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This covers HF propagation, a topic in some ways more complex than VHF propagation, as it involves the ionosphere, and thus depends on sunspot cycles to a far greater extent.
At times, especially when there is sunspot activity, this works up to and beyond the "11 metre" band (27 MHz), where CBers talk of "working skip". It also extends into the VHF-Low area, such as 30 to 40 MHz, previously used heavily for forestry, electrical transmission repair workers, bush-fire control and police, so when this "skip" was running, the dopey LA police dispatchers would be trying to tell south-coast NSW (Australia) bush fire captains to get off "their" frequency.
Over 11 years, the activity of the sun becomes more and less, although in one of every two cycles the maximum is less pronounced.
Sunspots are areas of darkness on the surface on the sun. These can be view by projecting the image of the sun onto a card using a pinhole in a second card held in front of it, or projected using a small telescope, such as a rifle scope, also with a card around it. These are in areas of high magnetic flux. High sunspots correlate to a more strongly ionised ionosphere, meaning radio waves are more strongly refracted. Low sunspot numbers correlate to poor propagation, especially for upper HF and 6 metre bands.
Low sunspot numbers also correlate to a reduction in temperatures on earth, although, in recent years it led only to a pause in the upward trend, getting the science deniers all excited. An extended period of few sunspots from 1645 to about 1715 was termed the "Maunder Minimum" for Annie Russell Maunder and E. Walter Maunder; in combination with volcanic activity, resulted in a cooler period in North America and Europe. This, coupled with the restriction to the flow of the Thames by the medieval London Bridge (not Tower Bridge), allowed the river to freeze, and thus "Frost Fairs" on the frozen surface.
Unfortunately some hams get all discouraged, and sell their gear during the minimum, rather than pursue different aspects of the hobby.
The surface of the sun rotates on its axis in 28 days, or more correctly, rotates such that the same point is facing the earth 28 days later. This means that if there is a high number of sunspots facing earth for several days, this may be repeated 4 weeks later.
Zero sunspots does NOT mean no propagation, but it is likely this would take place at lower HF frequencies.
If two HF stations are within a few kilometres of each other, and there is not a significant ridge between them, which would also impede a VHF signal, there should be a ground-wave path.
At most times over moderate range, bands such as 80 metres provides reliable night-time propagation, and 40 metres local daytime coverage, and DX at night. 20 metres provides daytime DX. Above these frequencies, from 15 metres to 6 metres, and 4 metres in Europe and Africa where it is available, high solar activity means that these bands go from being short range to being DX bands. (This also applies on 27 MHz CB.)
The sun emits electromagnetic radiation from radio signals, including microwaves, to light, including ultraviolet, and X-rays. These all take 8 minutes to reach us. The strength (flux) of this emission at 10.7 centimetres (around 2800 MHz or 2.8 GHz) is a predictor of ionospheric behaviour.
You can see images, and read more here: Wikipedia: Sunspot. You can also use a card with a pinhole to project an image of the sun onto a second card; or place a card around a small telescope, such as a telescopic rifle sight, and use this to project onto the card.
Both large X-ray bursts, and Coronal Mass Ejections, may have a serious negative impact on HF communications, including what may be termed a "communications blackout".
While there were episodes of strong solar activity during mid and late 2023, thankfully these only brought about Aurora to lower latitudes, and poor HF propagation. I did manage to produce a photograph with a dull red glow, using a 30 second exposure at ISO 3200.
A Class-X flare, at level X6.3 occurred late on 22 February 2024 UTC, which was 8:30 standard time (9:30 summer time) in eastern Australia on Friday the 23rd, meaning we were essentially facing the sun. This meant that HADARC's 40 metre net went from good signals from stations across eastern NSW (VK2) to nothing but the most local stations being audible, in a moment.
CMEs are matter, so take typically a few days to arrive. They consist of charged particles. Among other things, the cause aurora, a display of typically green or red light in the direction of the poles.
Off the exam, if you watch TV, or listen to radio delivered via satellite, either to your home, or to the broadcasting site on the local hill, then near the solstices, the sun may "process behind the satellite", meaning at some point during the day for maybe 20 minutes, the sun's RF emission will swamp the satellite's signal. Where I live this occurs for maybe a week each spring and autumn, for about a week, during late morning or early afternoon.
