COMPACtenna VHF/UHF: What the Patent and Tests Establish

The engineering question is not whether COMPACtenna products can make contacts. They can. The useful question is which performance claims have been demonstrated for which model, installation and metric—and which claims still require a calibrated comparison.

Start by Naming the Exact Antenna

“The COMPACtenna” is not one fixed antenna. The manufacturer lists multiple mobile, land-mobile and scanner products with different dimensions, bands, matching arrangements and power specifications. The present 7.5-inch 2M/440 model is not the same product as the 9-inch 2M/440+ tested by QST in August 2022.

Figures from one row cannot be silently assigned to another. For example, the 2022 review quotes a nominal 5(+) dB-MEG claim and particular power limits for the 9-inch 2M/440+. The current page for the 7.5-inch 2M/440 gives different model-specific figures. A responsible installation follows the current manual and rating for the exact part in hand.

What Dr. Jack Nilsson’s Patent Describes

U.S. Patent 9,407,001 B2, granted to Jack Nilsson in 2016, describes a single conductive sheet formed into a three-dimensional spiral, with dielectric material preventing adjacent turns from making electrical contact. The claims describe proportions between the element’s height, width, sheet length and operating wavelength. A cable conductor can feed the radiative element, while the other conductor can connect to a ground plane or counterpoise.

That is a real and distinctive geometry. Distributed inductance, capacitance and radiation can all be part of the same structure; an external lumped loading coil is not required for an antenna to be electrically short and resonant.

“Magnetic Field Resonator” Is a Product Description

The manufacturer uses the term Magnetic Field Resonator. It should not be read as a separate long-range propagation mode or as an exception to Maxwell’s equations.

Every practical antenna has electric and magnetic near-field components, and radiation in the far field contains coupled electric and magnetic fields. The local E/H ratio and stored energy depend on position and geometry, but a receiving station kilometres away does not receive an independent magnetic-only radio wave.

The safe technical description is therefore:

That statement respects the invention without turning a trademarked explanation into a new law of physics.

Compact Resonance Does Not Prove Low Loss

For a first-order antenna loss model:

The loss term can include conductor, dielectric, joint, matching, mount and ground/counterpoise loss. A compact radiator may integrate its matching function elegantly and avoid a visibly separate coil, but geometry alone does not disclose those resistances.

Fundamental small-antenna work, from Chu and Harrington through modern efficiency-bound research, shows the recurring trade among electrical size, bandwidth, efficiency and stored energy. The complete mobile system includes the vehicle body, so its electrical size is not determined by the 7.5- or 9-inch top unit alone. Even so, a compact top structure does not receive a free exemption from loss and bandwidth constraints.

Low SWR proves something narrower: at the measurement plane, the impedance is reasonably close to the line impedance. A well-matched lossy structure and an efficient radiator can both show 1.5:1 SWR.

What the 2022 QST Review Actually Found

The ARRL QST review evaluated the 9-inch 2M/440+ on a vehicle magnetic mount and on a station counterpoise. It reported average measured SWR of about 1.8 on the vehicle and 1.5 on the station arrangement. The reviewer made local repeater, more distant repeater and satellite contacts, and found the base-station performance comparable in that operating experience to a Diamond NR22L vehicle-mount antenna.

Those are useful findings. They show that the reviewed sample could be installed with a usable match and could close practical links. The review does not describe a calibrated substitution range, Wheeler-cap test, reverberation-chamber efficiency test or full-sphere realised-gain and polarisation measurement.

MEG Is Not a New Name for Gain

dBi expresses gain relative to an isotropic radiator. dBd expresses gain relative to a half-wave dipole, and for the same direction and conditions:

Mean effective gain (MEG) is different. In established mobile-antenna usage, MEG relates the antenna’s complete directional and polarisation response to the statistical angular and polarisation distribution of incident power in a stated environment. It is not an intrinsic free-space number that can be converted to dBi by adding a constant.

A reproducible MEG result therefore needs:

• the complete antenna-plus-vehicle configuration;
• calibrated three-dimensional gain patterns for both orthogonal polarisations;
• the angular and polarisation power distribution used for the environment;
• the reference, averaging convention and uncertainty; and
• the frequency and installation geometry.

Without those items, “3 dB-MEG” or “5 dB-MEG” should be presented as a manufacturer-specific figure, not as ordinary 3 or 5 dBi gain. It may point to a useful multipath objective, but it is not independently comparable until the method and reference are published.

