself. They've got the algorithms down really good.

Check it out on the web at Lawo.com and look for the radio products, the radio consoles and find the crystalCLEAR console. Oh, on the webpage there's also a short video of Mike Dosch, Director of Virtual Radio Projects at Lawo. He is demonstrating how the console works. Check it out. Thanks to Lawo for sponsoring "This Week in Radio Tech."

All right, Mr. Tobin, we were going to do some talking about towers on "This Week in Radio Tech." I didn't really want to talk about the mechanics and the steel and the guy-wires. That is a great subject, but it's not really what I wanted to cover today. I was interested in covering more of the electronics side of what happens on a tower, some of the things that have to do with-yeah, they're mechanical, they're electromechanical, they have to do with RF-I'm talking about antennas and feed line, maybe strobe light systems.

With antennas, the interesting and often times difficult problems that can crop up, it's hard enough for us as engineers to fix a problem on the ground with a workbench and good lighting and good weather and no 50 mile an hour winds, but if you're trying to solve an interesting antenna tuning problem on a tower or maybe there's some reflected power coming from a 12 bay antenna and you don't know where it's coming from, that's got to get solved and it may take a person with some real skills to handle that.

Let's talk about that. Chris, what are your thoughts on the whole subject of troubleshooting up high? Hello? Chris? Is he there?

Chris: That's weird. Can you hear me?

Kirk: Yeah.

Chris: You can hear me but the video is not moving anywhere.

Kirk: I guess not.

Chris: I'm relaying four different relays in the Skype connection. That's why. Last week there were zero.

Kirk: Oh gosh. Hey, I tell you what, I'd be glad to continue on for just a moment with some thoughts if you want to get reconnected. How about that?

Chris: I guess we'll have to give that a try.

Kirk: Okay. Good. So, I'm going to go back to Chris and ask him for his thoughts. But here are some of my thoughts. I said it takes a special kind of talent, a special person. A little bit later in the show, we have a video of my friend John Hettish. He runs a small tower company here in middle Tennessee, where I live.

John has the skills that it takes not only to climb towers and to be safe about that kind of thing, but also to use some various pieces of equipment that you might take up a tower, connect to various places in the feed line or into the antenna and find out where the problem is. This is really sophisticated stuff. You can do some of this from the ground if you're well-coordinated with the guy on the tower. But I tell you what, it can be really tough working 600, 800, 1,200, 2,000 feet above the ground solving what are very expensive problems that can happen.

So, Chris, you're back. Let's talk about that subject. Go ahead.

Chris: I'm back, hopefully moving in my video in color. We'll see how it goes. There we go. All right. Very good.

Well, as I was going to say, yes, tower work, towers in general are definitely something you have to take very seriously. The best thing to start with is make sure you can find a tower crew or company that is well-known, does a lot of work in the cellular industry so they're constantly busy and you have a good relationship with.

It's important, as Kirk just pointed out, if you have the guy up in the tower working with troubleshooting and you're at the base, you want somebody that gets it, knows it, understands that it's going to take a little time to figure things out and is willing to work with people eon the ground when time is of the essence. I can tell you that I've worked with a couple of crews where they knew their stuff and it was pretty easy to get things done in the bad weather at the heights they were working at. That's the first thing I always tell folks, find the right tower crew, otherwise you'll be in big trouble.

Kirk: Yeah. Just how you do that might be kind of interesting. But let me ask you a question. The cellular industry has sprung up over the last 20 years or so. 25 years ago there were barely any cell towers across the country and now they're everywhere. There are some on a hilltop just around the next ridge from my house here. Do you feel that the level of technical expertise of tower crews has gone up since the cellular industry has required so many tower crews and some sophistication in putting up antennas, aiming them, making sure they work properly?

Chris: Yeah. I don't think it ever went down. I think what's happened is the cellular industry as a client has made demands of the tower industry, the tower crews to be on their game because as we know with the cellular industry, any interference or any time that there's a cellular site that can't function, that's thousands of dollars per minute that's lost. So, the phone companies go to great lengths to make sure that the industries they talk to or work with are on the top of their game.

So, it may be by default that more tower crews have become more skilled, but I wouldn't say the skills went away. They were probably far and few. But some of the crews out there now, all they do is cellular. If they go to broadcast it's sort of like, "Uh... Okay, what do you need us to extend? How do we do this?"

Kirk: Yeah. Here's what surprised me. We'll watch this video in just a little bit. My experience with tower-realize that I worked in small markets. You work generally in larger ones. But in small markets where I worked at, we'd hire a tower crew and what we got was a tower crew.

We didn't get any troubleshooting capability except, "We'll unbolt this connection, open it up and look and see if there's water, if there's soot in there from a flameout inside. We'll make sure the bullet's not split where the hardline connects together. We'll look for leaks in a coax," that kind of stuff. But never anything more sophisticated than that up on the tower.

The most sophisticated thing I'd ever had done by a tower crew was to disconnect the antenna and temporarily put a dry load, a dummy load on top of the coax so we could then run tests from the ground, either with a time domain reflectometer or an admittance bridge or whatever it might me, SWR bridge. So, we could see if the conditions changed between antenna-we determine is the problem in the coax or the problem in the antenna?

So, that's the most sophisticated service I ever had. But we're going to watch a video in a little while that shows John Hettish using some sophisticated gear. I'm not even sure what it is. Maybe you can help identify it when we watch the video later on. So, to me, that is a really big step up where you've got some tower guys-maybe they had this kind of expertise 20 years ago I just didn't get that because that's not what we hired. For me, the consulting engineer was on the ground with his vector impedance bridge or his time domain reflectometer.

So, how have things changed in your mind? Same now or different now?

Chris: Well, they definitely have changed. I will say that I've worked with crews the same way. You send them up and they basically pop open the termination and off you go. So, I would say what's changed is that because of the increased need for mobile devices and those types of transmitter sites, a lot of the cell tower companies that did just basic tower climbing, basic cable assembly have stepped up and now decided they now have to do more diagnostics and work with the consultants, otherwise basically they wouldn't get any business.

Kirk: Yeah.

Chris: I know working with one tower crew for many years, they were strictly pretty much broadcast radio/TV and they got the occasional 9x job. That's how far back this goes. So, then all of a sudden after two or three jobs and they were being required to certify they're installations, make sure that ground connections meet the standards that are industry. They started realizing, "Maybe we need to up our game and start really going after this business." Now, many, many years later, they're number two in the tri-state area for tower work when it comes to cellular.

