The AM Forum

 Ameritron suggests looping the coax before it enters their remote coax switch. This is supposed to reduce damage from a lightning strike/near miss.
 What is the theory behind this?

Thanks, Roland...............

I don't know about that, but I've always heard to loop the coax like that to form a sort of common mode choke.

Even better if you loop it thru a toroid core or two as Nautel recommends.

73DG

A loop creates inductance just like a coil.  Lightning doesn't like inductance.  But, don't bet the farm that a loop in your coax in going to protect you from lightning strikes.

Always disconnect your antenna cables from your rigs when not in use.  The disconnected cables should then be grounded.

Fred

Also don't make the loops the wrong size.

Here is an interesting tutorial on feeding base-fed monopoles, beginning at page 10.  The writer claims that lightning loops are unnecessary (p.14).

http://www.nxtbook.com/nxtbooks/newbay/rwee_20120613/#/10

When Chris came down last week with his impedance bridge and we measured my antenna impedances, we found that adding even a few inches of wire to the horizontal lead  running from the matching network/measuring instrument to the base of the tower at the insulator made a noticeable change to the impedance reading.

good chance a toroid will explode if placed as a common mode choke on coax.
Lightning currents will saturate it very quickly. Air core choke is better, but a good long duration strike will go right through the choke. Best thing to do is have a good ground on the shield before it goes into the building

Lightning is NOT DC, but a wave form at about 1 Mhz. It's RF, not DC.

Being that, a bit of inductance in series to the antenna is useful for keeping lightning out of the shack.

Almost every AM broadcast station feeds its tower(s) with a lightning loop from the antenna tuning units, usually 2 or three turns of 1/2" copper pipe in a 2 or 3 foot diameter loop. Or you can use toroid cores, but they tend to get hot and unreliable with lots of RF flowing through them. And they will likely explode during a direct lightning hit.

A ham station could use several large turns of coax, taped together for the same effect. Just a few turns maybe a foot in diameter. Smaller than that, you lose usefulness as the stroke will just arc right across the inductor.

Bill

On the two 5 kW AM broadcast stations I take care of we have one turn loops between the base of the tower and the ATU, big coils in the ATU between the output of the ATU to ground and a spark gap between the base insulator and ground. Also have three inch steel balls between the base of the tower and the ground system. Take lightning strikes all the time and other then the transmitter cycling not much else happens. The FM transmitter sites we ground the transmission line where it connects to the antenna, where it departs the tower and before it enters the building. Three of my FM sites are the largest structures in the county so they always get struck without many issues. Every engineer I have talked with has a theory on how and what lightning will do, if it goes from cloud to ground or ground to cloud, weather it’s the difference of potential or the electro magnetic pulse that dose the damage, if a thousand little discharge points dissipate lightning before it strikes and everything else you can imagine. I just believe in lots of ground strap, and a loop or two cant hurt.

The key thing during a lightning strike is to ensure everything is at an equal potential inside the transmitter/equipment building/residence.

It doesn't matter if everything in the shack is elevated to 100,000V during a strike, you have to make sure that everything is also elevated to equal voltage.

For example, an AM or FM broadcast site. You put a ring of copper strap around the building. Mr. Faraday will say everything within that ring is all at the same voltage, therefore no harm will result.

So you put Johnny Balls at the base of the tower, separated enough so they don't arc over during normal operation. But lightning strike *will* arc across them, taking most of the energy down to earth at the base of the tower.

You put an inductor between the tower and the transmitter building. If a ham setup, a few turns of coax, about a foot in diameter, taped together. No more than that, or it will arc over during a strike.

You put a grounding ring around the house or ham shack. Heavy gauge copper braid or strap.Everything is connected to it. Transmitter, linear, receiver, audio gear. Everything within that ring is completely protected from the strike. See Mr. Faraday Cage, again.

Even better is to put the coax loop choke at the base of the tower, then bury the cable underground the rest of the way to the ham shack.

And disconnect during storms.

You do need a good ground at the base of the tower or mast. I have a 4'x4'x4' hole that my tower base is buried in concrete. The hole is lined with 6" wide copper strap (flashing copper) that the tower is bonded to with #4 copper wire.

You need to go *around* the concrete with the grounding strap. You do *not* want the bolt to travel; through the concrete, or it could explode.

In spite of a number of strikes, I have never had a single problem with lightning strikes. And here in Colorado, it's worse than anywhere else, except for Florida.

