End fed wire antennas are one of the simplest antennas to construct and erect. These antennas have been used for many years and provide a particularly adaptable form of antenna, especially for newcomers to radio communication.
What is often loosely termed a long wire antenna simply consists of a longish length of wire that is connected to the transmitter or receiver, preferably via an antenna tuner.
Strictly speaking a long wire antenna is just that - a very long piece of wire - many wavelengths long. However the term is widely used to describe a random length of wire used to receive and often transmit signals on the HF or short wave bands.
In reality, the term long wire antenna, should be replaced with the term end fed wire, unless it the antenna is many wavelengths long and a true long wire antenna.
What is an end fed wire (long wire)
The end fed wire antenna simply consists of a length of wire that is as high and reasonably long as possible. The wire is then connected to the transmitting and receiving radio communication station.
The antenna wire is then typically take out of the radio room, or shack and taken to a horizontal section that runs above obstructions.
Once the wire leaves the receiver, transmitter, or antenna tuner, the wire starts to act as an antenna, picking up signals and radiating them.
For best receiving performance and also to ensure that when used with a transmitter, the correct impedance is seen, an antenna tuner or antenna tuning unit, ATU should always be used.
The antenna tuner is placed between the transmitter or receiver and the antenna wire. If a tuner is not used, then the impedance of the antenna will not match that of the receiver or transmitter input and this will result in lower efficiency. Also the transmitter may have trouble matching to this, and this may result in lower power output, or even damage to the transmitter output.
A further requirement is that it is necessary to have a good radio earth - this is not the protective means earth, but an earth connection against which the long wire antenna or end fed wire antenna can work.
The wire to the earth connection should be as short as possible, otherwise the inductance etc in the wire will start to place the station at an RF potential above ground.
End fed wire length
It is often thought that an end fed wire should be a quarter wavelength long on the major band of use. An end fed wire of this length presents a low impedance at the feed point and this enables it to be matched very easily.
However the current flowing in the antenna gives rise to the radiation. Looking at the current distribution in a quarter wavelength antenna it is found that the current rises as the distance increases from the end, and reaches a maximum a quarter wavelength from the end. In other words a quarter wavelength antenna has its current maximum, and hence the maximum radiation at the feed point.
As a result the quarter wavelength antenna has its maximum radiation, and also pick up at the feed point. Typically the feed point will be next to the radio: transmitter, transceiver, or receiver and this results in local pick-up of noise etc and this can mask the wanted signals. Also for transmitters, lots of radiation occurs near the radio and this can cause interference to many other problems with electrical and electronic items. Even if the antenna is not a quarter wavelength long, some pick up and radiation will occur near the radio and this is not good.
The same is true for any antenna that is an odd multiple of quarter wavelengths long.
However, if the antenna is not an odd multiple of quarter wavelengths long, then it can be difficult to match.
End fed wire advantages and disadvantages
The long wire or end fed wire provides an ideal solution for many radio communication stations, but it is not the best option for many instances.
Before settling on the use of a long wire or end fed wire antenna, it is wise to consider both its advantages and its disadvantages.
- Low cost
- Multiband operation possible
- Simple to erect and install
- Provides multiband operation
- Can receive high levels of local interference
- Can give rise to interference to other local users
- High levels of radiation close to the transmitter can give rise to RF feedback creating odd effects.
- Requires good earth connection
Installing a long wire / end fed wire antenna
The end fed wire antenna, or as it is often called, the long wire antenna is very easy to install and it is cheap in terms of the components required.
In essence the main components required for an end fed long wire antenna are the antenna wire itself and some insulators to place at the end of the wire.
The antenna wire should be hard drawn. As copper is very soft and ductile, normal copper wire tends to stretch very quickly, and what may have been a taut antenna wire, can soon sag if the correct wire is not used.
Hard drawn copper wire has more strength and will not stretch nearly as much.
Another component that is required (but not essential) for a long wire or end fed wire antenna is the insulators. One is needed for each end of the wire, or if it is bent, anywhere that the wire comes into contact with a rope, etc.
As would be expected, antenna insulators are made from highly insulating material. They are also ribbed so that there is more surface length across which any leakage current must pass. This ensures that they have the highest possible level of insulation.
Many insulators are made of ceramic which is glazed, but many others are made from plastic - these are might lighter, but ceramic is often the preferred type.
Variants of end fed wires
Normally an end fed wire s a random length of wire erected as high and reasonably long as possible. However there are other variants on the basic theme that can be used to improve the performance.
- Multi-wavelength long wire: A true long wire antenna is multiple wavelengths long. It is found that for a quarter wavelength end fed wire, the maximum radiation is at right angles to the wire. As the wire is lengthened, it is found that the radiation pattern becomes more complicated, but the maximum radiation, and hence also the pickup, aligns progressively with the line of the antenna. The longer it becomes the more directive it becomes in the line of the antenna wire.
A true long wire, that is several wavelengths long, is therefore a directive antenna with the maximum sensitivity and radiation along the line of the antenna wire itself. This form of antenna is a true long wire antenna.Read more about . . . . multiple wavelength long wire antenna.
- End fed half wave antenna: One method of providing a multi-band antenna for the amateur radio or ham bands is to use an end fed half wave antenna. This antenna is a half wavelength at the lowest frequency of operation, and then as the other bands on which t can be used are harmonically related, it provides a multiple number of half wavelengths.
The feed impedance is high, and to enable this to match to a coaxial feeder a balun, or to be more exact an Unun (unbalanced to unbalanced) transformer is used. Ununs with a turns ratio of 9:1 are commonly used, but others with higher ratios are also used dependent upon the design. This trasnsformer acts an impedance step up to enable the low impedance 50Ω coaxial feeder to match the high impedance antenna. This type of antenna enables the antenna to be fed with coaxial cable and the feed point to be removed away from the house or radio room to a point where reception of household electrical noise will be less, and radiation of undue amounts of signal in the vicinity of the transmitter itself will be greatly reduced.Read more about . . . . end fed half wave antenna.
- W3EDP antenna: The W3EDP antenna is a form of end fed wire that has been in use for many years and was first described in 1936, it has become popular, especially with ham radio low power or QRP enthusiasts.
Read more about . . . . W3EDP antenna.
End fed wire antennas can work very well under many circumstances. They have some disadvantages, but with careful installation, they can work well and be particularly versatile offering multi-band operation.
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