Kirk: We'll see if we can get your video going again. Something that I've noticed, though, a big change is the size of the test gear. Twenty years ago, it wasn't possible or it wasn't practical to take a time domain reflectometer up the tower because it weighed 50 pounds and it was as big as a suitcase. Now you've got things that are much more handheld in size, virtually the size of a thick iPad. You can get oscilloscopes, time domain reflectometers and various different kinds of equipment in that size of a package.

You know, the ideal situation with any antenna and coax is that power, RF power, leaves the transmitting device. It doesn't matter if it's an FM transmitter, television, cellular, microwave, this power leaves the transmitter, leaves the final amplifier there. It travels up the coax, or maybe in the case of really high frequency, a waveguide.

The idea is it's not going to be impeded, reflected. It's going to see a constant impedance as it travels, hopefully smoothly, up this coax. Then it's going to reach the antenna. The antenna is supposed to be matched or tuned such that it presents a non-reactive load at the end of the coax at the same impedance as the coax. That's the whole idea here for maximum power transfer from the transmitter through the coax and into the antenna. That's the ideal.

Anything that varies from that is not ideal. Anything that varies from that will result in power, RF power, getting reflected like a mirror or a partial mirror getting reflected back down to the transmitter. In almost every case, that's what we're trying to avoid, reflected power. We want all that power to flow smoothly all the way to the antenna. And then in the antenna-I like to think of antennas this way.

Chris, tell me if you think this is nuts. I always thought of an antenna as an interface between the electrical world and the atmospheric world. Our atmosphere tends to have a characteristic impedance. So, really an antenna is an impedance. Yes, it's a device that turns the electrical oscillating wave into an electric field and magnetic field. To do that most efficiently, it's an impedance matching device, to match the impedance of the coax and the transmitter to the impedance of the atmosphere.

I may be all wet on that, but when you look at a microwave horn that we used to use, like for AT&T long lines and they had what started out as a waveguide. It goes into a horn that gradually spreads out and matches the impedance to that of the outside world, the atmosphere. That's the results of the maximum transfer. Am I all wet on that, Chris?

Chris: No, no. Not at all, actually. That's probably the best way to put it, going from the electrical to the atmospheric. The atmospheric would be the free space attenuation in the air. That's a known constant. And yes, the waveguide is a boundary device. It can be rectangular or circular. That guides the RF signal, the electrical part up through a path. Then when it gets to that horn, that widening space, it shoots it out and makes sure that it gets to the other end. So, yeah.

Kirk: So, the point there was anything that disturbs that relationship-it's really a physical world thing. Coaxial cable is the size and shape that it is because that's what works well. Fifty ohms, not only is it a standard we came up with, but it also happens to be convenient for the size of parts and just getting things to work well. If our standard was 4,000 ohms, then it might be more difficult to make things work as well.

So, am I right? Anything that disturbs this efficient transfer of signal to the outside world, that's where our problems begin.

Chris: Yes. Then you start getting into-after you've cleared the problem with the line tuning because basically what you're doing is tuning the line to the antenna-after you've got that matched and working, then you have to worry about the physical world outside around the antenna and what effects that has on it. But yes, the line tuning is key.

Kirk: Gotcha. This also explains why different antennas are different shapes and different sizes. So, we as broadcast engineers, we're pretty familiar with the shape and size of an FM antenna. There are different designs, some kind of proprietary, others just really well known. There's the double-arrowhead design that Jampro made famous and other companies too. There the Rototiller design that ERI made famous.

Before had those circular polarization designs, we had designs that were dipoles. They were dipoles up in the air, stacked up. They were vertical dipoles and there were ways of doing horizontal dipoles. Then I guess one of the first circular antennas was the ring stub design, where there's a ring of an antenna-that's the horizontal part-and then just as the rings come around and come together, they turn different directions, one up and one down, and that makes the vertical component of the antenna. So, what you got is a horizontal radiation and a vertical radiation out of the same piece of bent metal. So, that was an early circular design.

But those all look different from other designs. Remember television batwing antennas? Can you tell me anything about how those things worked? How did a batwing antenna function?

Chris: Basically, the batwing, if memory serves me right-it's been a while. I watched one come down a couple of years back. It's basically a radiator dipole, a radiator in front of a mesh. So, if you could picture it. The batwing was the shape. I'm using my fingers to make the shape of batwings. That was basically your ground plane. In front of that was a dipole that radiated against it and created the pattern.

Kirk: Oh, so the batwings themselves didn't... Okay.

Chris: Yeah. And the TV signal is horizontal. So, that's what they did.

Kirk: Okay.

Chris: That's what it was. Batwings were popular because it was broadband. You could tune it. You could do a lot. You could shape the signal. Then if you're UHF, you have the slotted antenna. So, it's a pole with slots in it and then inside is hollow and those slots are cut in certain wavelength sizes to radiate the signal out and create a pattern as well.

Now, as you mentioned earlier, antennas have different shapes and sizes due to the frequency. So, the best way to understand that physical being is to look at a piano and look at the strings. The lower in frequency, the larger the diameter. The higher in frequency, the smaller the diameter of the string.

Same is true with antennas and RF. RF works in the same fashion. So, mid-frequency, we'll call it that, FM band, 88-108 megahertz is somewhat of a relatively average-size thickness. Go lower in frequency to say an AM antenna and what do you have? You have two feet, three feet in width and several hundred feet in height. Go the other direction and let's go to say our Wi-Fi antenna and the Wi-Fi antenna-I'm holding a similar thing in my hand-now becomes something the length of someone's hand open. It's about half the diameter of your finger. That's the higher frequency.

So, there we go. We just went the full spectrum from several hundred feet high to several feet wide to a wavelength FM is about five feet or six feet in length. So, we just take that horizontal pole of a five foot antenna, twist it to shape either a circular thing or a circle with little tops and bottoms and there's your antenna.

Kirk: So, what are some of the things that typically go wrong with antennas? Let's think in the realm of FM because a lot of the listeners and viewers to our show are engineers that take care of FM stations. I take care of several myself. So, what are the most common things that go wrong in the world of FM on towers, between the coax or section outlines, hardline or antennas with power dividers or end-fed, center fed? Give me your thoughts on that.