Bill

I've mentioned this on the forum several times before.

Lightning hits are really hard to withstand.  In this analogy, you have two choices:

Say you have a really mean bully in your neighborhood.  He is coming to beat you up.

You:

A...Suit up with padding and such to hope to avoid any broken bones or lacerations, and let him have at you :o.

B...Direct him somewhere else, and he leaves you alone :). 

I have installed static dissipators on many buildings and towers, all of which sustained damage from previous hits.  These items are relatively inexpensive and durable.

After installation, not one of the protected sites has been hit.

http://www.nottltd.com/index.html

I don't have any pecuniary interest in Nott Ltd, but I sure do believe in their products' ability to prevent lightning strikes and the resultant damage. 

I always leave any grounding systems in place, they can't hurt.

73DG

lightning is a complex waveform. Take a look at RTCA DO160 ane check out waveform 5A 40usX120us. Pretty low frequency component and lots of energy.
Common mode chokes only help in low level high frequency induced strokes like waveform 2 or 3 where there isn't a lot of energy. you are dreaming if you think a bead will do anything for high energy. The only thing you can do it try to divert the energy to ground so no voltage is sent back into the building. E=IR so do the math a good lightning hit can be 200,000 amps. Say you are .01 ohms to ground your coax shield is sitting at 2000 volts during the stroke.

Yea, I kind of buy into the grand elevation thing on how everything gets elevated when you take a strike and as long as everything is tied together real well it all goes up and down together with no damage, kind of figure that why sometimes have issues with phone lines and phone couplers burning out on the remote system being the phone company is at a different potential from the site. The other question is the EMP thing, the idea that when lightning strikes the tower and travels down the tower and lines to ground it produces a huge magnetic pulse and that pulse is what's doing the damage. Sounds like a load of crap but I do know from first hand experience at television transmitter sites back in the days of analog tube displays that you would come out to the site and have to de-gauze  all the color monitors after a storm because they would get magnetized  and know that once I left a laptop connected to a service port on a transmitter with a cheap non shielded serial cable  and after a storm came back to find both the serial port on the laptop and in the transmitter whacked  so want to think that was a EMP thing. Has nothing to do with the subject but always thought the whole nuclear bomb EMP threat was a load crap also being that at radio and television sites we have been experiencing huge EMP events for years and those worlds never came to an end so don’t buy into the whole thing about nuclear EMP destroying everything for miles and miles. Don’t remember much that’s useful from physics but recall something about magnetic fields decrees by the square of their strength so it would take some huge fields like the local field generated by close proximity to a lightning strike to do any damage and the strongest fields can be stopped by the smallest amount of shielding. But what do I know, not even cretin on how to pronounce the word nuclear. Torks off the liberals I work with when I use the Bush pronunciation.

The premise of adding cable or feed impedance to sensitive equipment attached to a tower is that lightning energy has alternate paths to ground which are less damaging, like a grounded tower, and / or close-spaced spark gaps.   More current will flow through lower-impedance paths.

Even a shunt-fed folded unipole (grounded tower) needs a feed spark-gap due to induced current.

There is much anecdotal evidence of success using toroidal common mode chokes on AM tower feeds - which are connected 24/7 to a solid state transmitter.

Chris

The ferrites shown in the previous photo by me are supplied by Nautel, and they have detailed instructions provided for installing them.

Not only are they used on the output coax, but every cable in or out gets them.

Running one of their new transmitters without them will make any warranty very hard to secure in the event of lightning damage...

73DG

More anecdotal evidence:

In a former life where I had a fleet of tower sites fed with rural power, lightning energy entering via AC mains initially caused much havoc - several fails per site per summer.  I modified the aerial utility AC mains feed with a three turn coil of all conductors, about 3-4 feet in diameter.  
It took some persuasive effort to get the utility to so this, but it was done at low cost.

It made a huge improvement in storm-related reliability - lighning-induced problems fell dramatically.  I also added some MOVs, but they rarely failed.  I believe the biggest improvement was the added inductance, allowing more of the current to flow through the utility's arrestors.

Chris

Direct strikes are hard to beat in the typical ham installation; but the, much more common, close strikes should be helped by some of these methods.

Put a Stati-cat or two on your tower and you won't get hit.

