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A proper 'gator, or a real crocodile?
EME is conducted on VHF, UHF, and microwave bands.
Originally EME (Earth-Moon-Earth) involved Morse code, using high power and multiple Yagis. "Super-stations", with a large array of many Yagis allowed SSB contacts, including with the normally CW stations. Nowadays, modest power, about 400 watts; and a single Yagi of a reasonable length can make these contacts, using digital modes such as Q65. Four Yagis are however preferable.
Both the length of the path to and from the moon; and fact that the moon has poor reflectivity for signals, is spherical, and has a rough surface means that the signal returning to earth is very small. The signal also undergoes Faraday rotation, meaning circularly polarised antennas are ideal. Another option is switching between vertical and horizontal antennas.
The path is also shortest at the moon's perigee, the lowest point in its orbit. This is thus a time the examiners suggest scheduling contact attempts. The highest point is the apogee (a word also used to describe something like the high-point of a person's career). A closer moon is also effectively a little "wider" in terms of the percentage of signal which strikes the surface.
Beginners with antennas which can only be rotated horizontally can work off the moon when it is rising or setting. In any case, when the moon is low is when it is possible to work from Australia to the Americas, or to Africa or Europe. The maximum distance around is around 20,000 km.
You should avoid having the sun or the Milky Way behind the moon, as both generate a lot of RF noise. The sun also swamps signals from geostationary satellites when the sun is behind them.
Despite the comments above, the ability to use legal power (1500 watts) can be valuable. Australian stations may be able to obtain a "high power permit" for EME use.
The phase of the moon is of no significance, at least on dates which are not April 1. I have seen one April issue article going into great detail, claiming it did.
Librartion is listed as a reason for fading by the examiner. It means variations in the orbit of the moon.
Meteors entering the atmosphere result in a region of ionised gas along its path in the upper atmosphere, specifically the E layer. The most suitable bands are 28 MHz to 148 MHz. Thus 6 metres works well. For Europeans, so does 4 metres.
160 metre and HF signals can travel more than half the way around the world, such as south from Sydney, and up the Atlantic to Britain, rather than across Asia. My TAFE teacher said he used to work the UK long-path from Sydney regularly before work. I can't remember definitely if it was on 20 metres, but the exam certainly says this is the most common band on which long-path occurs.
This occurs as the conditions for propagation over the short path do not exist, but they exist over the long path. In the example above, Asia would still be in darkness, while the Atlantic would still be in sunlight, or dusk.
While the exam does not discuss this, long path occurs on 6 metres as well, although this is an occasional event.
Radio waves consist of electrical and magnetic components, which are at 90 degrees to each other.
The direction of the electrical field determines the name of the polarisation. Thus a vertical antenna on a car, or a vertical Yagi, generates a vertical signal, popular for FM, DMR, and AX-25 packet. A horizontal dipole or Yagi generates a horizontal signal, popular for SSB, CW, and any weak signal modes. The latter applies to Halo and Big-Wheel antennas.
Note however the question asks the direction of the travel of radio waves. This is at right angles to both these directions, so if the electrical component is going vertically, the magnetic north and south, then my Yagi is sending vertical DMR signals to the east (or west). Were I to change polarisation to use SSB in a contest with stations to the east then the electrical would be north-south, the magnetic up-down, and the wave travelling to the east.
For a simple VHF vertical, the electrical component is vertical, the magnetic component is horizontal, and the signal radiates in all directions. If you look at the wave travelling in a single direction then again, travel is at right angles to the two components, away from the antenna.
As mentioned above, various systems use circularly polarised waves. In thee cases these components of the wave rotate. A wage can be left-hand CP, or right-hand CP.
Popular with Hams, Yagis with both vertical and horizontal elements staggered along the boom generate CP signals. Some mount the antennas with elements diagonally, so they look like &atimes;, rather than +. This ARRL article describes some you can build: Circularly Polarized Yagi Antennas for Satellite Communications. Each one is for a single band, in contrast to the "Arrow" satellite antenna, which is just a 2 metre linear Yagi, and a 70 cm linear Yagi, on one boom, at 90 degrees to each other.
Helical Yagis do the same, and are visible around Canberra, pointing north and somewhat upwards, where agencies are using upper VHF or low UHF to communicate via satellite with field operators, who presumably use something less conspicuous. I'm wondering if you could gut something like a UHF CB (used throughout the region), and replace the innards with an advanced SDR.
Serious FM broadcasters also use it, as listeners are often in cars with antennas at various angles, amongst trucks, poles, overhead wires, etc, all metallic. Others use Hi-Fi units with horizontal wire dipoles, or horizontal 3 element Yagis, etc. The broadcasting antennas use interlaced C or V shaped elements, placed of 45 degree angles. GPS uses RHCP.
