RF earth of antenna and counterpoise

The RF ground (earth of the high frequency) is very important in antennas of the earth types such as a long wire antennas and the rod antennas. When it is not possible to ground it to the earth, it is effective when the one that is called a counterpoise is used.

Importance in RF ground of earth type antenna

The RF ground of the earth type antenna is a part of the antenna. For instance, it is good and the electric wave doesn't fly only in having extended the rod antenna in the handicap transceiver of CB (citizen's band of 27MHz) and the handicap transceiver of 50MHz of amateur radio.

Does the electric wave often fly far with the transceiver in the hand firmly, and when the transceiver is put, has not it been experienced not to communicate well? The human body does the role of the RF ground (earth) to this.

I used the whip antenna of building at this time into though I had communicated with the AM handicap machine named FD-AM3 of 50MHz with each bureau from Ontakesan in Ome City, Tokyo to the capital district neighboring prefectures when I was a university student. However, the flight of the radio wave was a little undesirable.

At this time, the lead wire of 1.5m(It was 50MHz and λ/4) was brought so that be so. When this is connected with the metal department of the transceiver, I remember other party's signal ever more strengthening. This lead wire did the role of the RF ground of the antenna (earth).

What is the counterpoise?

The counterpoise is a virtual earth installed on the earth side of the monopole antenna (long wire antenna, rod antenna, and single antenna), and the one that it doesn't ground to the earth but a big electric wire of about a metallic mesh and 1/4 wavelength was radially installed on several earth sides.

You may originally put on the ground in the one to connect a part of the antenna that should be grounded to the earth as a counterpoise, and you may separate from the ground. Moreover, it is possible to lay underground under the soil.

It becomes possible for the electric wave to fly to the distance because it can raise the feeding point if the counterpoise is set up high on ground.

The length of the electric wire becomes long or becomes a large range, and it becomes the one of a character the re-different from the earth earth though this seems just like the earth earth if it lays without insulating it under the soil.

Moreover, the ground resistance lowers very much in a frequency that is lower than the shortwave if the length of the counterpoise becomes hundreds of meters from several meters, and it is also shallow under the soil also even how many and lays.

Ground resistance and counterpoise of the earth

The loss occurs because the ground resistance of the earth becomes the radiation resistance of the antenna (radiation resistance) and a series if the earthing antenna is grounded to the earth. And, the radiation efficiency of the electric wave (radiant efficiency) worsens if the ground resistance cannot be disregarded compared with the radiation resistance of the antenna (radiation resistance).

However, the loss doesn't occur generally in a very big counterpoise compared with wavelength because resistance is almost 0.

When there is no necessary counterpoise

The power strip might work like the counterpoise when not putting it though the counterpoise is necessary in commercial power source's equipment. It becomes easy for the power strip to become like the antenna when this is a transmitter and to generate TVI (radio disturbance to the television) and BCI (radio disturbance to the radio).

There is danger to which the noise that comes from the power supply increases when this is a receiver. The counterpoise is very important like this.

It is a problem that grounds the point of the counterpoise to the earth.

The person who grounds the point of the counterpoise to the earth is this generally has the problem unusually though it is. It is because the feeding point becomes a voltage maximum point of parting by 1/4 wavelength when it grounds to the earth the counterpoise of 1/4 wavelength ahead the potential of this earth point lowers. In a word, the standing wave will get on the counterpoise.

When the case of the transmitter is touched, it is likely to get an electric shock by the high frequency when it becomes easy to generate TVI and BCI thus or transmitting power is large.

Such an example is hit when grounding it from the second floor to the earth. It is possible to solve it by connecting it through the coil that obstructs RF (radio frequency) from the viewpoint of dangerous prevention if it grounds it from the second floor to the earth. The counterpoise is used for RF.

When the building is ferroconcrete, the iron frame and the entire reinforced concrete in the building can be used as an earth by grounding it to the window frame. In this case, the counterpoise is not especially necessary.

Application of counterpoise to antenna

The corresponding part is a counterpoise in the playground of ground-plane-antena though whether it qualifies is not understood. apply to the antenna of the counterpoise