Chris: Well, let's see... Things that go wrong-not because of installation or anything, just normal operating parameters-typically depending upon what part of the country you're in, if you're in let's say the Northeast, what you'll have during the summer months are very extreme humid and sticky conditions. As we know with humidity, moisture is a very good conductor of electricity. So, RF will find its way around that.

So, depending on the age and installation or the stresses on the tower or the antenna itself, you run the risk of things shorting out. If something shorts out at a high-power FM, the end result sometimes is a black puff of smoke and a hole in the antenna or transmission line.

And then go to the other end of the spectrum, if it's during the winter months and you're in the Northeast or Northwest and you have conditions of icing, ice adds weight to a structure and depending on how your structure is designed and how the antenna cable, transmission line is attached to that structure, as it twists, it puts stress on the wire.

So, think of it as like if you're pulling cable in a pipe in your office or shop or studio. When you pull on it, you're stretching. So, picture several hundred feet of inch and five-eighths hanging on a tower. Hopefully the hangers are holding it in place so it's not stretching. Now add ice to that and have the tower twisting.

Now, it may not seem like much, but when I was working with folks at ERI, Tom Solomon and his team once, one of the tower guys were explaining the physics behind icing and twisting of a tower and what happens. It's over a period of time. This doesn't happen in one season. But eventually as it's twisting and moving, you can stress the transmission line. If you have several splices in the line or one or two connections, they get stressed and then a leak forms. Then your hydrogen and nitrogen leaks out and air gets in and things happen. That's what could go wrong at an FM site outside of say a lightning strike or a nearby lightning strike in that case.

You know what's another common thing that happens with towers that goes wrong?

Kirk: What's that?

Chris: Tower climbers working on your tower-maybe not your tower-maybe on a shared tower working on someone else's system stepping on your transmission lines bumping your stuff. I'll tell you this. A couple of years ago, while working at the Empire State Building trying to troubleshoot a problem with the FM master antenna system, it was discovered that one of the transmission lines got stepped on. How many things are up there? There's a lot of stuff.

Kirk: Yeah.

Chris: So, there's a perfect example. Everything is working just fine until somebody slips, hits it. The transmission line looks normally because it's hard to see if it's bent or damaged. Then over time, because it's 100 kilowatts of RF going through the transmission line, something fails. You never know when that happens. It's not like you're going to notice.

Kirk: You know, you brought up something. First of all, you mentioned holding all that line up. So, let's say you're using semi-flexible coax, not hard rigid transmission line. You've got what they call a kellem grip. It works like Chinese fingers. Every couple hundred feet or so, you put a kellem grip on the coax and then it hangs. The kellem grip is attached to the tower and it hangs by that. Of course, those need to be placed strategically so that the line is supported in several places depending on how long it is and it's equally supported.

So, you don't want all the weight on the phalange, the connector at the top of the coax. I've had that happen before. I worked for a little station in Mount Sterling, Kentucky and we noticed that our signal over time was getting worse and worse. Sometimes after a rainstorm we'd get some terrible reflected power. The station wasn't all that powerful. I think it was just a kilowatt FM transmitter, like a Collins 820d transmitter. It was just getting worse and worse.

Well, we got a tower crew up there. This was my first experience with FM antennas. The crew got up there and found out the outer conductor of the coax had broken and pulled away from the outer conductor of the connector. This is an inch and five-eighths coax. All that was left was the inner conductor of the coax just barely making connection with the bullet that was pushed into it from the dual bullet at the connector.

It was mechanically attached a few feet lower, but apparently it had slipped down. Here's the thing. You were talking about stretching and some twisting-vibration. If you ever go spend some time on a tower and you sit up there during a windstorm or just during some wind, wind will sit there and vibrate the tower depending on all kinds of torsional value and moments and things like that.

But you can get a tower that just sits there and the antenna just goes back and forth and back and forth and back and forth. For days, weeks, months, years on end, every time the wind blows it sits there and vibrates. You know that's got to doing some bad things to the coax, to the rigid transmission line and to the bullets as they sit and wiggle, wiggle, wiggle for years. Something bad is going to happen. There you go.

Chris: That's absolutely right. I've been up on towers. What was the highest I've been? 300 feet maybe? One of the jobs I did many years ago, I remember going up, it was about three and change and I had to sit and wait because one of the other guys was coming up with some tools. We had hoisted up seven-eighths line for a [inaudible 00:29:31] antenna system. We hoisted it up and there were a couple of issues we had. So, we had to wait for some stuff to come up.

As I'm sitting up there, so to speak sitting, exactly what you described takes place. One, the wind is blowing through your ears and around you and it's very noisy. And then there's this very subtle feeling that the Earth is moving beneath your feet, or you're standing on the latter ledge of a tower belted in. But you feel the movement.

You realize where you are and what's going on and why things happen on a tower the way they do and why tower crews and the standards that they follow are specific to how to tighten a bolt, what's used to tighten a bolt, what type of metal is used for the bolts on a tower, all these methods, why would you lanyard your tools to your wrist when you're on a tower, things like that. So, yeah, the environment on the tower is not as pristine as you might think.

Kirk: It is not. I've been surprised several times climbing towers with just how much vibration and torsional woes were going on. We were talking about wavelength earlier. You mentioned FM wavelength and how the higher the frequency, the lower the wavelength.

I just happened to, on a shelf over here in the office, have this. It's a Ku-band LMB, low-noise block amplifier. This is the end that most people are familiar with. This is where an F-connector and RG6 coax with an F-connector on it will connect and take this back inside to a satellite receiver inside the building. This end is the end that bolts to the ring mount on the satellite dish.

Well, if you look closely there-let's see if my camera will do that-that little piece of white there, that's Teflon. That little piece of Teflon is actually covering up the antenna. That's the actual antenna. It's less than a quarter-inch long. It's just a piece of metal cut to a very precise length. And that antenna goes inside.

Chris, would that be a quarter-wavelength of this frequency? Is that what that antenna probably is?

Chris: A Ku is 14 gig. It could be. It could be a quarter-wave.

Kirk: It wouldn't be a lot less than a quarter-wavelength. They wouldn't have good transfer. So, the big rectangular area, if you can put me on again, the big rectangular area there is the size of the waveguide. If this were being carried by wave guide, it would be that size. Then the little antenna inside there is what transmits energy into the waveguide or receives it back out. In this case, the waveguide is just a little short thing that goes to where the ring is on the feed horn of the satellite dish.

