K2AV Low Band Antenna Solutions
BOG Elevation and Azimuth Plots based on lengths and separation of the first set of BOGs deployed
Guy Olinger, K2AV has been instrumental in the design and implementation of highly innovative and efficent Low Band Antenna projects that have been field trialed and installed for permenant use at WØUCE and other stations. Examples and details of several projects are shown below:
160 Meter Folded Counterpoise
K2AV's 33' x 33' Folded Counterpoise (FCP) provides a highly effective means to greatly reduce ground loss associated with Inverted L, Vertical or any other type antenna that requires radials. Using an FCP for DXpeditions or in situations where installing a dense buried radial field or resonant raised radials is impractical is especially beneficial. Thanks to K2AV's research and development efforts, his FCP and Isolation Transformer make it possible for almost anyone to get on Top Band even with a modest Inverted L or vertical antenna. In order to employ an FCP, a home brew or commercial Isolation Transformer as specified below must be used. DO NOT attempt to use an FCP without the specified isolation transformer as it simply will not work.
Scroll down past 160 FCP for information regarding 80 meter FCP and Isolation Transformer and 160/80m configurations.
160 / 80 Meter Inverted L with 33' x 33' FCP Configuration as installed at WØUCE
K2AV 160 / 80 Meter Inverted L Matching System as installed at WØUCE
5 Element Vertical Fan installed at former WØUCE QTH
K2AV 75' per side Bi-Directional East / West Loop on Ground (LOG) RX Antenna as installed at former WØUCE QTH
K2AV Two Element Beverage on Ground (BOG) RX Antennas installed at former WØUCE QTH
- The ONLY means of achieving the required degree of Isolation is to use the Isolation Transformer specified
- Tests using 1:1 Baluns and Line Isolators ALL FAILED - It is a waste of RF Power, Time and Money unless the specified Isolation Transformer is employed
- DO NOT attempt to use Insulated Window Line for the FCP - Field Tests proved it does not work - too lossy
- Use #12 Bare wire for FCP elements - Moisture gathers on insulated wire and detunes the FCP
- 4 - 6" Spacing between FCP elements is ideal
- Small diameter PVC Spreaders work well - use caps on both ends and drill a small weep hole in the bottom cap
- There is no specific number of spreaders required, just as many as needed to maintain constant separation
- It is best to install the FCP in a straight line; the overall length is 66' - If bends are necessary due to space limitations, the first 10' on either side of center must be straight in order not to deminish current cancellation Feed Impedence will change with FCP orientation in relation to the horizontal part of an inverted L but operational peformance will not be diminished
- FCP Orientation: The FCP can be in line or at right angles to the horizontal section of the inverted L
Bottom element 8' above ground
4" Vertical space between elements
FCP Isolation Transformer as installed at W4KAZ
FCP Isolation Transformer Information
While the K2AV isolation transformer may employ the same physical components as a balun the simularity stops there. Unlike a balun there is no connection of any kind between the primary and secondary windings.
An Amidon T300A-2 #2 material powdered iron toroid transformer core has twenty bifilar turns (7.5 Feet) of double polyimide insulated #14 wire covered with teflon sleeving.
One wire is the primary, the other is the secondary for both pairs. The low MU powdered iron toroid was selected to avoid heating and also provide the required coupling.
Field tests with other core choices failed in spectacular fashion. We have yet to have a single Isolation Transformer failure in the field for any cause though we would not expect it to survive a direct lightning strike.
Scroll down for additional K2AV Lowband Antenna Project Information
160m FCP Matching Transformer & Curent Block
Ten Buried 25' Bare Copper Radials
This Matching System is different than the prescribed K2AV FCP Isolation Transformer. The 160m Section employs a matching transformer and separate coax block which forces the antenna to use the FCP versus the feed line coax shield
80m Link coupled tank circuit matching system
Balun Designs custom designed FCP Transformer Model 1142s provides the highest possible isolation between input and output. There is no direct electrical connection between the input and output thus all RF energy is conducted through the specialized iron powder core and transformer windings. Specifications meet K2AV FCP Isolation Transformer requirements for use with a 33'x33' 5/16th Wavelength Folded Counterpoise for 160 meters.
Balun Designs K2AV 160 & 80m FCP Isolation Transformers Now Available
FCP Isolation Transformer Winding and Transformer Weatherproof Enclosure Mounting
Photos courtesy of Jim - K8OZ
The number and placement of spreaders and / or support poles will vary between installations
K5AF 160m Dipole Versus Inverted L with FCP Antenna Compairison Test Results
Right click on Phased Side By Side BOG File then Save As to download the EZNEC file used to create the latest version of side by side BOGs.
80 Meter FCP Information
FCPs are frequency sensitive and must be 5/16 wave. An 80m FCP is 16.5 feet per side
A simple setup (FCP and Isolation Transformer) for 80m requires an 80m winding. Balun designs can provide a custom wound device with evenly spaced 15 bifilar turns or they can also be home brew, the wire lengths are 6' 2" for 80m. Use the same materials and techniques as described above for a 160m Isolation Transformer when making an 80m version.
