Why is the invisible part of this radio tower so important?
out in this field there are hundreds of wires buried underground technicians use soldering and even thermite to build these ground systems this is one of the most important parts of an AM broadcast tower and you'll probably never see it my dad and I had the opportunity to talk to someone I nicknamed the ground Whisperer and like many who deal with high power AM radio this guy had some stories there was a nursery next door and the operator of the nursery called the station one day and said y'all going to do something something my violets won't go to sleep this is Kevin kid he has uh been called in on many uh interesting projects over the years uh ground systems he has a company am ground systems we think there's plenty of information here that you'll be interested in what we have here is the base of an AM radio tower the obviously the tower going up the cone-shaped device there between the bottom of the Tower and the uh concrete is actually a ceramic insulator uh that entire Tower is being supported by that insulator and big towers like well KMOX or uh the WLW Tower or WSM in Nashville uh they same deal they have an enormous insulator under them and you know the KSD towers that the four-legged guys they have one on each leg so that's another they have two uh on the base of a self-supporting tower you have the tower is sitting on an insulator similar to this but coming up through the center of that there's a enormous bolt and there's another insulator similar to that sitting on top of it with a cap on it that actually is uh holding the lifting pressure I'll be darn so those are torqued down and holds the tower up straight yeah and then I think I have a picture when the towers fell over from being in the field and seeing one of the legs popped up and it had a big it might have been a b or something a piece of something in the middle generally it's a big bolt goes all the way through the bottom insulator through the leg and then through the top insulator you notice that the insulator has uh the top of it is Aluminum the bottom of it is Aluminum but it's all ceramic in between some of these are Hollow some are not uh some of them are empty some are oil filled mhm um some of them are cone shaped like this some are uh just a cylinder it all depends on the manufacturer and but the straps going up the outside of it is grounding the base of the insulator and not only does that provide the path to ground for the uh the AR Gap helps to dissipate the lightning strike be before it actually does any damage in the building and notice this one spaced about a qu of an inch or so depending on the power of the station uh they can actually be M usually much closer than you would actually think U before they Arc over from the transmitter MH um you know how and that would affect would that affect the impedance wouldn't it of the transmitter if you get too close uh some but what the problem you run into you may adjust it and be perfectly fine with a transmitter on but you have a lightning strike it arcs across and then it's close enough that the transmitter actually will maintain the arc that's the next thing that happens is the AR Gap balls fall off and you have no more AR Gap uh these are solid steel they're welded they're just a large steel ball bearing um some of the AR gaps you see are uh a hollow aluminum ball that's threaded and it just threads down onto a piece of copper tubing they will literally just melt and fall off these probably not when it actually arcs between them uh for that instant that it is arcing uh it's basically a dead short ground mhm uh and many times you'll see uh vswr faults on transmitters after a lightning strike it was strikes not what caused it it was the ark yeah that caused it because briefly the tower was shorted ground it also be from a hot dog sometimes made a huge difference in my life in his in his document onity of location of women says now we're standing on top of uh probably 120 uh radials going out these straps go down the side of the pier and connect to a strap that goes around the perimeter of the pier mhm uh generally that's only sometimes it's on the surface sometimes it's sometimes feet deep um I'm glad to see that this one is not uh but the radials come up and are bonded uh to that perimeter strap now from that perimeter strap there this strap you see coming out of the bottom of the tuning unit over here that should come over and connect to the perimeter strap and then there should be a buried strap and we would hope it would be several feet deep just to keep somebody from finding it that goes either from here to the other Towers or from here to the building so it sounds like there's a lot going on my dad wanted to know what does Kevin think is the most important thing in a grounding system but what are the most critical things you think about the ground systems in general to get that signal out the main thing you want to do is make sure that all grounds are ground that they're all the same ground you you should have station ground M all of the ground should be tied station ground it's a little contrary to uh uh National electrical code to actually achieve the best stability and protection for the equipment um because with a neutral and a ground and I'm not advocating for that uh but if you have a neutral and a ground that's two different CRS uh those grounds to give best RFI protection RF protection and lightning protection really need to be the same ground but that's um to comply with national electrical code you can't do that yeah uh so actually all grounds need to tie firm to station ground I've U actually I've found my own clients that uh would have a lightning problem and uh we're going to drive a ground rod outside right here and connect this console to it well the lightning problem gets worse the lightning actually hits the Tower or power or whatever goes to that ground rod radiates out through the uh ground and now they have just driven an antenna down here to pick up that energy and instead of it actually the idea is that you bring all grounds to the same level at the same time so there's no difference in potential look outside any building with electrical service you'll probably see a ground rod somewhere providing a safety ground with AM radio you actually need multiple ground rods and it can be difficult to determine exactly how many and where to put them I don't know that anybody's figured out the exact correct way to calculate six ground rods three ground rods 10 ground rods but I've seen a bunch of different configuration I assume you have too uh well many U a ground rod uh