Once we move further apart, at any one time, between any two points there may or may not be an HF communication path. When there is, there is a LUF - lowest usable frequency, and a MUF - the maximum usable frequency.
When the difference between the LUF and MUF closes to zero, there is no propagation via the ionosphere.
Given that between the traditional bands, 160, 80, 40, 20, 15, and 10 metres, there are the WARC bands, 30, 17, and 12 metres, there is a reasonable chance that one will fall between the LUF and MUF. At night this may instead be the 60 metre band. This one is only available in some countries.
Perhaps not mentioned on the exam, noise on the lower HF bands, such as 80 metres can be a problem. At the same time, the MUF can be below 7 MHz. In this case, the solution can be to use the 60 metre (5 MHz band).
If you are a ham in a country which is yet to enact the outcome of the latest World Radio Conference to permit Amateur operations on 60 metres, contact the national or federal communications or posts & telecommunications minister, to give the national regulator a prod. This currently includes Australia.
Around the world, especially in countries where HF communications are important, government agencies provide predictions of the conditions over the upcoming week, and beyond.
One of the markers of 6 metre propagation was long distance propagation of the lower VHF analogue TV channels, but these are rapidly being replaced by digital systems, and while in some cases they are using the US ATSC system on low VHF, in most cases DVB-T is in the upper VHF and lower UHF bands only. Note that the TV related answer to the question regarding testing for HF propagation is one of the wrong ones, because this is outside the HF bands in the question.
(DVB-T, is apparently less easy to decode under DX conditions. Incidentally, choosing ATSC over the near global DVB-T was all about having consumers pay for equipment made more expensive by the inclusion of patented techniques, which require the payment of fees by the manufacturers).
Even at lower HF, such as 40 metres, propagation from Sydney to Central Western NSW can develop between 9 and 10 am, and even when this path is closed, it is possible to hear stations from Victoria or Tasmania. One odd phenomena was than club members in northern Sydney could talk locally via NVIS or ground-wave, while two members who had moved away, one to Newcastle, the other to the Snowy Mountains, could have a separate conversation on the same frequency, skipping over us, then sometime later re-appear on the Sydney net.
As you may expect, the higher F layers provide longer distance single hop propagation that the lower E layer. Not mentioned in this paper, but rather in the Extra, signals can make several hops to provide much greater communications distances than mentioned in the questions below. This can be by bouncing off the ground and back to the ionosphere; or it can be by travelling to a second, more distant area of the ionosphere, without touching down, called a "chordal hop".
A single E-layer hop provides coverage over nearby states if in the US, or nearby countries for Europeans. A single F-layer hop may cross the US or EU; or perhaps the Atlantic, or from eastern Australia to NZ.
The magic numbers are 1200 miles for the E-layer, and 2500 such units for the F2.
Frequencies approaching the MUF are most likely to provide the best propagation over the greatest distance using ionospheric or "sky-wave" propagation.
Note that, for some hams, they are not seeking the optimal frequency to communicate with a place right now, but may be looking for a time when there is propagation on a particular band. This is because they are trying to get an award, such as Worked All States, or DXCC on a particular band.
The Australian Space Weather Forecasting Centre provides services of global significance. The left hand menu provides both Australasian and Global services. For hams useful examples include: Hourly Area Predictions (HAP) charts (maps) and the more advanced HF prediction tools. The Local Area Mobile Predictions (LAMP) charts, such as for UK Cadets, are also useful. Ionograms show the height of reflective layers above the station in question, across the HF spectrum, noting that a few only show historic data.
The Ionosondes used to generate ionograms may be heard as an occasional "whoop" or "chirp", as they sweep the spectrum. It appears that LSB should produce downwards tone, USB upwards.
The US (NOAA), Brazil, and the UK are examples of other operators of these systems. The UK system requires registration (free and instant), providing access to the current Ionosondes, and some information on interpretation. Data from Chilton should be available, and potentially Port Stanley. Choose here: Index. (Stanley has been down for some time, as of 2 June 2024.)
