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EFHW Antenna Length Formula:
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The EFHW (End-Fed Half Wave) antenna length calculation determines the optimal length for a 5/8 wave antenna based on the operating frequency. This configuration provides good radiation efficiency and impedance matching characteristics.
The calculator uses the EFHW antenna length formula:
Where:
Explanation: The formula calculates the physical length of a 5/8 wave antenna based on the operating frequency, using the standard conversion factor of 468 for velocity factor in wire antennas.
Details: Accurate antenna length calculation is crucial for optimal antenna performance, proper impedance matching, and maximum radiation efficiency. An incorrectly sized antenna will have poor performance and high SWR.
Tips: Enter the desired operating frequency in MHz. The frequency must be a positive value greater than 0. The calculator will provide the optimal antenna length in feet for a 5/8 wave configuration.
Q1: Why use a 5/8 wave antenna instead of other lengths?
A: A 5/8 wave antenna provides a good compromise between gain, radiation pattern, and physical size, often offering better low-angle radiation than shorter antennas.
Q2: What factors affect the actual antenna length needed?
A: Actual length may vary based on wire type, height above ground, nearby objects, and environmental factors that affect the velocity factor.
Q3: Can this calculator be used for any frequency?
A: Yes, the formula works for any frequency, but practical considerations apply for extremely high or low frequencies.
Q4: How accurate is this calculation?
A: The calculation provides a good starting point, but final tuning is usually required to achieve optimal SWR and performance.
Q5: What about impedance matching for EFHW antennas?
A: End-fed antennas typically require an impedance matching network or transformer, as their impedance is not 50 ohms at the feed point.