1. Offset Fed Dipoles: The Quest for a Simple Multiband Wire Antenna
Hap Griffin WZ4O
July 2013

2. The Conventional Half-Wavelength Dipole
½ λ

3. Resonance and Standing Waves on an Antenna

4. Standing Waves on a Transmission Line

5. Current, Voltage and Impedance on a Dipole
Standing Wave
Current

6. Current, Voltage and Impedance on a Dipole

7. Current, Voltage and Impedance on a Dipole
Ohm’s Law: R = E/I
Impedance: Z = R ± X

8. Dipole Operated on 2nd Harmonic Frequency
Impedance
Voltage
Current
Ohm’s Law: R = E/I Impedance: Z = R ± X

9. Dipole Operated on 3rd Harmonic Frequency
Impedance
Voltage
Current
Ohm’s Law: R = E/I
Impedance: Z = R ± X

10. Dipole Operated on 4th Harmonic Frequency
Impedance
Voltage
Current
Ohm’s Law: R = E/I
Impedance: Z = R ± X

11. Dipole Operated on Fundamental and 2nd Harmonic Frequencies
Fundamental Impedance
2nd Harmonic Impedance
Feedpoint Impedance is vastly different on fundamental frequency vs 2nd harmonic

12. Fan Dipole for Two Frequency Bands
Fundamental Impedance
2nd Harmonic Impedance
Feedpoint Impedance is low on frequencies at which each dipole is ½ wavelength and very high on others

13. Dipole Operated on Fundamental and 2nd Harmonic Frequencies
Fundamental Impedance
2nd Harmonic Impedance
Feedpoint Impedance is vastly different on fundamental frequency vs 2nd harmonic
Result is very high transmission line VSWR on even harmonics, relatively low on odd harmonics

14. VSWR vs Matching Antenna Impedance to Transmission Line
VSWR = Antenna Feed Impedance
Transmission Line Impedance
Example: Transmission Line Impedance = 50 ohms Antenna Feedpoint Impedance = 75 ohms
VSWR = 75/50 = or 1.5:1

15. Dipole Operated on Fundamental and 2nd Harmonic Frequencies
Fundamental Impedance
2nd Harmonic Impedance
Feedpoint Impedance is vastly different on fundamental frequency vs 2nd harmonic

16. Dipole Operated on Fundamental and 2nd Harmonic Frequencies
Fundamental Impedance
2nd Harmonic Impedance
Feedpoint Impedance is vastly different on fundamental frequency vs 2nd harmonic

17. Dipole Operated on Fundamental and 2nd Harmonic Frequencies
Fundamental Impedance
2nd Harmonic Impedance
Feedpoint Impedance is same on
fundamental frequency and 2nd harmonic, but is higher than at a center feedpoint.

18. Impedance Transformation With a Balun

19. Dipole Operated on Fundamental and 2nd Harmonic Frequencies w/ Offset Feedpoint
Fundamental Impedance
2nd Harmonic Impedance
Balun

20. Dipole Operated on Fundamental and 2nd Harmonic Frequencies

21. Q of Offset Fed Dipole Decreases (Bandwidth Increases)

22. The Original Windom Antenna

23. Modern Version – The Offset Fed Dipole

24. Array Solutions
7-Band 2KW- $259

25. Buckmaster
7-Band 300 W - $209
7-Band 3 KW - $299

26. Radioworks
7-Band 1.5 KW - $139