Rules of thumb when using a pair of FCP's for 160 and 80
1. Maintain 4" spacing between wires.
2. FCPs must be switched as only one can be connected at a given time
3. 80 and 160m FCP's can be mounted parallel to each other, side by side or one above the other - maintain 2 feet separation
4. Install and tune the 160m FCP before tuning the 80m FCP as there will be some interaction on 80m but not lossy
5. Only one FCPs can be a "simple" configuration the other will have to be operated as a switched in network in order to deal with the "simple version's" band length. Additional information in this regard is forthcoming
Latest Version K2AV side by side BOG Loop
Isolation Transformer & FCP Materials Source List
Amidon T300A-2 Powdered iron toroid (Amidon)
Teflon Sleeveing (Amidon)
#12 AWG standard wall teflon tubing 15'
Polyimide Insulated Wire (The Wire Man)
#635 Double polyimide insulated #14 AWG, 15'
#12 Hard Drawn Bare Copper Wire
The Wireman #538
FCP XFMR Enclosure: Carlon E989NNJ-CAR
4x4x2 Junction box with gasket cover - Lowes Home Depot and Electrical Distributors
75 Foot per side #18 Teflon Insulated wire
DX Engineering BFS-1 Beverage Feed
Understanding Bifilar Windings
Bifilar describes wire which is made of two filaments or strands and is commonly used to denote special types of winding wire for transformers.
When winding an FCP transformer consider and treat the two teflon sleeved poliymide 14 guage wires as if they were a 7.5 foot length of two conductor moulded lamp cord. Keep them flat against the tororid as you wind turns around the core. Taping the two insulated conductors together will help keep them aligned side-by-side as you wind your "Zip Cord" Transformer Windings.
Toroid Winding DWG. by K9JWV
Important: Isolation Transformer Testing
When finished winding an FCP Isolation Transformer, use an ohmmeter and for illustration purposes, assuming you are using an SO239 connector for coax input and post insulators for connections to the FCP and vertical conductor, MAKE SURE you DO NOT see a short between the shell of the coax jack and either post going to the FCP or vertical conductor connection point or between the center conductor and either post. To finish the check, you SHOULD see a short between the two posts. You SHOULD also see a short between the shell and center conductor of the coax jack.
"Think Zip Cord as you wind"
K2AV Folded Counterpoise Article
Published In May/June, 2012 Issue
of the National Contest Journal
Left Click on the Icon above to open
Where FCP's fit in the world of 160 counterpoise
Radials and the vertical radiator both produce RF fields in the ground. Where the fields from the radials and the field from the vertical are equal and opposite phase, the fields cancel without inducing lossy current in the ground. If the fields don't cancel, both the radials and the vertical radiator induce lossy currents in the ground.
(1) Traditional buried or elevated radials, full size, dense, uniform length and spacing, remain the best possible option as they have a high degree of vertical vs. radial RF ground field cancellation that other solutions (including the FCP) do not offer. This is the gold standard.
(2) The RF fields from a sparse, non-uniform length, or non-uniformly spaced radial field are irregular and "lumpy." The field from the vertical radiator is smooth and uniform. Therefore they only partially cancel each other, and the leftover fields induce lossy currents in the dirt. In the worst cases power loss in the ground can far exceed the radiated power. The loss in a given poor radial installation increases dramatically as the dirt conductivity goes good to average to poor to awful. The poorer the dirt the closer your radial installation must to stay to the gold standard to avoid significant losses.
(3) When good-enough radials over your dirt can't be done, then there is no way for the radials to cancel the vertical wire's RF field at the ground and the system is lossy. There are two design strategies available to mitigate those losses:
(a) Elevate the base of the vertical wire to reduce the vertical wire's RF field at ground. There is a large difference in ground fields between wire base at ground and wire base up 8 feet or 2.5 meters.
(b) Design the counterpoise to have as little RF field at ground as possible, thus leaving only the reduced vertical wire field loss from a) to reduce your radiated signal.
(4) Two counterpoise designs use both these strategies for their efficiency:
(a) The FCP which requires a linear 66 foot space for deployment. This solution reduces RF ground fields by folding a single 5/16 wave wire to three folds designed to produce equal and opposite fields from the folds at the ground.
(b) ON4UN's 4 times 1/8 wave elevated radials, which require a 90 foot square space for deployment. This solution reduces RF ground fields from the radials by shortening them.
(5) An FCP is not magic. It has no gain. An FCP improves an antenna system by replacing more loss with less loss. Some have been able to erect better wires in the air because the small size of the FCP allowed better placement of the antenna. Such a multiple factor improvement project sometimes produces startling changes. Of course, the biggest improvement is when the FCP makes possible the first 160 antenna on the property.
If an FCP is too much a leap of faith, and you really want radials but can get nowhere close to the gold standard, and you have the 90 by 90 foot square space to put up four 63 foot elevated radials, then do ON4UN's four by 1/8 wave elevated radial installation. It's documented in any of his low band DXing books. Important: Do not lay out the 4 x 1/8w installation with your house inside the 90 by 90 foot space outlined by connecting the ends of the four radials. If you have to do that to fit it on your property, the house will become a loss factor, and the FCP will be the superior solution.
Click on the red button to view W1UJ's FCP Construction Photo Series