TI-84 Evo Basic: Half-Wave Dipole Antenna Length
Introduction
The length of a half-wave antenna is calculated by:
L = λ / 2 = (VF * c) / (2 * f)
VF: Velocity Factor. This can be calculated or given from a table. The program on this blog uses a table of values (see Velocity Factors Used below)
c: Speed of Light in a Vacuum. c = 299798458 m/s ≈ 983571056.43 ft/s
f: Frequency in Hertz.
L: length in meters
There is a commonly used formula for length in feet:
L = 492 * VF / f
where f: Frequency in Megahertz (10^6 Hz)
Where does the 492 come from? The speed of light in feet is used:
c / (2 * 10^6) = 983571056.43 / (2 * 10^6) ≈ 491.78553 (rounded to 492)
(f had to be converted to Hz)
Velocity Factors Used
Polyethylene Coaxial Cable (POLYTH. COAXIAL): VF = 0.66
Form/Air Coaxial Cable (FORM/AIR DIELECTRIC): VF = 0.84 (average)
Solid Dielectric Twin Lead (SOLID DIELECTRIC): VF = 0.82
Open Wire Line (OPEN LINE WIRE): VF = 0.98 (average)
(see source, Gilani)
TI-84 Evo TI-BASIC Program: DIPOLE
Code:
“EWS 2026-07-08”
ClrHome
Disp “HALF-WAVE DIPOLE ANTENNA”
Input “FREQUENCY IN MHZ? “, F
Menu(“TYPE OF ANTENNA”, “POLYTH. COAXIAL”, 1,
“FOAM/AIR DIELECTRIC”, 2, “SOLID DIELECTRIC”, 3,
“OPEN WIRE LINE”, 4)
Lbl 1: .66 → V : Goto 0
Lbl 2 : .84 → V : Goto 0
Lbl 3 : .82 → V : Goto 0
Lbl 4 : .98 → V : Goto 0
Lbl 0
299792458 * V / (F * 1E6) → W
W / 2 → L
Disp “WAVELENGTH (M):”, W, “LENGTH (M):”, L
Examples
Example 1:
Inputs:
Frequency: 15.5 MHz
Foam/Air Dielectric
Output:
Wavelength: 16.24681708 m
Antenna Length: 8.123408539 m
Example 2:
Inputs:
Frequency: 40 MHz
Open Line Wire
Output:
Wavelength: 7.344915221 m
Antenna Length: 3.627457611 m
Sources
Gilani, Amin Shah. “Essential Equations for Amateur Radio Operators: A Handy Reference” June 24, 2023. Accessed July 2, 2026. https://blog.gilani.me/2023/06/essential-equations-for-amateur-radio-operators-a-handy-reference/ (Note: some of this was written using AI)
Glover, Thomas J. and Young, Richard A. Desk Ref Sequoia Publishing, Inc: Anchorage, AK 4th Edition, January 2022. pg. 326
Omni Calculator “Dipole Calculator” Last updated January 17, 2025. Accessed July 10, 2026. https://www.omnicalculator.com/physics/dipole
Eddie
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