A shortwave end-fed antenna (EFHW) is a very popular type of shortwave antenna.（HF）End-fed antennas are widely favored due to their ease of installation, multi-band operation capabilities, and lack of ground requirements. Unlike traditional center-fed half-wave dipole antennas, end-fed antennas feed power at the antenna's end.
- Principle
The principle of a half-wave antenna relies on the characteristic of a half-wave resonant circuit presenting high impedance at its end.
Half-wave dipole characteristics: A wire with a length of half a wavelength (λ/2) has the maximum current and minimum voltage (low impedance) at its center point, while its ends have the maximum voltage and minimum current (high impedance). For a standard half-wave dipole antenna, we typically feed it at the center point, where the feed resistance is approximately 50-75 ohms, which can be directly connected to a coaxial cable.
End-fed principle: An end-fed antenna utilizes the high impedance characteristic of a half-wave dipole at its end. Because the end impedance can be as high as several thousand ohms (typically around 2000-5000 ohms), in order to match this high impedance to the commonly used 50-ohm coaxial cable, a high impedance transformer (typically a broadband matching transformer with a ratio of 1:49 or 1:64) is needed. This transformer converts the high impedance into an impedance close to 50 ohms, thereby achieving effective connection with the coaxial cable.
Multi-band operation: A significant advantage of a feed-point antenna is its inherent multi-band resonance characteristic. A feed-point antenna designed for a specific fundamental frequency (e.g., the 80-meter band) will also exhibit half-wavelength resonance at integer multiples of that frequency (e.g., the 40-meter band is twice the 80-meter frequency, the 20-meter band is four times the 80-meter frequency, and the 10-meter band is eight times the 80-meter frequency). This is because a conductor of length N×(λ/2) will also exhibit approximately high impedance at these frequencies, allowing for matching with a single transformer. This means that a single antenna can cover multiple amateur shortwave bands, such as 80 meters, 40 meters, 20 meters, 15 meters, and 10 meters.
- Advantages
Easy to set up: Only requires one support point to hang the antenna end, and the other end can be freely lowered or extended horizontally, without the need for complex two-point symmetrical supports. Ideal for outdoor installations, QRP (low power) operation, or users with limited space.
Multi-band operation: This is its biggest advantage. With a single antenna and a matching transformer, it can cover multiple amateur radio shortwave bands (such as 80 meters, 40 meters, 20 meters, 15 meters, 10 meters, etc.), greatly simplifying the antenna system.
No ground plane/counterpoise is required: Unlike vertical antennas, end-fed antennas do not require a complex radial ground plane. While an inductor (or balun) is still ideally needed at the feed point to suppress common-mode current on the coaxial cable, similar to that used with center-fed dipole antennas, the grounding requirements are significantly lower than those for vertical antennas.
Excellent concealment: A thin, long cable can be easily retracted or blended into its surroundings when not in use, providing good concealment.
- Disadvantages
High Voltage Danger: The feed point is a high-voltage point. During transmission, especially at high power levels, there will be relatively high RF voltages near the feed point, posing a risk of electric shock. It is essential to ensure that the feed transformer and connecting parts are well insulated and kept away from areas accessible to humans.
Common-mode current in coaxial cable: Due to asymmetrical feeding, the outer shield of the coaxial cable is prone to generating common-mode currents, which cause RF energy to flow back into the receiver, causing interference.（RFI/EMI）This can affect the performance of the transmitter and receiver, and may cause radio equipment itself to generate RF voltage. To suppress common-mode current, it is strongly recommended to install a high-quality common-mode choke or balun (typically a 1:1 current balun) at the output end of the transformer (near the coaxial cable connection).
Matching transformer efficiency: Transformers inherently have some losses, especially at high power levels, which can lead to heat generation and reduced efficiency. Poor-quality transformers can result in even greater losses and overheating.
Frequency, impedance, and resonant point sensitivity: Although it is a multi-band antenna, the actual resonant points and impedance for each band may not be perfectly accurate. Optimal matching can be achieved by trimming the antenna length or adjusting the transformer.
Environmental Sensitivity: The impedance and radiation characteristics of the antenna end (excluding the feed point) are significantly affected by the surrounding environment, such as buildings, trees, and ground.
- Installation method
The installation of end-fed antennas offers relative flexibility, and here are some common methods:
Horizontal Mounting:
This is the most common method. The antenna cable is laid horizontally, with one end connected to the feed transformer and the other end pulled up to a high point (such as a tree, mast, or building) using an insulated rope.
Advantages: Low radiation angle, suitable for long-distance DX (DX = distant/long-range).
