Can a 20 m Vertical Beat a Yagi? Compare the Installed Pattern
Can a 20 m Vertical Beat a Yagi? Compare the Installed Pattern
A Yagi on a tower can be an excellent DX antenna. A vertical can still win on a particular path when height, terrain, ground loss, clutter, azimuth and elevation put more realised gain where the signal must leave. Compare the installations, not their reputations.
RF.Guru working definition: Common-mode current is the non-cancelling phasor-sum current in a specified set of conductors, evaluated at a defined cross-section and using a declared current-direction convention. In the intended differential transmission-line mode, the outgoing and return currents are equal and opposite, so their phasor sum is zero. When they do not cancel, the remaining current must close through another reference or return path—such as the outside of a coax shield, a mast, equipment chassis, station wiring, nearby structures, earth, the operator, or distributed coupling through the environment.
This broader working definition is especially useful in practical antenna systems. On transmit, non-cancelling current on the outside of the coax can make the feedline and connected structures part of the radiating antenna system unless that path is intentional, clearly defined and properly controlled—for example by providing the required return path and placing a suitable common-mode choke at the correct boundary.
The usual comparison—“a beam has gain, a vertical has a low angle”—throws away nearly everything that determines a real contact. Gain is directional, elevation is path-dependent and both antennas become part of a larger current-and-environment system when installed.
Why Mark’s Video Belongs Here
In How a Vertical Antenna Can Beat a Yagi on a Tower, Mark, K3ZD—Ham Florida Man—uses Joeri/ON6URE’s RF.Guru height-and-site argument to challenge the automatic “tower wins” conclusion. Mark identifies the RF.Guru article and closely follows its practical warning: a 15 m installation can be workable, but clutter can move useful energy away from the angles a path needs.
The video’s fixed angle, height and radial figures are examples, not antenna-class ratings. The durable point is the comparison method: declare both installations and compare realised gain at the required azimuth and elevation, together with loss, noise and operating constraints.
A Yagi’s Free-Space Gain Is Only the Beginning
A Yagi’s specification normally describes gain and front-to-back behaviour for a declared model, frequency and environment. Once the antenna is placed over real ground, the direct field combines with ground-reflected fields. Height in wavelengths changes their relative phase and therefore the elevation lobes and nulls. The tower, mast, feed line, guy system, roof and nearby conductors can also carry or induce current.
That does not make a Yagi unpredictable or ineffective. It means that “three elements at 15 m” is not a complete pattern specification. The ARRL’s own height studies show different elevation responses for the same Yagi at different heights and different useful-angle distributions for different paths. There is no single height at which a 20 m Yagi becomes universally correct.
DX Does Not Have One Take-Off Angle
At 14 MHz, the free-space wavelength is about 21 m. Expressing height as a fraction of wavelength is useful, but it does not select the best elevation angle by itself. The supported ionospheric modes and their arrival or departure angles vary with path length, direction, time, season, solar conditions and frequency. ITU-R P.533 therefore predicts a distribution of path modes and elevation angles rather than prescribing one universal “DX angle.”
A low lobe can help a long path and still miss a shorter path that is supported at a higher angle. A higher antenna can develop additional lobes and nulls rather than simply pushing one lobe lower. The relevant comparison is gain over the angular region that matters for the intended paths, not only the angle of the largest lobe.
A Vertical Starts With a Different Pattern—and a Real Return System
A vertical monopole over a horizontal return structure tends to produce omnidirectional azimuth coverage and energy toward lower elevations. Its realised performance depends on conductor loss, the complete radial or counterpoise system, soil coupling, matching loss, nearby objects and common-mode current. A low elevation lobe is not automatically a strong one.
The return current does not disappear when the radiator is a half wave or when feedpoint impedance is high. It can divide among a deliberate counterpoise, feed-line exterior, mast, ground coupling, enclosure capacitance and station wiring. A separately designed choke can control the downstream coax path, but its impedance and position must be measured for the installed system.
Radial design is a wire-budget and loss problem, not a magic count. Compare total conductor length, radial lengths and distribution, soil, burial or elevation, feedpoint height and accepted power. A statement such as “32 radials is enough” has no transferable meaning without those conditions.
Terrain and Clutter Must Be Modelled, Not Assigned a Rule of Thumb
Sloping ground can change the far-field elevation response in a favoured direction. Buildings, trees, roofs and metal structures can scatter, absorb or reradiate energy. Their effect depends on dimensions, material, distance, orientation, conductivity and the complete antenna current distribution. Fixed clearance rules such as half, one or two wavelengths are not universal pattern guarantees.
