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Subelement J
Antennas
Section 64
Voltage, Current and Power Relationships
What is the current flowing through a 52 ohm line with an input of 1,872 watts?
  • 0.06 amps.
  • Correct Answer
    6 amps.
  • 28.7 amps.
  • 144 amps.

What is the current flowing through a 52 ohm line with an input of 1,872 watts?

6 amps.

From m25mcinerney89:

\[I=\sqrt{\frac{Power}{Resistance}}\] \[I=\sqrt{\frac{1,872\text{ watts}}{52\text{ ohms}}}\] \[I=\sqrt{36}\] \[I= 6\text{ amps}\]

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The voltage produced in a receiving antenna is:
  • Out of phase with the current if connected properly.
  • Out of phase with the current if cut to 1/3 wavelength.
  • Variable depending on the station’s SWR.
  • Correct Answer
    Always proportional to the received field strength.

The voltage produced in a receiving antenna is:

Always proportional to the received field strength.

Antennas generate radio signals from the voltage send by transmitters. Then, they receive signals sent and change them back into voltage for receiver processing.

The signal sent/received consist of magnetic and electric radiation at right angle to each other, affected by the shape of Earth, creating the horizontal and vertical polarizations, based on the antenna shape.

To describe the voltage created in the receiving antenna, the term "antenna factor" is used. It is the amount of electric field strength to produce One (1) volt in the receiving antenna. In other words, it is the created voltage from the received electrical field.

Antenna Factor == Electrical Field Strength / Volts received

Thus, voltage produced is always proportional to the received field strength.

For a well-illustrated information, please see Electronic Design site, for the article Welcome To Antennas 101

Please see the Antenna Theory site for the article Antenna Factor

Another valuable resource is the Interference Technology site article Antenna Fundamentals.

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Which of the following represents the best standing wave ratio (SWR)?
  • Correct Answer
    1:1.
  • 1:1.5.
  • 1:3.
  • 1:4.

Which of the following represents the best standing wave ratio (SWR)?

1:1.

As long as SWR is 1:1.5 or less, it is the best.

Please see Right Channel Radios site for the article HOW TO INTERPRET SWR METER READINGS

Also, see CB World site for the article What is SWR and why is it SO important?

See the ARRL pdf article Understanding SWR by Example

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At the ends of a half-wave antenna, what values of current and voltage exist compared to the remainder of the antenna?
  • Equal voltage and current.
  • Minimum voltage and maximum current.
  • Correct Answer
    Maximum voltage and minimum current.
  • Minimum voltage and minimum current.

At the ends of a half-wave antenna, what values of current and voltage exist compared to the remainder of the antenna?

Maximum voltage and minimum current.

For more information, please see the EEEguide site for the article on Antenna Characteristics: Current and Voltage Distribution

See Electronics Notes site for the article Dipole Antenna Current & Voltage Waveforms

Also, see Wikipedia's article on Dipole antenna

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An antenna radiates a primary signal of 500 watts output. If there is a 2nd harmonic output of 0.5 watt, what attenuation of the 2nd harmonic has occurred?
  • 10 dB.
  • Correct Answer
    30 dB.
  • 40 dB.
  • 50 dB.

An antenna radiates a primary signal of 500 watts output. If there is a 2nd harmonic output of 0.5 watt, what attenuation of the 2nd harmonic has occurred?

30 dB.

From aaronnpny:

If Ps is the signal power at the transmitting end (source) of a communications circuit and Pd is the signal power at the receiving end (destination), then Ps > Pd.

The power attenuation Ap in decibels is given by the formula: Ap = 10log(Ps/Pd)

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There is an improper impedance match between a 30 watt transmitter and the antenna, with 5 watts reflected. How much power is actually radiated?
  • 35 watts.
  • 30 watts.
  • Correct Answer
    25 watts.
  • 20 watts.

There is an improper impedance match between a 30 watt transmitter and the antenna, with 5 watts reflected. How much power is actually radiated?

25 watts.

From cowboybilliards:

30 - 5 = 25


See Wikipedia's article on Effective radiated power

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