Off the exam, DXCC is the DX Century Club, a certificate for Amateurs who have contacted or "worked" 100 countries, or country-like entities, such as autonomous regions (eg, Åland, south-west of Finland), the constituent nations and crown dependencies of the UK, and various islands. The United Nations HQ and the ITU HQ are also entities.
A range of national associations provide these certificates to hams in their countries. They may also issue awards relating to their region. That said, if you are outside the US and wish to get Worked All States, you would apply to the ARRL.
Kaliningrad (currently an isolated portion of Russia), and Asiatic Russia are separate to European Russia, as is Franz Josef Land in the Arctic. Hopefully Putin will be unequivocally removed from office soon, and Russia's relations normalised.
Entities are added or deleted due to decolonisation, the formation of new countries (South Sudan) and reunification (Germany), or even the whim of a committee re-interpretation of rules regarding the separation distance of islands. It is possible that something like working the same Scottish Amateur the day before, and on the first day of Independence may count as two countries.
The island territories around Australia are further examples, each having the VK9 prefix. A few have resident Amateurs, but some are only "activated" by periodic DXpeditions. The sovereign territories of "Heard Island and McDonald Islands", Macquarie Island (nominally part of Tasmania), and the Antarctic claims are VK0. Tasmania (VK7) is not an entity, as it has islands close to Victoria (VK3), and a 85 metre land border on Boundary Islet (oops). The nations which make up the Realm of New Zealand are each entities, as are several islands and territories of the nation of New Zealand (Aotearoa).
Likewise, Alaska, and multiple US related islands count as entities. Some are not occupied, and thus the USPS is unable to deliver mail there, meaning the FCC has decided to refuse to issue callsigns for them, despite allocated prefixes, so ordinary calls with a location suffix must be used. Saint Pierre and Miquelon is FP; Greenland OX. CM and CO are Cuba, and yes, US Hams are free to speak to them. Canada has various V prefixes, plus two extra entities: CY0 is Sable Island (population 3); VY9 St Paul Island (uninhabited). The Bahamas, Bermuda, and various other nations, colonies and similar political entities in this area, which are DXCC entities. Mexico, and the nations of Central and northern South America are likely easy to contact. Of course, you and a buddy or two can set off to be the DX!
Perhaps the smart ham club would ensure school, public, or community libraries on populated islands have ham radio licence manuals relevant for licensing by the administering country's government.
For Europeans there are many nations in the EU and beyond; microstates, such as San Marino (Y7); areas related to Spain, the Balearic Is. EA6-EH6, Canary Is (EA8-EH8), and the exclaves in northern Africa, Ceuta & Melilla (EA9-EH9); Israel (4X & 4Z); Gibralter (ZB2); Cyprus (5B, C4, P3) and the UK Bases there (ZC4); and the nations of north Africa. Stand on Snaefell on the Isle of Man (GD) and you can work this island, Scotland (GM), England (G), Wales (GW), Ireland (EI & EJ), and before a possible upcoming reunification, Northern Ireland (GI). These would need to be direct contacts, not via a repeater to count.
Both Taiwan (Republic of China), prefix BU-BX; and China (PRC), prefix B, are valid countries for DXCC, for territories they have control over. (Both governments claim all sovereignty over all such territory, and a country can only have diplomatic relations with one Taipei or Beijing.) Countries, even with their own parliaments, which are not recognised by the UN tend not to be DXCC entities; Somaliland, as opposed to Somalia, is an example.
The Vatican is HV (it also has a reliable postal service, with its own stamps, and yellow post boxes).
With headquarters in Rome, the Sovereign Military Order of Malta is a medical aid organisation recognised as sovereign since 1113(!), uses 1A (and provides a limited postal services). This is different to Malta, 9H. The UN and ITU share 4U.
A list is here: WIA: DXCC List The ▲ & ▼ arrows allow sorting by various criteria (although as of early 2024 the script is not behaving). You can also search for "arrl dxcc list pdf", given the file name of the PDF of the current version contains a year number; ignore the link to the page listing a printed version fro sale.
