Power Supplies Section 5-3

The most common power supply converts household ac current into smooth dc current by using a regulated circuit (T6D05)

Regulated power supplies are best because they prevent voltage fluctuations from affecting the functions of the radios sensitive circuits ( T4A03).

A mobile transceiver can run off of the cars regular 12 volt battery. (T5A06) For safety reasons: the negative connection of the transceiver should connect to the batterys negative terminal or to the engines block ground strap. (T4A11)

Sometimes others can hear a high pitched whine that varies with the speed of your engine. This is called alternator whine and is cause by noise in the electrical system inside your own vehicle. It can be removed by a dc filter at your radio. T4A10

T4A03 Which is a good reason to use a regulated power supply for communications equipment? A. It prevents voltage fluctuations from reaching sensitive circuits B. A regulated power supply has FCC approval C. A fuse or circuit breaker regulates the power D. Power consumption is independent of load

T4A10 What is the source of a high-pitched whine that varies with engine speed in a mobile transceivers receive audio? A. The ignition system B. The alternator C. The electric fuel pump D. Anti-lock braking system controllers

T4A11 Where should a mobile transceivers power negative connection be made? A. At the battery or engine block ground strap B. At the antenna mount C. To any metal part of the vehicle D. Through the transceivers mounting bracket

T5A06 How much voltage does a mobile transceiver usually require? A. About 12 volts B. About 30 volts C. About 120 volts D. About 240 volts

T6D05 What type of circuit controls the amount of voltage from a power supply? A. Regulator B. Oscillator C. Filter D. Phase inverter

What could be happening if another operator reports a variable high-pitched whine on the audio from your mobile transmitter? A. Your microphone is picking up noise from an open window B. You have the volume on your receiver set too high C. You need to adjust your squelch control D. Noise on the vehicles electrical system is being transmitted along with your speech audio

Batteries supply dc power in place of ac power supplies. The chemicals in disposable batteries can be used only once and then discarded (ex: zinc carbon batteries) (T6A11)

In Rechargeable batteries the chemical reaction can be reversed and the battery is recharged. (ex: a fully charged nickel-Cadmium battery has a 1.2 voltage. ) (T6A10)

Storage batteries (deep cycle marine or RV batteries) store A LOT of energy. They are often left connected to a charger and kept fully charged with a trickle current.

In an emergency, a 12 v battery can be recharged by connecting it to a vehicles battery and running the engine. (T0A08)

Care must be taken when charging or discharging a battery, if it is done so too quickly it can vent flammable hydrogen gas that can cause an explosion. (Remember the Hindenberg!

T6A10 What is the nominal voltage of a fully charged nickel-cadmium cell? A. 1.0 volts B. 1.2 volts C. 1.5 volts D. 2.2 volts

T6A11 Which battery type is not rechargeable? A. Nickel-cadmium B. Carbon-zinc C. Lead-acid D. Lithium-ion

T0A08 What is one way to recharge a 12-volt lead-acid station battery if the commercial power is out? A. Cool the battery in ice for several hours B. Add acid to the battery C. Connect the battery to a cars battery and run the engine D. All of these choices are correct

T0A09 What kind of hazard is presented by a conventional 12-volt storage battery? A. It emits ozone which can be harmful to the atmosphere B. Shock hazard due to high voltage C. Explosive gas can collect if not properly vented D. All of these choices are correct

T0A10 What can happen if a lead-acid storage battery is charged or discharged too quickly? A. The battery could overheat and give off flammable gas or explode B. The voltage can become reversed C. The memory effect will reduce the capacity of the battery D. All of these choices are correct

RF Interference (RFI) Section 5.4

As the number of electronic devices continues to increase so does the possibility of interference between them and your amateur station. Radio frequency interference (RFI) RFI can occur in either direction---to or from the Amateur radio equipment

Every transmitters RF output signal contains weak harmonics of the desired output signal and other spurious emissions that can cause interference to nearby equipment.

