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Here's what I have come to know about lightning.? The trick with lightning is less about ground and more about making sure that the lightning's energy is routed past (not through) you and your equipment.? Disconnecting the equipment is a common and effective method, so long as it can be done well before any strikes.? Being caught in the act of unscrewing that last connector when the strike occurs will get you a cameo appearance on a Saturday morning cartoon...? And, to be clear, a "strike" doesn't necessarily involve a direct hit.? Anything within miles can result in a significant local disruption.

The best approach involves two points.? First is to provide a path to Earth - where the lightning strike was going in the first place - that goes past your shack.? Lightning arrestors on all lines with a stout connection to a proper ground rod is a standard means to do this.? During a strike, the arrestor conducts the current coming down from the antenna to the ground rod, instead of letting it continue on the coax into the shack.

Second is perhaps the trickier part, and where that non-direct strike effect is dealt with.? A non-direct strike will raise the potential of the earth itself, but in an uneven way.? Closer to the strike will be higher than farther away.? The problem is that you need to make sure that all of your equipment - ALL of it - remains at a common voltage.? Note that this doesn't mean that it remains at a constant potential, but it doesn't have to.? Consider birds sitting on power lines; they don't care that they are at a kilovolt or two above ground because there's no current going through them.? Not so the squirrel with one paw on the line and another on the metal support pole.? So, make sure that everything has a common "ground" connection to each other, and to that same place the lightning arrestor is connected.? The lightning arrestor will rise in potential above ground during a strike, but if everything else rises exactly along with it, no current will flow.?

The complicating factor is when things are separated, which they usually are.? In my house, for example, the shack and its "ground window" are on one side of the house, and the electrical panel (where the equipment power is sourced) is on the opposite side.? I need to be sure that a strike doesn't raise the potential of the ground window and all of my equipment that's connected to it different from the electrical system they are plugged into.? If they did, then there would be a surge of energy through the equipment into its power cord and over to the electrical panel which has its own ground.? That means that I needed to run a wire to bond the ground stake on the ham side over to the electrical panel's ground to keep them at the same potential.? To this end we ran a fat wire (#6, I think) from one to the other.? But to this thread's comments, I did not mess with how the electrical panel manages its grounding with respect to the safety (green wire) and neutral (white) wires.? That's set by the local electrical code; here we connect them together, but that varies around the planet.? I only bonded the shack ground stake to panel ground, at the same place the panel's existing ground is attached.

Hope this helps,? (and that I got the details right!!).

Greg? KO6TH

On Sat, Nov 16, 2024 at 05:10 PM, Glenn Little wrote:

How do you prevent damage from a lightning event if everything is not referenced to one ground (earthing point)? The potential difference between the two, or more, earth points can be very substantial. This potential difference is what causes the damage.

Glenn

A single "ground" makes little or no difference. You need all aerials and power cables, Cable TV, phone cables disconnected. A strike even 100m from the utility cables (even buried electricity, phone, cable TV etc) can induce 1000s of volts and destroy front ends of TV, radio, DSL modem, cable modem, analogue dial up modem. Even blow the tops of the RS232 interface ICs on the motherboard (amazingly a plug-in RS232 card and new modem worked once they repaired the exchange, the Mobo survived).

There are reasons for a single electrical safety earth do to with ELCB / RLCB / RCCB tripping and safety. As mentioned, the UK mostly is a different scheme (3rd wire with earth to substation) to Ireland (an earth spike per meter box and no 3rd wire). Unlike USA, UK & Ireland homes are only single phase. The houses alternately use the three phases in built up areas, so don't share any electrical device connection with a neighbour without suitable isolation or barrier earth (shared TV aerials or sat dishes).

Radio earth connections want to be short to earth spike so there may be more than one.

Solar systems on a roof need the frames to a single earth to minimise static damage, useless on a direct or close strike. The battery negative should not be earthed except in certain circumstances. The neutral on an off grid PV inverter needs a single earth before the trip switch. Earthing (other than the isolated metal frames) of PV systems connected to a grid need an expert.

A Satellite dish or Aerial pole should go to a local earth spike to minimise static (dry wind) or damage from nearer but not direct hit lightning. The satellite dish electronics (ODU, LNB etc) should not be directly earthed.

It's complicated. But a single earth doesn't help with lightning. Disconnecting everything works best, but not fool proof if you get a direct hit.

See also EMP.

