Antenna polarization in amateur radio skywave propagation

Experimental evidence and what operators at each end can observe

Research review • 28 October 2026

HF skywave propagation can change a signal’s polarization substantially, but it does not reliably erase the importance of antenna polarization or physical orientation. A distant station’s antenna orientation is an unreliable guide to the polarization arriving at your receiver. Your own antenna still selects part of that arriving field, and its directional pattern and noise response remain important.

Brief summary

The strongest direct evidence comes from controlled 40-meter measurements and six-meter amateur-beacon experiments. They show both recognizable polarization modes and time-varying received polarization. Broader HF work extends the discussion to long, multi-hop paths and to the different reports heard at opposite ends of a contact.

Reading guide. The physics and ideal calculations come first, followed by the experimental review and its limits. The practical sections then explain what the two operators may observe and how to compare antennas. References and verification links follow. Bracketed labels identify sources; hypothetical examples are labeled explicitly.

How polarization changes along a skywave path

Refraction and polarization are different properties

Refraction changes the direction in which a wave travels. Polarization describes how its electric field varies in the plane perpendicular to that direction, once the wave is back in approximately free space. A wave can be bent toward Earth while also changing polarization; bending alone does not specify what polarization will arrive.

The ionosphere is an electron plasma embedded in Earth’s magnetic field. Its response depends on direction. The two characteristic magnetoionic modes are called ordinary and extraordinary, abbreviated O and X. They generally have different phase accumulation, attenuation and propagation delays. Their polarization depends on geometry; the description as two opposite circular waves is a useful approximation for suitable paths, not a universal definition. [R1, R3, R7]

An ideal two mode explanation

The following is an idealized physical explanation, rather than an additional measured result. Imagine that a linearly polarized transmitted wave excites two opposite circular components. If they reach the receiver with equal amplitudes, their sum is linear. A change in their relative phase rotates the resulting line. Unequal amplitudes generally produce an ellipse; if one dominates strongly, the result approaches that component’s circular polarization.

This explains how one transmitted polarization can yield several received states without requiring the signal to become unpolarized. In real ionospheric geometry the characteristic waves may themselves be elliptical, and several arrivals may overlap, so the simple circular construction becomes an approximation.

Rotation and depolarization must be distinguished

A clean ellipse whose major axis rotates with time is still polarized. Depolarization is a statistical description: over the stated time and bandwidth, no single fixed polarization state accounts for all measured power. Averaging a changing polarized wave for too long can lower its measured degree of polarization. The averaging interval and receiver bandwidth therefore belong with any claim that a signal is depolarized.

“Random polarization” can mean an orientation that is unpredictable to the operator, rapid fluctuations within a measurement, or genuinely low degree of polarization after averaging. Those meanings are not interchangeable. A signal-strength meter on one antenna cannot distinguish them.

Faraday rotation is not the whole story

Differential phase between magnetoionic components can rotate polarization. Differential attenuation, different paths and modal selection can also change ellipticity and amplitude. The familiar inverse-square frequency approximation for Faraday rotation should not be used as a complete calculation of a refracted HF path near its turning region. Geometry and the plasma properties along the actual path matter. [R6, R8]

Circular handedness needs a convention tied to the direction of travel. A label applied to an upward wave cannot simply be transferred to the downward wave without checking that convention. Measure the actual receive branches before choosing a supposedly correct circular hand.

How the two modes produce the received polarization

Figure 1. Schematic paths and an ideal circular-component construction. Shapes show the electric-field tip over one cycle at a fixed point, viewed in a plane transverse to the arriving wave. Paths and polarization states are not measured data.

Equal opposite circular components combine into a line whose orientation depends on relative phase. Unequal components produce an ellipse; one dominant circular component approaches a circle. The circular-mode model is an approximation for suitable geometries. Actual O and X polarizations depend on propagation direction relative to Earth’s magnetic field. See R1, R3 and R7 for experimental context.