So, antennas come in all shapes and sizes. That's one of the little bitty ones. What can go wrong here? Well, not a lot. We had an episode of "This Week in Radio Tech" years ago called "Bees in the Feed Horn."

Chris: Yeah. What goes wrong with a satellite downlink? Well, let's see, it goes out of alignment, somebody pokes the dish, the LNB may just fail.

Kirk: I took the cover off and it's a solid block here. Any moisture gets in this, it's really bad.

Chris: And also, you have to remember too, at those frequencies you don't want noise, you don't anything else because why? Low-noise board converter is what it says, low-noise. You're trying to capture a signal. Mind you, you're trying to capture a radio signal 22,000 miles above the Earth's surface.

Kirk: From space...

Chris: Yes. It's not a comet. It's not a Rosetta. But you're trying to get it from what looks like a VW bus flying in a figure-eight above the Earth. That little quarter-wave antenna has to pick the signal out. You can just imagine how much electronics have to be used to make the noise flow really low.

Kirk: Oh, yeah.

Chris: 14 gigahertz to try to pick out that signal.

Kirk: And a little droplet of water, as I was getting to, represents a huge bunch of inductance or capacitance or something. It really screws with the circuitry. The circuitry has got to be bone dry. You can't have bits of moisture landing here and there on the circuit boards because the frequencies are so high, the wavelengths are so short and the tolerances are so tight in the tuned circuitry that's in there that a drop of water will just totally screw it up.

Chris: Don't forget, a drop of water at Ku frequencies is the resident frequency of the signal. So, you would actually wipe it out.

Kirk: There you go. Absorb all the signal right there.

Chris: That's' it.

Kirk: Chris, if engineers watch or listen to the podcast here, you probably deal with 950 megahertz gear. You might deal with SDL transmitters and receivers. And if you're like me, you have found out the hard way that a drop of water at the wrong place inside an N-connector that's typically used with a half-inch coax or LMR 600 coax or seven-eighths coax. A drop of water in the wrong place in an N-connector? Signal is over. Game's over. It's awful at that point.

Chris: Yeah. Moisture in general, water in general, when it comes to electrical devices-in this case RF signals-they don't mix very well. They don't do that very well at all.

Kirk: Yeah. No kidding. So, I want to hit one other subject here before we go to our next break. On the phone you and I were talking about this issue that comes up from time-to-time. I think it's typically called passive intermodulation.

Chris: Yes. That's correct.

Kirk: Tell us what that is. I've got a story to tell about that from Memphis, Tennessee and a 300-killowatt FM station and the havoc wreaked there. But how would you define what is passive intermodulation and what kind of problems does it cause?

Chris: Okay. Well, I'm assuming-I'll make the assumption and I probably shouldn't. We'll do the whiteboard as to why you don't assume. Anyway, moving right along with that joke, passive intermodulation, as the term says, it's passive. Intermodulation takes place in many things, in many devices, many circuits. Intermodulation is basically the mixing of more than one signal-two, three, four.

Out of those summing of the signals is a resultant third or fourth signal. That's active. That's when you intentionally are actively mixing signals together-for example, a transmitting site that has more than one transmitting emitter, more than one transmitting antenna. So you have two FM antennas on a tower, they mix. Hopefully they are separated in such a way that the frequencies don't mix and create a third frequency smack in the middle of a TV channel. Oops. Yes, I did work at a place that had that problem. That was fun.

So, then you have what's called passive intermodulation. Passive intermodulation has become more prevalent in the last several years because of the mobile industry's need to have high-density cell sites. We'll call them that. Passive is a result of connectors that aren't properly terminated.

It may be environmental where you have a railing or a hand rail on a staircase and the joints where the bolts of the railing connects to the wall or support structure become corroded, rust. And then, believe it or not, because this railing and the rusted bolt that's holding it to the metal support structure happens to be in the near field of an antenna radio signal, the radio signal actually excites the corrosion. That takes you back to the early days of radio reception known as the cat's whisker.

Kirk: Yes, the crystal radio.

Chris: That's it. Your crystal radio was an exciting device. You excited the whisker.

Kirk: I've heard that if you didn't have a germanium diode or a cat's whisker, you can still make a crystal radio using a rusty razor blade.

Chris: That's where I was going with this.

Kirk: Ah, okay.

Chris: The same principles you would use in the crystal radio set of the early days are the same principles that plague us today in modern times. I'll have some fun with this. It's annoying because you can't always track it down because it's excited by a source that you don't know.

I can tell you this from personal experience in working with a project this past year and helping a government agency troubleshoot a problem that created all kinds of issues. We spent months trying to find and isolate this.

If you could just picture trying to figure out where an intermod third-resultant interfering radio signal was appearing from the rooftop of several different skyscrapers in New York City, you can just imagine what we had to go through. I was on top of the Citicorp building for many months, many hours, on top of the Empire State Building, on top of the MetLife building, on top of the Trump Tower building, on top of some other building. I'm not even sure what the name of it is. But the agencies that were up there, we couldn't talk about what they did. We were up there; we couldn't talk about what they did.

We were trying to triangulate by using directional antennas to point in the direction of the interfering passive intermodulation signal. So, this passive intermodulation signal was actually a byproduct of two other signals and created a third one. It landed right on a coastguard frequency.

Kirk: I've heard this said in maybe a little bit of a different way. It's saying the same thing you're saying, but I always heard the word-and I like this word-dissimilar metals . . .

Chris: That is part of it. Yes.

Kirk: When you have two dissimilar metals in contact with each other, you can have a non-linear electrical connection, that is electricity won't behave the same way going through that direction in one direction versus the other or in either direction, it's non-linear. It doesn't have a curve of voltage current resistance and all that kind of stuff. It doesn't follow old law, how about that?

Chris: It becomes an unstable varactor basically

Kirk: There you go, another way to say it.

Chris: Yeah. What you're talking about is the same thing. That's why dissimilar metals have the same issue. That's why you don't do aluminum with steel or copper. You'll see the result.

Kirk: When you build flag poles, towers, railings on buildings as you mentioned, roof flashing-when you use building materials to make things, you end up with dissimilar metals touching each other. You might end up with corrosion between two of the same metals, but the corrosion makes it dissimilar between the two.

