K2AV Low Band Antennas
BOG Elevation and Azimuth Plots based on lengths and separation of the first set of BOGs deployed
Z Slope Elevation Plot
Z Slope Azimuth Plot
Guy Olinger, K2AV has been instrumental in 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 most 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, it simply won't work.
Scroll down past 160 FCP for information regarding 80m FCP and Isolation Transformer and 160/80m configurations
33' 33'
Feed Point
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
South
K2AV Two Element Beverage on Ground (BOG) RX Antennas installed at former WØUCE QTH
FCP Construction
- 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
84.5'
Bottom element 8' above ground
4" Vertical space between elements
33'
33'
46.5'
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
COAX CENTER
COAX SHIELD
FCP FEED
ANTENNA FEED
160m FCP Matching Transformer & Curent Block
Ten Buried 25' Bare Copper Radials
Note
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
K2AV 33x33 FCP
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.
Coax Center In
Coax Shield In
Balun Designs K2AV 160 & 80m FCP Isolation Transformers Now Available
Ground Level
FCP Isolation Transformer Winding and Transformer Weatherproof Enclosure Mounting
Photos courtesy of Jim - K8OZ
160m FCP as installed at K2AV
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
Double Click on Image to view .pdf file.
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
West
East
Favored Directions
North
75 Foot per side #18 Teflon Insulated wire
DX Engineering BFS-1 Beverage Feed
RG-6 Coax to Shack
Note
A more efficent method of feeding a LOG Receive Loop is to use an Isolation Transformer similar to the FCP Xfmr detailed above.
Check back for details regarding how to build a feedpoing transformer and also a switchable, multiple direction LOG Receive Antenna