What an ideal receiving antenna accepts

These calculations isolate polarization. They assume a plane wave, equal directional gain, correct impedance matching and no environmental noise differences. They are not a prediction that two real antennas will produce these exact readings.

Linear polarization mismatch

For a linear wave and a linear receiving antenna, accepted power due to polarization alignment is proportional to cos² θ, where θ is the angle between their electric-field directions. Taking 10 log10 of that fraction gives the relative power in decibels.

If the arriving line rotates, a fixed antenna can move from a strong response into a deep null. The wave can retain substantial total power while one antenna’s output fades. A real null is usually limited by imperfect polarization purity, additional arrivals and surrounding objects.

Circular reception and averages

An ideal circular wave divides its power equally between two orthogonal ideal linear receive channels. Each is 3.01 dB below a perfectly matched circular receiver of equivalent gain. Rotating one linear antenna within the transverse plane does not change that ideal coupling.

A uniformly distributed linear orientation also gives a mean accepted fraction of one-half on any fixed linear antenna, because the average of cos² θ is one-half. This conditional average is not evidence that real skywave polarization is uniformly distributed. Even when the average applies, individual fades can remain very deep.

For an ideal ellipse with major-to-minor electric-field amplitude ratio a/b, the power difference between linear antennas aligned to its two axes is 20 log10(a/b). A 3-to-1 ellipse therefore permits about 9.54 dB difference. An elliptical wave is not automatically orientation independent.

Why two channels can help

Two calibrated orthogonal linear channels can, in the ideal model, recover the field’s two components. Simple selection uses the better branch. Coherent combining must account for their relative phase; blindly adding voltages can cancel the wanted signal. Practical improvement depends on branch noise, calibration, loss and how differently the branches fade.

Equal average power does not mean equal outage probability. An operator trying to complete a weak contact may care more about the fraction of time a message is readable than about average signal strength.

Why a fixed antenna can fade

Figure 2. Ideal linear polarization coupling calculated from cos² θ. The top panels hold the arriving wave fixed and rotate the receiving axis. The curve is a calculation, not an experimental measurement.

For a fixed receiving axis and a rotating arriving field, the same curve describes changing polarization coupling. Real antenna gain, noise, local surroundings and additional arrivals are held out of this ideal comparison. An ellipse has different responses along its two axes; only the ideal circular case is independent of linear-axis angle under equal-gain conditions.

Polarization changes and waveform distortion

Changing polarization does not necessarily corrupt the information carried by a signal. A receiver may simply accept less power from an otherwise undistorted waveform. Conversely, a signal with a fairly stable polarization can still suffer multipath distortion. These are different mechanisms and call for different remedies.

A simple physical model

Imagine two copies of the same transmitted waveform arriving with different strengths and delays. At one frequency their fields may add; at another they may partly cancel because their relative phase is different. The antenna’s polarization response weights each copy before the receiver processes the sum. Changing polarization can therefore change both signal strength and the apparent mixture of paths.

In a two-ray idealization with delay difference Δt, the interference pattern repeats in frequency about every 1/Δt. As a hypothetical calculation, a 1 millisecond separation gives a 1 kilohertz spacing. This describes two discrete rays with a fixed delay separation; it must not be equated automatically with a published mean delay-spread value.

What an operator might hear

For a narrow carrier, the main observation may be amplitude fading. Across a wider voice or digital signal, different frequency components can experience different gains and phases. Audio may sound hollow or change tone, and a digital decoder may lose performance even when the overall signal meter remains respectable. These are plausible symptoms, not a diagnostic proof of a particular mode or hop.

A bandwidth change can alter both the noise admitted by the receiver and how much of a distorted waveform is retained. Compare antennas at the same bandwidth and mode before assigning a difference to polarization. Different digital-mode reports can also use different reference bandwidths.

Why selecting one mode does not cure every fade

Separating characteristic modes can remove interference between those selected components in a suitable geometry. A selected mode can still contain more than one ray, and its amplitude can still change. The same-mode fading identified in the satellite work is an experimental reason to keep this distinction. [R12]

A successful diversity system exploits complementary observations. It does not restore a signal that is absent from every branch, and combining can be ineffective if the useful signals fade together. Receiver processing must also avoid adding unwanted relative phase errors.

