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The K2AV FCP: 5/16 Wave Single Wire Folded CounterPoise
Efficient Low Band Counterpoise for Confined and Unlimited Settings
Help with the Frequently Chosen Inverted L (and Other Aerial Wires) over an 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.  

K2AV 33' x 33' 160m Folded Counterpoise (FCP) and Isolation Transformer
To inverted L, Vertical, T or other aerial wire
Amidon T300A-2 #2 material powdered iron toroid core
Winding: 20 bifilar turns* teflon sleeved double polyimide insulated AWG14 (Wireman #635)
Coax Center Conductor   Feed Line   Coax Shield
FCP is made with #12 solid bare copper wire. For best results place the bottom wire of the FCP 8 - 10 feet above ground
* Bifilar turns: Instead of the two windings kept separate, one wire on one side of the toroid and one wire on the other side, the two wires are kept in a pair like a length of zip cord. The PAIR of wires is wound around the toroid twenty times. For the application 15 feet of wire and teflon sleeve, cut in half, provides the required PAIR length of 7.5 feet.
Original Drawing W0UCE, updated

extending the Single Drawing FCP Description:
(a) For single band use: The ±33 feet (±10m) above is for 160m. For 80m use ±16.5 feet (±5m), 60m ±11.2 feet (±3.4m), 40m ±8.2 feet (±2.5m), 30m ±5.7 feet (±1.75m). All bands use 4 inch (100 mm) wire spacing. For multi-band usage, see (k), (m) below.
(b) Always connect an isolation transformer per drawing above. The aerial wire uses the end of the parallel wire or bifilar winding also connected to the coax center conductor. Newer Balun Designs™ units have labels next to the 1/4 inch studs. Hold an older 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 diminish deliberate field cancellations designed into the FCP, raising RF field intensity at ground, increasing 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 so extensively because most FCP installers chose the L as aerial wire for their restricted situation. The L can be practical and very effective if properly placed, designed and tuned. See both and to build and optimize an efficient inverted 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, including permissable bends, 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) Winding wire lengths apply to 160m or 80m single band use and a single T300A-2 or T300-2D core, or two stacked T300-2 cores. Alternate configurations are discussed at
(h) Metric Dimensions, with small, harmless round-offs of SAE measurements 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, just not smaller. 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 (20m and more) or (18m and less).
(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
(n) When measuring R & X with RF analyzer at the Isolation Transformer, avoid false readings, see

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.**

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, seven 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 on whatever aerial wire in use. 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.


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.