Further information and images (including the broadcast ones) can be found here: CP Crossed Yagis, and in this PDF: CP Antennas Explained, without the Maths
Loss between CP and linear antennas is low, around 3 dB, far less than between vertical and horizontal antennas, or between LHCP and RHCP.
When regular linearly polarised radio waves hit a refractive medium, they refract, but a portion refracts in an unusual way, resulting in the generation of elliptically polarised waves. The Wikipedia article on Ordinary and Extraordinary Waves has interesting demonstrations of this, affecting light waves.
Until recently unexplained, this is a phenomena in which stations, especially on 6 metres, can communicate if they are a similar distance from the geomagnetic equator, a line which varies somewhat from the regular equator. Tubular formations, arcing to high altitude over the equator are now understood to provide these paths. The abbreviation is TEP.
The classic long distance multi-hop path involves signals being refracted, via the ionosphere, then bouncing from the earth's surface, before again refracting from the ionosphere (and so on) before reaching the receiving station. The alternative is that the signal reaches the higher F-layer, is refracted, then travels some distance, before again refracting from the ionosphere, before returning to the surface for reception. More than two refractions may occur. The benefit is that the signal suffers less loss, partly because it is not relying on reflections from earth.
Diagrams online suggest that this tends to happen via paths which are in darkness, even if the stations half a world apart are in daylight; while those involving bounces from the earth's surface are in daylight. Others indicate that the signal becomes trapped in the F-layer for some distance (behaving a little like a tropospheric duct, I suppose).
You can watch this video regarding it here: Chordal Hop Propagation
One of the hobbies adjacent to Amateur Radio is Medium Wave broadcast band (AM) DXing, logging stations beyond their official service areas. This can use anything from a car radio (which have RF amplifier stages, unlike some low coast radios) to high-end receivers (Icom R-9500, etc), the receiver of a high-end Amateur unit. A few tens of metres or wire, up to a Beverage, or a loop consisting of multiple turns of wire on a timber frame. Another option is a monster loop-stick antenna, consisting of two bundles of 7 ferrite rods, glued together, then these bundles glued end to end, with enamelled wire wound on them, and mounted so it can be rotated.
Stations in rural Queensland can be heard in NSW, along with those from Victoria, and 1035 kHz from NZ. Occasionally longer distance propagation, such as Australia to Alaska is possible.
Propagation on this band is very much more effective in the hours of darkness, when the D-layer dissipates, so that thee signals reach the higher layers, allowing propagation over hundreds to low thousands of kilometres.
Before things like radio via satellite TV systems this was the only way for many to get news, although Australia did have domestic shortwave services, the last in the Northern Territory, shutdown by the right-wingers in 2017, as they primarily served remote first nations communities with vital weather information, as well as news, entertainment, and Aussie Rules game calls.
These effects were also used for eastern European countries to provide news and cultural broadcasts to western Europe in the 1980s, in addition to longwave and shortwave broadcasts. Significant power was often used, to ensure reception by simple consumer radios.
While not on MW, Radio Habana Cuba does broadcast into the US, in English and Spanish.
Given 160 metres is just above the upper end of this band, it most often has longer distance propagation during periods of darkness at both stations.
In the daytime ground wave is the primary mode of propagation. This requires vertically polarised signal, generated by a vertical antenna or "mast"*. Ideally it would be 40 metres tall or more, although in practice it is likely less. The higher the frequency, the smaller the ground-wave range.
An off-exam comment is that serious 160 metre operations often use more than one antenna, say a vertical for transmitting, and a wire for receiving, although this is not necessary to try the band. While dipoles are not necessarily commonly used on this band, they remain an option for those with the land available.
MW (AM) broadcasting generally aims to generate ground-waves, so as you drive near your local swampy or estuarine area, you may see a large guyed vertical tower, to generate the required vertically polarised signals. Meanwhile, operating very close to salt water can be an option for portable MF / HF operation as it can provide good DX.
From 2.3 to somewhere north of 5 MHz (depending on the country and the legality of the operation) several bands such as 120 metres are used for "tropical band" broadcasting. This is partly because the medium wave band suffers from interference from frequent lightning storms in the tropics. These signals can often be heard beyond the tropics in the evening.