73DG

Have a six fifty tower in Delaware (WDPB-TV) that we installed the whole Stati Cat song and dance ten or fifteen years ago. Still gets hit, just not as much. The tips of the nails melt on a direct strike. Not saying it don’t work, just nothing is 100%

I lost my best 0-10 amp thermocouple RF ammeter in a lightning strike. Not sure if it was direct or a near-hit, since I was away from home at the time.  The antenna feedline was disconnected at the tower and everything was grounded, but the buried coax line I was using at the time between shack and tower picked up enough induction surge to turn the meter to charcoal.  There were even carbon traces all over the front of the meter scale.  Nothing else was damaged, except for a few of the a.c. light switches in the house that were welded open or closed.  Fortunately, they are all the old buzzard type switches with ceramic body and nothing more that a piece of heavy paper serving as a front cover under the switch plate (most of those having long since rotted away with age), so all it took was removing the switch plate and a small thin screw driver and a shot of WD-40 to fully restore them to operation again. The slider-type a.c. power switch on a nuvistor rf pre-amp was also welded in position.  I replaced it, and nothing else in the pre-amp was damaged.  I still have it but don't use it any more.

I found this thread very interesting. I recently moved my shack from a front corner bedroom to a 10 x 20 shack. Power for the new shack in the
back yard is obtained from the houses' breaker, fed through 8-3/G cable fed through 3/4" schedule 40 PVC pipe 24 inches below the ground to the
shack.

The shacks' internal safety ground and neutral wires are connected together at the shacks' breaker box. A #8 solid copper wire connects
from the safety ground and neutral wires to a ground rod driven into the ground at the shacks' power entrance. The #10 solid copper wire, part
of the 8-3/G wire, is also connected to the shacks' breaker box ground then runs in the same schedule 40 3/4" PVC pipe back to the  house and
connects to the house breaker box ground. This places the shacks' ground and the house ground at the same ground potential with the shack
having a ground rod at the shacks' power entrance.

The shacks' coax runs out through a hole in the shacks' floor to a connection to the left of the shacks' front steps, I haven't finished the
installation yet. The remaining coax runs underground through 1/2" PVC pipe to an Ameritron RCS4 switch that's mounted on the back yard
chain link fence vertical support pole.

If I suspect a T'Storm will occur, one is forecast, or I leave the house for any length of time when a T'storm may occur, I disconnect the coax
at the RCS4 switch and also at the connection next to the shacks' steps. I then temporarily locate the shacks' coax on hooks, above ground on
the side of the shack.

My biggest concern is whether I have taken all the steps necessary to ensure the power grounds in the house and the shack are correct.
The other question is, I assume each tower leg (I'm installing a 30 foot self supporting tower) must be grounded and the tower ground must
be connected to the shack and house ground through underground solid copper wiring so the tower, shack, and house grounds are all on the
same ground potential. Also how many Poly-Phaser lightning devices are needed for a tower, rotor, and wire coax connections? I assume one
for each or do I need one at each end of each coax feed and rotor wire?

73s
Mike
W5RKL

Lighning can get anything.   This myth some hams nurture is that broadcast stations can take a hit and drive on.   Yes and no.  You can do the perimeter ground thing and cadweld strap and the rest of the nine yards and turn your QTH into a commercial broadcast site but you won't be immune from damage.  One of the local 1-As a few years ago took a direct hit on their tall stick and it wiped out most of the tuning house and they had to spend a nice chunk of money on a new DX50.    Some hits are worse than others (positive strikes are hell).

As a ham I just unplug and disconnect everything.  This doesn't mean all the professional methods are pointless or no good--they are worth doing if you want to do them because what they give you is a higher probability of avoiding damage, or extreme damage.  Just don't think they guarantee immunity. 

Rob

Rob, there is a lot of truth to what you say. Bear in mind that a broadcast station with a 300-700 foot tower is guaranteed to be hit many times a year. And the majority of the time, they escape any damage. One of our AM sticks is 667' tall and a lightning counter (yes, they make one) records dozens of direct hits every year with no damage at all. The transmitter pops off the air fora few seconds due to high VSWR, then it comes back.

These days, I see a lot of neglect in AM broadcast sites. Broken or stolen ground straps, missing or corroded apart ground systems and radials, even johnny balls spaced so far apart as to be nearly worthless. As long as the place in nominally on the air, no one pays attention to these things. Until the damage is done.

