Feedpoint Height Guidelines for the Inverted-L EFOC17/29

The EFOC17/29 is an off-center-fed, 4:1 UNUN-matched wire antenna designed for multi-band operation. In its inverted-L configuration, feedpoint height becomes a major factor in performance — not just for SWR behavior, but also for your radiation take-off angles and noise pickup.

Understanding the Height Factor

An inverted-L is essentially two antennas in one: a vertical section that favors low take-off angles for DX, and a horizontal section that supports both DX and NVIS depending on its height above ground. The vertical portion benefits from being as tall as possible, while the horizontal portion’s height determines whether your radiation is more skywave-steep (NVIS) or shallow (DX).

Reasonable Feedpoint Heights in Real Installations

In the real world, trees, buildings, and masts dictate what’s possible. Here’s a practical guide:

• Minimum functional height: ~3 m (10 ft). Works for NVIS and short-range comms, but DX efficiency will suffer on the low bands.
• Good all-rounder height: 5–6 m (16–20 ft). Vertical section still gives useful DX angles on 40 m and up, horizontal section high enough to reduce ground losses.
• DX-optimized height: 8–10 m (26–33 ft). Lower take-off angles improve long-haul contacts, especially if the vertical section can be lengthened.

Tip: The “reasonable” height is the one you can install safely and keep clear of obstacles — chasing an extra meter isn’t worth compromised guying or mechanical risk.

Balancing NVIS and DX Goals

For mixed operation (contesting, emergency NVIS, and DX), a feedpoint at 5–6 m with the horizontal leg sloping slightly upward to 10–12 m is an excellent compromise. This keeps high-angle radiation for close-in coverage while lowering the average take-off angle enough for intercontinental work on the higher bands.

External Tuner Requirement

While the EFOC17/29 covers multiple HF bands, an external tuner is still necessary for most inverted-L installations. Some bands may naturally present an acceptable SWR (often 40 m and 20 m), but others will fall outside the matching range of a direct 50 Ω connection. A good wide-range tuner — either at the shack or, ideally, at the feedpoint — will ensure full coverage and minimize coax loss on the mismatched bands.

Bands below the red SWR=3 line are generally within most tuner ranges, while those above it will require more matching range.

Practical Installation Notes

• Keep the 4:1 UNUN off the ground — at least 1 m clearance to minimize detuning from soil coupling.
• Use a 1:1 choke at the feedpoint or a few meters down the coax to suppress common-mode currents.
• Where possible, route the horizontal wire away from metal structures and large trees.
• Don’t obsess over perfect right-angle geometry — a slight curve or zig-zag in the horizontal section has minimal effect on pattern at HF.

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