*In Australia you need to apply for a "mast", never a "tower", or the council loses their tiny minds, thinking of a huge commercial structure. Smaller antennas, such as VHF or UHF Yagis, VHF+ verticals, small-medium dishes, shade structures, flagpoles may comply with Exempt and Complying Development Code. The part re height is a little garbled, and while the they probably intend to place a limit of 10 metres above ground, if can be read that the support structure (mast) may be 10 metres, with an antenna on top of that. Thus a 1 metre post may support a 43 foot (13.1 metre) radiating element.
The DX Engineering 160 Meter THUNDERBOLT Vertical Antenna mounts on thick-walled tubing with 0.9 metres above ground, 1.2 metres below.
Temperature inversions are can cause "ducts" to form, which convey radio waves over significant distances. For VHF (especially 2 metres) into the microwave band ranges of 150 to 500 km (100 - 300 miles) are possible. In Australia east coast highs causing hot, dry summer weather also indicate VHF-DX may be possible. Where I live Telstra periodically screws up, and my town loses coverage from the single site on the nearby hill. Interestingly, taping a 'phone to a 8 metres of tubing may mean it catches a signal from a distance cell. Or ducts form at 3 or 4 am, so that the signals bend to near ground level, and various notifications or SMSs arrive.
This occurs when a section of the E layer becomes strongly ionised, allowing upper HF through to VHF signals to propagate several thousand kilometres. This includes 2 metres, 4 m, 6 m, and 10 m bands, 11 metre CB, FM broadcast, and previously TV (which has mostly vacated the bands which are enhanced by this, although ATSC 3.0 can benefit), and exceptionally, 1.25 metres. The normal upper limit (MUF) for E-layer is 15 MHz. Whether Sporadic-E, or tropospheric ducting, is responsible, long distance propagation can occur on marine VHF (156 to 162 MHz).
There would also be opportunity for confusion on aviation VHF, although flight numbers or callsigns are used frequently for safety: "Wombat 215 descend to 2000". Roger Sydney Approach, Wombat 215 descending to 2000". Or for general aviation, "Yankee Juliet Sierra, maintain 3000", meaning VH-YJS. If they start hearing "Thanks Auckland, Kiwi one-sux climbing to 5000" clearly something odd must be happening.
It occurs close to the summer solstice in each hemisphere, and to a lesser extent the winter one. It most often occurs between sunrise and sunset.
There is a handy diagram at: Wikipedia: Sporadic E propagation
For 8 metres (40 MHz+) and 5 metres (56 MHz) sporadic-E apply, as would meteor scatter, allowing typically one-way reception, or for beacons to be heard. Were they available where TEP occurs, the same would apply. Low and mid-band VHF used by various agencies would also be affected. Ditto F2.
While UV light is part of the process, metallic material ablated from meteors is likely also be a factor.
Off this section at least, F2 the upper layer of the ionosphere, normally only supporting HF can provide an increase in the MUF over paths such as Europe to Australia rising through 11 and 10 metres, to low VHF, 6 metres, and a little higher. This also allowed very long distance propagation of analogue TV in the lowest channels. It is less common than Sporadic-E.
FM-DX and TV-DX are also hobbies, often using high gain Yagis, or arrays of them.
The Space Weather Service of the BOM in Australia has a great guide, in PDF form, with two editions: 2016 version and Undated version
The UK Six Metre Group is here: UKSMG
As always, these are the actual questions from the Extra licence exam pool, as published by the NCVEC.
E3A01
What is the approximate maximum separation measured along the surface of the Earth between two stations communicating by EME?
A. 2,000 miles, if the moon is at perigee
B. 2,000 miles, if the moon is at apogee
C. 5,000 miles, if the moon is at perigee
D. 12,000 miles, if the moon is "visible" by both stations
This is something like 19,000 km, or 12,000 statute miles, answer D.
A friend's first EME contact was from Sydney to Switzerland. The moon was low in the west at this time in Sydney.
E3A02
What characterizes libration fading of an EME signal?
A. A slow change in the pitch of the CW signal
B. A fluttery, irregular fading
C. A gradual loss of signal as the Sun rises
D. The returning echo is several hertz lower in frequency than the transmitted signal
This is fluttery, irregular fading on the signal, answer B.
E3A03
When scheduling EME contacts, which of these conditions will generally result in the least path loss?
A. When the Moon is at perigee
B. When the Moon is full
C. When the Moon is at apogee
D. When the MUF is above 30 MHz
The moon is at its perigee, the lowest part of its orbit, answer A.
This is also when people talk about a "super-moon" if it coincides with full moon, as it appears a little larger than normal.
E3A04
In what direction does an electromagnetic wave travel?
A. It depends on the phase angle of the magnetic field
B. It travels parallel to the electric and magnetic fields
C. It depends on the phase angle of the electric field
D. It travels at a right angle to the electric and magnetic fields
The signal travels at a right angle to the electric and magnetic fields, answer D.
