6m / 10m - Dual-Band Rotatable Dipole Antenna
(610-DBRDA)
The K3SNO - 610-DBRDA represents a sophisticated, true 10 Meter ½-wavelength tunable dipole antenna. The 6 Meter component functions as a genuine ½-wavelength tunable parasitic monopole radiator, which functions by mutual coupling. The coaxial connection is routed through a 1:1 Current Balun/Choke to the 10m dipole, making no direct physical link between the 10m and 6m radiators. When transmitting 6m frequencies, the 10m dipole induces radiation in the 6m monopole through the principle of mutual coupling. This phenomenon, which is commonly observed in various antenna configurations (such as Yagi-Uda antennas), can sometimes be seen as a disadvantage; however, in this instance, it is leveraged to enhance performance of the 610-DBRDA.
Mutual coupling refers to the electromagnetic interaction that occurs between the elements of an antenna array. The current generated in the 10 Meter driven antenna elements is influenced not only by its own excitation but also by the excitation of the adjacent 6 Meter antenna element. This phenomenon of mutual coupling is prevalent in high-frequency structures where the elements are in close proximity to one another. Specifically, when the 10 Meter dipole transmits 6-meter VHF energy, it generates an electromagnetic field that induces a current in the 6 Meter monopole that is within this field. The tuning of the 6 Meter monopole enables it to resonate with the electromagnetic energy transferred from the 10 Meter dipole. Conversely, during reception, the energy received by the 6 Meter monopole also couples back to the 10 Meter dipole, reinforcing the concept of mutual coupling. This interaction enables the antenna to operate effectively with a single coaxial feed while radiating on two distinct frequency bands.
Given that these bands are 10 meters and 6 meters, this setup serves as an ideal introductory antenna project for newly licensed Technician Class Operators in the United States, providing them with valuable insights into antenna theory, construction, and practical experience with 10-meter HF and 6-meter VHF (often referred to as the "Magic Band") phone operations.
Additionally, this procedure includes the construction of a 1:1 Current Balun/Choke as part of the antenna assembly. A dipole antenna is inherently balanced, consisting of two identical conductive elements that are symmetrically fed, resulting in equal but oppositely directed currents in both elements. The placement of a Current Balun/Choke at the feed-point of a dipole antenna serves multiple purposes: 1) it matches the balanced antenna to the unbalanced coaxial cable; 2) it prevents any common mode currents, arising from imbalances in the system, from traveling back down the coax braid towards the radio (i.e., into the operator's shack); and 3) it minimizes noise and interference that the receiver may encounter, thereby enhancing the clarity of reception at the radio.
The antenna exhibits an azimuthal radiation pattern of approximately 75 to 90 degrees at its -3dB points, which can vary based on the height of the antenna and the conductivity of the ground beneath it. When installed at a height between 24 and 27 feet above well-conductive ground, the antenna achieves a take-off angle of 15 to 18 degrees in the elevation plane, making it particularly effective for DX operations.
The 6m and 10m bands are tuned independently, meaning that adjustments made to one band do not influence the tuning of the other. When correctly assembled and calibrated, the antenna typically exhibits a low Voltage Standing Wave Ratio (VSWR) of less than 1.5:1 across both bands, with each band offering a bandwidth of over 2 MHz at a 2:1 VSWR. The antenna is compatible with a 1-1/2” mast pipe and can be installed with or without a lightweight rotator; however, the use of a rotator is advisable.
When utilizing this antenna primarily for Phone communication, it is advisable for the user to adjust the tuning to the center of their designated frequency range to optimize signal transmission and reception. For instance, a US General Operator concentrating on Phone DX should set the 10m antenna to 28.600 MHz, ensuring that the 28.300-28.900 MHz "DX Slot" achieves the lowest possible Voltage Standing Wave Ratio (VSWR). The situation is somewhat different for the 6m band; given that the US Calling Frequency is 50.125 MHz, it is recommended that all users in the United States tune their 6m antennas to this frequency.
Specifications:
Antenna Power Rating: 1500 Watts PEP
Impedance: ~50 ohms
Gain: 2.15 dBi
Front to Back Ratio: 0 dB
Weight: <6 pounds
Turing Radius: 8 foot 2 inches
Maximum Mast Size: 1.5 inches
Wind Surface Area: 1.5 square feet
Maximum Wind Speed: 100 MPH
Bandwidth:
10 Meters: < 2:1 28 MHz - 29.7 MHz
(Assembly instructions recommend tuning 10m between 28.400-28.600 MHz in the US.)
6 Meters: < 2:1 over any 2 MHz portion of the band
(Assembly instructions recommend tuning 6m to 50.125 MHz in the US.)
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20 Page Detailed & Illustrated Complete Build Instruction PDF
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