The double bazooka antenna, often described as a coaxial dipole, is a time-tested antenna design widely used by amateur radio operators. Its popularity comes from a combination of simple construction, predictable impedance behavior, and noticeably lower received noise compared to thin wire dipoles.
Instead of relying solely on wire elements, the bazooka antenna uses sections of coaxial cable as the radiating structure, allowing the outer braid to act as the main radiator. This configuration introduces distributed capacitance and inductance, which improves bandwidth and stabilizes the feedpoint impedance.
How the Double Bazooka Antenna Works
At its core, the antenna consists of a single coaxial section that is center-fed, with the coax shield intentionally opened at both ends. RF current flows along the outside of the braid, forming an effective half-wave radiator.
The inner conductors of the two coax halves meet at the feedpoint, while the outer shields are bonded in a way that preserves electrical balance. Because the feedline connects directly at the electrical center, the antenna naturally exhibits good symmetry and consistent radiation patterns.
This design reduces sensitivity to nearby objects and tends to suppress common-mode noise, especially in electrically noisy environments.
Why Hams Choose the Double Bazooka Antenna
Operators often notice that the double bazooka antenna delivers quieter reception on HF bands, particularly on 20 meters and above. The coaxial construction slightly broadens the SWR curve, making the antenna more forgiving across the band without frequent retuning.
While its radiation pattern is similar to a half-wave dipole, the bazooka antenna’s stability and noise performance make it especially attractive for SSB, digital modes, and weak-signal operation.
Length Calculation Method
The dimensions of a double bazooka antenna are based on long-established empirical formulas that already account for typical coax velocity factors.
Total Antenna Length (meters):
460 ÷ Frequency (MHz)
Coaxial Section Length (meters):
325 ÷ Frequency (MHz)
The coaxial section length refers to the entire radiating coax segment, which is divided equally by the feedpoint during construction.
Construction Considerations
Good results depend on using quality 50-ohm coaxial cable with consistent braid coverage. The outer braid should remain natural copper or tinned silver, as it forms the actual radiating surface. Avoid decorative plating or unnecessary metallic sleeves.
Keep solder joints short, symmetrical, and mechanically secure. At VHF and UHF frequencies, even small asymmetries can shift resonance noticeably.
About Velocity Factor and Length Calculations
Unlike many other antenna designs, the velocity factor of the coax does not affect the length calculations for a classic double bazooka antenna. The standard empirical formulas used for determining antenna and coaxial section lengths already account for the electrical behavior of the coax in this specific configuration.
As a result, builders do not need to adjust the formulas based on velocity factor. This simplifies construction and makes the antenna more forgiving when using different coax types, provided the shield construction is appropriate.
Using 75-Ohm TV Coax in Double Bazooka antenna
A double bazooka antenna can also be constructed using 75-ohm television coax, provided the correct type is selected. Many low-cost TV coaxial cables sold in hardware stores use aluminum shielding, which should be avoided. Aluminum braid cannot be soldered reliably and will lead to poor electrical and mechanical connections.
If 75-ohm coax is desired, cables with copper shields are strongly recommended. Proven options include RG-59 Belden 8212 and RG-11 Belden 8261, both of which use copper braid and are suitable for antenna construction.
Choosing the Right Coaxial Cable
The choice of coaxial cable plays a critical role in the performance and ease of construction of a double bazooka antenna. In practice, simple coax is often the best choice for this design.
Coaxial cables that use double shielding with bonded foil layers should be avoided. Foil shields make construction difficult because the foil is often fused to the dielectric. For example, in cables such as LMR-200–type constructions, the foil layer is bonded tightly to the insulation, making it extremely difficult or impossible to remove cleanly when preparing the radiating sections.
Commonly used and proven coaxial cables for building this antenna include RG-8, RG-8X, RG-58, and RG-213. These cables use traditional braided copper shields that are easy to work with and solder.
RG-8 and RG-213 have a larger diameter, which results in a slightly wider operating bandwidth. However, this also increases the weight of the antenna. When building larger antennas, such as for the 80-meter band, the additional weight can place mechanical stress on the end connections where the coax transitions to the antenna tips. Extra care should be taken to reinforce these points, and installation may be more challenging due to the added mass.
Installation and Performance
When installed horizontally, the double bazooka antenna behaves much like a traditional dipole, producing a broadside radiation pattern. Mounting height has the same influence as any half-wave antenna, with improved low-angle radiation as height increases.
Although the antenna is naturally balanced, adding a simple choke at the feedpoint can further reduce unwanted feedline currents, especially on HF.
Source Acknowledgment
This construction guidance is consistent with the work of David, K3DAV, as documented in “Build a Double Bazooka Antenna (K3DAV Version)”, archived at:
https://web.archive.org/web/20210207004525/https://radioaficion.com/
Related Posts
- Understanding the Bazooka Coaxial Dipole Antenna Design
- Sleeve Dipole Antenna Design Using Coaxial Cable – A Technical Deep Dive
- FM Bazooka Antenna for Superior FM Radio Reception (88–108 MHz)