What makes antenna grounding "good"?

[hacivat]

TL;DR Summary

What makes a grounding "good"?

I have purchased a mini whip antenna, made my installment plan however someone has warned me about grounding issue. He said that it makes a lot of difference if the grounding of an antenna is good and advised not to trust to electrical outlet grounding of the house.

My question is very elementary. What makes a grounding "good"? I am planning just to dig a copper rod in the garden and connect with copper cables. I mean is that what it is all about? Or is there some technical detail I should be aware of like size of the rod, soil type, any kind of extra ingredient I should put when I am burrying the rod (I saw people pouring coal for example in a video).

Any answer justifying the physics is very much appreciated. Thanks in advance...

 

[Baluncore]

I have purchased a mini whip antenna, ...

Which antenna did you buy ?
What will you use it for ?
What frequency band or range will it be used on ?
Will you transmit and receive ?

 

[hacivat]

Which antenna did you buy ?
What will you use it for ?
What frequency band or range will it be used on ?
Will you transmit and receive ?

It is a mini whip antenna. Only for receiving, 0-30 MHz. For short wave listening with an SDR mainly.
It is an active antenna by the way, which means you have to supply electricity. Designed by PA0RDT.

http://www.pa3fwm.nl/technotes/tn07.html

 

[Baluncore]

The braid of the coax will act like a counterpoise.
The ground rod should go deep enough to contact damp soil.
The ground rod will protect your radio from nearby lightning strikes.
You may find that the coaxial braid is more important than the antenna element since the signal is the differential voltage between the end of the braid and the element patch.

 

[hacivat]

Thank you, I see your point, the model I purchased is easier to handle since coax from the antenna is coming to a splitter. Splitter splits DC connection from ground connection. For DC, I'm going to use an adepter (or better option, a battery maybe). So what I have to concentrate is just the grounding part. I install a simple copper wire to the copper rod in the garden. Right?

It's good you have mentioned "damp" soil, 30 cm deep would be enough?

 

[Baluncore]

It's good you have mentioned "damp" soil, 30 cm deep would be enough?

I do not know your soil conditions, so I do not know how deep your soil is always wet. You might live on top of a sand dune in a desert.

Ground rods are not critical for amateur receive-only experiments. Push the ground rod in as far as you can so a lightning strike will go to ground, rather than through the power adapter, radio or computer. Keep lightning out of the house mains wiring.

 

[Tom.G]

A "Rule-of-Thumb" for a "good" ground is an 8ft. (2.5M) Copper rod driven fully into the soil. This is adequate for power line grounding, and lightning rod grounding if it is at or very near the base of the mast. Highly recommended if you have thunder storms in your area.

The major drawback to this is the Copper rod has to be fairly large diameter to be driven that deep; and Copper is Expensive!

For this reason a Copper plated steel rod is sometimes used.

Cheers,
Tom

 

[artis]

@hacivat As far as I'm aware there is no point in using copper which is more expensive and less robust instead just use ordinary metal that is galvanized for anti-corrosion, the resistance of soil is higher than that of copper and even steel so I'm not sure whether using copper would make a difference.
As others have pointed out the greatest difference would be achieved if the rod was driven to the point of the local ground water level.

 

[hacivat]

A "Rule-of-Thumb" for a "good" ground is an 8ft. (2.5M) Copper rod driven fully into the soil. This is adequate for power line grounding, and lightning rod grounding if it is at or very near the base of the mast. Highly recommended if you have thunder storms in your area.

The major drawback to this is the Copper rod has to be fairly large diameter to be driven that deep; and Copper is Expensive!

For this reason a Copper plated steel rod is sometimes used.

Cheers,
Tom

That was exactly the sort of thing I was asking for, thank you...

 

[hacivat]

@hacivat As far as I'm aware there is no point in using copper which is more expensive and less robust instead just use ordinary metal that is galvanized for anti-corrosion, the resistance of soil is higher than that of copper and even steel so I'm not sure whether using copper would make a difference.
As others have pointed out the greatest difference would be achieved if the rod was driven to the point of the local ground water level.

In principle yes but, practically mixing different type of metals in electrical conductivity always leads to some issues I suppose?

 

[artis]

@hacivat why do you think it always leads to some issues ?
Metals are coated frequently with a different finish, like back in the day many telephone cables used a metal wire coated with copper.
You can just look for commercial lightning rods I think, they will be ok for your application.

As for the wet soil, well it depends on where you live, some places have water in the well as high as 1 metre below ground, I have been in other places where water starts at -5 stories below ground approximately or lower.