Pattern and Polarisation Claims Need Full-Sphere Data

A compact structure mounted near a vehicle corner can excite currents on both the antenna and vehicle. That can change elevation, azimuth and polarisation compared with a conventional vertical in the centre of a roof. The result may be beneficial on some paths and detrimental on others.

Elliptical polarisation is not a single badge attached to an antenna. In a given direction, it requires orthogonal electric-field components with a defined magnitude ratio and phase difference. Those quantities can vary strongly around the sphere. Proving a broad elliptical-polarisation claim requires the two polarised far-field components versus angle, not a drawing of the radiator or a few successful contacts.

Likewise, a “broad” elevation pattern can mean less peak directivity because radiated power is spread over more angles. That may improve coverage in a changing mobile environment, but it is not automatically more gain. Pattern shape, radiation efficiency and realised gain must be reported separately.

Why Corner Mounting Can Help—And What It Changes

The manufacturer recommends mounting certain models at an upper vehicle corner. This is plausible installation advice: the counterpoise geometry, nearby metal and current paths are different from those at the centre of a large roof, and the impedance can move closer to the intended operating region.

It also makes the vehicle part of the measured antenna. A corner installation is generally not azimuthally symmetric. Vehicle size, roof rails, glass, hatch seams, cable routing, bonding and mount contact can change match and pattern. The QST SWR result confirms the match of its tested arrangements; it does not provide a universal corner-mounted pattern.

Does a Strong Magnetic Near Field Reject Noise?

Not as a general rule. Received noise depends on the source, distance, coupling path, spectrum, polarisation, antenna pattern, vehicle current distribution, feedline common mode and receiver.

A different antenna pattern can reduce pickup from a particular local source. A compact antenna can also have lower absolute gain, which reduces both external signal and external noise; when receiver noise remains well below the external noise, the signal-to-noise ratio may change very little. Neither effect proves that “magnetic” construction inherently rejects man-made noise.

Test noise claims by switching rapidly between antennas at the same position and frequency, recording calibrated signal and noise separately, and repeating with multiple source directions and operating environments.

Will It Beat a Quarter-Wave, 5/8-Wave or Collinear?

There is no universal answer. On a clear terrestrial horizon path, a properly installed antenna with higher realised gain at the required elevation and polarisation has the link-budget advantage. A taller collinear can concentrate more power near the horizon, while a compact antenna may be mechanically convenient, less conspicuous or less vulnerable to impact.

In urban multipath, one pattern may outperform another at one street corner and reverse a block later. That does not create gain; it samples different combinations of reflections, diffraction and polarisation. A fair comparison requires equal accepted power, rapid switching, the same mount or a documented mounting correction, many routes and frequencies, and a statistical result rather than the best anecdote.

Power Ratings Are Model- and Mode-Specific

The current manufacturer pages give different maximum powers by band and emission mode for specific products. The 2022 review reproduced a different set for the 9-inch 2M/440+, including a stated duty-time limitation. Do not apply a number from one model to another or treat SSB PEP as continuous FM or data power.

At minimum, verify the exact model, frequency, waveform, duty cycle, mount, ambient temperature and installation instructions. Stop if SWR drifts, the mount or feed region becomes hot, insulation softens or the antenna changes mechanically. A published nominal rating is not permission to ignore connector, cable, mount or exposure limits.

A Measurement Programme That Would Settle the Claims

1. Identify the specimen. Record model, serial or production revision, dimensions, mount, cable and vehicle.
2. Move the reference plane. Calibrate impedance to the feed point and document the complete sweep, not only the best SWR.
3. Measure efficiency. Use an accepted reverberation-chamber, Wheeler-cap or equivalent calibrated method appropriate to the complete structure.
4. Measure full-sphere realised gain. Record both orthogonal polarisation components, mounting position and uncertainty.
5. Calculate MEG transparently. Publish the incident angular/polarisation distribution and integration convention.
6. Run controlled mobile A/B tests. Switch rapidly against named references, sample many routes and report distributions.
7. Verify thermal limits. Apply defined modes and duty cycles while monitoring the radiator, feed, mount and cable.

This programme could confirm important advantages. It could also show that the main benefit is compactness and installation convenience rather than exceptional free-space gain. Either result would be more valuable than an unqualified decibel.

The Balanced Verdict

COMPACtenna products do not need extraordinary physics to be useful. A compact radiator that fits where a quarter-wave or collinear does not can be the antenna that stays installed and makes the contact. That is a legitimate system advantage.

The stronger gain, polarisation, noise and MEG claims deserve stronger evidence. Name the exact model, distinguish manufacturer specifications from independent results, and match every conclusion to the metric that was actually measured.

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