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Subelement G4

AMATEUR RADIO PRACTICES

Section G4E

Mobile and portable HF stations; alternative energy source operation

What is the purpose of a capacitance hat on a mobile antenna?

  • To increase the power handling capacity of a whip antenna
  • To reduce radiation resistance
  • Correct Answer
    To electrically lengthen a physically short antenna
  • To lower the radiation angle

A "capacitance hat" is a device on the end of a mobile antenna which acts to electrically lengthen a physically short antenna. The device, usually made up of a ring, or an arrangement of rods, is used on the top of the antenna. The device increases the capacitance of the antenna, which causes it to act electrically "longer."

SILLY HINT: A "top hat" makes a short person look taller/longer.

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What is the purpose of a corona ball on an HF mobile antenna?

  • To narrow the operating bandwidth of the antenna
  • To increase the “Q” of the antenna
  • To reduce the chance of damage if the antenna should strike an object
  • Correct Answer
    To reduce RF voltage discharge from the tip of the antenna while transmitting

(D). A "corona ball" on a HF mobile antenna is used to reduce high voltage discharge from the tip of the antenna. The sharp tipped mobile antenna can discharge extra voltage that builds up as an electrical arc or coronal discharge. The corona ball device reduces the chance of forming such arcs.

Study Tip: Corona (virus) is a *transmitting" pandemic. Associate Corona with the word transmitting which appears in the correct answer.

Reduce corona voltage/hysteria by putting a ball/cap on it.

Definitely want to REDUCE covid.

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Which of the following direct, fused power connections would be the best for a 100-watt HF mobile installation?

  • Correct Answer
    To the battery using heavy-gauge wire
  • To the alternator or generator using heavy-gauge wire
  • To the battery using insulated heavy duty balanced transmission line
  • To the alternator or generator using insulated heavy duty balanced transmission line

The best direct, fused power connection for a 100-watt HF mobile installation is a connection directly to the battery using heavy-gauge wire. This ensures the radio can handle the high current needed without causing voltage drops. Avoid using the auxiliary outlet, as it cannot handle the required power.

For setups with multiple power connections, it’s also a good idea to use a bus bar, preferably a radio/avionics bus bar, to safely distribute power to additional devices. This helps keep wiring organized and prevents overloading the battery terminals.

When connecting directly to the battery, take precautions to avoid corrosion by using a protective sealant on the terminals, and ensure the wiring is safely routed through grommets or protective sheaths to avoid damage. Also, fuses should be installed as close to the battery as possible on both the positive and negative leads.

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Why should DC power for a 100-watt HF transceiver not be supplied by a vehicle’s auxiliary power socket?

  • The socket is not wired with an RF-shielded power cable
  • Correct Answer
    The socket’s wiring may be inadequate for the current drawn by the transceiver
  • The DC polarity of the socket is reversed from the polarity of modern HF transceivers
  • Drawing more than 50 watts from this socket could cause the engine to overheat

(B). It is best NOT to draw the DC power for a 100-watt HF transceiver from an automobile's auxiliary power socket because the socket's wiring may be inadequate for the current being drawn by the transceiver. Instead, the unit should be powered by connecting heavy gauge wire leads to the battery terminals, with fuses on the leads located as close to the battery as possible.

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Which of the following most limits an HF mobile installation?

  • “Picket fencing”
  • The wire gauge of the DC power line to the transceiver
  • Correct Answer
    Efficiency of the electrically short antenna
  • FCC rules limiting mobile output power on the 75-meter band

Keyword: most

Picket fencing relates generally to weak FM signals. While there are FM operations on the 10-meter band, this would not impact any other HF band.

The wire gauge of the transceiver's power line could impact maximum power output, but this is a variable highly in the control of the radio owner.

There isn't a FCC rule limiting mobile output power.

HF antennas are often electrically short, and are highly inefficient. This is an impact on all HF bands.

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What is one disadvantage of using a shortened mobile antenna as opposed to a full-size antenna?

  • Short antennas are more likely to cause distortion of transmitted signals
  • Q of the antenna will be very low
  • Correct Answer
    Operating bandwidth may be very limited
  • Harmonic radiation may increase

One disadvantage of using a shortened mobile antenna as opposed to a full size antenna is that operating bandwidth may be very limited. The fractional wave electrically short antennas have low impedances at the feed point and very narrow frequency ranges. Unfortunately, it just is not practical or safe to attach the length of antenna required for efficient transmitting, especially at HF frequencies.

Key: "limited antenna" a.k.a mobile, limited bandwith

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Which of the following may cause receive interference to an HF transceiver installed in a vehicle?

  • The battery charging system
  • The fuel delivery system
  • The control computers
  • Correct Answer
    All these choices are correct

All of these choices are correct

Yes, the alternator ( battery charging system) can give off a whine. Yes, the fuel pump ( fuel delivering system) can give off a similar whine. Yes, the control computer can give off stray rf interference. So all of these choices are, indeed correct. All I can say is, modern vehicles were not designed for the average ham.

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In what configuration are the individual cells in a solar panel connected together?

  • Correct Answer
    Series-parallel
  • Shunt
  • Bypass
  • Full-wave bridge

Solar cells provide DC power similar to a battery. Each solar cell provides a specific amount of power based on light conditions. Desired output voltage is generated by connecting cells in series (like multiple AAs in a flashlight). Desired current is generated by connecting banks of solar cells in parallel. Thus, Series-parallel is the correct answer.

The distractors shunt and bypass divert power away from components.

The distractor Full-wave bridge is for converting AC to DC, but solar generates DC power.

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What is the approximate open-circuit voltage from a fully illuminated silicon photovoltaic cell?

  • 0.02 VDC
  • Correct Answer
    0.5 VDC
  • 0.2 VDC
  • 1.38 VDC

The current standard modern, well-illuminated (full sun exposure) photovoltaic cell has an approximate open-circuit voltage of 0.5 Volts DC. These cells may also be known as solar or photoelectric cells. The maximum current that a photovoltaic cell can provide is dependent on the total surface area of the cell. Individual standard cells may be arranged together to form solar panels for larger power requirements.

For more info see Wikipedia: Solar cell

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Why should a series diode be connected between a solar panel and a storage battery that is being charged by the panel?

  • To prevent overload by regulating the charging voltage
  • Correct Answer
    To prevent discharge of the battery through the panel during times of low or no illumination
  • To limit the current flowing from the panel to a safe value
  • To prevent damage to the battery due to excessive voltage at high illumination levels

A diode only lets current flow in one direction. The direction you want if you're collecting solar energy is from the solar panel to the battery. The diode will prevent the energy from going in the other direction when the battery has more energy than the solar panel (during the night or other periods of low light).

Silly Hint: A Diode is Directional, preventing a change of direction of current, and therefore preventing Discharge, all words beginning with D-I-.

Note: When a Zener diode is used to control voltage it does so with reverse polarity compared to a diode that would prevent energy from going to the panel. A Zener diode limits the voltage, but not the current nor the power.

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What precaution should be taken when connecting a solar panel to a lithium iron phosphate battery?

  • Ground the solar panel outer metal framework
  • Ensure the battery is placed terminals-up
  • A series resistor must be in place
  • Correct Answer
    The solar panel must have a charge controller

SILLY HINT: For those that work out at a gym lifting weights, when "lifting iron" (lithium iron), you need to do so in a very "controlled" (controller) manner. The correct answer is the only one with the word controller in it.

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