A flat-ground model is still useful when its assumptions are declared. It isolates the effect of electrical height and ground parameters. It does not establish the pattern of an urban garden, a ridge, a seafront site or an antenna beside a building. Add measured terrain and conductors where the decision depends on them, then test model sensitivity instead of reporting one plot as certainty.
Compare Realised Gain at the Same Path Angle
The useful quantity for transmitting is realised gain in the wanted direction. It combines radiation pattern, conductor and ground loss, matching loss and mismatch at the declared source plane. For receive, wanted-signal gain alone is insufficient: local noise direction, common-mode pickup, receiver headroom and resulting signal-to-noise ratio also matter.
EIRP(az,el) = Paccepted × Grealised(az,el)
Use consistent linear units in the equation or add the corresponding quantities in decibels. Paccepted belongs at a declared plane; transmitter output is not the same as accepted antenna-system power after tuner, feed-line and matching losses. The same normalization is required for both antennas.
Common-Mode Current Can Rewrite Either Pattern
A Yagi’s driven element may be geometrically symmetric while its installed feed system is not electrically balanced. A vertical intentionally uses an asymmetric radiator-and-return geometry. In both cases, unintended feed-line-exterior current can make the coax, tower and station part of the antenna, changing pattern, noise pickup and RF exposure.
Do not infer balance from the antenna name or a low SWR. Measure exterior current at multiple positions and frequencies. Specify a choke from its complex common-mode impedance, loss and thermal behaviour under the actual installation conditions, then remeasure the current distribution.
Make the Comparison Falsifiable
- Declare both geometries. Record element dimensions, height, orientation, radial or return system, tower, guying, feed-line route and nearby conductors.
- Define the objective. Name the paths, frequencies, operating times and the azimuth/elevation region that matters.
- Normalize power. Account for tuner, feed-line, matching and ground losses at the same reference plane.
- Validate the current path. Measure feed-line-exterior current and include conductors that participate in the model.
- Compare patterns, not peaks. Inspect realised gain across the useful angular region, including nulls and sensitivity to terrain and material assumptions.
- Use rapid A/B/A field checks. Switch antennas quickly, log wanted signal and noise separately, and restore the first state to reveal propagation drift.
A directional Yagi may dominate when it is high enough for the required path, pointed correctly and installed with controlled feed-line current. A vertical may be the better station tool when it places more realised field into the supported angles, covers several azimuths without a rotator or simply fits the site better. Neither conclusion is contained in the antenna label.
Primary Engineering Sources
- ARRL — Antenna Height and HF Elevation-Angle Planning: calculated Yagi elevation patterns at multiple heights and path-angle distributions.
- Recommendation ITU-R P.533-14 — Method for the Prediction of the Performance of HF Circuits: path modes, elevation angle, field strength and reliability.
- NTIA Report 99-368 — Antenna Modeling: numerical modelling near lossy Earth, including Sommerfeld/Norton treatment and far-field gain.
- IEEE Std 149-2021 — Recommended Practice for Antenna Measurements: terminology and methods for defensible antenna-pattern and gain measurements.
Practical Conclusion
Mark’s provocation is useful because a tower invoice is not a propagation model. A well-installed Yagi is a formidable antenna, but it does not win every path merely by being a Yagi. A well-installed vertical can beat it when the complete site puts more realised field into the angles and directions that matter.
Replace the slogan with four records: the installed current path, realised three-dimensional pattern, accepted-power budget and path-angle objective. Then the better antenna for that contact becomes a testable result instead of folklore.
Mini-FAQ
- Is 15 m high enough for a 20 m Yagi? It can be useful, but height alone cannot answer. Compare its modelled and measured realised gain across the elevation angles required by the intended paths, including local terrain and clutter.
- Does a vertical always have the lower take-off angle? No. Geometry, return system, soil, loss, surroundings and frequency shape both the strength and angle of its lobes.
- Do I need exactly 32 radials? No universal count applies. Radial length, distribution, elevation or burial, soil and total wire budget determine the trade.
- Does a half-wave vertical need no return path? No. Its return current can use a deliberate conductor, coax exterior, mast, capacitance and other attached structures; the installed path must be identified and controlled.
- Is a vertical necessarily noisier on receive? No. Compare wanted-signal SNR, noise direction, common-mode pickup and receiver headroom at the site.
- What is the fairest field comparison? Normalize accepted power, switch rapidly, record signal and noise separately, and repeat the starting condition to expose propagation drift.