Where to connect the HF antenna when not in use?

[neazoi]

Hi,
Currently I disconnect the antenna connector when not in use, so that I avoid burning the rigs front ends during storms etc.

But what is the best solution?

1. Disconnect the antenna?
2. Connect the antenna to the mains ground? (an RF ground is not available, the antenna is balanced)
3. Connect the positive and negative of the antenna with a discharge tube?
4. A combination of the above?

 

[vfone]

Connecting the antenna to the mains ground is the worst solution and should be avoided in any cases.
The best is to make your own separate ground, designated only for your shack.
Check this video how to make your own ground connection:

Be sure that the ground rod is introduced vertically into the ground (at least 1m). Some people mistakenly place the ground rod horizontally, at few cm under the ground.
When you get a solid and separate ground connection, you can connect the antenna directly to that ground, or through a discharge tube.

 

[neazoi]

The best is to make your own separate ground, designated only for your shack.

I am afraid this is not possible to make a separate ground (no ground near).

Remember I am talking about a disconnected antenna, so the purpose of grounding it would be to send the positive charges from the ether to the ground. I am not talking about using this ground for rig or transmitting purposes. So why do I need an RF ground?
The other way, use a discharge tube to "consume" these charges. Or just leave the antenna disconnected, if nothing else can be done. So which one should I prefer?

 

[FvM]

Nobody suggested a RF ground, rather a lightning rod ground. The problem is with possible lightning strikes to the antenna. Without a separate ground, the lightning strike jumps over to the next power cable, possibly destroys electrical devices or hurts persons, maybe also set fire to your house.

A discharge tube can only "consume charges" when it's connected to a good ground, it may also clamp indirect lightning overvoltage if the antenna stays connected to the receiver.

For indirect lightning effects, e.g. occuring when a lightning strike happens in the vicinity, the classical suggestion of disconnecting the antenna cable (and the receiver power) still makes sense.

 

[neazoi]

For indirect lightning effects, e.g. occuring when a lightning strike happens in the vicinity, the classical suggestion of disconnecting the antenna cable (and the receiver power) still makes sense.

Yes I do not say that the antenna or electronics could survive a direct lighting strike. I refer to the static (positive) built on long antenna wires which could attract direct lighting. It is this I am trying to avoid. So you say to just disconnect the connector from the rigs, ok.
How about grounding both the central conductor and the braid of the coaxial to the house mains ground? Wouldn't that simply force the positive charges to the house ground so that they do not stay on the antenna? Remember, I am talking only with the cable disconnected from the transceivers.

 

[betwixt]

I refer to the static (positive) built on long antenna wires which could attract direct lighting.

If I understand you, it isn't the devastation of the lightning strike that concerns you but the increased chance of the antenna being hit if it already has a charge on it. To be honest, I don't think lightning would be any more likely to hit the antenna whether it was grounded, tied to mains earth or left floating. A few volts compared to the Megavolts of the strike would make an insignificant difference.

If possible I would ensure that any very high voltage has a discharge path to the real ground if possible to stop a strike passing high current through anything else. If static build up on the antenna worries you, wire a 1M resistor from the antenna to ground to leak any charges away. A value that high wouldn't upset any RF on the wires.

Brian.

 

[neazoi]

If static build up on the antenna worries you, wire a 1M resistor from the antenna to ground to leak any charges away. A value that high wouldn't upset any RF on the wires.

You mean the RF ground?
1M shunt to gnd when operating 100W through the coaxial????

 

[volker@muehlhaus]

To be honest, I don't think lightning would be any more likely to hit the antenna whether it was grounded, tied to mains earth or left floating.

Lightning will go the "easiest" (smallest impedance) path, so grounding would make your antenna more "attractive" in my opinion.

 

[betwixt]

You mean the RF ground?
1M shunt to gnd when operating 100W through the coaxial????

Sorry for being ambiguous, what I meant was you could connect 1M to real ground, or even mains earth to discharge static from the disconnected antenna (like an anti-static wrist strap works) and it could be left connected without having any adverse effect when the antenna was put back into use.

I try to visualize this from the lightning bolts view - it wants to land on something as near to ground potential while being as close as possible. It 'sees' a contour map below it where peaks are the easiest path to aim for, the contours are complex as they follow natural and man-made structures on the ground. Just about anything higher than your antenna would be a better landing choice and the difference between a floating or grounded antenna would make little difference unless it was the tallest structure around. It is true that grounding it might make a small difference but then consider that if it is left floating and it was hit, the antenna and cable would still find another route to ground and the chances are it would be through something inside your house!

Brian.

 

[neazoi]

Lightning will go the "easiest" (smallest impedance) path, so grounding would make your antenna more "attractive" in my opinion.

The way I had that on my mind has that the ground has "negative" potential and the lighting has negative so they repel. But the objects onto the ground may develop positive potential on their top. And this is what attracts lighting according to the "map" you said. I might be wrong though.

 

[betwixt]

The 'normal' static potential in dry air, which is what you mostly have in your region, is about 250V/m. I'm not sure how high your antenna is but I would guess the potential is relatively small compared to the overall PD of a lightning flash. It is a matter of proportion, almost certainly a flash would hit something even slightly higher nearby than your antenna.

Brian.

 

[volker@muehlhaus]

It is a matter of proportion, almost certainly a flash would hit something even slightly higher nearby than your antenna.

It really depends what is the smallest impedance path for the flash to get to ground. High but isolating will not be hit.

We have a nice demonstration at Deutsches Museum Munich in their high voltage lab.

Buildings and church at minute 8:30

 

[vfone]

I know that lightening is a very common phenomenon in Greece:

Real Time Lightning Map

See lightning strikes in real time across the planet. Free access to maps of former thunderstorms. By Blitzortung.org and contributors.

www.lightningmaps.org

When is about safety, myself I would never say that the ground is too far. Exists earth ground connections placed at tens of meters far from a radio shack.