Whats this coax in a fruit jar stuff?

Let me see if I can sum up what rich is saying, and if I'm mistaken he can correct me. Basically there are three scenarios.

1. No grounding but good static disapation on the system. Charge doesn't collect due to static disapation and hopefully no lightning strike. If no strike, no damage.

2. Grounding (insufficient) and no static disapation on the system. Charges collect on the antenna (because it is connected to the ground) and in the sky until lightning strikes, antenna-to-sky. Equipment is damaged.

We assume that if you don't know to do anything for static disapation, you won't know how to sufficiently ground either. So, if you ground your system, but don't do anything for static disapation, you will be worse off because you are making your antenna the tallest thing with charge on it and giving a great path to your equipment

3. Sufficient grounding and static disapation on the system. Charge doesn't collect because of static bleedoff, and if it does the equipment isn't damaged do to sufficient grounding.



So, grounding attracts lightning to the antenna, but a static disapator deters it. A static disapator is the ounce of prevention (preventing the strike), and grounding is the pound of cure (if a strike does occur).

QRN;

Yes, I see where you are coming from now, if you include static dissipation in your grounding schemes. I think we both agree on the practical issues. However, the problem is that the average radio operator hears "grounding" and immediately drives a single 5 ft. galvanized rod into the ground 3-4 feet. they then clamp a 10-12ga kinked wire to the tower leg with a hose clamp and attach it to the ground rod. They might even use a bronze clamp there. They don't usually think to bond the tower sections to each other and don't even think about static dissipation. This is the danger of telling people to ground. These poor grounds will not carry the current of a lightning strike. Also, the matching sections of most amateur antennas will fail, or develop so much resistance during a strike, that the voltage will find an easier path to ground through the equipment. Dissipating the positive charge that builds on the antenna structure is the easiest way to prevent damage for the average person.

By the way, if grounding does not attract lightning, then why to the power companies string a ground wire over the top of the high voltage transmission lines? They call them shield wires. They are there to attract and absorb the lightning strike instead of the main lines.

thetnhillbilly;

Your summation is quite accurate. The difficulty in explaining this whole thing arises from the positive ions involved. Most people think of the earth and grounding to it, as if they were hooking up to the negative terminal of a battery. It is counter-intuitive to think of a positive charge traveling through the ground wire and up a tower.

I prefer the ounce of prevention route. QRN believes in using a belt and suspenders. His way is good, also.

Rich

There is no doubt that grounding is critical, but poor grounding and cable routing can make things just as bad as not having any, if not worse.

The nature of lightning (charge) means any conductive object that is high in the air will take a strike before an insulator at the same height. So an antenna will become a possible path of discharge should a strike occur anywhere nearby - it needs protection added.

One of the biggest mistakes the novice makes is to string the coax through the air and bring it straight into the shack. Even if the coax is "always" disconnected when not in use, the energy delivered through the coax end into the shack area is enough to cause serious damage...

The coax needs to be brought straight down the tower, tree, mounting post, and then connected to a ground bonded lightning suppressor right there. The ground rods need to be uniformly spaced around the base of the tower to dissipate energy in a uniform pattern - energy dissipation saturation is a bad thing. The ground cables and straps need to be adequately sized using straight sections to limit parasitic inductance and buried to help dissipate energy.

The coax should then be buried, or placed in a conduit, when bringing it back towards the shack. Before bringing the coax into the shack, there should be another ground system installed at this location with lightning protection installed here too. The installation should follow the same practices used at the base of the tower. Oh, and one more thing, this ground connection needs to be bonded via cable to the service entrance utility ground or there will be ground loop potential between the outlet hot/nuetral/ground and equipment chassis's.

Now, to really make sure the equipment is protected, all of the equipment in the shack needs to have its own ground connection to a single point connection (bus) that connects via a single ground cable directly to the outside ground system.

