1. What is an Off Center Fed Dipole?

An Off Center Fed Dipole (OCFD) is a variation of the standard dipole antenna where the feed point is not at the center (50%) but offset, typically at 33% from one end. This configuration provides multi-band capabilities and different impedance characteristics.

2. How Does the Calculator Work?

The calculator uses the standard dipole formula with a 33% feed point:

Where:

• \( L \) — Total length of the dipole in feet
• \( f \) — Frequency in MHz

Feed Point: The calculator positions the feed point at 33% of the total length from one end, which typically provides an impedance around 200 ohms.

3. Advantages of OCF Dipole

Details: The off-center feed creates multiple current maxima at different frequencies, allowing the antenna to work on multiple bands without traps or matching networks. It often provides good performance on fundamental and odd harmonics.

4. Using the Calculator

Tips: Enter the desired operating frequency in MHz. The calculator will provide the total length and optimal feed point position. For multi-band use, calculate for the lowest frequency you plan to use.

5. Frequently Asked Questions (FAQ)

Q1: Why use a 33% feed point?
A: The 33% feed point provides a good compromise between impedance matching and multi-band performance, typically presenting around 200 ohms impedance.

Q2: What kind of balun should I use?
A: A 4:1 current balun is commonly used to match the ~200 ohm impedance to 50 ohm coax.

Q3: How high should I install the antenna?
A: For best performance, install at least 1/2 wavelength above ground at the lowest operating frequency.

Q4: Can I use this for multiple bands?
A: Yes, OCF dipoles often work well on fundamental and odd harmonics (e.g., 40m, 20m, 15m, 10m).

Q5: What about the radiation pattern?
A: The pattern is similar to a standard dipole but may have slightly different lobe structure on harmonics.