How to read the experimental numbers

Antenna gain, polarization isolation, delay spread, fading margin and decoder improvement answer different questions. A 25 dB isolation result cannot be substituted for a 25 dB improvement in voice readability. An improvement measured against one receive branch does not automatically describe the advantage over a different antenna installation.

Experiments on 40 meters and 160 meters

Separating the characteristic modes on 40 meters

Witvliet and colleagues used a linearly polarized beacon and switched circular receive polarization over a 104.5 km Netherlands path in March 2014. The paper reports the frequency as approximately 7 MHz; its beacon spectrogram places the signal around 7.038 MHz. During opening and closing intervals, when only the extraordinary mode returned, measured isolation exceeded 25 dB. [R1, especially Figures 20–23]

This demonstrates strong polarization selectivity under those conditions. The 25 dB figure is a modal isolation measurement, not a promise that replacing any ham dipole with a circular antenna gains 25 dB. Measurements switched between channels, and the reported isolation applies to the tested path and intervals.

Daytime preservation and nighttime irregularity

A later experiment used 200 W at 7.03825 MHz over 105 km in October 2014, alternating transmit and receive circular senses. Direction finding supported single-hop F2 propagation during daytime. Matching modal polarization produced roughly 18–20 dB stronger reception than the orthogonal choice, with antenna purity limiting interpretation. [R2]

During an X-class solar flare, the ordinary and extraordinary signals dropped about 35 and 45 dB, respectively, while characteristic-wave polarization remained recognizable. At night, after the critical frequency fell below the operating frequency, the remaining fluttering signal had random polarization. The exact scattering origin was still under investigation. These are different propagation regimes, not contradictory outcomes. [R2]

Spanish amateur frequency field validation

The 2019 instrument paper describes Spanish operation near 7.04 MHz under an amateur license. Probes cycled circular and linear polarization; coherent measurements recovered phase as well as amplitude. Field validation showed opposite circular states in the corresponding intervals and rapidly changing polarization during a linearly transmitted interval. The Netherlands portion used approximately 6.99 MHz under experimental authorization and belongs outside a strict amateur-band subset. [R3]

Supporting observations on 160 meters

Vanhamel, Machiels and Lamy used paired WSPR receiving stations to compare antennas and investigate propagation on 160 meters. They associated received signal-to-noise variation with polarization shifts and tentatively suggested a connection to the electron gyrofrequency. Their signal-strength observations are useful operational evidence, but do not fully reconstruct polarization or conclusively establish that mechanism. [R4]

These results establish measured effects on specific paths. They do not determine how often polarization changes across all HF contacts, nor how quickly a particular station’s polarization will vary tonight.

Six meter evidence and diversity reception

Sporadic E signals from amateur beacons

Deacon and colleagues’ 2022 study used six European amateur beacons between 50.4 and 50.5 MHz, received in southern England during summer 2018. Paths were about 1100–1650 km, selected to favor single-hop sporadic-E propagation. Crossed receiving antennas and coherent sampling allowed polarization reconstruction with corrections for ground effects. [R7]

The transmitted signals were nominally linear, while received signals were overwhelmingly elliptical. No depolarization was observed in the analyzed examples. Some paths showed more stable polarization associated with geometry relative to the magnetic field. The authors interpreted the results as evidence of magnetoionic double refraction. “In every recorded case” applies to that dataset, not to every six-meter opening. [R7]

Why the measurement method matters

Their earlier IEEE paper developed the 50 MHz polarimetric system and presented initial case studies. It explicitly analyzed ground-reflection amplitude and phase bias, finding accurate reconstruction possible only within the stated angular conditions below the pseudo-Brewster angle. This is a reminder that the field at an installed antenna includes the local ground interaction; two uncalibrated meter readings are not a complete polarization measurement. [R6]

Measured diversity benefit near 7 MHz

A related 2015 EuCAP paper measured both circular receive channels on a 110 km NVIS path and reported an 8–11 dB reduction in required fading margin compared with one circular channel. This is peer-reviewed conference evidence, listed separately from journal papers. Its result concerns fading margin and a particular comparison baseline, not a universal antenna-gain increase. [R5]

Practical interpretation. A second channel can be valuable because its useful signal remains available during some fades on the first channel. A second antenna that always suffers the same fade, or delivers mostly extra noise, offers much less benefit. A system should be judged after feed losses and receiver noise are included.