E3A05
How are the component fields of an electromagnetic wave oriented?
A. They are parallel
B. They are tangential
C. They are at right angles
D. They are 90 degrees out of phase
These are at right angles, answer C.
E3A06
What should be done to continue a long-distance contact when the MUF for that path decreases due to darkness?
A. Switch to a higher frequency HF band
B. Switch to a lower frequency HF band
C. Change to an antenna with a higher takeoff angle
D. Change to an antenna with greater beam width
The lower the sun, the lower the frequency, so switching to a lower band may well allow resumption of communications, answer B.
60 metres is one of the bands useful for dusk or night-time communications.
E3A07
Atmospheric ducts capable of propagating microwave signals often form over what geographic feature?
A. Mountain ranges
B. Stratocumulus clouds
C. Large bodies of water
D. Nimbus clouds
Ducts often form over bodies of water, answer C.
E3A08
When a meteor strikes the Earth's atmosphere, a linear ionized region is formed at what region of the ionosphere?
A. The E region
B. The F1 region
C. The F2 region
D. The D region
The is the E layer, answer A.
E3A09
Which of the following frequency range is most suited for meteor-scatter communications?
A. 1.8 MHz - 1.9 MHz
B. 10 MHz - 14 MHz
C. 28 MHz - 148 MHz
D. 220 MHz - 450 MHz
28 to 148 MHz are the most suitable bands, answer C.
In part choice of band depends on local practice, and bands are available to willing participants, 6 metres (50 MHz) is often the ideal band. 4 metres (70 MHz) also has potential, for those in Region 1.
E3A10
What determines the speed of electromagnetic waves through a medium?
A. Resistance and reactance
B. Evanescence
C. Birefringence
D. The index of refraction
The index of refraction is a way of expressing the inverse of the speed of light in a vacuum (the constant c), answer D.
Signals slow slightly in air, varying with temperature and pressure, permitting bending of the signal at transitions, such as temprature inversions. Dielectric materials (plastics) can also influence microwave signals too.
E3A11
What is a typical range for tropospheric duct propagation of microwave signals?
A. 10 miles to 50 miles
B. 100 miles to 300 miles
C. 1,200 miles
D. 2,500 miles
Tropo carried microwave signals can travel 150 to 500 km (100 - 300 miles), answer B.
For Sydney-siders things such as Hornsby to Cabbage Tree Mountain north of Port Stephens (190 km); or Carlingford to Wagga Wagga (370 km); are in this range.
E3A12
What is the cause of auroral activity?
A. The interaction in the F2 layer between the solar wind and the Van Allen belt
B. An extreme low-pressure area in the polar regions
C. The interaction in the E layer of charged particles from the Sun with the Earth’s magnetic field
D. Meteor showers concentrated in the extreme northern and southern latitudes
Fast moving charged particles from the sun interact with the Earth's magnetic field, creating visible emission from the sky, and reflecting radio signals, answer C.
E3A13
Which emission mode is best for aurora propagation?
A. CW
B. SSB
C. FM
D. RTTY
As the signal is fluttery (distorted) due to the motion of the charged regions, CW works best, answer A.
E3A14
What are circularly polarized electromagnetic waves?
A. Waves with an electric field bent into a circular shape
B. Waves with rotating electric and magnetic fields
C. Waves that circle the Earth
D. Waves produced by a loop antenna
CP waves have a rotating electric and magnetic fields, answer B.
E3B01
Where is transequatorial propagation (TEP) most likely to occur?
A. Between points separated by 2,000 miles to 3,000 miles over a path perpendicular to the geomagnetic equator
B. Between points located 1,500 miles to 2,000 miles apart on the geomagnetic equator
C. Between points located at each other's antipode
D. Through the region where the terminator crosses the geographic equator
TEP is propagation between two mid-latitude points roughly the same distance either side of the magnetic equator, for stations 2000 to 3000 apart, answer A.
This typical figure is 3200 to 4800 km.
E3B02
What is the approximate maximum range for signals using transequatorial propagation?
A. 1,000 miles
B. 2,500 miles
C. 5,000 miles
D. 7,500 miles
TEP provides a range of up to 8000 km, or 5000 miles, answer C.
E3B03
At what time of day is transequatorial propagation most likely to occur?
A. Morning
B. Noon
C. Afternoon or early evening
D. Late at night
Afternoon or early evening, answer C.
Presumably, the recently discovered tubular structures evolve in the presence of solar radiation.
E3B04
What are "extraordinary" and "ordinary" waves?