If any of the shack equipment is grounded using a daisy chain ground connections, there is enough energy in a strike to cause the various equipment to float at different reference voltages, which can be very large in magnitude, so possible/probable damage is likely due to the currents and voltages present.

In this case, an ounce in prevention is worth more than you can imagine...

Just my $0.02

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How and why does an airplane get hit by lightning? It is not grounded and sometimes catastrophic results happen. quote]

If memory serves my right there has been only one case of lighting bring down an airplane and it was in the late 50's, I don't remember what kind it was. I flew commercaily for 25 years and like all commercil pilots if you fly long enough you will get hit. I have been hit once over AZ and it entered the tip of the nose and exited the tail and knocked one of the generators off line. That by the way is probably what was going on during your flight when the lights were going off and on, the crew was re-setting the gen's. Now what does happen quite often is aircraft will not be bonded good or not have enough static wicks
and if your going fast through light rain or ice crystals the aircraft will build up a static charge so great that when it discharges it will blow holes in the plane, I have had that happen two or three times.

After reading this thread, I thought I'd put in my 02. First of all, putting the end of the coax in a fruit or pickle jar is a myth, a very dangerous one at that. I know a guy several years ago that swore by it.....his day came, lightning hit his antenna (aluminium groundplane), came in to the house....exploding the jar and setting his house on fire (house was saved). He was told that had he been in the same room as the jar, he could have been seriously injured or killed either by lightning, flying glass, fire or all the above. Also aircraft can and do get struck by lightning, I know this because I used to work for an air freight company and have seen the results of a strike on a DC-8, and how glad the flight crew was to get out of that plane.

wow!

great discussion guys!

HamminX, thanks for the insights, i am beginning to get a new perspective on this stuff.

so, what steps can the averge joe ham op. take to provide good static dissipation on their grounding system?

lets say, for example, an alum. groundplane antenna, on a metal mast going all the way to the ground.
shack would be on the first floor.

i imagine this describes a large number of current radio setups.

loosecannon

PLUTO said:

After reading this thread, I thought I'd put in my 02. First of all, putting the end of the coax in a fruit or pickle jar is a myth, a very dangerous one at that. I know a guy several years ago that swore by it.....his day came, lightning hit his antenna (aluminium groundplane), came in to the house....exploding the jar and setting his house on fire (house was saved). He was told that had he been in the same room as the jar, he could have been seriously injured or killed either by lightning, flying glass, fire or all the above. Also aircraft can and do get struck by lightning, I know this because I used to work for an air freight company and have seen the results of a strike on a DC-8, and how glad the flight crew was to get out of that plane.

Click to expand...

Ditto. In 1977 during the height of the CB popularity, there was a case in Shelby, NC, reported in that town's paper, that lightning hit a coax in a Mason jar and exploded severely injuring several members of a family! Mostly by flying glass! They were lucky they were not killed!


CWM

Hey, this guy has a nifty idea...about 1/2 way down the page:

http://www.athensarc.org/ladder.htm

Please explain how you 'ground' a dipole? Plus, just fill that mason jar with some corn and if 10 million jigawatts hits it, you will have some potent 'White Lightening'.

kc4eoe said:

Please explain how you 'ground' a dipole? Plus, just fill that mason jar with some corn and if 10 million jigawatts hits it, you will have some potent 'White Lightening'.

Click to expand...

Put a choke across the center conductor and shield. Pass the jar.

Old thread, but interesting.
As you were!

I am planning to put up a 4 element Sirio and am going to redo my station ground. I am going to add a box outside the shack to bring the coaxes and ground into. I Plan on using the Polyphaser devices on the coaxes and the MOV devices on the individual rotor cable conductors. This guy makes some really nice boxes, but I already have a junction box that I salvaged from an old machine that was being dismantled. It has epoxy paint and a urethane door gasket. I just have to figure out a good way to mount it to the vinyl siding.

https://www.kf7p.com/KF7P/JunctionsBoxes.html

Here is some old information about station grounds:

https://www.w8ji.com/station_ground.htm