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EFHW Antenna Length Formula:
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The EFHW (End-Fed Half-Wave) antenna length formula calculates the optimal length of a half-wave antenna based on the operating frequency. This formula is commonly used in amateur radio and antenna design to create efficient resonant antennas.
The calculator uses the EFHW antenna length formula:
Where:
Explanation: The formula calculates the physical length of a half-wave antenna by dividing the constant 468 by the frequency in megahertz, resulting in the length in feet.
Details: Accurate antenna length calculation is crucial for creating resonant antennas that maximize signal transmission and reception efficiency. Properly tuned antennas reduce standing wave ratio (SWR) and improve overall radio communication performance.
Tips: Enter the frequency in MHz. The value must be valid (frequency > 0). The calculator will provide the optimal antenna length in feet for a half-wave end-fed antenna.
Q1: Why is the constant 468 used in the formula?
A: The constant 468 accounts for the velocity factor of electromagnetic waves in a typical wire antenna, which is approximately 95% of the speed of light in free space.
Q2: Can this formula be used for other antenna types?
A: This specific formula is designed for half-wave end-fed antennas. Other antenna types (quarter-wave, full-wave, etc.) require different calculations.
Q3: How does antenna material affect the length?
A: Different materials have slightly different velocity factors, but the 468 constant provides a good approximation for most common wire antennas.
Q4: Should I add extra length for tuning?
A: It's often recommended to cut the antenna slightly longer than calculated and then trim to achieve the lowest SWR at your desired frequency.
Q5: Can this be used for both transmitting and receiving?
A: Yes, the formula works for both transmission and reception, as antenna resonance characteristics are the same for both operations.