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End Fed Half Wave Antenna Formula:
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An End Fed Half Wave (EFHW) antenna is a type of wire antenna where one end is connected to the transmitter/receiver and the other end is left open. It's popular among amateur radio operators for its simplicity and effectiveness, especially in portable operations.
The calculator uses the formula:
Where:
Explanation: This formula calculates the physical length of a half-wave antenna for a given frequency, which is optimal for efficient radiation and reception.
Details: Proper antenna length is crucial for maximum power transfer, impedance matching, and efficient signal radiation. An antenna that's the correct length for the operating frequency will perform significantly better than one that's not properly tuned.
Tips: Enter the desired operating frequency in Hertz (Hz). For best results, use the center frequency of the band you plan to operate on. The calculator will determine the optimal half-wave length for your antenna.
Q1: Why is a half-wave antenna length important?
A: A half-wave antenna is resonant at the operating frequency, providing better impedance matching and more efficient radiation than random lengths.
Q2: Does this calculation account for the velocity factor?
A: This calculation provides the theoretical length in free space. For practical antennas, you may need to apply a velocity factor (typically 95-98% for wire antennas) to account for the surrounding environment.
Q3: Can I use this for multi-band operations?
A: An EFHW antenna designed for one frequency will work on odd harmonics (e.g., an antenna cut for 7MHz will also work on 21MHz), but may require additional impedance matching for optimal performance.
Q4: What about impedance matching?
A: End-fed half-wave antennas typically require an impedance matching transformer (often 49:1) to match the high impedance at the end of the antenna to the standard 50-ohm transmitter output.
Q5: Are there safety considerations with end-fed antennas?
A: Yes, end-fed antennas can develop high voltages at the feed point and far end. Proper insulation and safety precautions are necessary, especially when operating with high power.