Contrary to intuition, usually, the damage done to an AM BC transmitter from a strike is done via or with respect to the AC power lines, not the antenna system. Hence the advice to unplug the whole ham shack during a storm is a wise one.

Bill

I'm not sure that's a good idea. I believe there should be one and only one point in the entire system where ground and neutral are connected together, and that's at the entrance to the main panel, right at the meter.  Beyond that, the neutral should be treated exactly the same as a hot. I believe some local codes state that it is ok (but not required) to connect ground and neutral together at the entrance to a separate exterior building, but I can't see that it would serve any purpose, and could introduce ground loops, since the safety ground would be forced to carry current whenever the neutral has any potential ≠ absolute zero volts. A separate shack is electrically no different from an addition physically attached to the house, and at every locality, I'm almost positive that the code prohibits connecting ground and neutral together at any point in the house beyond the main panel.

But there should be a good heavy safety ground, complete with rod, right at the shack, and better still, a few ground radials bonded to where the rod is driven into the earth, and a heavy copper wire, #4 or #6 or larger, firmly connected between the shack ground rod to the main entrance ground rod at the meter.  In mine, I didn't run the separate safety ground wire through the same underground conduit that carries the 3-conductor power cable between the buildings, but buried the ground wire about 4" under the surface of the soil, much like a ground radial, running it in a perfectly straight line between the two rods.

I have noticed that I can temporarily short the safety ground to the neutral at the fuse box in the shack using a clip lead, and sometimes see a small but visible spark just as I make the connection. Unless everything in the shack is turned completely off, there is nearly always a small voltage difference between ground and neutral, and if something heavily loads down the line, such as an electric heater, air conditioner or the transmitter plate supply  running full strap, this potential difference can jump up to several volts.  Inevitably, if any audio equipment in the shack is running at the time, as soon as I touch the tip of the lead to the conductor, I hear a click in the speaker and the hum level goes up.

In addition, a few years ago I added an isolation transformer between the 115v power mains and the receiver/audio/speech equipment and other station peripherals, so that one side of the 115v mains voltage is not near zero with the other at full voltage, but instead use a mid-tapped choke across the output of the isolation transformer to simulate a mid-tapped secondary, with the mid-tap connected to the safety ground, which means that all the peripheral 115v equipment associated with the station is running with balanced power line voltage, each side at nominal 57.5 volts above ground. This made no detectable difference with some equipment, but in others, it audibly affected the quality of the hum and/or reduced it a few more dB.

That is required by the NEC.

Bill

Power for the shack is 240VAC from the house panel.

The house panel has all house wall outlet safety grounds and WHITE neutral wires connected together on the house panels' neutral buss bar.
The house ground rod is also connected to the house panels' neutral buss bar.

Power to the shack is 240VAC over 8-3/G wire, taken from the house panels' main power buss through a dual breaker. The 8-3/G RED and BLACK
wires connect to the house main power buss and the "WHITE" and #10 solid copper wire connect to the house panels' Neutral buss bar.

The other end of the 8-3/G wires connects to the shack panel, RED and BLACK to the shack panels' power buss, the WHITE wire and
the #10 solid copper wire connect to the shack panels' Neutral buss.

Each 120VAC outlet in the shack, there are 5, and the single 240VAC outlet, have the safety ground and Neutral wires connected together
on the shack panels' Neutral buss bar.

I questioned the electrician if connecting the safety ground and White neutral wires together in the shack panels' Neutral buss bar was
according to code and he said yes. I thought the shack wiring was considered a "sub paneL" but he said no. The only thing he said I
didn't need was the ground rod outside the shack that connects to the shack panel Neutral buss bar. He said the house already has a
ground rod so an additional ground rod was not needed at the shack. I insisted on the ground rod so he installed it and connected it to
the shack panels' neutral buss bar.

As I said, I'm not an electrician and that's why I hired a licensed electrician to do this job. I don't want something major to happen because of a
wiring error.

73s
Mike
W5RKL

Hi Bill, thanks--yes I hasten to add they take a lot of hits or nearby hits with little or no damage and that incident I was thinking of was unusually bad. 

rob

In my experience it is a rare "licensed electrician" who understands effective lightning protection.

The main principle is providing a more attractive (low impedance) alternate path for the stroke current to flow to ground.  NOT flowing through expensive equipment or your electrical system.  AM stations have exceptionally low impedance ground connections due to all of the radial wire surface area in contact with soil spread over a wide area.

