Bob Rose, KC1DSQ & Bob Glorioso, W1IS
Introductions1,2
Ten Meters is still open and 6 Meters is hot on FT8 these days. As a general rule; put your antenna as high as possible, but a dipole at 45 ft sends a significant amount of energy up where it is wasted, Figures 1a and 2a. The stacked dipoles redirect the vertical energy to a useful direction, Figure 1b and 2b. Stacked dipoles deliver 3 dB of gain over a single dipole at the same height.
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Figure 1a. 6-meter Dipole at 30 ft
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Figure 1b. 6-meter Stacked Dipoles at 30 ft
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| Figure 2a. 10-meter Dipole at 50 ft | Figure 2b. 10-meter Stacked Dipoles at 50 ft |
This configuration creates strong bidirectional lobes at a low take-off angle of 10 degrees.
Design
The antennas consist of two horizontal dipoles stacked vertically with a separation of 12ft 8 inches and 22 ft 5 inches, Figure 3 and Figure 4 respectively for 6-meters and 10 meters. The impedance of each dipole is transformed to 100 ohms so they can be wired in parallel to form a 50-ohm load. The transformation is implemented with ¼ wavelength sections of 75-ohm coax. However, the vertical separation is greater than a half wavelength, so the two ¼ wavelength feeds will not be long enough. Therefore, top dipole feed is increased to a ¾ wavelength section of 75-ohm coax. That introduces an unwanted 180-degree phase shift. The 180-degree phase shift is eliminated by reversing the coax connection to one of the dipoles. For one dipole, the center conductor is connected to the right arm of the dipole. For the other dipole, the shield is connected to the right arm of the dipole. Net result, the dipoles are each 100 ohms and in phase.
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| Figure 3. Stacked 6 Meter Dipoles, Layout |
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| Figure 4. Stacked 10 Meter Dipoles, Layout |
Construction
The antenna uses about 40 feet of #14 insulated wire like THHN or Davis RF, 6 insulators, 23 feet of RG-59, 4 PL-259 connectors, one T connector, 2 Type 43, Clamp-on Ferrites (Mouser 623- 0444176451), and 100 feet of Paracord, Figure 1. The Balun/Choke is 2 turns of RG-59 through the Ferrite core positioned close to the feed point of each dipole. The two dipoles are built, one with 16 ft 10 inches of RG-59 (top dipole), the other with 5 ft 7 inches of RG-59 (bottom dipole).
Tuning
Before attaching the bottom dipole, connect a T connector to the upper dipole. Then install an SO-239 with a 100-ohm non-inductive resistor soldered across it to the T and connect a length of 50-ohm coax to the bottom of the T. Launch to the desired height, 45-55 feet and adjust the length for low SWR on the part of the band you are interested in. Make sure each leg is the same length. Adjust the bottom dipole to be the same length per leg.
Final Assembly
Remove the 100-ohm resistor and connect the two dipoles together with the T. The 50-ohm feedline is connected to the T using a dual SO-239, bullet, connector. The bottom dipole is suspended from the top dipole using Paracord. Launch the antenna to the desired height. The insulators for the bottom dipole are anchored to the ground with Paracord to keep the bottom dipole from sagging towards the middle. Be sure to observe the polarity reversal for one dipole: the center conductor for the top dipole goes to the same side as the shield for the bottom dipole. If this is not done correctly, the pattern will send most of the energy straight up with little or no energy going towards the horizon.
The SWR is less than 3:1 across each band and if you tune the antenna for the middle of the lower half of each band the SWR will be less than 2:1 from 50 to 52 MHz on 6-meters and less than 2:1 from 28-29 MHz in 10-meters. We tested 6-meter antenna using a KX3 at 5 watts with the top dipole at 30ft with several locals up to 20 miles away with S-9 plus signal report and the 10-meter antenna with a KX3 running 10 watts on a day when we were recovering from a recent CME and worked several stations along the east coast from our Central Massachusetts location. We also used It for FD under equally trying conditions and worked what we could hear at 100 watts.
Summary
We were very pleased with the ease of implementation and performance of this simple, inexpensive way to double our radiated power on six and ten meters.
References:
- KD9EJA, https://bcham.org/stacked-dipoles/
- “Wire Antennas 160 meters to 70 cm: Concepts, Construction and On the Air,” 2023, Bob Glorioso, W1IS and Bob Rose, KC1DSQ, OCFMasters.com, HRO Salem, NH, HamRadio.com and Ama