What these observations do and do not establish

Together, the amateur-frequency measurements support two conclusions: launch polarization may not be preserved, and the arriving signal can still have a definite polarization that a receiver can exploit. Changing polarization, stable elliptical polarization and low measured polarization over an averaging interval are all physically different outcomes.

None of the single-hop experiments establishes a rule for every multi-hop DX path. Extending their numbers directly to another band, latitude, antenna height or solar condition would require additional measurements.

The multi hop evidence in detail

The Antarctica to Spain experiment

Bergadà, Alsina-Pagès and Hervás studied a 12,760 km link from Livingston Island to Cambrils, estimating approximately four hops. A transmitting monopole fed simultaneous reception on a monopole and an inverted-V separated by 25 m. The campaign covered 36 days in early 2011 and swept much of HF, including amateur-frequency regions; it was not confined to ham allocations. [R8]

They compared narrowband signal correlation and wideband delay and Doppler behavior. Frequency-resolved results showed that reception differences persisted over the long path and depended on frequency and time. Their two receive antennas differed in pattern and installation as well as nominal polarization, so the measurements do not isolate polarization alone. [R8]

The published frequency description contains inconsistent unit typography. Its grid and plots concern MHz HF signals. Detailed examples in the paper also include non-amateur frequencies; those examples should not be relabeled as ham measurements. The approximately four-hop interpretation was not a measurement of each individual bounce. The results were described as preliminary. [R8]

What multiple hops add

The following is physical interpretation. Each ionospheric passage can change the relative contributions of the characteristic modes. Intermediate ground or sea encounters can weight the field components differently and add phase shifts. Several routes can reach the receiving station together. A small change on any route changes the final vector sum.

This can make the arriving polarization harder to predict from the launch antenna. It does not require the final wave to become unpolarized. A complicated sequence of coherent transformations can still produce a definite ellipse. When many components fluctuate within a receiver’s averaging interval, the measured result can instead appear partly depolarized.

The claim about a fixed number of hops

No experimental threshold in this evidence set establishes that polarization becomes irrelevant after a specified number of hops. Testing that claim would require controlled comparisons over known hop geometries, similar antennas, calibrated polarization channels and enough conditions to separate hop count from distance, fading and frequency.

The long-path experiment is evidence against treating the two installed receiving antennas as interchangeable. It is not a measurement of how much polarization alone contributed to their difference, nor proof that one orientation must always win.

What the DX operator can infer

A long path makes the distant station’s launch polarization a weak predictor of the best local receive setting. Try the available receive choices and compare readability or decoding success over time. Do not assume that matching the distant antenna is optimal, and do not assume all local orientations are equivalent.

How multiple hops and the two stations affect a contact

Figure 3. An illustrative sequence of four hops and two complete station chains. The sketch is not a ray trace or a reconstruction of the Antarctica–Spain measurements. Ellipses indicate possible local states in transverse planes, not a predicted evolution.

Several transformations can make the final state hard to predict without making it unpolarized. On the reply, the stations exchange transmitter and receiver roles, and the local noise environment also changes. Compare power, antenna responses, timing and noise before interpreting unequal reports as evidence of polarization nonreciprocity. See R8 and R13 for the experimental findings and limitations.

Supporting experiments outside amateur allocations

These papers explain mechanisms or communication effects that the amateur-frequency studies alone do not resolve. Their measured frequencies and path types are stated so that supporting evidence is not mistaken for a direct ham-band replication.