I looked it up in several NEC "Handbooks" in my library, and a copy of the early 1980s NEC.  I could find literally pages devoted to grounding, but the only thing I could find on that specific topic was in the earliest (1940) edition.  It says that the neutral in a separate building that is part of a single system may be grounded, but didn't imply that it was required. They mentioned that this situation is found most often in farm buildings that operate off the main house's electrical system, but that's not too different from a separate ham shack.

The NEC is like attempting to decipher the schematic of a ricebox. They have topics and sub-topics detailed in minutia, but if it is in any logical order, I haven't figured it out, and the index in the back of the book is about as useful as the search function on this BB.

But still, I can't figure out why a separate building would be treated any differently from a room added on to the main house, since it would make zero difference electrically.  In the latter case, it is a strict no-no to ground the neutral anywhere else but at the one point at the main panel entrance.

Codes notwithstanding, I'll still use whatever results in the least RFI and hum in the audio equipment.  If they changed the code since my book was published, I'm still covered, since my ham shack was built in about 1930 and pre-dates my 1940 book, so any existing electrical wiring would be grandfathered. And to boot, despite some extremely close if not  direct lightning hits, I have had relatively little lightning damage, and I don't even use any lightning loops.

Don,

I'm not surprised you don't have many lightning problems.  I recall seeing signs of arc-overs on your tower spark-gap.  And how many feet of buried copper wire do you have in the ground ... ?

Chris

Good conductive paths to ground are great if you're buying into the elevated theory; don’t help much with the EMP thing and the Stati Cat people will tell you all about how their product prevents strike in the first place. Thousand points of discharge or light or something like that. More than likely jinx myself by saying this but at the several broadcast sites I have had little or no damage by lightning to the RF equipment, tons of damage to telephone stuff. But other times have had strange things like last year had a lightning strike burn a small hole thru the copper alloy body of a multibay antenna and not affect the antenna or on air operations, just lost pressure on the antenna and line and that’s how we discovered the problem. Lightning dose weird things, just yesterday we had a storm in town and less than a quarter mile away from the five hundred foot very well grounded Stainless G7 tower for WCPB-TV the lightning avoided that structure and struck instead the steeple of an old church in town and blew half the shingles from that structure. Don’t know if they had a lightning rod or not but it did blow the hell out of that church. Go figure.

The "elevated theory" is the basis for the single-point ground attachment method - always a good idea but not always practical.

Most AM tower spark-gap arc-overs are due to the "emp" induced energy from a nearby strike and not direct hits, but as heights get taller direct hits become more frequent.

Hate to endorse any particular product, but with the advent of the "Optelator" damage via dial-up phone line connections are pretty much a thing of the past.  The product optically couples tx & rx via four inches of fiber, entirely without metallic connection.  It does reduce the level a bit however.

Tower mounted antennas are most vulnerable when at or close to the top.  As painful as it is to give up height already purchased in steel, side-mounted FM antennas do much better with lightning when the top bay is at least ten feet below the top. 

Chris

Why not just add relatively cheap tubular mast to the top of the tower, to extend above the FM antenna?  That should be sufficient for lightning protection and you wouldn't have to mount anything on it.

I live on a corner and there is a power substation at the corner. The substation is about 500 feet from the house. The substation receive power
from a 60KV line that hangs from 2 200 foot tall metal poles, one of which is about 250 feet or so from the house. I had the electric company
out tracking down a noise source, turned out to be a blown lightning arrestor in the substation. The lineman said I'm protected from a strike
by the metal pole that's closest to the house. Both poles get hit quite a bit during the 8 years I have lived here. My neighbors' house is
about an additional 200 feet farther away from the pole, had a 60 foot pine tree received a direct hit. The pine tree was 10 feet from his house.
I'm not sure if the 60KV pole actually provides any protection or not. I can only say, knock on wood, we have not been hit during the 8 years
we have lived here and I hope we don't get hit in the future. The substation also has a tall wooden telephone pole with a 6 foot tall metal
rod on top with a large diameter, possibly #4 copper wire, running down the pole to a ground rod. This pole is situated in the middle of the
substation.

73s
Mike
W5RKL

That is also done, often with multiple-point "spike-ball" style lightning rods / "static dis-chargers".

