The Double-Bazooka Dipole Is Not Antenna Medicine

The double-bazooka is a real antenna, not snake oil. It is also not a magical upgrade to every dipole or inverted V. Its coaxial sections form part of the radiator and a frequency-dependent network. That can change the impedance curve, but every claimed benefit still needs its own measurement.

What the Coaxial Sections Actually Change

A common double-bazooka construction uses coaxial sections around the centre of a roughly half-wave radiator, with the shield and inner conductor connected in a topology that creates resonant transmission-line sections. The outside of the shield participates in the antenna current; the fields inside the coaxial section create a separate transmission-line response.

That is more than a fat piece of wire. The result depends on the coax characteristic impedance, velocity factor, attenuation, physical length, conductor dimensions, end connections and the wire extensions. Installation height, inverted-V angle, nearby conductors and the feedline route then change the antenna-terminal impedance and current distribution.

Because the topology contains resonant line sections, it is normally a band-centred design. Calling it “broadband” without stating the frequency interval, SWR limit, accepted loss and preserved pattern hides the engineering question.

Bandwidth Needs a Name and a Price

Several bandwidths matter:

• Impedance or SWR bandwidth is the frequency range that meets a declared terminal or transmitter-plane criterion.
• Efficiency bandwidth asks how much accepted power reaches radiation rather than conductor, dielectric, joint, matching or feedline loss.
• Pattern bandwidth asks whether the useful azimuth and elevation field remain where the operator needs them.
• Power bandwidth includes voltage, current, heating, insulation and connector limits.

A coaxial resonator can reshape reactance around its design frequency. The larger effective conductor diameter can also make the impedance curve less steep. Resistive and dielectric loss may broaden a low-SWR curve as well. These mechanisms can appear together, so a wide analyser trace alone cannot say which one delivered the bandwidth.

ARRL’s published double-bazooka analysis has long treated the topology as a dipole plus resonant coaxial sections, with limited impedance-bandwidth improvement in the analysed configuration. That is a useful warning, not a verdict on every construction. Different coax, proportions, feed arrangements and installations create different networks and must be measured as such.

Low SWR Does Not Rank Radiation Efficiency

The ordinary wire dipole and the double-bazooka both contain conductor, joints and dielectric. The double-bazooka usually adds more interfaces and places dielectric in strong internal fields, but that does not prove it must always be less efficient. A thin or corroded wire dipole, lossy tuner, poor feedline or bad connector can lose more.

Conversely, the bazooka’s low SWR cannot prove superior efficiency. A dissipative network can reduce the magnitude of reflections reaching the measurement plane. A fair comparison puts the reference plane at the same place, measures or removes feedline and matching loss, records accepted power, and evaluates radiated field or gain with uncertainty stated.

A tuner adds another reference plane. It can transform the load presented to the transmitter, but it does not remove loss in the radiator, coaxial sections or feedline, and it does not turn a monoband current distribution into a useful multiband pattern.

Symmetric Construction Does Not Guarantee Balanced Current

The two coaxial radiator halves may look symmetric on the workbench. Installed current balance still depends on the feed connection, feedline route, support ropes, mast, ground, nearby wiring and unequal capacitive coupling. The feedline’s exterior is an available conductor unless the complete geometry and common-mode boundary prevent significant current there.

A feedpoint choke may be appropriate, but its job and placement must be defined. Measure complex common-mode impedance across the required band, verify differential insertion loss and power handling, then map exterior current on the installed feedline. A fixed mix, fixed turn count or attractive dB label is not a substitute for that check.

The same rule applies to a simple dipole or inverted V. A choke does not make the radiator “inherently balanced”; it changes the impedance of an unwanted current path. Its effect depends on the rest of the loop.

Antenna Noise Is Signal Reception From an Unwanted Direction or Path

A passive reciprocal antenna does not identify a waveform as wanted signal or noise. Reports that one antenna is “quieter” can be real, but the cause may be a different pattern, polarization response, feedline common-mode pickup, height, orientation, mismatch, loss or measurement timing.

More loss lowers signal and external noise together. That may make an S-meter look calm without improving signal-to-noise ratio. A changed pattern may reject a local source and genuinely improve SNR at one azimuth while making another direction worse. The claim therefore needs simultaneous or restored-baseline A/B/B/A reception, the same receiver state, and signal and noise recorded separately.

Construction Is Part of the RF Circuit

The double-bazooka’s extra joints and exposed coax ends are not an automatic failure, but they require deliberate work. Record the actual cable rather than assuming a generic velocity factor. Keep dimensions and connections repeatable. Provide strain relief so the electrical joint does not carry the span tension. Seal against water while allowing the assembly to avoid trapping moisture.

Water ingress changes dielectric loss and velocity factor; braid corrosion changes resistance; a crushed or sharply bent coaxial section changes geometry. Inspect and remeasure after weather exposure. A simple wire dipole has fewer internal interfaces, but its centre insulator, wire terminations, feed connector and choke still need the same honesty.

Run a Comparison That Can Answer the Claim

• Define the purpose. State the band, mode, power, duty cycle, pattern and bandwidth criterion.
• Build comparable geometries. Put both antennas at the same height, orientation and inverted-V angle, clear of different nearby objects.
• Retune each candidate. Do not force identical physical lengths onto electrically different structures.
• Fix the reference plane. Measure complex impedance at the feedpoint or de-embed the feedline; do not compare two different cable transformations.
• Account for loss. Measure feedline, matching and network loss, inspect joints and follow temperature under representative power.
• Map unwanted current. Scan feedline-exterior current and repeat after moving the cable or adding the intended choke boundary.
• Measure pattern or field. Use controlled geometry, polarization and distance, with a stable source and uncertainty budget.
• Test receive SNR. Use simultaneous receivers or rapid A/B/B/A switching, not contacts made on different days.

IEEE 149 treats radiation pattern as a measured antenna property and sets out antenna-range and instrumentation discipline. Roy Lewallen, W7EL, shows why feedline current and the current loops around a balun must be analysed explicitly. Together they lead to a better answer than a slogan on either side.

Primary and Authoritative References

• ARRL — A Truly Broadband, Efficient Low-Band Dipole
• ARRL Antenna Book, 25th edition
• Roy Lewallen, W7EL — Baluns: What They Do and How They Do It
• IEEE 149-2021 — Recommended Practice for Antenna Measurements
• Keysight — Impedance Measurement Handbook

Joeri’s Bottom Line

The double-bazooka can be an interesting monoband antenna and a worthwhile experiment. It may present a useful impedance curve in a specific installation. What it cannot do is guarantee wideband efficiency, current balance or lower noise by topology alone.

If the bazooka wins your comparison, keep it. Just make sure it won on the metric you care about—not because loss, a moved reference plane or yesterday’s propagation made the trace look friendly.

Questions, antenna-factor records or height trials to share? Contact RF.Guru.