A digital ground to ground link at 5 point 4 MHz

Male and colleagues measured ordinary and extraordinary NVIS channels at 5.4 MHz. They examined availability, channel correlation and delay spread, then applied polarization diversity. The paper reports roughly 0.3 ms mean delay spread for both modes, 15 percent higher availability for the extraordinary mode, and up to 4 dB improvement with diversity. The availability figure is the authors’ reported comparison, not an all-band operating probability. [R9]

Direct satellite polarization measurements

Danskin and colleagues transmitted at 10.422 MHz from Ottawa during April 2016 and used crossed satellite dipoles. Power oscillated between the dipoles while measured polarization remained high during strong-signal intervals. This directly illustrates changing orientation without complete depolarization. The geometry was transionospheric, not an Earth-to-Earth returning path. [R10]

Pandey and colleagues examined a 12 May 2017 transmission at 5.382 MHz to the same instrument family. Received ellipticity changed from about −19 degrees through linear to +30 degrees, with relatively stable orientation. Ray tracing supported a single-mode interpretation. It is an observation plus model-assisted interpretation, rather than a general rule that any individual mode must keep fixed ellipticity along every path. [R11]

Separating different sources of fading

James and Prikryl analyzed a 1978 Ottawa-to-ISIS 2 experiment at 9.303 MHz. Fades of about one to a few hertz were measured. Most were interpreted as Faraday-type interference involving O and X components, while others involved different rays of the same mode. Mode separation can therefore address one source of fading without eliminating all fading. [R12]

A test of the two directions of a link

Zhou and colleagues alternated transmission and reception between Wuhan and Wanning, about 1360 km apart, on 27–29 March 2009 using identical sounders and horizontal log-periodic antennas. Their comparisons of group distance and Doppler supported reciprocity under the tested conditions. That establishes agreement in the measured channel properties, not identical signal reports or polarization transfer for every pair of antennas. This was broader HF sounding, not a dedicated ham-band experiment. [R13]

These supporting papers strengthen the distinctions between field polarization, receiver output, waveform distortion and two-way readability. Their numerical results should not be transferred unchanged to a different amateur-band contact.

What operators at opposite ends actually observe

From one station to the other

Call the stations A and B. A’s antenna launches a field with a directional pattern and polarization that depend on the installation and departure angle. The propagation channel transforms that field. B’s antenna responds to the arriving directions and polarization, and B’s receiver adds its filtering and processing. B hears the resulting signal against B’s local noise.

On the reply, B becomes the transmitter and A becomes the receiver. Those two complete station experiences need not sound alike. Transmit power, receiver bandwidth, local noise, interference and measurement conventions can differ even if the propagation loss were identical.

An illustrative link budget

Hypothetical example, not a measured contact. Suppose A uses 100 W and B uses 10 W. Equal path and antenna factors would make A’s signal arrive at B 10 dB stronger than B’s signal arrives at A. If A’s receive noise is also 10 dB higher, B’s reply has a further disadvantage. A could have about 20 dB worse received signal-to-noise ratio than B, without invoking polarization nonreciprocity.

The general relationship is received power equals transmitted power plus antenna gains in the relevant directions, minus propagation and system losses, with a polarization coupling factor included in the complete link calculation. Readability depends on received signal relative to noise within the chosen bandwidth, not received power alone.

Reciprocity needs a stated meaning

An antenna’s transmit and receive pattern reciprocity does not, by itself, prove that the full ionospheric channel is reciprocal. A magnetized plasma requires care in applying reciprocity arguments. Equally, an unequal report is not evidence that the propagation channel is nonreciprocal. Delay symmetry, polarization transfer, absolute power and signal-to-noise ratio are different comparisons. [R13]

A useful two-way comparison records both stations’ power, antenna setting, receiver bandwidth, noise floor and timing. Keep the frequency the same and alternate directions quickly enough to reduce changes in the ionosphere. An ordinary conversation with different power levels and changing interference does not isolate polarization.