I forget exactly what the legal limits are regarding height extensions above the top beacon, and where they have to be declared.  20 feet comes to mind but I can't remember if that counts toward busting the limits of the lighting requirement for the height - for instance lots of 499 foot towers built to avoid the more stringent lighting requirements for 500 and above.  But these rules have changed in recent years with strobes ...

That site that had the hole burnt into the antenna is WQHQ; a class B (50kW ERP) FM that has an eight bay Dielectric antenna that has its top bay located just about five feet below the top of the tower with the entire antenna assembly being about sixty feet long. On that tower there is a lightning rod that extends above the top beacon but in this case the lightning decided not to strike that but instead hit the outside tip of the center support pipe on the bay and burnt a hole about a 1/8 inch clean thru the stainless steel pipe. Couple pictures of what the bay looks like and the tower rigger who had to climb up six hundred and fifty feet to replace it. Like I said before had no idea what happened because everything was on air and normal except we lost pressure on the line and antenna and received telemetry about that. The antenna, bays and transmission line are all hallow and we keep a nitrogen charge on them and if the lines drops pressure that generates a fault in the remote system and calls you. I was also involved with the replacement of a four bay ERI FM antenna for WSCL this spring. That antenna developed a problem in the tuning slugs and started to burn there and proceeded to burn up most of the hardware above the network and the inter bay connectors. The soot and fire damage resulted in having to replace the entire antenna for around $30,000.00 not including installation. The popular speculation is that this was also caused by lightning although all the damage started around the stub section at the base of the antenna and the antenna is side mounted at five hundred feet fifty or sixty feet below a forty foot high television antenna. So when it comes to lighting, where, when and what it's going to do all bets are off. In regards to the phone stuff, I have seen the optical things before and thought they looked like they would work good, may have to think about getting a couple for the more problematic sites. The thing I do most often is just load up on these little cheap phone line protectors that plug into a wall outlet and the phone line loops thru them. They have fusses and other junk in them that blows out but generally the equipment is protected downstream of them so after a storm will often end up going around to sites and replacing the blown ones but that also provides job security. Here's a question, at the WJDY AM site I have a two tower 1.470 5.0 kW station that has the transmitter building located two hundred feet from each tower. The ATU at the base of each tower are connected back to the transmitter building by 7/8" healiax cable and each tower is around 180 feet tall. Each tower has a ground matt and around a hundred radials that have all been installed back about forty years ago.  This site has the most problems with phone lines. Program audio is provided by a STL to the site so that’s not an issue but the remote control for the transmitter constantly is having issues. Almost every storm the phone coupler gets wacked, have on occasion had things like the telephone block outside distroyed and once or twice seen the service loop from the phone company blown apart. Remember that the transmitter building is at least two hundred feet from the towers and the equipment, except the remote never have any issues so why does the phone line keep exploding? My best speculation at this point is that the grounding system looks so good to the phone line that any strike on the phone line around the site and the potential wants to travel here to dissipate? But that's just a guess; twenty years ago I would have explained it all, now I just don’t know. It may not have a lot to do with AM but lightning is a fascinating subject and seeing what it's done is always fun to talk about.

 Thank you all for the information. Is there any virtue in using AlphaDelta ATT3 G50 Static Discharge Protectors?
 If so, would I need one for each antenna? I am contemplating a variety of wire antennas, each of which will feed into a remote coax switch.

Roland........
 

The in line static protectors can't hurt. If you are using tube receivers, you probably won't need them. Also be sure the static protector can handle RF if you are going to transmit.


In general, lots of good grounding and bonding info in doc like this.

http://www.qwest.com/techpub/77355/77355.pdf

Those poor tower guys are often making less than $15/hr.
To swap out light bulbs, sometimes.

For one of the toughest, ballsiest jobs on the planet.

God Bless them.

Bill

That's what the guys who do the actual work get paid. But the station usually pays a sub-contractor a lot more per climber even when it's a one-person job.  Can't understand why a professional tower climber wouldn't contract his work independently and keep everything for himself.  

Back in 1964 I climbed a 365' tower and replaced all the bulbs, for $30.  Seemed like big money back then.  A couple of years ago I was offered a retired BC1-F by a small station in exchange for replacing the lights on a 250' tower, but I had a physical infirmity at the time and couldn't do the work (since then fully recovered), plus moving the double-wide 3000 lb. transmitter and hauling it 100 miles.

