What are the benefits of an EFHW antenna for 10-12 meters?
End-Fed Half-Wave (EFHW) antennas have several benefits, especially when used for the 11-meter band (27 MHz), which is popular among CB (Citizens Band) radio users and amateur radio operators. Here are some key advantages:
Simple Construction and Easy Installation:
EFHW antennas consist of a single length of wire and a matching network, making them relatively simple to construct compared to more complex designs.
They can be installed in a variety of configurations (e.g., horizontal, vertical, sloping, inverted-V) to fit different space constraints.
High Efficiency:
Since an EFHW is a resonant antenna on its fundamental frequency, it can be very efficient. The absence of significant losses typically associated with feedlines (especially in non-resonant or poorly tuned antennas) can lead to better performance.
Low Profile and Stealth:
EFHW antennas can be made less conspicuous than large beam or vertical antennas, which is advantageous for those in restrictive environments (like HOA-regulated neighborhoods).
No Need for a Ground Plane:
Unlike quarter-wave verticals, an EFHW does not require a ground plane. This makes it a good choice for installations where establishing a good ground system is difficult or impossible.
Multiband Operation with a Tuner:
While naturally resonant at the half-wave frequency, with the addition of an antenna tuner, EFHW antennas can often be used effectively on multiple bands.
Good for Portable and Field Use:
Due to their simplicity and ease of installation, EFHW antennas are popular for portable operations, like field days, camping, or emergency communications setups.
Low Take-Off Angle:
When installed properly, especially in a horizontal or inverted-V configuration, EFHW antennas can have a relatively low take-off angle, which is beneficial for long-distance, or DX, communications on the 11-meter band.
Cost-Effective:
They can be made with common and relatively inexpensive materials, making them a cost-effective solution for many radio operators.
Despite these benefits, it’s important to consider the specific requirements of your operating environment and goals. For instance, the high impedance at the feed point requires a good matching network (like a 49:1 unun), and the full half-wave length for the 11-meter band (around 17 feet or 5.2 meters) might be a constraint in some settings. As with any antenna, optimal performance depends on proper design, installation, and tuning.
EFHW antenna design for 11 meters (27 Mhz)
Designing an End-Fed Half-Wave (EFHW) antenna for a specific frequency, like 27 MHz, involves several considerations, including the physical length of the antenna, the materials used, and the matching network required to handle a high power level like 2000 watts PEP (Peak Envelope Power). Here’s a basic approach to designing such an antenna:
Calculate the Length of the Antenna:
The formula for a half-wave antenna is: 468 / Frequency in Mhz.
For 27 Mhz, the formula 468 / 27 = ~ 17.33 feet of 12 or 14 AWG copper wire.
Design the Matching Network:
An EFHW antenna presents a high impedance at the feed point, typically around 2500-5000 ohms.
A matching network (like a 49:1 Unbalance input) is necessary to match this to the 50-ohm impedance of most transceivers.
The matching network components must be rated for 2000 watts PEP. This often means using a large toroid core and thick wire for winding the transformer.
Consider the Feedline:
A good quality 50-ohm coaxial cable should be used, RG-400 is a good choice.
The feedline length can affect the SWR (Standing Wave Ratio) and should be considered in the overall design.
Installation Considerations:
The antenna should be installed as high as possible for optimal performance.
It can be installed in various configurations (straight line, inverted V, etc.) depending on available space.
Safety and Legal Compliance:
Ensure that the antenna is installed in a location where it does not pose a risk to people or property, especially considering the high power levels.
Check local regulations regarding antenna structures and power limits for radio transmissions.
Testing and Tuning:
Once constructed, the antenna should be tested with an SWR meter or antenna analyzer.
Adjustments may be needed to optimize performance for the specific installation.
Consider Environmental Factors:
The antenna must be built to withstand local weather conditions.
Use of weather-resistant materials and proper grounding for lightning protection is important.
Remember, this is a basic guide and assumes some knowledge of antenna theory and construction.
What ferrite core mix should I use for the unbalanced impedance of an EFHW antenna for 27 mhz?
For building an unun (unbalanced to unbalanced transformer) for an End-Fed Half-Wave (EFHW) antenna at 27 MHz (11-meter band), the choice of ferrite mix is crucial to ensure efficiency and effectiveness, especially at higher power levels. The most commonly recommended ferrite mix for this frequency range is Type 43 or Type 61.
