Explain what mobile antenna parts do, how to power and quiet a mobile radio, and how solar panels charge a battery safely.
Syllabus: Mobile and portable HF stations; alternative energy source operation
Compendium articles on the ideas in this lesson, beyond what the exam asks.
Practise the 11 pool questions for this group. Answers are shuffled, and every one comes with a one-line "why".
HF wavelengths are too long for a full-size whip on a car. A capacitance hat (and loading coil) electrically lengthens the short antenna. A corona ball on the tip reduces RF voltage discharge from it.
The price: the electrically short antenna's efficiency is the biggest limit on HF mobile, and its operating bandwidth is very limited, so you retune when you change frequency.
RememberHat lengthens, ball calms the tip. Short means inefficient and narrow.
A 100 W radio draws a lot of current on transmit. Connect it directly to the battery with heavy-gauge fused wire. The dash auxiliary socket's wiring may be inadequate for that current. The alternator is not the place to connect.
The vehicle itself makes receive noise: charging system, fuel delivery, and control computers can all interfere.
RememberBattery, heavy wire, fuse. Not the dash socket.
A fully lit silicon cell gives about 0.5 V open circuit. Series strings add voltage and parallel strings add current, so a panel's cells are wired series-parallel.
RememberOne silicon cell: about 0.5 V. Panels are series-parallel.
| Part | Job |
|---|---|
| Series diode | stops the battery discharging through the panel in low or no light |
| Charge controller | regulates charging; required with LiFePO4 batteries |
A diode alone does not regulate voltage or limit current.
RememberDiode: one-way valve. Lithium iron phosphate needs a charge controller.