The FCP on 80 Meters: When a Counterpoise Gets Mistaken for an Antenna

This article responds to the HamAnalyst post on the 80 meter FCP and focuses on the modeling logic, feed-system assumptions, and what the FCP actually is in an antenna system.

A recent HamAnalyst article presents a 4NEC2 model of an 80 meter “FCP antenna” and concludes that the system is a serious DX solution because it shows a low takeoff angle, a broad low-angle lobe, and a successful FT8 evening. That already sounds persuasive. The trouble starts when the same article treats the modeled 717 Ω reactive feedpoint and 24.5% efficiency as non-representative because the isolation transformer was not modeled, while still treating the radiation-pattern conclusion as essentially trustworthy.

For readers who want the original claim in context, the article discussed here is Modélisation de l’antenne FCP 80 mètres on HamAnalyst.

First correction: the FCP is not the radiator

The first conceptual fix is simple but important. The radiator is still an inverted-L. The FCP is the folded counterpoise... the return system. That distinction is not cosmetic. It changes what the article is actually proving.

K2AV’s own descriptions make this clear. The FCP is a compact folded return system intended to reduce local ground loss when “good-enough” radials cannot be done cleanly. He explicitly says the FCP is not magic, has no gain, and is not equivalent to dense, uniform radial fields. So the accurate description is not “a remarkable new antenna,” but “an inverted-L using a compact folded counterpoise.”

Why the low-angle lobe does not prove the FCP is extraordinary

Once that distinction is restored, the low-angle pattern becomes much less mysterious. An inverted-L on 80 meters, especially one with a meaningful vertical section, is expected to launch lower-angle energy than a low horizontal dipole. That is ordinary antenna behavior, not evidence that the folded counterpoise itself is doing something revolutionary as a radiator.

So when a model shows a broad low-angle lobe, the first explanation is not “the FCP is exceptional.” The first explanation is “this is what an inverted-L tends to do.” The fair comparison would keep the same inverted-L and change only the return system underneath it. That would tell you what the FCP is actually contributing.

The isolation transformer is not a magic 717 Ω to 50 Ω converter

This is where the HamAnalyst argument becomes weakest. The article reports a modeled feed impedance of 717 Ω at 88.7° and explains that this is mainly because the isolation transformer was omitted, while implying that the transformer in real life “brings” the impedance back near 50 Ω. That is not how K2AV describes the device.

In K2AV’s original NCJ article, the component is a 1:1 isolation transformer. Its primary job is to block feedline common-mode current and force the intended return current into the FCP. K2AV then explains that the impedance at the transformer output can vary widely depending on the aerial wire, the earth, nearby conductors, and other installation details. His own remedies include changing radiator length, adding a series capacitor, or using a separate coaxial matching transformer. In other words, isolation and matching are not the same thing.

If the feed system is omitted, confidence in the rest should drop, not rise

There is also an internal inconsistency in the modeling logic. If the NEC source is placed directly between the radiator and the folded counterpoise, then the model already assumes an ideal isolated differential feed at that junction. In that case, blaming the strange impedance and low efficiency on a “missing transformer” no longer makes much sense. If, on the other hand, the real feed arrangement and real current-return path were not properly represented, then the uncertainty affects more than just SWR. It also affects confidence in how the system current is actually being distributed.

That does not make the model useless. It means the model should be used comparatively and cautiously. Once the feed system is admitted to be central to the outcome, you cannot conveniently discard it for the impedance discussion while keeping full confidence in the pattern story.

What W8JI adds to the picture

Tom, W8JI, sharpens the same criticism from a more system-level direction. His point is not that a folded counterpoise can never work. His point is that hams too often credit the folded return system for behavior that really belongs to the inverted-L radiator, the feed arrangement, or the way the comparison was framed.

On his FCP comparison page, W8JI models the same basic inverted-L over several return-system arrangements. In one 1.83 MHz example with the FCP-style system at 8 feet, he shows roughly 29.1 Ω feed resistance, about −0.9 dBi gain, and about 26.2% efficiency. Other return-system choices in the same comparison set produce different impedance, gain, and counterpoise-to-ground voltage behavior. His broader point is not “the FCP never works.” His point is that the complete return system matters, and that better-looking total efficiency does not automatically mean better low-angle DX radiation.

That is a far more careful reading than saying: the pattern is still trustworthy, the odd impedance is just a missing transformer issue, and the low efficiency is merely a fictitious artifact.

Why the 24.5% efficiency number cannot be waved away

The HamAnalyst article treats the modeled 24.5% radiative efficiency as something fictitious, then substitutes an asserted real-world number around 70–80%. That leap is not established by K2AV’s published material. What K2AV discusses is the FCP as a low-loss alternative to bad radial compromises, not a blanket promise that every 80 meter inverted-L/FCP installation will land near 75% total efficiency.

In fact, K2AV also says the FCP is not equivalent to dense, uniform quarter-wave radials, and that the approximate break-even point versus raised quarter-wave radials is somewhere around four radials. That lines up remarkably well with ordinary practical intuition. If you really can deploy four proper elevated radials of equal current and keep feedline common mode under control, the special case for the fold-back becomes much weaker.

So the right conclusion is not that 24.5% must be correct. The right conclusion is that it cannot be dismissed simply because a transformer was omitted. The real installation still needs a more disciplined argument.

What the FCP is actually good at

None of this makes the FCP pointless. Quite the opposite. The fold-back exists for a real reason. It shrinks the footprint of the return system and exploits field cancellation near the counterpoise center when the property is too narrow, cluttered, or asymmetric for clean elevated radials. In that role, the FCP is clever engineering.

But that is different from calling it a fundamentally superior radiator. The fair description is much simpler: the FCP is a compact low-loss return system for an inverted-L when “good-enough” radials are not practical.

What the HamAnalyst article really proves

Once the overclaim is stripped away, the HamAnalyst article still shows something respectable. It shows that an inverted-L can make DX contacts on 80 meters, and that a compact folded counterpoise can be a workable small-lot return system. That is already a useful result.

What it does not prove is that the FCP itself is the hero of the radiation pattern, that the omitted feed system is irrelevant, or that one evening of FT8/PSKReporter results means the antenna “rivals much larger installations.” A single evening of spots may be interesting... but it is not the same thing as a rigorous system comparison.

Bottom line

The FCP deserves credit for what it is: a smart counterpoise compromise for restricted properties. It does not deserve to be mistaken for the main radiator, nor used as an excuse to separate pattern claims from feed-system realities. Once the counterpoise gets mistaken for the antenna, ordinary inverted-L behavior starts being sold as something much more exotic than it really is.

Source context

HamAnalyst: Modélisation de l’antenne FCP 80 mètres

K2AV / NCJ: A 160 Meter Counterpoise for a Postage-Stamp Lot

K2AV: Executive Summary on the FCP

W8JI: Folded Counterpoise Systems

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