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
All original content copyright, © 2011-2026. Edward Shore. Unauthorized use and/or unauthorized distribution for commercial purposes without express and written permission from the author is strictly prohibited. This blog entry may be distributed for noncommercial purposes, provided that full credit is given to the author.