What each operator can say with confidence

“The second receive antenna made your signal readable here” is a direct observation. “Your transmitted polarization was converted to vertical by the third hop” requires substantially more evidence. The first statement is useful for completing a contact even when the second remains unresolved.

Matching the other station’s visible antenna orientation is therefore an unreliable operating rule. Choosing a receive configuration from actual local signal-to-noise measurements is more defensible. Transmit and receive choices may differ when noise and available antenna systems differ.

Practical operating examples

These scenarios are interpretations of the physics, not additional field experiments or promises of improvement.

A horizontal dipole works a vertical antenna on HF

A successful contact does not mean polarization ceased to exist. The arriving field may be elliptical or rotated, so the local antenna can accept a useful component. Different launch and arrival angles, radiation patterns and ground effects also matter. The free-space ideal of a 90-degree mismatch cannot be applied solely from the physical labels horizontal and vertical at the two stations.

One receive antenna fades while another stays readable

That is consistent with polarization fading, but also with pattern differences or different interference pickup. If both orthogonal field components are measured coherently and their calibrated total stays steady while power shifts between them, the case for polarization redistribution is stronger. If both fade together, total path loss or common multipath cancellation may dominate.

A circular antenna reduces some fades

On a suitable path, one circular receive channel can favor one characteristic mode and reduce interference between modes. It can still fade because the selected mode itself has multiple rays or changes in amplitude. Choosing the opposite circular sense may select a weak or unavailable component. Observing both channels can avoid committing permanently to the wrong one.

A beam beats a wire after a long multi hop path

That can result from higher gain toward the useful arrival directions, rejection of unwanted directions, different noise pickup, polarization coupling, or some combination. A stronger reading alone does not identify which factor caused the advantage. Rotating the beam changes its directional response as well as its relation to the arriving field.

A vertical has a stronger signal but worse copy

Hypothetically, one antenna could increase the desired signal by 3 dB while increasing local noise by 8 dB. Its signal-to-noise ratio would be 5 dB worse. Listen or decode using equivalent bandwidth and processing. An S-meter comparison that ignores the noise floor can select the less useful antenna.

A low dipole works nearby stations but misses DX

This can be explained by elevation coverage before invoking polarization. A low horizontal dipole can favor steep angles; the useful long-distance path may arrive much lower. Polarization changes during propagation cannot recover power that the transmit antenna did not launch into a usable direction, or remove a receive-pattern null.

A six meter opening favors an unexpected orientation

Sporadic-E polarization can differ from the beacon’s nominal linear launch state. Try both available receive orientations if practical, but account for the pattern and ground reflection. The beam configuration that works best for one path need not be best for a different direction or a later event.

How to compare antennas without fooling yourself

The following is a proposed practical procedure. It is designed to distinguish an operational benefit from a claim about its physical cause. It is not a substitute for a calibrated polarimetric experiment.

Define what you want to improve

Choose the useful outcome before testing: fewer failed decodes, longer readable intervals, better signal-to-noise ratio, or reduced deep fades. Record the band, frequency, path distance, approximate direction and time. Avoid describing the path as a known number of hops unless you have measurements supporting that geometry.

Make a fair comparison

Use simultaneous receivers if available. Otherwise switch antennas in a repeated alternating sequence, with intervals short compared with the observed fading, and repeat enough times to expose the variation. Keep bandwidth, mode and processing the same. If measuring power, fix gain settings or use calibrated receiver data; automatic gain control can hide amplitude changes.

Measure the desired signal and nearby noise separately. Record feed loss and antenna settings. A WSPR or digital-mode report is useful, but its integration time can average over short fades. Rapid switching alone does not make two dissimilar antennas an isolated polarization comparison.

Test polarization with the right equipment

The stronger arrangement uses two orthogonal elements with known directional responses and two phase-coherent receiver channels. Calibrate amplitude and phase differences through the antennas, cables and receivers. Account for coupling, local objects and ground reflection. Reconstruct the polarization state and report the averaging time and bandwidth.

