Why do some antennas work better than others? It all comes down to radiation resistance. This number tells us how well an antenna can turn electrical energy into radio waves. Think of it like a water pipe – the right size lets water flow perfectly.
How To Measure Your Antenna’s Efficiency
Suppose, I am working with my radio engineering team today. We have a half-wave dipole antenna that operates at 14 MHz. The antenna length is 10 meters, and we need to know its radiation resistance to match it with our transmitter.
Calculate Radiation Resistance Step by Step
- For a half-wave dipole, use this formula:
Rr = 73 ohms (base value) - Account for height adjustments:
- Ground height = 1.5 wavelengths
- Adjustment factor = 1.05
- Put it all together:
Final Rr = 73 × 1.05
Final Rr = 76.65 ohms - Check antenna current:
- Power = 100 watts
- I = √(P/Rr)
- I = √(100/76.65)
- I = 1.14 amperes
Quick Tip:
For most practical half-wave dipoles, start with 73 ohms and adjust based on height. Every quarter wavelength change in height affects resistance by about 5%.
Why Use This Calculator?
Wrong resistance matching can waste power and cause poor transmission. The calculator helps prevent these problems and saves hours of manual testing.
FAQs:
Q: Does antenna thickness affect radiation resistance?
A: Yes, thicker antennas have slightly lower resistance.
Q: Can radiation resistance be zero?
A: In theory yes, but real antennas always have some resistance.
Q: How often should I check radiation resistance?
A: Check after installation and when making any physical changes.