So, you've got all these opportunities in an urban environment, at a tower farm or a rooftop location, to have dissimilar metals contacting each other. When you have that, you have the opportunity for if you're in the field, I guess it would take two because on signal wouldn't necessarily do it. But two signals, mixing on this dissimilar metal connection, can very well result in that connection emitting intermodulation energy. That is energy at other frequencies besides the two or more that are hitting it. So, it becomes a wildly complicated math matrix of how many different frequencies it could possibly be.

So, my quick story, similar to yours, is in Memphis, Tennessee, you've got a big high-power radio station there, an FM that's grandfathered in at 300 kilowatts. I think it's 300 kilowatts vertical and 100 kilowatts horizontal. It's WMC FM. They're far enough from the airport for the towers to be legal, but the signal strength is just huge. So, you had a tower here or there. You had a location, some FAA equipment in a building. The problem was they kept complaining. Pilots kept complaining about hearing WMC on their aviation frequencies.

Well, WMC wasn't transmitting on those frequencies. It wasn't too hard to prove with a tap into the coax of WMC's transmitter and a spectrum analyzer, "See, it's clean. We're not transmitting any energy on aviation band frequencies. We're totally legal, both near to the carrier, medium to the carrier and at second, third, fourth, fifth harmonics from the carrier."

Now, the aviation band is just above the FM band. I'm not sure what was mixing with what. But another FM station, for example, if WMC is on 100 megahertz and there's another station on, say, 92 megahertz and they mix together and there's a resulting piece of energy at 108 megahertz. Well, it's the bottom of the aviation band right there. The aviation band, 110, 114 megahertz, 125 megahertz. You can see that you can get energy into that band. It was being caused by corroded connections.

It turned out it was corroded connections on whip antennas that, if I'm not mistaken, that were in the charge of the FAA. It was their antennas that actually had the dissimilar metal connection. The broadcast engineers, since it appeared they were causing the problem even though they weren't, they were charged with having to track it down.

So, over time, stuff gets rebuilt with better metals, newer stuff, hopefully better stuff and we get rid of the problem over the long-haul. But it's the kind of thing that can crop up again and again just because it's out in the environment.

Chris: Oh yeah. There are a lot of things that the environment destroys or wreaks havoc on. That's why you want to galvanize metal when you're doing it outdoors and make sure that it's setup properly. What's that? Go ahead.

Kirk: Does galvanization last forever or for the useful life of whatever's galvanized or does it wear off?

Chris: It eventually wears off. But depending on if the process is done right, it will last a long time. I've been at sites where it's been there for many, many, many years. I've also been at sites where people don't galvanize joints and all of a sudden they're coming back a year later to rusted angle iron. It's not good.

Kirk: So, if you've got a galvanized tower and let's say you have one of those grounding kits for the coax, maybe an Andrew or Cablewave grounding kit. You might have a bolt hole in the tower. It's meant for it. But it's galvanize. You cinch the bolt down. Don't you now have dissimilar metals maybe?

Chris: Yes.

Kirk: If it's not tight-a lot of times nowadays good practice is they'll go back and first of all they'll scrape and then they'll bolt it together and then they'll go back and spray paint over it or spray galvanization or spray paint over it to keep moisture out over the long haul.

Chris: Yes. What you do is you scrape off the galvanizing to make the contact of the metal to the tower. Then you secure it. Then you would spray a galvanizing paint, a material on that joint so you restore the galvanizing effect. You paint over it for the tower painting purposes and just for weather protection.

I was just talking to someone today about that regarding an ENG microwave receiver on top of a tower, complaining about the grounding and the lightning keeps blowing up the receivers. He showed me the pictures of their setup. We're looking at the cables and I'm like, "Where is that ground wire going?" He goes, "Here." I go, "That might be part of your problem. You didn't really ground it. So, your nice three-foot microwave spinning dish, 7-gig dish is basically insulated from the tower and sitting out there waiting to get zapped."

Sure enough, when we talked to the manufacturer, he goes, "No, that can't be." The manufacturer comes over. The application engineer, first question out of his mouth is, "Okay, you're on a tower, how high up?" "300 feet." "Okay. Where is this tower located?" "On a hill." "Okay. Here in the Northeast?" "Yes, it's over in New Jersey." "Okay. Great. What kind of grounding did you do? Let me see the pictures. Yeah. There's your problem."

Here's why that was the problem. The connection for the RF signal, the video for the return ENG signal from the helicopter was being converted from RF to fiber and down the tower on fiber. So, the fiber you can't jump with the lightning. It's a non-conductor. So, the only other place that the lightning could wreak havoc is where you didn't properly ground it. It was the ground cable.

Kirk: How does that receiver get power?

Chris: I'm sorry. They have a 48-volt line that's also insulated.

Kirk: Ah, okay.

Chris: It runs with the fiber. There's a mechanism they use for isolating the transient protection. But the thing was he said once you don't have a proper ground, the entire radome, the cover of the dish, the cover of the assembly and the metal base that it sits on becomes just an antenna waiting to be zapped.

Kirk: Yeah.

Chris: Then he showed us some pictures and other client locations where they had a similar situation. I was like, "Wow, look at that." But you can galvanize the connection you make to the tower and restore it and make sure it's right. That's standard practice.

Kirk: You're watching "This Week in Radio Tech" or listening to it with Kirk Harnack along with Chris Tobin. We're hoping that Dave Anderson can join us, either he's in route or not going to be able to join us, but maybe he can in the last few minutes of the show. Dave has been on the show before and he's done a lot of tower work this past summer. If he doesn't get on this time, we'll get him again another time. He was at an SBE Ennes workshop today in Tampa. So, we'd like to talk to him about that if he does show up here.

Hey, our show is brought to you in part by Telos Systems, the folks that hired me. I really appreciate that. I also appreciate them sponsoring "This Week in Radio Tech." I want to tell you about the Telos VX Broadcast Voice Over IP Phone System, VoIP phone system. It's the first VoIP phone system meant just for broadcasters.

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All right, Chris Tobin. We have a video that I would like to watch a few minutes of. Some time we're going to have this guy as a guest. He's really busy. He's hard to catch. It's John Hettish. He runs Middle Tennessee Two-Way Service, I think is the name of his company. He's got a bunch of videos on YouTube, though. If you will go to YouTube and look up "John Hettish," you'll find his channel. You'll find lots of videos. He's all about tower safety, doing things right. The guy is just amazing. He's part of our SBE chapter here in Nashville.

So, without much further ado, Andrew, can you show us a few minutes of this video? Chris, take a good look and see if you can identify what John's doing here.

Chris: Okay.