 

[hacivat]

@hacivat why do you think it always leads to some issues ?
Metals are coated frequently with a different finish, like back in the day many telephone cables used a metal wire coated with copper.
You can just look for commercial lightning rods I think, they will be ok for your application.

As for the wet soil, well it depends on where you live, some places have water in the well as high as 1 metre below ground, I have been in other places where water starts at -5 stories below ground approximately or lower.

Oh sorry, I should have been more clear. What I mean is the difference between the work functions of metals create some activation in the contacts leading to higher risk of corrosion, oxidation (or even electrolysis if working in an aquaeous (or damped?) environment) which eventually might alter the resistivity. Although the majority of the answers given here including yours is referring to the risk of lightning which is of course the main issue I was missing by only concentrating on a low noise level antenna.

 

[artis]

yes that might be true @hacivat but trust me a rod that is used as an receiver antenna ground will have such tiny current and voltage that I doubt you will ever get any such effects.

 

[dlgoff]

Not about antenna grounding but still a nice reference:
https://www.ecmweb.com/basics/bonding-grounding/article/20891808/grounding-vs-bonding-part-1-of-12

 

[tech99]

It is a mini whip antenna. Only for receiving, 0-30 MHz. For short wave listening with an SDR mainly.
It is an active antenna by the way, which means you have to supply electricity. Designed by PA0RDT.

http://www.pa3fwm.nl/technotes/tn07.html

The purpose of the ground connection is to reduce noise pick up on the cable. I think what you are proposing will be fine. If you have noise pick up (from computers, broadband etc) then maybe put some ferrites on the cable.

 

[tech99]

The purpose of the ground connection is to reduce noise pick up on the cable. I think what you are proposing will be fine. If you have noise pick up (from computers, broadband etc) then maybe put some ferrites on the cable.

If the antenna takes a lightning strike, the miniwhip is going to be destroyed no matter what grounding you provide. The circuit of the mini whip does not seem to provide any static protection on the input so a nearby strike might also take it out. I suggest you disconnect your equipment from the antenna when it is not in use.

 

[Baluncore]

The purpose of the ground connection is to reduce noise pick up on the cable. I think what you are proposing will be fine. If you have noise pick up (from computers, broadband etc) then maybe put some ferrites on the cable.

First understand how this amateur antenna works.
The antenna is a grounded λ/4 vertical whip, made from the vertical coaxial cable braid.
The outside of the coaxial braid will pick up the vertical component of HF signals, and noise.

On top of the whip is an RF voltage sensitive patch that is capacitively coupled to the regional RF and ground. The voltage difference between the patch and the top of the coaxial whip is amplified and transmitted down the isolated transmission line, the inside of the coaxial cable.

Near the external coax braid resonant frequency most of the signal energy comes from the braid amplitude, away from braid resonance most signal comes from coupling of the patch to the incident RF electric field.

This antenna is very similar to the sense antenna used with Huff Duff = allied HFDF during WW2. There, an electric field sense whip was installed at the the top of a ship's mast above the crossed loops, and so it was necessary to compensate for the mast resonance phase ambiguity.
https://en.wikipedia.org/wiki/High-frequency_direction_finding#Description

Running the coax through a ferrite core will further isolate the antenna since the whip is no longer grounded at RF. The core will double the resonant frequency of the braid, making the coax a λ/2 dipole.

Coaxial cable is not a good lightning conductor because it has an outer dielectric insulation with Er that will slow propagation of a strike impulse. A strike will puncture the insulation and jump around the outside of the inductive ferrite core. The coaxial external insulation may start to burn.

 

[artis]

Well after all there is a reason why radio antennas are not used as lightning rods but instead special steel poles with sufficient thickness and no plastic insulation are used instead.
So my advice to @hacivat would be to focus on the radio application for the antenna and if needed use a separate purpose built lightning rod installation.

Although I don't have any data on this I haven't seen or heard many antennas being regularly hit by lighting, in fact I haven't seen that many buildings and their lightning rods hit by lighting. And I do live in an area where we have thunderstorms in the summer.

 

[Rive]

Summary:: What makes a grounding "good"?

I am planning just to dig a copper rod in the garden and connect with copper cables.

An often missed point: grounding must be well connected. It's great that you have a copper rod connecting to the groundwater, but if you have too much (sometimes even just one is too much) twists and turns (maybe: bottlenecks) along the way to the point where the grounding is actually connected, then it's no good.