Note that if a person is operating a station under a CEPT agreements (Recommendations T/R 61-01 or (05)06); under Inter-American Telecommunication Commission (CITEL) rule, or bilateral arrangements, then the contact counts for the country in which the operation is taking place. Thus FK/VK2YJS counts for New Caledonia, MM/AG6LE for Scotland (currently a part of the UK, this may change). You could be talking to a station operating mobile in the UK, and if they cross the Welsh - English border eastbound, they change from 2W0ABC to 2E0ABC (or GW7XY to G7XY)- two countries in one QSO!
In some cases islands are protected areas with strict restrictions on access to protect the ecology.
By the way, Russia and Belarus have been suspended from the CEPT, and thus the agreements above. This currently does NOT prevent you making contacts with stations there, should you wish.
As with VK0, the various other Antarctic claims are also counted as entities.
There are several ways to assess the current propagation situation:
These include using the NCDXF / IARU International Beacon Network on 14.100, 18.110, 21.150, 24.930, and 28.200 MHz. The North American ones are located in Hawaiʻi, California, on the UN building in NYC (4U1UN), and Nunavut, northern Canada. Downunder they are in New Zealand and Perth. Using the top of the hour as a reference, the station 4U1UN in NYC transmits on 14.100 MHz. It the next 10 second block, it transmits on 18.110 MHz while the 14.100 baton is passed to VE8AT in Eureka, Nunavut, Canada; then to California and across the Pacific, through Asia and Israel, to Europe, Africa, and South America, finishing in Venezuela. Given that there are 18 stations, the cycles starts again 3 minutes (180 seconds) after the top of the hour, and so on. See: NC DX Foundation Beacons and WIA IBP information page
While these have been replaced by a question regarding Reverse Beacons, they are still of importance to Amateurs interested in making international or transcontinental contacts.
From 10 metres and up, US Amateurs may operate beacons under their personal licence, in accordance with their licence conditions. In Australia Amateurs must obtain a specific beacon licence, except for operation in periods during which the transmitter is attended. In both cases it may be best to operate it in co-operation with a club.
There are many other beacons, starting at 28 MHZ (10 metres) which typically send their callsign in Morse, often continuously. They go through VHF, UHF, and into the microwave bands, the highest in Australia being at 24 GHz. Occasionally beacons are licensed in non-Amateur spectrum to allow things such as research, and early notification of openings.
Things like hearing NZ CB on 26 MHz can also indicate high HF propagation. Shortwave reception may also be useful, noting however that in many cases these stations operate an 100 kW or more.
A Reverse Beacon receives your signal, sent in Morse, and publishes your callsign on the reverse beacon website, with frequency information. To use them send CQ DE WG7ABC or TEST DE WG7ABC, repeating the call a few times. These, and and a separate network also listen for the IARU beacons above. These appear to be what the examiner is referring to by "a network of receiver stations". You can visit: www.reversebeacon.net/
The KiwiSDR system is a groups of Software Defined Radios connected to the Internet. These allow is anyone (Ham or otherwise) to listen to radio signal in any analogue voice mode, DRM, or CW, from Longwave to 30 MHz, and a few also covering 6 metres. Thus you can wear headphone, and listen to your own signals. SAM is Synchronous AM, which assists receiving signals under some fading conditions. See: KiwiSDR
One distractor mentions hearing dots sent by your own station. This would require that your signal travels all the way around the world, something NOT necessary for you to communicate with stations across the ocean, or across the continent. The time between transmission and the signal arriving is about 1/7 second, and this is not necessarily a common thing, as there may not be paths for the frequency you using covering a full circle that often. Another way to think of it is that there may be a short path or a long path, to a distant place, but not both.
These are actual questions from the General exam pool. They use statute miles, 1.60934 km or 1,609.34 metres, or 5280 smelly feet, rather than the nautical version.
G3A01
How does a higher sunspot number affect HF propagation?
A. Higher sunspot numbers generally indicate a greater probability of good propagation at higher frequencies
B. Lower sunspot numbers generally indicate greater probability of sporadic E propagation
C. A zero sunspot number indicate radio propagation is not possible on any band
D. A zero sunspot number indicates undisturbed conditions
A higher sunspot number correlates with better propagation for the upper HF (and low VHF) bands, answer A.
This includes 6 metres, but can reash 4 metres (70 to 70.6 MHz), Ireland has 8 metres (40-45 MHz plus smaller segments), and 5 metres, 54 to 69.9 MHz. WL2XUP was an Experimental station, running a beacon at 40.6635 MHz.
