Физика
Проверенный калькулятор с прозрачной формулой
Antenna Length Calculator.
Calculates the physical length of a half-wave dipole antenna for a given frequency, considering the velocity factor of the conductor.
Ваши данные
Как это работает
- 1
Enter the operating frequency in MHz.
- 2
Enter the velocity factor of the conductor (typically 0.95 for copper).
- 3
The calculator computes the half-wave dipole length using the formula.
- 4
The result is the physical length in meters.
(299.792458 / frequency_mhz) * 0.5 * velocity_factorЧасто задаваемые вопросы
What is a velocity factor?
It is the ratio of the speed of a wave in the conductor to the speed of light in vacuum. It accounts for the slower propagation in real materials.
Why is the length half the wavelength?
A half-wave dipole is resonant when its length is approximately half the electrical wavelength, which gives a low impedance at the feed point.
Can I use this for other antenna types?
This formula is specific to half-wave dipoles. Other types like quarter-wave monopoles or Yagis have different length relationships.
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Результаты
Формула проверенаОценка только для общего руководства — проверяйте важные решения с соответствующим специалистом.
Как это работает
Calculates the physical length of a half-wave dipole antenna for a given frequency, considering the velocity factor of the conductor.
- Enter the operating frequency in MHz.
- Enter the velocity factor of the conductor (typically 0.95 for copper).
- The calculator computes the half-wave dipole length using the formula.
- The result is the physical length in meters.
Формулы
Математика, лежащая в основе этого калькулятора, изложена так, чтобы вы могли проверить результат.
Half-wave dipole length
c is the speed of light (299.792458 m/s), f is frequency in Hz, Vf is velocity factor.
Example:
Input: f = 100 MHz, Vf = 0.95
Calculation: L = (299.792458 / 100e6) × 0.5 × 0.95
Result: ≈ 1.42 m
Примеры из реальной жизни
Где этот расчет встречается в повседневной жизни.
Amateur radio
Build a dipole for a specific band, e.g., 20 meters (14 MHz).
Example: For 14.2 MHz, length ≈ 10.0 m with Vf=0.95.
FM broadcast reception
Construct a simple half-wave dipole for better FM reception.
Example: For 98 MHz, length ≈ 1.45 m.
Wireless experiments
Prototype antennas for IoT or hobby projects.
Example: For 433 MHz, length ≈ 0.33 m.
Советы и частые ошибки
Tips
- Use a velocity factor of 0.95 for bare copper wire, 0.80 for coaxial cable as a radiator.
- Cut the antenna slightly longer and trim for best SWR.
- Account for end effect by using a factor of 0.95 to 0.98.
- For a quarter-wave monopole, divide the dipole length by 2.
Common Mistakes to Avoid
- Forgetting to convert frequency to Hz when using the formula manually.
- Using the speed of light in km/s instead of m/s.
- Ignoring the velocity factor, leading to a too-long antenna.
Допущения и ограничения
- Use the stated inputs and units.
- Results are estimates for planning and education.
- Check measurements and source data before making an important decision.