EFOC17 as an OCFD Antenna Installation Guide

Thank you for your order! You have received 18 and 5 meters of high-quality antenna wire, 14 meters of coaxial cable (EXTRAFLEX-BURY-7), and a large ferrite choke, which can be used in several configurations. Below are practical starting dimensions and installation guidelines for this antenna.

Inverted V Configuration

• Recommended antenna wire length: approximately 16-17 meters (about 83%) (16.6m)
• Recommended counterpoise length: approximately 3-4 meters (about 17%) (3.4m)
• A practical setup is to install the antenna in an inverted V or sloping configuration, with the wire ends dropping to around 5-6 meters above ground.
• Recommended feed point height: 9-10 meters
• Compared with a perfectly flat-top installation, an inverted V often lowers the feed impedance somewhat, can shift resonance dips slightly, and usually gives a more omnidirectional radiation pattern.

Choke Placement and Feedline Isolation

A high-impedance common-mode choke (high-Z choke) is required directly at the feed point. This is the most important choke in the system, because it prevents the feedline from becoming part of the antenna and helps keep common-mode currents under control.

• Required: one high-Z choke directly at the feed point
• Optional: one extra choke at the bottom of the mast or where the coax leaves the antenna area
• Optional: one choke before the shack entrance
• Optional: one extra choke before the rig if there is still local RF interaction or noise pickup

Using more than one choke can further reduce unwanted common-mode current, improve pattern stability, reduce local noise pickup, and help produce more repeatable SWR results.

Optimizing SWR Measurements

To achieve the best performance from your end-fed antenna system, follow these SWR optimization practices:

• Measure away from nearby metal objects: Keep your analyzer, feedline, and body away from gutters, railings, metal roofs, and other conductive structures that can distort readings.
• Check multiple frequencies: Measure across all intended bands to verify where the resonance dips actually fall.
• Do not let the feedline influence the result: Proper choking and clean feedline routing are essential for accurate measurements.
• Prefer measuring at a decoupled point in the system: In many practical installations, the most stable measurement point is after the first choke, or even after the second choke, rather than directly at the feed point area where the analyzer itself can influence the antenna.

For more details on optimizing SWR measurements for end-fed antennas, visit:
https://shop.rf.guru/pages/optimizing-swr-measurements-for-end-fed-antennas

Folding Back vs. Cutting Wire for Tuning

If your antenna needs tuning, it is usually better to fold back the excess wire instead of cutting it immediately. This allows easy adjustments without permanently shortening the antenna. If cutting becomes necessary, do so gradually and re-check resonance after each step.

For more details on folding back vs. cutting wire antennas, visit:
https://shop.rf.guru/pages/folding-back-vs-cutting-wire-antennas-essential-tips-for-optimal-performance

Tuning

Start by focusing on the 40M band, making sure the SWR dip appears just below the band edge.

For 20M and 15M, the SWR dip should ideally fall within the band, while on 10M it will often appear slightly above the band.

Keep in mind that antenna height plays a major role in SWR behavior. For more consistent multi-band performance, try to install the antenna above 8 meters where possible.

These reference measurements were taken using 30 meters of coaxial cable.

Installation Tips

• Insulation and tension: Always use proper end insulators and avoid excessive mechanical tension on the wire.
• Height considerations: More height usually improves overall DX performance, while lower installations may favor NVIS-style operation on lower bands.
• Tuning: Final wire lengths may need small adjustments depending on height, surroundings, soil, and installation geometry.
• Feedline routing: Keep the coax away from the radiator as much as practical, especially in the first section after the feed point.

For further assistance, feel free to contact us.