Formula Used
Free space wavelength: λ = c ÷ f
Effective wavelength: λe = λ × velocity factor
Target wire length: L = λe × target wavelengths × (1 − end correction ÷ 100)
Electrical length: Electrical wavelengths = actual wire length ÷ λe
Electrical degrees: degrees = electrical wavelengths × 360
The calculator uses c = 299,792,458 meters per second. Matching notes are planning guides, not a replacement for antenna modeling.
How to Use This Calculator
Enter the operating frequency and choose its unit. Add a velocity factor for your wire. Use 1.0 for bare wire in open air, or a lower value for insulated wire.
Enter the desired electrical length in wavelengths. Add an end correction if you want a practical starting length. Leave actual length blank when designing a new wire. Fill it when checking an installed antenna.
Select the feed type, power, and height. Press Calculate to show results below the header. Use CSV or PDF to save the same calculated report.
Long Wire Antenna Planning Guide
A long wire antenna is a simple conductor used for receiving or transmitting radio signals. It becomes a true long wire when its physical length is at least one wavelength on the operating band. That electrical size changes when frequency changes. The same wire can act short on low bands and long on higher bands.
This calculator starts with frequency. It converts the value to hertz, then finds the free space wavelength. A velocity factor reduces that wavelength when the wire is insulated or installed near other materials. The selected wavelength ratio then produces a target wire length. An optional end correction shortens the result for practical tuning.
The actual wire field is useful for checking an existing installation. It shows how many wavelengths the wire represents at the chosen frequency. It also converts that value to electrical degrees. These numbers help explain feed behavior, pattern shape, and tuning difficulty. Longer electrical lengths usually create more lobes and deeper pattern nulls.
Matching is only a guide here. Real impedance depends on height, soil, wire diameter, feed point, nearby objects, and counterpoise design. End fed wires often need a transformer or tuner. Center fed long wires often work better with balanced line and a good tuner. A current choke can reduce unwanted feed line radiation.
Use the height input as a planning clue. Low wires may work well for regional coverage. Higher wires usually lower the launch angle and improve longer paths. For accurate contest or station design, model the antenna with ground data and supports included.
The export buttons help save records. CSV is useful for spreadsheets. PDF is useful for reports or printed notes. Compare several frequencies before cutting wire. Leave extra length during installation. Trim slowly after measuring standing wave ratio. Weather, sag, and support angle can shift the final resonant point.
Keep safety in mind. A wire near power lines is dangerous. Use strong end insulators and weatherproof strain relief. Add lightning protection where codes require it. Disconnect equipment during storms. Mark support ropes clearly. Good mechanical planning protects people, radios, and the antenna system. Document each change, because small length adjustments can produce large tuning shifts across narrow amateur bands and crowded receiving locations over time.
FAQs
What is a long wire antenna?
It is a wire antenna that is usually at least one wavelength long on the operating frequency. It can create directional patterns and multiple lobes.
Why use velocity factor?
Velocity factor adjusts wavelength for real wire conditions. Insulation, nearby materials, and installation style can make the effective electrical length different from free space.
What does target electrical length mean?
It is the desired wire length expressed in wavelengths. A value of 1.5 means the target wire is one and one-half effective wavelengths long.
Is the impedance result exact?
No. This tool gives matching guidance only. Actual impedance needs measurement or modeling because ground, height, feed point, and nearby objects matter.
Should I cut the wire to the exact result?
Leave extra length first. Install the antenna, measure it, then trim slowly. Supports, sag, and insulation can shift the final tuning point.
Can this calculator be used for receive antennas?
Yes. It is useful for receive planning too. Matching may be less demanding, but noise, direction, and placement still affect performance.
What feed type is best?
There is no single best choice. End fed wires are convenient. Center fed wires can work well with balanced line and a tuner.
Why does height matter?
Height affects radiation angle, ground loss, and pattern shape. Higher installations often improve low angle radiation for longer distance contacts.