that is at least less than its own length uh close that is closer than its own length to another ground rod it's not hurting anything not going to hurt anything but it's not going to achieve any uh uh any extra dissipation of the energy into the ground they need to actually uh according to polyphaser and others uh they need to be about twice the distance there the length of apart if you got an 8ft ground rod they need to be about 15 or 16 ft apart the bonding is U probably 90% of the problems that I find with am ground systems is actually workmanship um people use uh the incorrect uh solder to just go to the hardware store get some uh acid core solder go build your ground system cover it up do that uh the lifespan of just plain hard hardware store acid cor aut uh below grade mhm except maybe in the desert is probably monuts mhm you could have a perfect ground system but nothing's connected to each other yeah the question that was burning in the back of my mind ever since seeing that camo X diagram was why do am tower sites have so many radials well first off the FCC says you have to uh there is a one radial is better than than no radials uh 120 radials which is a standard ground system is quite a lot better than one radial but probably not as much as you would think uh I I think I have the story right that back in uh the 20s when most of the am research was being done they put in uh uh the paper that was written on it I think had a they said they uh at 118 radials had saw no discernable difference between 118 and 112 whatever their last number was and someone asked why did you stop at 118 radial and said we run out of wire so much for that too that was that that was the uh that was the reason they stopped at 118 yeah and then and from a practical perspective also uh some radios are going to get broken or busted or some of your joints are going to be bad so having an extra number uh higher than you needed for efficiency makes sense it's much cheaper to do it all at once than to come back and wish you had them for radials is what a lot of ham antennas have uh you are actually approaching uh the not necessarily maximum efficiency but a very uh easily achievable level of efficiency just with four radials a lot of elevated ground systems only have four or six radials sometimes eight very seldom ever more than eight um a inground ground system system has uh is specified as 120 for an AM broadcast station um many am broadcast stations have at least 120 uh some like we were talking about k x uh I I think it's actually got 240 full length radials the almost all AM stations have either screen around the tower bases of some size usually 24 by 24 for the higher frequencies and uh 48x 48 for the lower uh or uh interspersed radials a long radial a short radial long radial short radial um usually those short radials are about 50 ft long where have you seen the worst damage that created signal issues for a station generally vandalism mm uh that's uh accidental things uh generally is a back ho or a trencher or whatever but the some of the worst damage it's it's always a vandalism I've had several that have been accidentally damaged uh usually by uh cable contractor uh coming in last telephone polls there another businesses over there coming in they just go straight across that has actually happened and actually I've had some with uh multi-tower arrays uh actually plow they they dug through the uh transmission lines MH that's a bad day I also wanted to know if there was an ideal depth to Berry radials and also what might happen when you short a tower through a hot dog straight into ground where does the energy go when we short that hot dog into the ground like it goes in the ground but what does that mean and if you had the copper lower in the ground would that be better or sand versus soil or you know that kind of uh it depends on the soil and now there again the physics of all that is way above me uh in normal Soul most ground systems are 4 to 6 in deep uh deep enough to keep it from coming to the surface and being damaged uh generally you don't want to go deeper than that but in uh certain soil conditions you can go many feet deep and not lose any efficiency once you uh uh most soil once you get uh below about 6 in uh then supposedly you start seeing a drop off in efficiency of the system mhm but the uh uh as I understand it I've never built one that was deep uh but in the midwest there are some ground systems that are five and six ft deep just uh for a tillage from what I understand the uh the better the ground conductivity uh as in the AM signal conductivity which is all in Midwest this area uh has good ground conductivity it can be deeper than say in Tennessee where I'm from uh our ground we have ground conductiv acties in the fs MH uh four to8 is uh I think normal for my area here it's probably what a 15 or or higher what are the main things like you're at a facility now you want to test how good is this ground system appear to be well there's several questions you normally that I normally ask uh how stable is it m uh have any lightning problems has there been any known vandalism or damage uh that actually is one of the best places to start uh but honestly the mark1 eyeball is one of the best uh uh tools the uh as we're going to do here digging around the towers actually doing a visual inspection of the uh the bonding around the bases um checking make sure that the tuning unit is tied to the uh uh Tower base uh strap and as we're questioning here is there a uh piece of strap binded there and coming back to the building now and what kind of tools would you have you have something you clip on here and you can run the radial out and detect them uh several different things U I have a couple of cable locators that we'll be using to run these out U I have and I didn't bring it with me uh I actually have a radial Chaser as they're called that is nothing more than a little fi F strength meter uh on a stick M um it just picks up the RF off of the radial itself the current flowing in the radial one of the ones I made just used a typical voltmeter and you could read the voltage off of it hey that's cool I can tell how much current's flowing have you ever tried walking across a field like this swinging a uh uh stick around and trying to read a voltmeter and then not fall out yeah yeah so I back to the headphones yeah well they and the uh the depth of them so like they may leave here at 6 or 8 in but in any time because of uh tractor driving or anything it would push those down uh then stuff going over the top so you go down at some point you wouldn't be able to detect it even though it's there