Two independent power meters can show that branches differ, but cannot generally distinguish an ellipse from a changing linear state because they do not measure relative phase. A complete result should retain both field-component amplitudes and their phase relationship.

Compare reliability over time

Keep time series and report typical performance together with fades. Compare the fraction of time above a readability threshold, a low percentile of signal-to-noise ratio, fade depth and decoding success. A few exceptional seconds should not decide a permanent antenna installation.

Include both directions when the question is two way

Ask the other operator to repeat a stable transmission and log actual power. Repeat with the roles reversed, keeping the same frequency and station settings where possible. Record the local noise at both ends. Treat any remaining directional difference as a finding to investigate, rather than immediately assigning it to polarization.

Use the result at the right level

A repeated improvement on the intended paths justifies using the better configuration operationally. A universal statement about polarization requires a broader dataset and stricter controls. There is no need to establish every mechanism before choosing the antenna that reliably completes your contacts.

Evidence limits and verification

What the evidence supports

The measured record contains preserved modes, changed ellipticity, rapidly varying orientation, polarization-selective reception, and irregular nighttime behavior. It supports keeping polarization in the explanation of skywave reception. It does not supply a universal rate of change, a universal best antenna orientation, or a hop count after which all orientations become equivalent.

The strongest practical inference is that propagation can weaken the relationship between launch polarization and the best receive setting. That is different from saying the arriving field has no polarization. Even when polarization coupling averages equally, antenna gain, arrival-angle coverage, feed loss and noise can still differ.

Studies kept in their proper roles

The main experimental group comprises work on approximately 7 MHz, 160 meters and 50 MHz amateur beacons. The multi-hop paper spans HF and is labeled accordingly. The 5.4, 5.382, 9.303 and 10.422 MHz work supplies supporting evidence outside the amateur allocations. The EuCAP diversity paper is a reviewed conference contribution, rather than a journal paper.

High-power ionospheric heating experiments are excluded from the evidence used to explain ordinary ham operation. They deliberately alter the medium. Theory and simulation explain mechanisms but are not counted as new measurements. General ham and commercial articles are not used to establish the scientific findings.

How to verify the findings

For each numerical claim, follow its reference to the original methods, figure or result. Check whether the comparison is antenna gain, modal isolation, signal-to-noise improvement or fading margin; those quantities are not interchangeable. Check whether measurements were simultaneous or switched, and whether the geometry was returning skywave or ground-to-space.

An institutional record links the 2016 solar-flare paper to the openly cataloged NVIS CIRC3 dataset, DOI 10.4121/21885825, released through 4TU.ResearchData. This provides an additional route to checking the experiment. Dataset availability has been verified from its catalog record; no independent reanalysis of the raw data is claimed here. [D1]

Terms used in the report

References for amateur frequencies

The links are clickable in Word. DOI text is retained for use from a printed copy. Bibliographic records sometimes abbreviate author lists; titles and identifiers provide the stable route to each publication.

[R1] Witvliet, B. A., et al. (2015). Measuring the Isolation of the Circularly Polarized Characteristic Waves in NVIS Propagation. IEEE Antennas and Propagation Magazine, 57(3), 120–145. DOI 10.1109/MAP.2015.2445633.

Publication | Manuscript or institutional access

[R2] Witvliet, B. A., van Maanen, E., Petersen, G. J., and Westenberg, A. J. (2016). Impact of a Solar X-Flare on NVIS Propagation: Daytime characteristic wave refraction and nighttime scattering. IEEE Antennas and Propagation Magazine, 58(6), 29–37. DOI 10.1109/MAP.2016.2609678.

Publication | Manuscript or institutional access

[R3] Witvliet, B. A., Alsina-Pagès, R. M., van Maanen, E., and Laanstra, G. J. (2019). Design and Validation of Probes and Sensors for the Characterization of Magneto-Ionic Radio Wave Propagation on Near Vertical Incidence Skywave Paths. Sensors, 19(11), 2616. DOI 10.3390/s19112616.

