The short path of a signal is the most direct straight line path from one location or station to another. The long-path refers to the exact opposite direction, at 180 degrees. Sometimes if there is local interference, the long- path will give you a better signal. However if conditions are good, you may actually get signal reception from both the short and long paths. As is takes slightly longer for the RF signal to travel the 180 degree path (around the world) you might hear that long path signal as a well-defined echo!

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The Maximum Usable Frequency (MUF) is the highest frequency you can use between two specific points that will allow your signal to reach the ionosphere, and be bent back to earth for reception rather than passing out into space. The MUF is dependent on the location of the two stations. So the path, distance and location are factors. The MUF is also very dependent on the amount of ionization of the atmospheric layers. The ionization of the ionospheric layers used for sky-wave propagation is affected by solar radiation, ionospheric disturbances, along with the time of day and season. Therefore choose answer All of these choices are correct.

For more info see Wikipedia: Maximum Usable Frequency (MUF)

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(A). Attenuation or absorption of radio signal is lowest at the frequency just below the Maximum Usable Frequency (MUF). The maximum usable frequency is the highest frequency you can use at a specific time and location which will still allow your signal to be reflected back to earth, rather than continuing into outer space! In this frequency region, the signal strength is higher, and the reflection distances can be longer. Then, just below (about 85% of) the MUF is the Optimum Working Frequency, where the attenuation of the propagated signal is lowest.

Note:

For more info see Wikipedia: Maximum Usable Frequency (MUF).

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A reliable way of detecting whether the Maximum Usable Frequency (MUF) is high enough to support skip propagation between your station and a distant location between 14-30 MHz (20-10 meters) is to listen on those bands for signals from distant or international beacons. If you can hear their signals from hundreds to thousands of miles away, its a good indicator that those bands are open for your long-distant contacts as well! DXers enjoy!

This question references an international beacon system run by the International Amateur Radio Union (IARU) that operates beacons from 14.100 - 28.200.

https://www.iaru.org/on-the-air/beacons/

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(A). This "Goldilock's" range below the Maximum Usable Frequency (MUF) and above the Lowest Usable Frequency (LUF) is just where you want to be with your transmissions. Above the MUF, is TOO HIGH and your signals will just keep going into outer space, under the LUF and your signals will be TOO LOW and get absorbed and won't even make it to the ionospheric regions where you want to be. The region in between is JUST RIGHT, and your signals will be bent back to earth.

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When your signal is below the Lowest Usable Frequency (LUF), the ionosphere completely absorbs or attenuates the signal rather than reflecting the wave back to earth. The signal just gets lost in the atmospheric noise.

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(A). The Lowest Usable Frequency (LUF) is the frequency point below which the signal will be completely absorbed or attenuated in the ionosphere rather than the wave being bent back to earth for reception. This LUF is the lowest usable frequency you can use for communications between two points.

For more into see Wikipedia: Lowest Usable Frequency (LUF)

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At the other end of the usable frequency range from the LUF is the MUF, or Maximum Usable Frequency for communications between two points. Above this frequency, the signal will not be bent enough by the ionosphere to return to earth for reception, but will continue out into space. The best frequency to choose for long-distance propagation is one just below this MUF.

For more info see Wikipedia: Maximum Usable Frequency (MUF)

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The F2 region is the highest region of the ionosphere, which is our "sweet spot" for long distance sky-wave transmissions. The F2 is highest during the middle of the day, when the sun's energy is the greatest. It gets even better during periods of high solar activity and high ionization of the upper atmosphere. The approximate maximum distance along the Earth's surface that is normally covered in one hop using the F2 region is 2,500 miles!

Note: Just remember that F2 can take you more than 2000 miles!

Silly hint: F2 ... only answer with a Five and a 2

Remember 1,200 miles being right? That was E. F2 = 2,500

E = 1,200

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The E region is region of the ionosphere that is the second lowest, just above the D region. The E region, like the F region is more ionized and so more usable for sky-wave signals during the day (especially around noon), but doesn't hold on to that energy for as much time during the day as the F region.

The E region still can support an approximate maximum distance along the Earth's surface in one hop of 1,200 miles.

Note; Remember that the longest distance achievable in one hop is using the F2 region for over 2,000 miles, whereas the E region gives us about half that distance or an "Everyday" level of 1,200 miles.

For more info see Wikipedia: E region

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In the case where the Lowest Usable Frequency (LUF) exceeds the Maximum Usable Frequency (MUF), there is no HF radio frequency that will support ordinary skywave communications over the path between the two points.

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The combination of atmospheric conditions and frequency could cause any HF signal between two points to be totally absorbed or attenuated and no signal will get through.

Just remember that both MUF and LUF are dependent on station locations as well as atmospheric conditions.

Its possible that you may be able to make that same path transmission at a different time with better ionization levels, or you might be able to communicate with another station at that time.

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