G3A02
What effect does a sudden ionospheric disturbance have on the daytime ionospheric propagation?
A. It enhances propagation on all HF frequencies
B. It disrupts signals on lower frequencies more than those on higher frequencies
C. It disrupts communications via satellite more than direct communications
D. None, because only areas on the night side of the Earth are affected
A Sudden Ionospheric Disturbance impacts the lower HF bands more than higher frequencies, answer B.
Given these are caused by X-rays emitted from flares, and X-rays arrive at the speed of light, hence the "sudden" nature of the occurrence, these affect earth-facing parts of the earth, in other words, those experiencing "daytime".
G3A03
Approximately how long does it take the increased ultraviolet and X-ray radiation from solar flares to affect radio propagation on the Earth?
A. 28 days
B. 1 to 2 hours
C. 8 minutes
D. 20 to 40 hours
As these are forms of electromagnetic radiation, like visible light, the standard 8 minutes to cover this distance applies, answer C.
G3A04
Which of the following are least reliable bands for long-distance communications during periods of low solar activity?
A. 80 meters and 160 meters
B. 60 meters and 40 meters
C. 30 meters and 20 meters
D. 15 meters, 12 meters, and 10 meters
Upper HF bands are least useful for long range communications during low solar activity, so 15, 12, and 10 metres, answer D.
CBers may recognise that the behaviour of traditional HF / 27 MHz / 11 metre CB varies over an 11 year cycle, with short range during some years; and long distance, occasionally global communications in others.
It could also be said that these bands behave more like VHF at these times.
G3A05
What is the solar flux index?
A. A measure of the highest frequency that is useful for ionospheric propagation between two points on Earth
B. A count of sunspots which is adjusted for solar emissions
C. Another name for the American sunspot number
D. A measure of solar radiation with a wavelength of 10.7 centimeters
The sun emits electromagnetic radiation on a wide range of frequencies or wavelengths, including the high UHF (low microwave) band, in this case those with a wavelength of 10.7 cm, the strength (flux) of which is a measure of the activity of the sun, answer D.
G3A06
What is a geomagnetic storm?
A. A sudden drop in the solar flux index
B. A thunderstorm that affects radio propagation
C. Ripples in the geomagnetic force
D. A temporary disturbance in Earth's geomagnetic field
Geomagnetic contains words meaning earth and magnetic, so it is a temporary disturbance in the Earth's geomagnetic field (magnetosphere), answer D.
G3A07
At what point in the solar cycle does the 20-meter band usually support worldwide propagation during daylight hours?
A. At the summer solstice
B. Only at the maximum point
C. Only at the minimum point
D. At any point
20 metres is a world-wide DX band, and provides daytime propagation at any time during the solar cycle, answer D.
G3A08
How can a geomagnetic storm affect HF propagation?
A. Improve high-latitude HF propagation
B. Degrade ground wave propagation
C. Improved ground wave propagation
D. Degrade high-latitude HF propagation
HF performance at high latitudes (polar and near-polar regions) is degraded, answer D.
Remember that ground wave propagation does NOT rely on the ionosphere, and that the only threat to communication using it is lightning crashes or other interference, either local, or carried into the area via the ionosphere. Recent (early-mid 2024) geomagnetic events have caused blackouts of HF communications, along with spectacular aurora (and crazies making inane posts about HAARP, spraying chemicals, etc).
G3A09
How can high geomagnetic activity benefit radio communications?
A. Creates auroras that can reflect VHF signals
B. Increases signal strength for HF signals passing through the polar regions
C. Improve HF long path propagation
D. Reduce long delayed echoes
Aurora, created by high geomagnetic activity, can reflect VHF signals, answer A.
If you have studied the previous pool, the long path answer has been removed as the "correct" answer.
G3A10
What causes HF propagation conditions to vary periodically in a 26- to 28-day cycle?
A. Long term oscillations in the upper atmosphere
B. Cyclic variation in Earth’s radiation belts
C. Rotation of the Sun’s surface layers around its axis
D. The position of the Moon in its orbit
The rotation of the surface of the sun causes a variation over a 28 day period, answer C.
