The Sun emits a nearly constant stream of physical particles known as Solar Wind, what happens when these particles strike the Earth's atmosphere?
Ions get thrown off and trapped in the atmosphere.
What is the result of an ultraviolet wave from the Sun striking a gaseous atom from the Earth's atmosphere?
An electron is dislodged from the atom. This process is called ionization.
When does "Recombination" occur, and what is the process?
At night, dislodged electrons recombine with atoms.
Of the Troposphere, Stratosphere and the Ionosphere; the Ionosphere is the most important to HF radio communications because of __________?
The presence of free electrons.
Why are higher operating frequencies required for HF long-distance communications during periods of high sunspot activity?
Ionization increases during periods of maximum sunspot activity.
If sunspots are tracked on an 11 year cycle, why does the sunspot number vary from day to day?
Diurnal (daily) differences are caused by the rotation of the Earth on it's axis during a 24 hour period.
Which type of irregular variation, often accompanied by a Solar Flare, can decrease the signal strength of HF communications for 45-90 minutes?
Increased X-ray radiation.
With the exception of the F region, the Ionosphere experiences less ionization during the winter months. This is an example of what type of solar variation?
If you were transmitting an HF Sky Wave from one location to another where would the Skip Distance be?
Between the transmit antenna and the point that the first reflected wave reaches the ground.
If you were transmitting an HF Sky Wave from one location to another where would the Skip Zone be?
Between the point where the Ground Wave ends and the point that the first reflected wave reaches the ground.
If you were to transmit a HF radio signal directly upwards (90o), and the signal does not return to Earth, what would be the cause?
The take-off angle was greater than the critical angle.
A radio is transmitting a HF signal at a take-off angle of exactly 90o. The frequency of operation is increased by 25kHz increments until, eventually, the signal is no longer refracted back to Earth by the Ionosphere. Why?
The critical angle is determined by the frequency.
How are the critical frequency and the maximum useable frequency (MUF) similar?
They change with time, season, etc...
From a purely physical point of view, a frequency of optimum transmission (FOT) very close to the MUF would be most suitable. Why is this impractical?
The MUF changes from day to dy.
With reguards to the maximum useable frequency (MUF), the lowest useable frequency (LUF), and the frequency of optimum transmission (FOT), which one can be affected by changing equipment and power out?
The lowest useable frequency (LUF).
When planning for HF Sky Wave, what are the determining factors for radio wave refraction?
In a field operating environment, when would an ionospheric sounder (chirpsounder) be used?
When determining the useable frequency.
In modern HF systems, what system has largely replaced HF prediction charts, propagation software, and ionospheric sounders?
Automatic Link Establishment (ALE)
A radio station transmitting on a directional antenna, pointed North, is received by another radio station located directly south. What is the most likely cause?
The backlobe from the antenna.
Do HF antennas require more real estate than VHF antennas? Why?
Yes, the frequency is inversley proportinal to the wavelength.
What are three important things when selecting the right Sky Wave antenna?
Type of coverage
In HF communications, exactly how long does a longwire antenna need to be?
The length depends of the frequency.
A field radio operator needs to set up a directional HF link, but only has access to a bi-directional longwire antenna. How can the longwire be made to be directional?
Terminate the end in a value of resistance equal to the impedance of the wire.
If the assigned frequency must ALWAYS be in the center of the occupied bandwidth, why do frequency managers issue Carrier, Offset, Window, Reference, or Dial (Coward) frequencies?
They all refer to the diaed in frequency.
What is the assigned frequency for a carrier K12000 (6K00B9W) ISB?
What is the only way to adjust the frequency of a transmitter?
Vary the carrier frequency.
When operating at maximum transmit power and utilizing a direct wave, or line of sight (LOS), what would be the most effective way to extend your communications distance?
Raise the antenna.
If there are no automated methods or joint standard methods for predicting which ground wave frequencies will propagate, then what would be the best practice(s)?
Plan on using a low frequency
A vertically polarized antenna
A low take-off angle (LTOA)
A near verticle incident Sky Wave shot (NVIS)
Would a MUF, LUF, and FOT chart for San Diego to Honolulu be practical for a shot from Seattle to Honolulu?
Yes, the SSN is the same, they are going to the same place, and neither location is close to the equator.
What could a radio operator or frequency manager use to gather ionospheric density data, thereby providing near real-time propagation information and frequency selection?
Ionospheric sounder or a Tactical Frequency Management System (TFMS).
From a planning standpoint, why is it considered more difficult to engineer a HF Sky Wave link than a HF Ground Wave link?
Because the uncontrollable comes into play-propagation medium, ionospheric density is changing, and atmospheric variations are constantly in motion.
What are the four major factors that affect the desired signal levels?
What is the Optical Horizon Distance?
The distance that can be seen LOS by the antenna.
What is the standard S/N Ratio at the Optical Horizon Distance (OHD)?
Which formula is used when solving for system gains and losses using distance?
-40LOGNewDistance - -40LOGOldDistance = Gain/Loss
If you needed a high gain, LOS antenna, but you had limited real estate in which to place the antenna, and limited power with which to power your LOS system, what type of antenna would serve your purpose and take up little space?
A Parabolic antenna.
Your Unit needs a new antenna for their microwave system, and they ask your advice on which type they should invent in. You know that this particular microwave link uses frequencies under 1 GHz and runs about 10km. What type of antenna would you NOT reccomend?
A Horn Antenna.
Although passive reflectors are not commonly used these days, which of the following scenarios could most likely warrant the need for one?
To angle a microwave link around large obstacles where changes in direction of 120o or less are required.
What is typically considered the "common gain" for a parabolic antenna?
40dBi or greater
Reflection and refraction over a microwave path can cause all the following except?
A large flat surface that acts simply as a reflector, describes what type of common repeater?
A Billboard repeater.
What is an advantage of a Microwave LOS system?
Hard to detect.
For a high-priority data link, why would a LOS system using higher frequencies be advantageous to the mission?
Low power transmit
Highly directional antennas
Hard to detect
Under ideal atmospheric conditions, with only one assigned frequency, what would be the most appropriate method of increasing the distance of a LOS system?
Raise the antenna height, do not adjust the take-off angle.
The boss wants to increase the distance of a LOS link, but it cannot be done with the current system configuration. When asked for your advice, which of the following options would you suggest as the best course of action?
Place a repeater system along the increased path.
In a situation where you only have one frequency, and multiple LOS systems of the same nomenclature, which of the following diversity types would offer the greatest diversity?
To avoid losses, __________ __________ between the LOS radio path and the terrain should be maintained.
If the relractive index for an average climate is 1.33, and it decreases to 1.0 for cold, dry climates, how would it increase or decrease for hot, humid climates?
Decrease to 0.66.
When the radio horizon extends slightly beyond the optical horizon the extension of the horizon distance is a result of __________?
Refraction in the Earth's atmosphere.
The term used, two or more frequencies over the same radio path, is called _________?
In troposcatter systems the attenuation increases as the __________ __________?
Tactical troposcatter systems normally operate at distances of up to __________?
The area of the troposphere seen by both the transmit and receive antennas is which of the following?
When working with VHF/UHF FM ground-to-ground systems, do not add __________ for the Fade Margin Threshold.
Using the principles of transposition, you can solve for the following factors when all other parameters are known:
Highest useable frequency
In the VHF/UHF FM ground-to-ground formula, the reliability ratio for Command & Control is __________?
__________ consists of all path losses, to include loss due to obstructions, if any.