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The K2AV FCP: 5/16 Wave Single Wire Folded CounterPoise
Efficient Low Band Counterpoise for Confined and Unlimited Circumstances
Help with the Frequently Chosen Inverted L (and Other Aerial Wires) over FCP
Other Loss Avoidance Opportunities and Techniques for the Low Bands

We hope this web site will be a basket of tools for your successful use. Every ham station is different and only you will be able to determine any application to yours. But from years of correspondence, issues detected at one station often repeat at others. So you just might find unexpected opportunities.

The short and linear FCP was designed to reduce ground losses from inadequate radial systems beneath inverted L's and vertical antennas. The FCP and Isolation Transformer allow us to get on Top Band and do well from small building lots and other confined circumstances. Other loss issues may be found and eliminated. We begin with the FCP, and then introduce Loss Issues below.

The Single Drawing FCP Description

Before the FCP was published in 2012, W0UCE laid out this drawing of the FCP. Tried and true, it has quickly explained the FCP ever since. Some looked at this drawing once and went out and built it. And it worked. So we have placed it in our opening screen.

The drawing has only minor changes since 2012. We have listed some below.

Please do not use the original NCJ magazine article, "The Wayback Machine," or archived or printed site articles for technical and construction information. Use k2av.com directly to see new and updated content. The version is at the bottom of the green index buttons.

extending the Single Drawing FCP Description:
(a) The ±33 feet (±10m) details above are for 160m. For non-multiband 80m use ±16.5 feet (±5m), 60m ±11.2 feet (±3.4m), 40m ±8.2 feet (±2.5m). Use 4 inch (100 mm) wire spacing on all four bands.
(b) Always connect an isolation transformer per drawing above. The aerial wire uses the bifilar winding end also connected to the coax center conductor. Newer Balun Designs units have labels next to the 1/4 inch studs. Hold an unmarked, unmodified Balun Designs unit, cover side with screws facing you, coax connector facing down. Connect the aerial wire to the right side stud and FCP to the left. Explained in
(c) !!! DO NOT CHANGE FCP WIRE DIMENSIONS TO IMPROVE SWR !!! Changes add loss. SWR does not predict performance. See
(d) Other antennas such as a T vertical or top-hatted vertical, etc, can be used effectively above an FCP. We treat the inverted L extensively here because FCP installers themselves so frequently choose the L for a small lot. The L can be practical and very effective if properly placed, designed and tuned. See all three: , and to optimize an L.
(e) We now recommend a minimum FCP height of 8 feet (2.5m) if at all possible, better 10 feet (3m). See other important FCP placement considerations at
(f) Use a minimum of spreaders between FCP wires. A 160 FCP only needs support at the center, at the two ends, and two spreaders between an end and the center. Keeping the number of spreaders low reduces dielectric material between FCP folds, reducing detuning and loss.
(g) The drawing's winding wire lengths only apply to 160m and a single T300A-2 or T300-2D core, or two stacked T300-2 cores. Alternate transformer configurations are discussed at
(h) Metric Dimensions, with harmless roundings to even metric numbers:
- The FCP is 10 meters from center to either end, 20 meters overall,
- at a recommended minimum height of 2.5 meters if possible, better 3 meters,
- the spacing between folded wires is 100 mm, and
- you may substitute locally available IEC wire size 4 sq mm for AWG 12. Exact AWG 12 wire is not required as part of the design. For the transformer's polyimide insulated AWG 14, we currently have no EU source for heavy polyimide insulated 2.5 sq mm copper and suitable matching standard wall teflon sleeving. If informed, we will include verified sources in our materials source listings.
(i) DO use the Isolation Transformer rather than a ferrite device at the feedpoint. Explained in from extensive FCP-related email and telephone consults over the years, we only and very strongly recommend the isolation transformer. See for instructions or commercial sources.
(j) If you must use a tower to support the bend of an inverted L, then depending on size use or (20+ 18- m).
(k) To operate both 160 and 80 meters on the same L over FCP, see
(m) To operate 160, 80 and 40 meters on the same L over FCP, see

The FCP "+" Project

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After Jack's FCP drawing and basic construction text, the rest of the FCP-related web site content exists because implementing FCP's exposed a Long List of RF loss Issues. Notably, eight green button topics treat inverted L issues. Remedying or designing around those losses exposed still more issues. "FCP+" is what we call a project that installs an FCP and remedies any loss issues. These RF Loss issues are treated in .

The "Plus" items are not required to make an FCP work. They just remove loss. The total loss remedy from a fistful of fraction of dB issues can exceed the major remedy of the FCP itself. FCP+ sometimes produces an amplifier's increase in TX signal strength without the amplifier.

At a particular ham station, which RF loss issues actually exist varies wildly. RF Loss remedies, in individual stations with their individual situations, can range from easy to impossible. Issues are not in the list because we are convinced they exist at your station. We list them because the individual issues have existed and have been remedied at multiple FCP project sites. Any issue might exist and be fixable at your site. Certain issues have proven common, with a select few more likely present than not.

Reading while planning a station makes very best use of the Loss List, avoiding RF losses in the first place.

The Story Behind the Drawing

You can read the story leading up to Jack's drawing in the first four columns of the original May/June 2012 NCJ article. Note that portions of the article's technical content are no longer current. **Please use the web site you are viewing now for all technical content and direction.**


Disclaimers: This web site is not a commercial enterprise. K2AV receives no royalties or compensation from any source for use of the antenna and transformer designs. The content of this site is published without charge for the furtherance of amateur radio and the benefit of the readership.

To the extent we can discern, we always try to upgrade our understandings and designs based on new discoveries and experience in the field and post those advances on this web site. However, a warranty of any kind, including merchantability or fitness for a particular use, express or implied, is explicitly disclaimed. See also this warning and disclaimer.

Balun Designs™ is a highly valued commercial resource, providing a source of professionally constructed transformers described on this web site. However, Balun Designs is not responsible for the design of said transformers, and not responsible for explaining how to use them. Balun Designs warrants their workmanship and that the 1142s uses the same design and materials specified on this web site for those winding their own transformers.