Kirk: Go ahead, Andrew. Ah, okay, we're starting at the beginning. Gotcha. He's got a Site Master. That's what he's got. I answered my own question. Here's John up on a tower. I hope he's all properly tied off and everything. This is going to be like "Mystery Science Theater 3000." We can just talk here, okay, Chris? We can give a running commentary. I asked for Andrew to have no audio from that because it's a bunch of wind noise. It's really wind up there.

Chris: Oh, yeah. I'm sure at that height, looking at that video, I definitely would hear wind.

Kirk: So, it looks like he's got a little strap there he's tying off that goes to probably his piece of test equipment in that bag. We didn't get to see how it's hooked up to the coax. It looks like there's an antenna bracket to the left there.

Chris: Yeah. It's an Anritsu Site Master. That's a good product. It's a popular product.

Kirk: Okay. In my contract engineering work and my current work, I've never gotten to use anything like this. So, tell me about what this product does.

Chris: It's basically a very specialized spectrum analyzer. You can use it for tuning up your HD signals for AM. You can use it for FM spectrum. In his case, he's probably using it for LAN mobile purposes. So, you can check the antenna. I can't think of the name of the technique now. You can check to see if the antenna is properly working, if it's tuned or if it's shorted or not.

Kirk: Now, when I bought a spectrum analyzer years ago, back when they were still so expensive. I couldn't afford much of one. But I didn't get the sweep generator option that came with it. But my understanding is you can get a spectrum analyzer with a sweep generator but it will put out a signal that sweeps and the spectrum analyzer sweeps at the same time and analyzes that signal and you can see how a signal gets accepted or rejected by what your connected to.

Chris: Yes. I have a cell site tester. Mine is a traditional, very large, size of milk crate, spectrum analyzer that I use for tuning up duplexers and filters for ham radio as well as broadcast. It has a tracking generator in it and that's what we do. We'd sweep the frequencies. On the display, you'll get either a peak that looks like a peak passing the frequency you want or you get a letter V and at the base of the V it's rejecting the signal that you want. So, that's what you'd use a tracking generator for.

The Anritsu is the same thing I have but now miniaturized because they can do that. It's pretty cool what you can do with that. So, he's probably doing exactly that, sweeping the line, looking at an antenna and seeing what's going on.

Kirk: I was going to ask-why would he be doing this way up at the tower instead of at the bottom? I guess because he doesn't want the coax to be part of the measurement equation.

Chris: Right. You have to bear in mind with your antenna-let's just assume it's a UHF antenna, standard land mobile antenna, a white stick. People see these all the time. So, it's basically a co-linear antenna. So, literally if you can picture pieces of coax that are cut and looped back and forth in a vertical position, that's how it basically looks.

In there, if one of those segments shorts out, the antenna will still function but not the way it should. The transmission line could hide or mask that as the problem because of the length of the line, the standing waves and everything else. That's why the Anritsu product and those other products, Agilent and others, a lot of times now you have to go up to the antenna and look at it. Back in the day you didn't have to because in most cases you could go to an FM Rototiller...

Kirk: He's looking at an FM antenna here. Okay.

Chris: The Rototiller to the left of the screen, that's an ERI Rototiller. Most times you could go up and look at it and see if there's any physical damage.

Kirk: Yeah. The interbay line right there looks brand new. Look at how shiny the brass is there or copper. Maybe he had to replace some interbay line or a bay on that antenna and now he's going back to measure. Maybe that's it.

Chris: That's very possible. In the interbay, depending on the design you have ferrites that are used to tune a section, tune out an interaction between the bays. It's hard to see with the display what he's trying to do. It looks like he's doing a sweep.

Kirk: We'll have John on the show sometime and we'll get him to tell us. How about that? It's kind of fun here to guess what he's doing.

Chris: Now, mind you, I've done this kind of work, not at that height. It looks easy in this video. But you have a lot of things working against you at this point. Picture your bodyweight now just hanging. If you look to the right-hand side of his hand, you see those struts, those pipes or metal rods?

Kirk: Yeah.

Chris: If you can think of the arch of your foot is sitting on that, not your entire foot, not from toe to heel, just the arch. Depending on the type of shoes you're using-you should be using steel shanks to support the weight-you stay on that little piece of metal for an hour or half hour and eventually your legs start to feel... I can tell you that it's not fun. Plus, at the same time, you're trying to work and do things. So, you're tied to the tower. You're not flush against it. But you can see how he's moving and notice it's very, very labored movement. It's not just, "Hey, let's move around and do stuff."

Kirk: I've got to believe that if you can do what John's doing here, you can go fix the Hubble space telescope.

Chris: It does take a certain type of person to do this kind of work.

Kirk: A lot of the same skills involved here with deliberate movements, being very deliberate on everything you do. He's moving away from it. I wonder why.

Chris: Oh, he's got to go maybe attach the coax to something.

Kirk: There's his safety line.

Chris: He should have two of those. There's the other one. I think he has a third one that actually is over his shoulder so that if he slips, it grabs him. You'll see it. I saw the red lanyard. That's the one on the right-hand side. It came over his shoulder in one of the earlier shots. That's what I have on my climbing belt.

Kirk: I got some heat on Facebook for not having proper climbing gear. So, I got proper climbing gear. The last time I climbed a tower it was two of those. That's a great knee shot there, John. That's just awesome.

Chris: I guess that's a helmet cam?

Kirk: Yes. He's got a GoPro. He's loving the GoPro cameras. He's loving doing these videos. There are just a ton of them on YouTube. If I didn't have so much to do, to me, this is entertainment. It's nice hearing what John says. I asked for Andrew not to do the audio because it's so much wind noise that you've really got to pay attention to hear what John's saying. In a few of these, I think he's gone back and narrated them after the fact so you don't have all that noise.

Chris: Yeah. It can be very noisy up there. Definitely. It looks like it's a good day for him.

Kirk: That's probably somewhere in Middle Tennessee. It's a beautiful part of the world to climb. I know there's lots of places that are green and pretty.

Chris: If you look down when they show his feet, you'll notice his entire body weight, gravity is working with you, is on the arch of his shoe. I'm just saying that because I've done this. I applaud people who do tower work. It is not easy.

Kirk: Especially if you don't do it very often. That's when you really don't have the muscles to support what you're doing.

Chris: You get a really good workout. I will tell you that. You will find out you have muscles you didn't' know existed after you've done a tower climb for a day.