 

[sophiecentaur]

A horizontal 'cross' of four wires, a quarter wave long, soldered to the Earth of the feeder and laid on the ground could be good, if you have the room (about 5m diameter but the wires wouldn't need to be the only objects there.). Many vertical monopoles for higher frequencies and mounted on chimneys, use four rods and that acts as a pretty good 'ground plane'. Having them λ/4 long presents a pretty good short circuit to take Earth currents from the outer of the feeder, which can present more or less any impedance to the feed point.

 

[tech99]

Active antennas are difficult for the reason that the feeder has very large interference pick up and there is a problem preventing this reaching the amplifier. The electric field lines from the antenna element terminate on the pole and the feeder, which seems highly undesirable as it couples interference voltages into the amplifier. A commercial active antenna I am aware of uses a large sheet of metal below the element upon which the field lines can terminate, reducing the coupling to the pole and feeder. The original version of the Miniwhip antenna was installed , I believe, on a flat metal roof, providing perfect operating conditions. I would have thought that a ground mounted position on a sheet of metal would be best. For vertical polarisation at HF, the reduction in signal compared with pole mounting will probably not be very much.

 

[davenn]

A "Rule-of-Thumb" for a "good" ground is an 8ft. (2.5M) Copper rod driven fully into the soil. This is adequate for power line grounding, and lightning rod grounding if it is at or very near the base of the mast. Highly recommended if you have thunder storms in your area.

The major drawback to this is the Copper rod has to be fairly large diameter to be driven that deep; and Copper is Expensive!

For this reason a Copper plated steel rod is sometimes used.

Cheers,
Tom

not in the communications industry and not in the power industry either in Australia or New Zealand
3 - 4 ft long 1/2 " and up to 1" diameter galvanised rods is the norm

Copper cables are commonly used as Earth mats

 

[StandardsGuy]

Summary:: What makes a grounding "good"?

I have purchased a mini whip antenna, made my installment plan however someone has warned me about grounding issue. He said that it makes a lot of difference if the grounding of an antenna is good and advised not to trust to electrical outlet grounding of the house.

My question is very elementary. What makes a grounding "good"? I am planning just to dig a copper rod in the garden and connect with copper cables. I mean is that what it is all about? Or is there some technical detail I should be aware of like size of the rod, soil type, any kind of extra ingredient I should put when I am burrying the rod (I saw people pouring coal for example in a video).

Any answer justifying the physics is very much appreciated. Thanks in advance...

If the antenna has no ground radials, then the ground on the end of the coax is an important part of the antenna. Otherwise it is only for lightning protection. A 10' piece of chain-link fence pipe is cheaper than an 8' copper rod, and will make a better ground. A hammer-drill will work well for pounding in the pipe, but a sledge hammer will do. If the ground rod is within 5' of your house, you are required to bond it to the power line ground with a large size (and expensive) cable, so I suggest it be farther than that. Use an automotive clamp or a self-tapping screw to secure the wire to the ground rod unless you are able to weld it.

Further lightning protection is desired such as a lighting protector in the coax cable or wrapping the coax around a toroid before it comes into the house.

 

[darth boozer]

It may be worthwhile to read this:
http://www.pa3fwm.nl/technotes/tn09d.html

 

[votingmachine]

A "Rule-of-Thumb" for a "good" ground is an 8ft. (2.5M) Copper rod driven fully into the soil. This is adequate for power line grounding, and lightning rod grounding if it is at or very near the base of the mast. Highly recommended if you have thunder storms in your area.

The major drawback to this is the Copper rod has to be fairly large diameter to be driven that deep; and Copper is Expensive!

For this reason a Copper plated steel rod is sometimes used.

Cheers,
Tom

I don't know the location ... but my electrician in Utah said code calls for two 8ft at least 6 feet apart. But our soil can be incredibly dry. He had stories about wrapping ground wire along long perimeters of basically dry stone.

Household plumbing is increasingly plastic rather than copper. It used to be that attaching a ground wire to the big copper water supply guaranteed conduction into a long stretch of ground. It is important to be cautious about that standard house grounding. But if the house electric ground is old-school, and attached to a long copper supply line ... I do trust that grounding.

 

[sophiecentaur]

It strikes me that there are two versions of a 'good earth'. One will protect you from lightning strike (that's the electricians version') and the other will protect you from interference and produce the sort of radiation pattern you are after. The RF Engineer's good Earth is as near as possible to the base of the antenna or, at least, will act like a large sheet of copper at a known altitude, which could be the four or more horizontal wires at the base of a monopole / whip (or even car roof).