Requirements: Requires two support points, but since one end is powered, the height of one of these points can be relatively flexible.
Sloped-supported structure (Sloper):
The power supply end is located at a higher elevation, with the antenna angled downwards.
Advantages: Only requires one high point for support, making installation very simple; sometimes exhibits directional properties in a specific direction.
Requirement: High point support.
Vertical Mounting:
The antenna is mounted vertically.
Advantages: Minimal horizontal space usage, good all-around performance, low angle radiation suitable for DX (long-distance) communication.
Requirements: The power supply transformer should be located near the ground, and the antenna needs to be securely supported.
Off-site installation:
Ideal for use in outdoor operations such as POTA (Parks on the Air) or SOTA (Summits on the Air). The antenna end can be extended using a fishing rod, branch, or other lightweight support.
Advantages: Fast deployment and disassembly.
Key components:
Wire: Used to create the antenna, the length is determined based on the lowest operating frequency ({length (meters)} = 142.5 / {frequency (MHz)}, for example, a 80-meter band requires approximately 40 meters of wire).
High-impedance transformer: Typically with a ratio of 1:49 or 1:64, to match the high impedance at the antenna end to a 50-ohm coaxial cable.
Common-mode chokes/Barren: Strongly recommended to be installed at the transformer output (before connecting coaxial cables) to suppress common-mode currents.
Insulator: Used to secure both ends of the antenna and provide insulation.
Support rope and support: Used for suspending the antenna.
- Electromagnetic wave mode
When a half-wave antenna is used for transmitting, its electromagnetic pattern is similar to that of a center-fed half-wave dipole antenna. However, due to the asymmetry in the feeding method, some additional considerations must be taken into account:
Main lobe and radiation pattern:
Horizontal Deployment: The radiation pattern is similar to that of a dipole antenna, with the strongest radiation perpendicular to the antenna direction (on both sides). The angle of elevation depends on the antenna height. A higher antenna results in a lower angle of elevation, making it suitable for long-distance DX communication.
Vertical antenna: Omnidirectional radiation, low elevation angle, suitable for DX, but may be less efficient for close-range communication.
Slant polarization: It has a certain directional characteristic, typically radiating more strongly in the direction of antenna descent. However, this depends on the angle of inclination and the surrounding environment.
Polarization:
Horizontal polarization: Primarily radiates horizontal polarized waves.
Vertical mounting: Primarily radiates vertically polarized waves.
Mixed arrangements (such as inverted V, oblique): These will produce mixed polarization components.
Higher-order harmonics: When the antenna operates on integer multiples of its fundamental frequency (e.g., an 80-meter antenna operating in the 40-meter and 20-meter bands), its radiation pattern becomes more complex, with multiple lobes. This typically does not affect its use as a multi-band antenna, but understanding this helps to understand its performance.
- Limitations in use
Noise pickup: Due to the high impedance characteristics of the feed point and the typical installation near the ground or radio equipment, end-fed antennas may be more susceptible to picking up nearby man-made noise (such as power line noise, computer noise, LED interference, etc.). Common mode chokes can help mitigate some of these issues.
Power limitation: The matching transformer has a power limit. If the power exceeds the rated capacity of the transformer, it may cause overheating, saturation, or even damage to the transformer.
Radio interference（RFI）: As previously mentioned, common-mode current is a common problem with end-fed antennas. If not effectively suppressed, RF energy can backflow to the radio, microphone cable, power cord, etc., causing interference with televisions/radios, speaker systems buzzing, abnormal operation of radios, and even "RF biting" phenomena.
The challenge of precise matching: While transformers can provide broadband matching, they may not achieve a perfect 1:1 SWR in certain frequency bands. This may require additional antenna tuning to fine-tune the match, or acceptance of slightly higher SWR.
High-voltage safety: The potential hazards associated with high-voltage power distribution points must be constantly monitored, especially in areas where people or pets may come into contact.
In summary, a shortwave feed antenna is a very practical and powerful type of antenna, especially suitable for amateur radio enthusiasts who prioritize simple installation and multi-band operation. By understanding its principles, advantages, disadvantages, and limitations, and by taking appropriate measures (such as using a common mode choke and observing safety precautions), you can maximize its effectiveness.
For beginners, the end-fed antenna is a very cost-effective option.
1. The finished antennas are relatively inexpensive, costing around 100 yuan (RMB) and can be found on Taobao.
2. The installation conditions are easy to meet.
3. You can achieve a good SWR without needing to adjust the antenna.
4. BG3ODZ, the leader on Bilibili, has achieved many results using an end-fed antenna. Who would you argue with?
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