I'm not afraid of heights as long as I have full confidence in the integrity of the structure I'm climbing on. But when I built my tower, I had to temporarily guy each section on the way up.  I couldn't relax working more than one tower section beyond the top set of guys and feeling the tower sway with my movements.

But once you get up beyond about 40 ft, it doesn't really make any difference, if you have the physical stamina for the climb.  You will be precisely as dead falling from a 40-footer as from a 400 footer.  Last year, at Field Day if I recall, there were a  couple of separate incidents where someone was killed when a tower or mast about 30 ft. high collapsed while they were on it.

Hi All,
 
 Thanks for all the great information. I am going to run my coax and control cable (for the remote coax switch) through schedule 40 plastic conduit.
 I thought since the pipe is going to the back of a storage shed, why not run a length of Romex as well as the shed is as yet, un-electrified.
 Would the Romex cause any problems when I eventually get my Ham ticket and start transmitting?

Thanks, Roland......

We discussed this in a previous thread:

I like the case where there is galvanic isolation between the main service and the remote service.
Don't recall the NEC term for this, but it exists. That way you can put your "ground" locally to the remote service, which would be the shack. (assuming a separate building)

I don't know but would presume that some method to handle a bleed of extreme over voltage from one side of the iso tranny ground to the other (like a spark gap or maybe a big ass MOV or Tranzorb) might also make sense.

It is studied and accepted practice that the self inductance of a large iso tranny will be a very effective transient killer, equal or better than more complicated active or passive methods - just bigger and heavier. :D

In a "regular" set up, where you have to run a long amount of copper back to the service, to me it looks like the self inductance of the wire and the vdrop could cause one side to be one heck of a lot higher than the other...  but obviously if everything rises *nicely* together, no damage; I'm not so sure that this will happen unless all the conductors have the same drop... so using a fat gauge for the "ground" run and a standard gauge for the others will create a differential voltage. Or so it seems to me.

In the case where you still bond back to the service entrance with a long run, it seems that maybe having the iso tranny in the other lines might be of some benefit, as those lines more or less float.

Those outside things like connections to twisted pair or cable definitely can cause a voltage difference, and blow up solid state things. It's easier than before to go wifi and get rid of those connections...

Oh, people have suggested using stainless steel chimney brushes up top on the tower... seems like it should work ok.

                   _-_-bear

I have a friend who had a problem with his computer controlled wave solder machine.
Software would get trashed whenever a storm came through. He added an isolation transformer that did nothing. Then he called me. I suggested he establish a ground after the transformer. He drove a rod into the floor beside the machine and never had another problem.

So... the ground with the transformer? Or just the ground?

                    _-_-bear

A lot of that cost is insurance- workers comp payments. Tower work is a hazardous occupation per man-hour and the cost of insurance is insane. Have an accident or a claim and the cost gets even more insane. There has been some online news about tower accidents the cell phone companies have had. Reports of too much rushing on the jobs.

Bill

In addition to adding the transformer.

A thunder head formed over the beach last night as I watched from inside the  house. I watched it grow taller and taller and wondered if it would turn into a tornado. It produced one good bolt close by. The 200 foot inverted U above the yard produced a good long duration arc against the ground. I wonder if it hit Joe PJP across the pond as it drifted south.

OK, here's a classic.

Last Saturday afternoon a big time strike hit one of the 350' towers of a Denver 50KW AM directional.

The tower and tuning building were grounded as best as humanly possible with perimeter ground straps 4 and 6" wide and the customary 180+ quarter wave buried radials. Far better than 99.99% of ham installations. It was only a few months ago when I had inspected the ground system. There was a multiturn loop of 3/4" copper between the tower and tuning house.

Well, last Saturday, a strike completely torched the tuning house. An aluminum and wood 10x10 foot prefab building. The tower matching network was in a solid steel enclosure containing the inductors and caps inside the building.

All burned to the ground. Austin tower light transformer? Melted. All torched. The copper inductors in the picture were once enclosed inside a stout steel enclosure, which was vaporized. The 3" buried Heliax feeding the tower? Vaporized back some 10 feet. Prolly a 100K worth of total damage.

Nature wins, again.

Now, what did I say about lightning protection?



Bill

Shoulda had your gap tighter ... ;D

In all seriousness, what investments do you like?  (I'll mark those off my list!)

well, I have some sort of employment security for the rest of summer- LOL Need to get the loader and backhoe out there.