G3A11
How long does it take a coronal mass ejections to affect radio propagation on Earth?
A. 28 days
B. 14 days
C. 4 to 8 minutes
D. 15 hours to several days
This question is about particles, which being matter must travel more slowly than light. They are never-the-less fast, arriving in 15 hours, to a few days, answer D.
This means that there is a period to prepare for the disruption to HF signals, and other issues, including impacts of power networks. These may also generate news stories regarding upcoming aurora.
G3A12
What does the K-index measure?
A. The relative position of sunspots on the surface of the Sun
B. The short-term stability of the Earth’s magnetic field
C. The short-term stability of the Sun’s magnetic field
D. The solar radio flux at Boulder, Colorado
It is the short term stability the magnetic field around the Earth, answer B.
G3A13
What does the A-index measure?
A. The relative position of sunspots on the surface of the Sun
B. The amount of polarization of the Sun's electric field
C. The long-term stability of the Earth’s geomagnetic field
D. The solar radio flux at Boulder, Colorado
This is the long term stability of the geomagnetic field ("geo" meaning relating to Earth), answer C.
G3A14
How is long distance radio communication usually affected by the charged particles that reach Earth from solar coronal holes?
A. HF communications is improved
B. HF communications is disturbed
C. VHF/UHF ducting is improved
D. VHF/UHF ducting is disturbed
HF communications are disturbed during this time, answer B.
Even in the late 1990s large aircraft such as Classic 747 models (-100, -200, -300) and 767s relied on inertial navigation and manual position reporting, meaning when "the ionosphere wasn't working" the faster 747s had to relay the positions of the slow 767s which they had overtaken flying out of Asia, forward to Australian ATC on VHF, remembering that VHF has hundreds of kilometres of range from high altitude.
That said, I have heard an aircraft on something like 8867 kHz USB reporting an air-conditioner failure, while somewhere near the Philippines, at home in Sydney.
G3B01
What is a characteristic of skywave signals arriving at your location by both short-path and long-path propagation?
A. Periodic fading approximately every 10 seconds
B. Signal strength increased by 3 dB
C. The signal might be cancelled causing severe attenuation
D. A slightly delayed echo might be heard
An echo may be heard, as the signal arrives via the two different paths, answer D.
Using SSB, the difference in the arriving signals will be great enough that they will not cancel each other.
G3B02
What factors affect the MUF?
A. Path distance and location
B. Time of day and season
C. Solar radiation and ionospheric disturbances
D. All these choices are correct
The paths Alaska to Hawaiʻi, Canberra to Afghanistan, or Florida to Spain each will behave differently. Reasons include because the distances are different; and that at a specific time, the time of day and seasons will be different in the areas each path crosses (Canberra is southern hemisphere so the opposite to the other locations). Solar behaviours and ionospheric disturbances will also vary these factors over time. Thus it is all of these, answer D.
You will also notice one runs north-south, one diagonally, and the last east-west. I mentioned Canberra - Afghanistan, as it was previously militarily significant. Middle East from Darwin remains in the Space Weather site.
G3B03
Which frequency will have the least attenuation for long-distance skip propagation?
A. Just below the MUF
B. Just above the LUF
C. Just below the critical frequency
D. Just above the critical frequency
The highest frequency available just below the maximum usable frequency is likely to give the best signal, answer A.
G3B04
Which of the following is a way to determine current propagation on a desired band from your station?
A. Use a network of automated receiving stations on the internet to see where your transmissions are being received
B. Check the A-index
C. Send a series of dots and listen for echoes
D. All these choices are correct
There the reverse beacons which you can see on the Internet, answer A.
G3B05
How does the ionosphere affect radio waves with frequencies below the MUF and above the LUF?
A. They are refracted back to the Earth
B. They pass through the ionosphere
C. They are amplified by interaction with the ionosphere
D. They are refracted and trapped in the ionosphere to circle the Earth
Signals between the LUF and MUF are refracted (bent) back to Earth, often allowing communications, answer A.
G3B06
What usually happens to radio waves with frequencies below the LUF?
A. They are refracted back to the Earth
B. They pass through the ionosphere
C. They are attenuated before reaching the destination
D. They are refracted and trapped in the ionosphere to circle Earth
These signals are attenuated (absorbed) by the ionosphere, answer C.
