Formula Used
The calculator uses the speed of light as 299,792,458 meters per second.
Wavelength: λ = c / f
Ideal 5/8 wave: L = λ × 5 / 8
Corrected radiator: Lc = L × velocity factor × (1 - end correction) - trim
Radial length: R = λ × 1 / 4 × velocity factor × radial percentage
Matching coil estimate: LµH = X / (2πf) × 1,000,000
Reflection coefficient: Γ = (SWR - 1) / (SWR + 1)
How to Use This Calculator
Enter your target frequency in MHz. Add the velocity factor for your chosen material. Use a small end correction for practical trimming. Enter radial details if you plan a ground plane. Add the reactance value if you need a matching coil estimate. Press calculate. The result appears above the form and below the header. Download the CSV or PDF for workshop records.
Example Data Table
| Band Example |
Frequency MHz |
Velocity Factor |
End Correction |
Use Case |
| CB |
27.185 |
95% |
2% |
Base vertical planning |
| VHF |
146.520 |
95% |
2% |
Two meter whip design |
| UHF |
446.000 |
95% |
2% |
Short vertical prototype |
5/8 Wave Antenna Guide
Why This Design Matters
A 5/8 wave antenna is popular on VHF, UHF, CB, and hobby bands. It is longer than a quarter wave whip. That extra length changes the radiation pattern. It usually lowers the angle of radiation. A lower angle can help ground wave range. It can also support strong local coverage.
Main Calculation Ideas
The calculator uses frequency, velocity factor, and end correction. Frequency sets the free space wavelength. Velocity factor adjusts length for real wire or tubing. End correction trims the physical radiator. This matters because tips and loading hardware add capacitance. The result is a practical starting length, not a final cut.
Matching and Radials
Matching is important for this antenna. A 5/8 wave vertical is not usually a direct fifty ohm load. Many builders use a base coil, matching network, or transformer. The tool gives a simple coil hint. It is only an estimate. Use an analyzer to finish tuning.
Radials also affect performance. A ground plane controls return current. Longer and more even radials usually improve stability. For mobile work, the vehicle body acts as the counterpoise. For base stations, several radials or a proper ground plane help more.
Practical Tuning Steps
Use the output as a design note. Cut the radiator slightly long. Install the antenna in its real location. Then measure SWR near the target frequency. Shorten the radiator in small steps. Recheck after each change. Save the final value for later builds.
A 5/8 wave design can be efficient. Yet placement still matters. Keep it clear of gutters, walls, and metal masts. Use good coax. Seal outdoor joints. Avoid guessing when power levels are high. Careful measuring keeps the station safer and cleaner.
Records and Safety
The calculator also converts units. You can compare feet, inches, meters, and centimeters. This makes workshop cutting easier. The CSV file stores values for records. The PDF file gives a printable summary. Both options help when several bands are being tested.
Do not treat any calculator as a license limit guide. Local rules still apply. Check band plans before transmitting. Keep antennas away from power lines. Leave space for wind movement. Label the feed line and matching parts. Good notes reduce repeat work. They also help you compare designs after real field tests and repairs safely.
FAQs
What is a 5/8 wave antenna?
It is an antenna with a radiator about five eighths of one wavelength long. It is often used as a vertical design for mobile, base, and hobby radio systems.
Why does velocity factor matter?
Real conductors and construction details can shorten the needed physical length. Velocity factor adjusts the ideal wavelength value to a more practical starting length.
Is the result ready for final cutting?
No. Cut slightly long first. Install the antenna, measure it, and trim slowly. Nearby objects and mounting height can change the final length.
Why is a matching coil shown?
A 5/8 wave vertical often needs matching at the feed point. The coil value is a rough estimate for canceling entered reactance.
Do I need ground radials?
A vertical antenna needs a return path. Radials, vehicle metal, or a ground plane can provide it. Better radials usually improve consistency.
Can I use this for any band?
Yes, enter the desired frequency in MHz. Always check local rules, band plans, power limits, and safe installation practices before transmitting.
What end correction should I use?
Small values like one to three percent are common starting points. Final correction depends on tip shape, tubing size, loading parts, and surroundings.
Why include CSV and PDF downloads?
They help save measurements, compare bands, and keep workshop notes. This is useful when testing several prototypes or rebuilding an earlier design.