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How do you prevent damage from a lightning event if everything is not referenced to one ground (earthing point)?
The potential difference between the two, or more, earth points can be very substantial.
This potential difference is what causes the damage.

Glenn

In UK the "house" ground is usually connected "earth" and connected to neutral at the substation (transformer for the locality). In Ireland there is supposed to be a 1.5m approx galvanised earth spike near the meter box or grid input and the neutral and earth are bonded there. That's quieter.

Maybe 50 years ago people might have used the water pipe as an RF earth, but that might be plastic. You're not supposed to use any utility pipes, central heating pipes etc as a radio Earth.

Don't connect your own Earth spike to the mains supply Earth. They need isolated, especially on the UK system as large currents might flow. The exception might be if your neutral and earth are bonded at the meter box and go to a nearby earth spike and there is no utility company earth.

Every non-loop aerial has a "counterpoise" even if you can't see it. A vertical needs either to be driven at earth level, or have 1/4 wave or more radials or counterpoise, or a sleeve that is earthed only at drive point with an internal diameter ratio with coax outer diameter to give the 50 or 75 Ohms. An unfolded, non-loop, dipole obviously has a "counterpoise".

The end fed Zepp (so called because used on the Zeppelins as a radio aerial) doesn't seem to have a counterpoise, but has really, on the modern version the feed line is the counterpoise. Similarly the over hyped G5RV is only a proper dipole at one narrow band, otherwise the feed cable is the aerial (and partly counterpoise) and then the counterpoise is really the shack earth.

The thing to avoid is an exactly half-wave radiator or counterpoise as that has a very high impedance.

-- 
-----------------------------------------------------------------------
Glenn Little                ARRL Technical Specialist   QCWA  LM 28417
Amateur Callsign:  WB4UIV            wb4uiv@...    AMSAT LM 2178
QTH:  Goose Creek, SC USA (EM92xx)  USSVI, FRA, NRA-LM    ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"

In UK the "house" ground is usually connected "earth" and connected to neutral at the substation (transformer for the locality). In Ireland there is supposed to be a 1.5m approx galvanised earth spike near the meter box or grid input and the neutral and earth are bonded there. That's quieter.

Maybe 50 years ago people might have used the water pipe as an RF earth, but that might be plastic. You're not supposed to use any utility pipes, central heating pipes etc as a radio Earth.

Don't connect your own Earth spike to the mains supply Earth. They need isolated, especially on the UK system as large currents might flow. The exception might be if your neutral and earth are bonded at the meter box and go to a nearby earth spike and there is no utility company earth.

Every non-loop aerial has a "counterpoise" even if you can't see it. A vertical needs either to be driven at earth level, or have 1/4 wave or more radials or counterpoise, or a sleeve that is earthed only at drive point with an internal diameter ratio with coax outer diameter to give the 50 or 75 Ohms. An unfolded, non-loop, dipole obviously has a "counterpoise".

The end fed Zepp (so called because used on the Zeppelins as a radio aerial) doesn't seem to have a counterpoise, but has really, on the modern version the feed line is the counterpoise. Similarly the over hyped G5RV is only a proper dipole at one narrow band, otherwise the feed cable is the aerial (and partly counterpoise) and then the counterpoise is really the shack earth.

The thing to avoid is an exactly half-wave radiator or counterpoise as that has a very high impedance.

hi folks
got a new
Panel Unit - ETCS2518403
Main Unit - CP6778033
PA Unit - CB1152002
it works!
Ok, I try out short wave first and FM radio - 2m and 70cm should work also...
I still have to install the final unit. This is not difficult. Alignment will be according to the service manual.
In sum: it is a brand new FT-81* in an old frame *big smile*
cheers for now - Ray, DL1EGR

please check

for more details...

Am 08.11.2024 um 13:53 schrieb ly5ez via groups.io:

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Hi

Just a thought, the calibration data is contained in the control head and so by changing the main board this may now be invalid, might be worth going through the calibration process..

Got Main Unit, PA Unit.?
Put them in the FT-817 shell. Rewirering was very easy. First power-up let the display blink in 1sec. interval, no audio (ex. 160m). Current as usual...?
?[F] & [V/M] & power on - sequence on #1 start... frustrating...
Today a FT818 Display Unit comes in. Will replace the FT817 Display Unit by this and hope....
cheer for now - Ray, DL1EGR

Recent subscriber, expect to have enough time to get a grip on my 817ND now, and thankful for the resource.

73