A. Extraordinary waves describe rare long-skip propagation compared to ordinary waves, which travel shorter distances
B. Independently propagating, elliptically polarized waves created in the ionosphere
C. Long-path and short-path waves
D. Refracted rays and reflected waves
These are elliptically polarised waves generated in the ionosphere, answer B.
E3B05
Which of the following paths is most likely to support long-distance propagation on 160 meters?
A. A path entirely in sunlight
B. Paths at high latitudes
C. A direct north-south path
D. A path entirely in darkness
160 metres is slightly above the AM / MW broadcast band. You may have noticed that the band is full of distant stations at night. These may cross the Tasman, or 1500 km, across land. Thus it is paths in darkness, answer D.
This was also used from eastern to western Europe, as well as Radio Free Europe into Russia on 1386 kHz, a service apparently recently discontinied by Putin's asset in Washington.
E3B06
On which of the following amateur bands is long-path propagation most frequent?
A. 160 meters and 80 meters
B. 40 meters and 20 meters
C. 10 meters and 6 meters
D. 6 meters and 2 meters
40 and 20 metres are effective DX bands, with signals easily going more than half way around the globe, answer B.
E3B07
What effect does lowering a signal's transmitted elevation angle have on ionospheric HF skip propagation?
A. Faraday rotation becomes stronger
B. The MUF decreases
C. The distance covered by each hop increases
D. The critical frequency increases
A good vertical antenna emits signals at a low angle of elevation, resulting in the distance covered by each hop increasing, answer C.
E3B08
How does the maximum range of ground-wave propagation change when the signal frequency is increased?
A. It stays the same
B. It increases
C. It decreases
D. It peaks at roughly 8 MHz
Ground wave in the primary propagation mode for medium wave broadcasting covering 150 kms or more in rural areas. Something like 27 MHz CB has a significantly shorter range, unless ionospheric propagation, or "skip" occurs. Thus ground-wave range decreases with frequency, answer C.
E3B09
At what time of year is sporadic-E propagation most likely to occur?
A. Around the solstices, especially the summer solstice
B. Around the solstices, especially the winter solstice
C. Around the equinoxes, especially the spring equinox
D. Around the equinoxes, especially the fall equinox
This is especially early summer, but also to a lesser extent early winter, around the solstices, answer A.
This is the timing of the late spring and early-mid summer VHF-UHF Field Days in Australia, and the occasional winter version.
E3B10
What is the effect of chordal-hop propagation?
A. The signal experiences less loss compared to multi-hop propagation, which uses Earth as a reflector
B. The MUF for chordal-hop propagation is much lower than for normal skip propagation
C. Atmospheric noise is reduced in the direction of chordal-hop propagation
D. Signals travel faster along ionospheric chords
The successive ionospheric reflections, without the intermediate reflection from the ground of typical multi-hop propagation, means the signal experiences less loss, answer A.
E3B11
At what time of day is sporadic-E propagation most likely to occur?
A. Between midnight and sunrise
B. Between sunset and midnight
C. Between sunset and sunrise
D. Between sunrise and sunset
While "sporadic" suggests randomness, and this can occur at any time, daylight hours are the most ussual times, answer D.
E3B12
What is chordal-hop propagation?
A. Propagation away from the great circle bearing between stations
B. Successive ionospheric reflections without an intermediate reflection from the ground
C. Propagation across the geomagnetic equator
D. Signals reflected back toward the transmitting station
These are successive ionospheric reflections, without the usual intermediate reflection from the ground, meaning less loss, answer B.
E3B13
What type of polarization is supported by ground-wave propagation?
A. Vertical
B. Horizontal
C. Circular
D. Elliptical
You will likely have noticed MW-AM broadcast antennas consist of tall vertical tower(s), producing a vertically polarised signal in order to serve a city or rural area via ground-wave propagation, answer A.
HF signals can travel along the terminator between daylight and darkness, termed the gray-line or grey-line. If you were aboard the ISS you would see this dusk or dawn zone as a broad grey line. This is useful for MW and HF propagation. This occurs because the D layer disappears rapidly at sunset. It also takes some time to build as the sun rises. The D layer absorbs MW and low HF signals, so when it dissipates signals can reach the higher layers.
For US listeners, this gives a chance to hear distant MW broadcast stations, and timing it so it is just dark at the station, but they are still at the higher daytime power and antenna configuration helps. These change monthly, so the darker end (or beginning) of the month is better.
On to: Propagation 2 - Radio horizon, propagation prediction & space weather
You can find links to lots more on the Learning Material page.
Written by Julian Sortland, VK2YJS & AG6LE, March 2026.
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