G3B07
What does LUF stand for?
A. The Lowest Usable Frequency for communications between two specific points
B. Lowest Usable Frequency for communications to any point outside a 100-mile radius
C. The Lowest Usable Frequency during a 24-hour period
D. Lowest Usable Frequency during the past 60 minutes
It is the Lowest Usable Frequency usable between two points, answer A.
This can be used to discuss current conditions, or part of a prediction of the best frequency to use in the future.
G3B08
What does MUF stand for?
A. The Minimum Usable Frequency for communications between two points
B. The Maximum Usable Frequency for communications between two points
C. The Minimum Usable Frequency during a 24-hour period
D. The Maximum Usable Frequency during a 24-hour period
It is the maximum usable frequency between two places, answer B.
Again, this can be now, or part of a prediction of the best frequency to use in the future. If you have brain-fade during the exam, remember that the alternative is LUF / Lowest, so M must be Maximum.
G3B09
What is the approximate maximum distance along the Earth's surface that is normally covered in one hop using the F2 region?
A. 180 miles
B. 1,200 miles
C. 2,500 miles
D. 12,000 miles
At its greatest, a single hop allows a signal to cross a continent such as Australia or the US, or link VK2 to ZL, around 4000 km, or 2,500 miles, answer C.
G3B10
What is the approximate maximum distance along the Earth's surface that is normally covered in one hop using the E region?
A. 180 miles
B. 1,200 miles
C. 2,500 miles
D. 12,000 miles
This covers something like Brisbane to Adelaide. The answer is 1900 km, or 1,200 miles, answer B.
G3B11
What happens to HF propagation when the LUF exceeds the MUF?
A. No HF radio frequency will support ordinary sky-wave communications over the path
B. HF communications over the path are enhanced
C. Double hop propagation along the path is more common
D. Propagation over the path on all HF frequencies is enhanced
It means there are no frequencies which allow ionospheric propagation, answer A.
When I used to listen to shortwave broadcasts in the 1980s, I believe this was most often the case between South Africa and south-eastern Australia. I certainly never heard an SABC station.
G3B12
Which of the following is typical of the lower HF frequencies during the summer?
A. Poor propagation at any time of day
B. World-wide propagation during daylight hours
C. Heavy distortion on signals due to photon absorption
D. High levels of atmospheric noise or static
If you've listened to a perhaps weaker AM (MW) station during a summer afternoon or evening in Australia or the south of the US, you have likely heard the lightning crashes, as well as static, which also affects the low HF bands, answer D.
I've certainly been on an 8:00 pm 80 metre net which was abandoned due to storms, despite them being beyond a distance which they presented danger from lightning strikes. In this case it appears likely storms were in northern Australia and/or South-East Asia, where it would have been the "wet season". No doubt the noise from storms also propagates from south of the US to stations within it, via the ionosphere.
The first series of "COBRA", a British TV drama is based around a very strong CME destroying a number of large transformers across England. With one less spare available than needed, the Tory (Conservative) PM predictably decided to deny the often Labour voting North-East power for the multiple weeks it took to have a new one imported, resulting in societal breakdown. (COBRA is an informal acronym for the Cabinet Office Briefing Rooms, used during disasters; and by inference, the emergency committee meetings held in it).
Having just violated the seventh commandment, a character looks out to window, to see a spectacular aurora over London. Such displays are rare this far south.
There was also a somewhat more tenuous story-line involving damage to GPS satellites (plausible) causing a commercial aircraft to crash onto a motorway (less plausible), also in the North-East, with many passengers ending up in a hospital reliant on generators.
"Ducting" is a phenomona of the troposphee (normal weather layer), and may be termed "tropo" or "tropospheric ducting". It is related to situations such as high pressure cells, and hot, dry early morning weather, often with fairly still air. For Sydney (Oz) this is somewhat unusual, where at least moderate humidity is the norm. They also occur in the evening.
On to: HF Propagation 2 - Layers, Critical angle, and NVIS
You can find links to lots more on the Learning Material page.
Written by Julian Sortland, VK2YJS & AG6LE, June 2024.
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