or uh no well with the cable locator if I'm putting with the cable locator actually injects a signal of its own I can either trace an existing the RF that's on it in most instances or I can I will actually put RF on it uh from the generator that's part of the uh the cable locor you do that you have to have the TR station off to do that so you can do that you can inject that in there and for most of us our radio guys like what we're injecting into a wire that's buried into the ground it just doesn't sound real it's like that just is the worst it's it's exactly the same thing the power companies and phone companies do when when they're tracing yeah uh Buri cable and so you can go feet several feet under or yeah well the anytime you're doing it inductively as in just setting the generator on it which is that's what it's meant to do U now you're limited to a foot or two uh at that but what um also have a clamp looks like a large amp clamp that I can actually clamp either around the individual wires or around the uh strap that's going around the the perimeter strap and uh then Trace that signal out uh one of my cable locators runs it I think it's something like 80 khz and um just a little green Le uh cable tracer we've talked a little bit about KY wires but uh there's insulators like why why are there insulators and also are they how do they affect the ground system because they're long wires that are I guess floating I don't know yeah well as a matter of fact they are floating the uh insulators and guys if the guy wires were not insulated if it was a steel wire that would be shorting the tower to ground at multiple points um and yes I actually did arrive on a site quite a number of years ago where somebody had built a tower 4 AM and had not put uh insulators in the guys um and we were we were going to be building a ground system for it and the engineer the local engineer had called me and said this thing just won't load up uh he had been trying to get a uh ATU built for it and they actually had a little power into it yeah but uh he had just had to Cobble this horrible massive uh ATU together and that just it measures crazy and and when I got there well you ever look at your guy wires yeah yeah there was no insulators in them so anyway they uh the tower crew as it turns out they had bought the tower crew just didn't know what they were there for they were in a drum they had bought the kit with the insulators tower crew just hadn't put them in and I've seen a lot of uh Towers where they insulate heavy like they'll put a 3ft or 6ot fiberglass Rod just to keep it off there yeah so keep the uh cable off the tower and I don't know if that's for arcs or what uh for arcs and uh of course a lot of FM Towers have those in them in where the aperture of the FM antennas would be these insulators are actually spaced at a non-resident length along the guywire m just to keep the wires themselves from becoming part of the antenna system we talk about grounding and everything else but the ultimate point is to get the signal to the listeners but I've always said it's like if I could remove uh last 20 years of industrial growth and Home Building and bridge building that would get my signal a better kick than fixing the ground systems would it be a good idea to build a neighborhood right around the base of a tower would that help the grounding or hurt the grounding hurt would that help the people living around it uh unaffected unless they have a toilet that talks about the radio station I've actually had several well uh built a 10 Kow heot a number of years go and there was a nursery next door and the operator of the nursery called the station one day and said y'all going to do something my violence my violets won't go to sleep and well my mother had grown violets so I know that they you turn the lights on so many hours a day and off so many hours a day it wasn't the fact that the lights were staying lit it was the fact that his timer was unreliable they apparently was coming on and going off and uh U we actually helped him get another timer and did a little grounding and solve the problem but his violets wouldn't go to wouldn't go to sleep and what about so you talk about the bonding piece so I've seen uh what's the flame Bond uh uh CAD weld cad welding Thermo whatever thermonuclear bonding I call that but maybe it's not quite that uh the but theic even uh yeah uh even the cad welds like I've seen them on poles uh around fence posts and things like that and I've seen them separate uh but most of them hold very well but like the the the Artistry part of that or the learning part of that like where do people uh get that is it do you guys go to the training sessions at cad welding companies there are uh uh training uh that either the cad Weld Company whoever owns them now uh ultraweld there's two or three different companies make those now and yes is training it's actually pretty simple U there's of course lots of stuff on YouTube and people doing dangerous things with it on YouTube but the the difference between the bonding that we do around a uh am Tower which is brazing using a silver called Silas uh silver copper Main Ingredients copper it's got uh some silver and phosphorus in it um it actually is just a filler metal just like solder just as if you were soldering something onto a circuit board the solder is the filler metal whereas with the exothermic uh it's actually melting it is melting those together uh they become one piece and I know my first experience with that was the uh if the if the copper gets too hot that's not good yeah so I've had that and I guess it's just a matter of uh trial and error when in your in your thing find some scrap don't do it on your uh first big project don't do it on the final stuff do it on the practice thing into the parking lot or something right I remember came W one of the drawings they have shows that they went from the tower above ground out to the you know they took the RF out and they had a a standoff little pole like this had four ground wires around it and the hot lead in the middle called five Wire yeah and they they shot that out there as their uh carrier wire and uh you would not think this but the old five wire and sometimes there was three wire uh one hot and either three or four or whatever around the outside of it is very efficient at am frequencies yeah wow very very little loss we'd like to thank Kevin for his time and his wealth of knowledge and next time you look at an AM Tower site know that Engineers respect the things you don't see just as much as the things you do they're keeping the signal strong and the equipment safe
2024-12-22 08:57