CC 50 kW AM stations are all monsters, I have never worked at one myself but I do have a couple 5 kW and have worked on many other 1 and 5 kW properties. Is it possible that what you are looking at is the result of the lightning strike causing damage to the ATU at the base of the tower and when the transmitter recycled the damaged ATU set itself on fire? I had an old style CP current meter in line in a steel Gates Radio cabinet with the phasing network fail once and the 5 kW transmitter acted like a plasma torch gone wild, first it burnt and destroyed the meter and then it arced from where the meter had been and burnt away at least three or four inches of steel from the cabinet.  When I got the call that it was off the air when I got to the site I started the transmitter and saw the purplish pink flame start burning the cabinet again. Funny thing is that while this was happening the transmitter did not go into VSWR fault. If a 5 kW can do this much damage and burn things like a Bakelite meter and steel plates a 50 kW can do way more damage and easily burn up a ATU building, I can kind see lightning starting a problem but have to wonder if you’re looking at damage that occurred because of the lightning but was also result of the output of the transmitter? Also do you ever do base current readings, not via Delta loop but with a real thermocouple meter? The couple people I know who work with the 50 kW stations always describe doing the base readings as an experience.

The transmitter is a Harris DX-50, and its VSWR trip was working FB as of last week. (I know, I accidentally tripped it during a pattern change test- LOL) There is also a VSWR trip test built into the transmitter. I've seen the box trip offline due to a nearby lightning strike maybe a mile away. Also, the logging in the remote control indicated a VSWR trip and power shutdown about the time the fire started. The tower ATU was a Kintronics inside a steel enclosure. Completely melted, the coils of copper tubing lying in the rubble were inside the steel enclosure. While there are a few thermocouple meters lying around, we always use the modern Delta ammeters built into the gear. About 32 amps of aref into that tower.

This is the worst damage I have ever seen, it's gotta be the result of one of those dreaded positive lightning bolts..?

looks like the resistance of the tower is a lot lower than the resistance of the ground system.

That damage looks "appropriate" considering the occasion.  I assume that the coil of copper tubing seen in the wreckage was once part of the tuning network.  Looks like the EMF in the lightning just literally sucked the coil together.   I have worked on several station's ATU's after a lightning hit and am reminded each time of the force generated by a lightning bolt.  G3 and G4 mica capacitors were vaporized-all that was left were the end plates.  The edge wound inductors were sucked together like a slinky.  The thermocouple base current meter was nowhere to be seen except for the two brass bolts that used to connect to it.

I built and still maintain a 6 tower 50kw site that, when we built it, installed a "cage" at the top of each tower (260') and after 13 years, have never suffered a direct hit that damaged anything in the ATU or tuning houses.  I've been inside the transmitter building during storms and have occasionally heard a few "snaps" from inside the phasor during thunderstorms, but nothing that appeared (or sounded like) a direct hit.   Like Bill's site, we also have a Harris DX-50 as the main, and the only thing that's happened to the transmitter in 13+ years is a few VSWR trips during storms.

When we built it, we used all state of the art techniques, perimeter straps,  120 1/2 wave radials for each tower, etc.  Aside from needing to replace a few contacts from the ATU contactors, so far at least, lightning has not caused any serious damage or taken the station off the air. 

Geez, I hope I haven't spooked it now.   :-X  .....I'm getting too old and fat to climb around that much any more.

73
Ted W8IXY

Looking at picture number one it looks like you can see the remains of the signal turn loop in the feed from the ATU building to the tower. So much for the inductance of the one turn protecting the ATU, with the lightning melting the ATU and all that how did the tower lighting circuit do? Can see the Austin ring looks ok. Do you have regular lights or LEDS on the tower? Have recently changed out all the side markers on my towers to LED lights and was wondering how they would do in a direct strike on the tower.

The Austin transformer is torched. The top support became unwelded from the core/winding from the blast. You can see the metal from the top support melted and dripped down the side of the coil which is now dangling by its wires. Tower has regular incandescent beacon lighting, The lighting control box has the front cover blown off of it. The whole enchilada is destroyed. Well, maybe the light bulbs on the stick survived...

Bill

Don't want to throw gas on the fire, but from the pic of the tower bottom, the concrete form that the tower rests on is leaning off to the side at a pretty decent angle... fyi.

                                    _-_- bear