Publication | Manuscript or institutional access

[R4] Vanhamel, J., Machiels, W., and Lamy, H. (2022). Using the WSPR Mode for Antenna Performance Evaluation and Propagation Assessment on the 160-m Band. International Journal of Antennas and Propagation, article 4809313. DOI 10.1155/2022/4809313.

Publication | Manuscript or institutional access

[R5] Witvliet, B. A., et al. (2015). Characteristic Wave Diversity in Near Vertical Incidence Skywave Propagation. 9th European Conference on Antennas and Propagation, EuCAP 2015, pp. 1–5. IEEE document 7228318. Reviewed conference contribution.

Publication | Manuscript or institutional access

[R6] Deacon, C. J., Witvliet, B. A., Steendam, S. N., and Mitchell, C. N. (2021; online 2020). Rapid and Accurate Measurement of Polarization and Fading of Weak VHF Signals Obliquely Reflected From Sporadic-E Layers. IEEE Transactions on Antennas and Propagation, 69(7), 4033–4048. DOI 10.1109/TAP.2020.3044654.

Publication | Manuscript or institutional access

[R7] Deacon, C., Mitchell, C., Watson, R., and Witvliet, B. A. (2022). Evidence for the Magnetoionic Nature of Oblique VHF Reflections from Midlatitude Sporadic-E Layers. Atmosphere, 13(12), 2027. DOI 10.3390/atmos13122027.

Publication | Manuscript or institutional access

References for multi hop and supporting experiments

[R8] Bergadà, P., Alsina-Pagès, R. M., and Hervás, M. (2017). Polarization Diversity in a Long-Haul Transequatorial HF Link from Antarctica to Spain. Radio Science, 52, 105–117. DOI 10.1002/2016RS006136. Broad HF multi-hop campaign.

Publication | Manuscript or institutional access

[R9] Male, J., et al. (2021). Analysis of the Ordinary and Extraordinary Ionospheric Modes for NVIS Digital Communications Channels. Sensors, 21(6), 2210. DOI 10.3390/s21062210. Measurements at 5.4 MHz.

Publication | Manuscript or institutional access

[R10] Danskin, D. W., et al. (2018). Polarization Characteristics Inferred From the Radio Receiver Instrument on the Enhanced Polar Outflow Probe. Journal of Geophysical Research: Space Physics. DOI 10.1002/2017JA024731. Measurements at 10.422 MHz to a satellite.

Publication | Manuscript or institutional access

[R11] Pandey, K., et al. (2022). Polarization Characteristics of a Single Mode Radio Wave Traversing Through the Ionosphere: A Unique Observation From the RRI on ePOP/SWARM-E. Journal of Geophysical Research: Space Physics, 127, e2022JA030684. DOI 10.1029/2022JA030684. Measurements at 5.382 MHz to a satellite.

Publication | Manuscript or institutional access

[R12] James, H. G., and Prikryl, P. (2006). HF Fades Caused by Multiple Wave Fronts Detected by a Dipole Antenna in the Ionosphere. Radio Science. DOI 10.1029/2005RS003385. Analysis of a 1978 experiment at 9.303 MHz.

Publication | Manuscript or institutional access

[R13] Zhou, C., Zhao, Z., Deng, F., Ni, B., and Chen, G. (2010). Midlatitude Ionospheric HF Channel Reciprocity: Evidence From the Ionospheric Oblique Incidence Sounding Experiments. Radio Science, 45, RS6017. DOI 10.1029/2010RS004477. Broader HF two-way sounding.

Publication | Manuscript or institutional access

[D1] Witvliet, B., van Maanen, E., Petersen, G. J., and Westenberg, A. J. (2023 release). Data set of a scientific experiment involving polarisation measurements in The Netherlands of electromagnetic waves refracted in the ionosphere, NVIS CIRC3. 4TU.ResearchData. DOI 10.4121/21885825. Dataset linked to R2.

Publication | Manuscript or institutional access