Note that the gain of a parabolic antenna is governed by the following:

\[G = \frac{ 4\pi{A} }{ \lambda^2 }e_A\]

Where:

• \(A\) is the area of the antenna aperture (the mouth of the parabolic reflector)
• \(\lambda\) (lambda) is the wavelength of the radio waves
• \(e_A\) is a dimensionless "aperture efficiency" parameter between \(0\) and \(1\)

It is clear that by doubling the frequency, the wavelength is halved. Using proportional reasoning, we see that substituting \(\frac{\lambda}{2}\) for \(\lambda\) results in a change in \(G\) by a factor of \(4\).

In decibels, \(10\log_{10}(4)\) is equal to \(6.02\text{ dB}\). Hence, the correct answer is "Gain is increased by \(6\text{ dB}\)".

Hint: The ideal value is the highest value.

Silly memory aid: "para" means fo(u)r in Spanish, and you'd need 6 dB to quadruple power

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The beamwidth of an antenna is the width of the radiation of the main lobe from the antenna. As gain increases, it can be expressed as making the main lobe thinner and longer or decreasing its beam's width. see: http://en.wikipedia.org/wiki/Beamwidth

-deanwj

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The signals from a satellite are necessarily weak so a high gain directional antenna must be used, and it has to follow the satellite as it passes overhead in an arc.

The sky above is a hemispheric dome and the antenna must point to any place in the dome expressed as azimuth, (the angle of horizontal deviation, measured clockwise, of a bearing from a standard direction, as from north or south.) and its elevation (the angle of verticle deviation measured up from the horizon).

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A small loading coil simply inserts a series inductive reactance that cancels capacitive antenna reactance.

By using a mobile antenna loading coil you will minimize ground related losses.

Mnemonic hint: High Ratio = Maximum Efficiency.

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Bandwidth is inversely proportional to quality factor Q, and \[Q = \frac{\text{reactance}}{\text{resistance}}\] Thus, adding reactance reduces (decreases) the bandwidth.

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Eliminate Distractors:

Lower Q - Actually raises Q by tuning antenna to be resonant

Higher Losses - Not an advantage

Greater structural strength - Nonsense

Only real answer is Improved radiation efficiency

Top loading is a methodology which increases radiation resistance, hence efficiency, even if the ground plane is substandard; seemingly a ubiquitous vertical antenna shortcoming. A top loaded vertical antenna has several advantages over the conventional vertical, but the biggest advantage is that it's shorter in length.

Source: Antenna 013: 20 Meter Top Loaded Vertical

Maximizing Efficiency in HF Mobile Antennas

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Think of those flat twin ribbon TV antenna wire with an impedance of 300 ohms.

The impedance of a folded dipole is 4x that of a half-wave dipole, which is 73 ohms.¹

73 x 4 = 292 ohms and 300 is the closest to this.

Memory trick: the 3 looks like it it has been folded, and the 00 looks like a cross section of 2 wires.

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The coil (inductor) is added to cancel out the capacitance already present in the circuit to try to achieve resonance.

It also facilitates a method to electrically shorten an antenna to "tune" to lower frequencies than the intended "designed" antenna length.

Silly hint: coil cancels capacitive reactance

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Radiation resistance represents the portion of an antenna’s impedance that corresponds to power successfully radiated as radio waves, as if the power were dissipated by a resistor. A higher radiation resistance generally means the antenna radiates more efficiently.

At the resonant frequency, radiation resistance is maximized, resulting in the most efficient radiation. Below resonance, the impedance becomes more reactive (usually capacitive), reducing the radiation resistance and making the antenna less efficient at radiating energy.

Thus, radiation resistance decreases below resonance.

Memory aid:
Below resonance = Resistance decreases. "Below" = Decrease.

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A wide, flat strap (preferably NOT braided, same reason as NOT stranded) has more surface area than an equivalent gauge wire. RF energy travels on the surface of the conductor. Greater surface area = greater conductor. Commercial broadcast stations have solid 00 ga. RF ground cables.

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The best ground is a low-resistance connection to earth. While a water pipe might accomplish that, ground rods is the answer they want on the test.

The reason why the water pipe is not the best answer is that usually the condition of the pipe and its connection to the ground is unknown. For example, it is likely to be corroded. ground rods are clad in copper and designed such that they don't have the corrosion problems of the average water pipe.

Another reason is that the metal section of a water pipe may be very short because someone at some point replaced the water main with PVC pipe but you're unable to see it since it is buried.

The other answers are wrong because: a resistor doesn't improve your ground, it only makes it worse, and a series RF choke either does nothing or makes things worse.

Hint: Ground=Earth.

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