This antenna represents my evolution of the End-Fed Half-Wave Sloper. It is can be resonant on 6 bands and does not require a tuner.
My End-Fed Half-Wave Sloper covers 40/20/15/10m nicely without needing a tuner. The issue at hand is that I have to carry separate antennas or wire elements for two of my favorite bands: 17m and 30m which can be very useful during contest weekends. My Linked End-Fed fixes this. By adding links to the 65.5-foot sloper we can add extra bands. Break points occur at approximately the 25 foot and 45 foot positions down the wire.
Theory:
While the impedance of a center-fed half wave dipole is approximately 73 ohms, the impedance of an end-fed half wave wire is much higher, like 2,000 ohms or more. A 49:1 transformer can be used to match the EFHW to your 50 ohm coax and transmitter.
While you could buy a ferrite toroid and wind your own transformer, by the time you add a SO-239 or BNC antenna connector and a suitable housing it might cost less to buy a ready-to-use unun like one I found on Amazon for < $30.
WARNING: The transformer significantly raises the voltage at the antenna terminal. A transmitter delivering 100 watts to a typical EFHW antenna will see about 500 volts (700 volts peak) at the output of the matching transformer. Keep the unun away from potential contact by people. This is why I suggest a configuration with the feedpoint (and far end) elevated well beyond reach.
reference: www.n6cc.com/end-fed-half-wave-wire-antennas/
Linked End-Fed Half-Wave Sloper
Linked End-Fed Components
Components:
• 49:1 unun transformer
• 65.5 feet of wire
• 2 split key rings for links
• 6 ring terminals
• 15 feet of paracord
• tent stake
Cut and tune the elements. Approximate lengths:
• 25 feet for 17m (green/yellow in photo)
• 20 feet adds 30m (white in photo)
• 20.5 feet adds 40/20/15/10m (black in photo)
I used 18 gauge wire scavenged from discarded vacuum cleaner power cords.
Simple Link Design:
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key ring with pieces of insulation
rotate ring 90 degrees for band switch |
TIP: Open both links and tune the 17m section first. Then close the upper link and tune the middle section for 30m. Finally, with both links closed, tune the bottom section for 40/20/15/10. |