Type 43 Ferrite:
Frequency Range: Type 43 is effective in the range of 1-300 MHz, making it a suitable choice for HF applications, including the 27 MHz band.
Properties: It provides a good balance between high frequency performance and saturation resistance, which is important for high-power applications.
For your specific case of 27 MHz, Type 43 ferrite is likely to provide a broader SWR curve, making it a more versatile choice if you plan to use the antenna across different parts of the HF spectrum. However, the actual performance will also depend on other design factors of the unun, including the number of turns, the quality of the winding, and the overall construction.
Type 61 Ferrite:
Frequency Range: Type 61 is also suitable for HF and lower VHF applications, typically up to 200 MHz.
Properties: It offers higher impedance per turn than Type 43, which can be beneficial in certain designs, especially where space is limited.
Considerations for Choosing Ferrite Mix:
Power Handling: For high power applications (like 2000 watts PEP), you need a ferrite core that can handle the power without saturating. Both Type 43 and Type 61 are generally good in this regard, but the physical size of the core also plays a role. Larger cores are typically better for higher power levels.
Core Size: Larger cores (such as T130, T140, or T200 sizes) are preferable for higher power handling and lower core losses. This is especially important for continuous duty modes like digital modes or contesting.
Turns Count: The number of turns of wire around the core must be optimized for the intended frequency and power level. More turns increase the impedance transformation but can also increase the risk of core saturation at high power.
Quality of the Core: Use high-quality ferrite cores from reputable suppliers. Poor-quality ferrites can lead to inefficiencies and heat generation at higher power levels.
Temperature Stability: Type 43 and Type 61 have different temperature stability characteristics. Depending on your operating environment, this might influence your choice.
In conclusion, both Type 43 and Type 61 are good choices for a 27 MHz EFHW antenna unun, with the specific selection depending on factors like power handling, size constraints, and availability. It’s also important to ensure that the rest of the unun’s design, including the winding technique and the enclosure, is suitable for the operating conditions and power levels you intend to use.
Further improve your 27 Mhz EFHW antenna by adding a common mode 1:1 choke to significantly reduce noise
Adding a 1:1 choke (common mode choke or current balun) to an End-Fed Half-Wave (EFHW) antenna, especially for the 27 MHz (11-meter band), can offer several improvements:
Reduction of Common Mode Currents: A 1:1 choke helps in reducing or preventing common mode currents on the feedline. Without a choke, the feedline can act as part of the antenna, picking up and radiating signals. This can lead to pattern distortion, increased noise, and potential RFI (Radio Frequency Interference) issues in your shack.
Improved Radiation Pattern: By minimizing the feedline radiation, the choke helps maintain the inherent radiation pattern of the EFHW antenna. This is particularly important for achieving the desired directional characteristics and optimal performance of the antenna.
Reduced Noise Pickup: A common mode choke can reduce the reception of unwanted noise on the feedline. This is especially beneficial in environments with high levels of electromagnetic interference.
Enhanced Safety and Reduced Interference: By limiting the RF (Radio Frequency) currents on the outer surface of the coax, a choke can reduce the chances of RF burns and interference with nearby electronic devices.
Balanced Current Distribution: A 1:1 choke ensures that the current is evenly distributed along the antenna element, which is essential for optimal antenna performance.
Implementation:
Location: The choke should be placed close to where the feedline connects to the antenna. This is usually at the end of the antenna where the matching unit (like a 49:1 unun) is located.
Design:
For 27 MHz, the choke can be made using several turns of the coaxial cable wound on a suitable ferrite core (like Type 43 or Type 31) or by using air-core winding (coiling the coax into several turns of a specific diameter).
Power Handling:
Ensure that the choke can handle the power levels you intend to use. For high-power applications, the choke design should be robust enough to avoid saturation and heat issues.
By incorporating a 1:1 choke into your EFHW antenna setup for 27 MHz, you can significantly improve its performance, reduce potential interference issues, and ensure a more consistent and efficient operation.
See youtube video:
https://youtu.be/ZH1YlzU21q8?si=uCIGEXn2w8i64FCN
and:
#344: ARRL 49:1 End Fed Halfwave UNUN transformer kit from HFKits - Build and quick bench test