Kirk: John here-I don't think I'm speaking out of school-he is either 70 years old or close to it. This man is fit as a fiddle.

Chris: Oh yeah. I used to have a guy who used to do tower work for me years and years ago. He was 73, still climbing the tower. If you watched him go up and if you didn't meet him at the base of the tower when he started and you just happen to come to the job after he was halfway up, you'd swear he was a young guy. You'd watch him go up and move from side to side on the tower face and move up and down.

His son, who worked with him, was, I think, 55. When they came down after the job was done, people would look around like, "That was you up there?" The guys are like, "Yeah. What's the matter? Am I too old?" But if you say in shape and keep your wits about you, there's no reason why you can't do it.

He's doing a sweep. That's a sweep pattern. I recognize that from my unit.

Kirk: So, it has a dip in the middle. It goes down. Is that were things are resonate?

Chris: It could be. It could be he's looking for resonance. The Rototillers typically are not center frequency. That's intentional. The reason it's intentional is because a de-tuning of icing on the antenna. I'm not sure in that part of Tennessee if icing is a concern.

Kirk: Oh, it is.

Chris: I know in the Northeast, I purposefully tune it off frequency just a little bit.

Kirk: Wow.

Chris: Oh, there's the transmission line that's unterminated.

Kirk: Ah, there you go. It must be a center-fed antenna. He's at the center point of that antenna. I've seen hardline that goes above. We see base below. He's at the top of the coax. This has to be the center feed of that antenna. It might be a six or eight-bay antenna. Who knows?

Chris: Yeah. But ERIs typically are fed from the bottom. That transmission line didn't look like it was part of the antenna.

Kirk: No, no, the black isn't.

Chris: Oh, yeah.

Kirk: Yeah.

Chris: I'm assuming the bays are turned off at the moment.

Kirk: I thought I've seen center-fed ERIs. I guess you're right. They're much more commonly bottom-fed. But if the power is high enough, you want to feed them in the center, don't you?

Chris: It depends. Yeah. I take that back. The black coax is not part of the antenna.

Kirk: There it is. I just saw it. There was an adaptor on the bottom of the center point of the antenna and that adaptor adapts-the inch and five-eighths or whatever size it is down to the N-connector.

Chris: To the N. Yeah.

Kirk: Oh, it's three and an eighth.

Chris: Oh, okay. There you go. That camera made it look like the cable is smaller. So, that's what it was. Got it.

Kirk: The cable may be an inch and five-eighths. But that input connector, that's a three and eighth-inch connector right there, unless it's two and a quarter. Of course, it's off the screen. I can't hardly see it.

Chris: Yeah.

Kirk: Well, I kind of like this play-by-play.

Chris: Look at the inside of that center conductor, that Teflon. Pretty black.

Kirk: On the top of the coax? Yeah.

Chris: On the top of the coax. Yeah.

Kirk: Well, the antenna has been there a while but the interbay line is new. That's what I said earlier.

Chris: I wonder if this was a catastrophic failure of something and that's why he's changing this out.

Kirk: I bet you it was. All right, guys. Oh, three-inch there. There you go. Well, three and an eighth.

Hey, our show is brought to you in part by friends at Axia Audio and their consoles. I just visited this really cool place in LA. I visited a place called Dash Radio. I can't give you a lot of websites here. Sometime in your free time, you might want to check out DashRadio.com. They have 60 channels of streaming audio. They kind of specialize and hip-hop and new rock and stuff that, frankly, I'm unfamiliar with nowadays. But they have a great iOS app.

Well, Dash Radio was the brainchild of DJ Skee. I don't know DJ Skee. Got to meet him, though. Really cool guy. And also a guy name John Halterman, who's the operations director there at Dash Radio. These guys are using Axia consoles. They have two rooms that they use for live productions. They have a big Axia Element console in one room.

They do all kinds of fun talk shows and talk about music, talk about life. Those shows air on one of their channels. They've got another smaller production room that they do go live from time to time. They also do production there. They have an Axia Radius console in there.

The place is just great. It's just delightful to see people-these guys aren't in the licensed broadcast business. They're in the streaming business. So, what I'm getting at is content creators, content creators no matter where you're going with your content, how you distribute it, you need equipment that's reliable. It works. It works like second-hand. You can just expect the way it's going to work. You don't have to fiddle with it and diddle with it. It's just going to work for you. That's what the folks at Dash Radio like about their Element console and their Radius audio console, both from Axia.

And guess what? They talk to each other. One cable. One cable between them from the trunk ports-they have a power station there and they have the Core 32 for the Radius console and they just plug them together with a piece of Cat6 and all of a sudden they're talking to each other. It's really cool. I've got some of these consoles myself at our stations in American Samoa. I've got an Element console in our station in Greenville, Mississippi. I just love these things. Andrew Zarian has got a Radius console at his place there at the GFQ Network.

One of the best things about these consoles, if you're going to bring in people remotely to talk, laugh, have fun, comment on things like Andrew does, like other podcasters do, you're going to want your console to handle mix-minus. That's a big problem. So many people get into producing shows and they don't know what mix-minus is and they have all this echo going on and it's just a mess.

Well, Chris Tobin can certainly attest to this. I can too and other guests of Andrew can too. The audio is always perfect. I never hear myself back in my earphone. I always hear the other guest and hear Andrew. It's just amazing the way that the mix-minus works on this console.

You may think, "Mix-minus, I've never heard of that. I don't know how it works. Is it important to me?" Yeah. It's really important to you. If you're going to talk to anybody on the phone, on a codec, on Skype, even people in the studio, you want the back feed, whether it's an actual mix-minus feed or a mix of everything feed, you want that to be right.

And Axia consoles do that automatically. It's one of the big features. It was a really innovative feature when it came out about 11 years ago. It still is today because it works so perfectly well. It's just amazing. I'd like you to check out these consoles. If you need a small console for your podcast studio, for your streaming audio radio station, for your broadcast station, for your TV station-yeah, there are Element consoles at TV stations running audio for newscasts and programs and local productions. They work just great for that.

Check it out, AxiaAudio.com. I'm so excited about the technology. It just freakin' works! AxiaAudio.com. Good stuff.

All right, Chris Tobin. This has been Episode number 235. Any closing thoughts about identifying and solving problems on towers way up there in the air where you can't get to them easily?

Chris: Well, I guess you have to take a methodical, measured approach to your problems. If you're an FM station and you're having issues with your signal and you think it's a tower-related signal, I guess the first thing to look at is a reflected signal, see if it's modulating with your carrier. If it's modulating with your carrier, odds are you have a problem with the antenna itself.

Check your nitrogen tanks if you're doing nitrogen to pressurize the line. See if you're making weekly measurements and keeping track of the pressure. Look to see if you're noticing a dip or rise in pressure depending on the weather because as the days get warm and cold, the cable contracts and expands. If there's a split in the transmission line, when the cable expands, it will seal up and it will stabilize.

When it gets cold, it will open and you'll lose pressure and your nitrogen tank will start to deplete. Or if you're running a compressor, then your compressor alarm should go off saying, "Hey, I've been running continuously now for the last six hours and I shouldn't be doing that."

Kirk: Yeah.

Chris: That's the early onset of what could be going wrong if you want to get an idea of things. Something else if you happen to be listening to your FM signal and you're hearing crackling sounds and you know it's not coming from your audio line, odds are your antenna elements are arcing.

I worked with a station that was not directly hit by lightning but coronal discharge was nearby. It shorted one of the bays in such a weird way that there's an insulator across the ring of the bay, carbon buildup. So, it just started shorting. As the station was modulating, the signal was going. The moisture in the air would affect it. So, at night, when it got real dry, it was like, "What the heck is that sound on the radio?" We went out to the tower site with binoculars, looked up at the bays and you could see little flickering light.

Kirk: Oh, never good.

Chris: Never good. Sort of like St. Elmo's Fire on a winter day.

Kirk: That reminds me. I had a station where we could hear crackling on the air. It was after a storm had gone through. Nobody had noticed, but it turned out that one of the guy-wires had broken. It was the guy-wire that went above the FM antenna. I don't know if it was done right. I don't think it had breakup insulators. I know it wasn't Phillystran.

So, I think it was steel guy-wire now just flopping around and hitting some of the antenna bays. Oddly enough, the transmitter didn't seem to care. But you could hear this noise on the air. In fact, it was also because of that arcing was making all kinds of spectrum up and down the FM dial and above.

Chris: That's what's known as a smart-gap transmitter.

Kirk: It was knocking out the satellite receiver. Whenever the wind would blow and start really crackling, the satellite receiver would go out. I'm sure there was who knows what kind of RF being produced right there in the area, right near the satellite dish, just 400 feet up or so.

Chris: Basically you're creating wide-band noise, ultra wide-band noise. So, the satellite downlink, which is what, 3 gigs, 3.4 gigs? Wide-band noise-remember, the satellite signal is what? How many microwatts?

Kirk: Teeny tiny.

Chris: And how many volts per meter is the smart gap transmitter or above it?

Kirk: It's bigger than I can show. Pretty huge.

Chris: Exactly. So, you're just swamping that LNB. It's like, "What the hell is that?"

Kirk: The troubleshooting, actually, was pretty easy. We stood around inside the building scratching ourselves for a while thinking, "What could this be?" Finally, I went outside for some reason, heard a noise, turned around and looked at the tower and thought, "Well, there's the problem. Right there is your problem. Your guy-wire is hitting the FM antenna."

Chris: Nothing beats getting a phone call at, what was it, 1:00 a.m.? Midnight? From your local police department telling you that your tower is on fire. "Can you come down to the transmitter building? We don't know what to do?" I'm like, "The tower is on fire? It's made of metal, non-flammable paint. Are you sure? There's no grass around. We have gravel 200 feet around the building. What can possibly be burning?" "I don't know but it's vertical, horizontal and it's all over the place." "Okay, this is really interesting. I'm on my way."

I get down there. You're driving down the street. You see your tower. It's a 475-foot tower. The tallest structure nearby is about two stories high. So, you've got a clear view of this for several miles. Believe it or not, I see what looks like flashes of light coming off the vertical parts of the tower and some of the horizontal guy-anchors. I'm like, "What the devil?"

It turns out to be a very dry night. It was a light dusting of snow. As it was described to me when I went to one of the schools and talked with a physics teacher, it's a form of St. Elmo's Fire. So, the RF signal from the AM station, it was an AM station, five-eighths wave so there was a lot of current there. So, the snow and the water pellets of the snow flakes, as they brushed along the metal structure, got ionized. The air was dry enough that there was no insulation. So, it was just perfect conditions. I kid you not, there were just sparks everywhere.

The fire department was just about the slam in the door with the axes when I got there. I was like, "Oh, thank goodness I got here on time?"

Kirk: What were they going to do? Aim the hoses up to the tower?

Chris: They had a fire hose at the door. I'm like, "Oh, there goes the Continental."

Kirk: Well, I'm glad you stopped them.

Chris: So am I.

Kirk: I've never seen St. Elmo's Fire on a tower luckily. I haven't seen that going on up there. But I've heard stories and seen pictures.

Chris: That was the only time I witnessed it. It was interesting at 2:00 in the morning.

Kirk: Chris, we've got to go. This has been fun. We're going to have John Hettish on, I promise you, on some future episode.

Chris: Absolutely.

Kirk: He will join us. We'll get Dave Anderson on. He was probably stuck in traffic in Tampa. I know he had a tough way to go to try to get home to join us. So, we'll have him on another time. But thank you for being here and your play-by-play commentary on the tower climb and the troubleshooting and your good advice on towers and solving problems when they're way up in the air.

Chris: Maybe what I'll do is if we have John on, I will get my gear on and hang from the base of a tower here in Manhattan and just do the show from there.

Kirk: Sure. It wouldn't be the craziest place you've done one.

Chris: That's true.

Kirk: Our show, "This Week in Radio Tech," has been brought to you by Lawo and the crystalCLEAR Virtual Radio Console. Thanks to Lawo. Also Telos and the Telos VX voice over IP phone system. It is amazing. It will save you money, sounds fabulous. Also, it does HD voice. I didn't get to tell you that. Check it out on the website. Also, Axia and the Axia line of audio consoles, including the beautiful, big honking element console and the cute little Radius console that does all kinds of good stuff too. Axia Audio on the web, AxiaAudio.com.

Thanks for joining us. Thanks very much to Andrew Zarian for producing tonight's show. We hope you'll tell your friends about us, like us on Facebook, follow us on Twitter. We'll see you next time on "This Week in Radio Tech." Bye, bye everybody.

Topics: Broadcast Engineering