To prevent harmonics from being radiated, a low pass filter must be installed at the transmitters connection to the antenna feed line. (T4A04)

Filters are an important way to prevent or eliminate RFI. Ferrite choke filters are an example of one type of filter used to reduce RF current flowing on the outside of cables. (T4A09)

Because cordless telephones are rarely designed to reject RF signals they often inadvertently act as a receiver (T7B04) The best way to reduce RFI in a cordless phone is to connect an RF filter at the telephone jack. (T7B05)

Very Strong signals may overwhelm a receivers ability to reject them. This is called fundamental overload. (T7B04) If a TV is receiving RFI due to overload then a filter at the transmitter will not solve the problemthe problem is with the receiver (TV)

Sometimes the interfering signals frequency is close to the desired signal's frequency, (for example a 2 meter signal from a transmitter is interfering with broadcast TV channels 2-13.) In this case a band–reject filter will filter only the 2 meter signals without filtering out the desired TV broadcast signals (T4A04)

Part 15 of the FCC rules governs the responsibilities of owners of unlicensed devices that use RF communications. 1. They cant cause a licensed station a problem 2. They must accept interferences caused by a licensed station

If there is an interference problem with a neighbor you should: Make sure your station is operating properly Make sure that your station is not causing interference with your unlicensed devices (TV and phone) Work with the other owner to determine the cause of the problem. If the problem cannot be eliminated then inform your neighbor of the rules.

T4A04 Where must a filter be installed to reduce harmonic emissions? A. Between the transmitter and the antenna B. Between the receiver and the transmitter C. At the station power supply D. At the microphone

T4A05 What type of filter should be connected to a TV receiver as the first step in trying to prevent RF overload from a nearby 2 meter transmitter? A. Low-pass filter B. High-pass filter C. Band-pass filter D. Band-reject filter

T4A09 Which would you use to reduce RF current flowing on the shield of an audio cable? A. Band-pass filter B. Low-pass filter C. Preamplifier D. Ferrite choke

T7B02 What is meant by fundamental overload in reference to a receiver? A. Too much voltage from the power supply B. Too much current from the power supply C. Interference caused by very strong signals D. Interference caused by turning the volume up too high

T7B03 Which of the following may be a cause of radio frequency interference? A. Fundamental overload B. Harmonics C. Spurious emissions D. All of these choices are correct

T7B04 What is the most likely cause of interference to a non-cordless telephone from a nearby transmitter? A. Harmonics from the transmitter B. The telephone is inadvertently acting as a radio receiver C. Poor station grounding D. Improper transmitter adjustment

T7B05 What is a logical first step when attempting to cure a radio frequency interference problem in a nearby telephone? A. Install a low-pass filter at the transmitter B. Install a high-pass filter at the transmitter C. Install an RF filter at the telephone D. Improve station grounding

T7B06 What should you do first if someone tells you that your stations transmissions are interfering with their radio or TV reception? A. Make sure that your station is functioning properly and that it does not cause interference to your own television B. Immediately turn off your transmitter and contact the nearest FCC office for assistance C. Tell them that your license gives you the right to transmit and nothing can be done to reduce the interference D. Continue operating normally because your equipment cannot possibly cause any interference

T7B07 Which of the following may be useful in correcting a radio frequency interference problem? A. Snap-on ferrite chokes B. Low-pass and high-pass filters C. Band-reject and band-pass filters D. All of these choices are correct

T7B08 What should you do if a Part 15 device in your neighbors home is causing harmful interference to your amateur station? A. Work with your neighbor to identify the offending device B. Politely inform your neighbor about the rules that require him to stop using the device if it causes interference C. Check your station and make sure it meets the standards of good amateur practice D. All of these choices are correct

RF Grounding Section 5.5

RF Grounding refers to keeping all the radio equipment at the same RF voltage. The goal is to prevent current from flowing between the different pieces of equipment.

RF current flowing in sensitive audio or data cables causes interference with the normal function of the station. RF feedback, which causes garbled distorted or unintelligible transmissions, is an example of this type of interference.

The best way to RF ground your equipment is to bond them together to a common ground bus, then connect the ground bus to your household ground rod with a short, wide (flat) strap.

T4A08 Which type of conductor is best to use for RF grounding? A. Round stranded wire B. Round copper-clad steel wire C. Twisted-pair cable D. Flat strap

T7B11 What is a symptom of RF feedback in a transmitter or transceiver? A. Excessive SWR at the antenna connection B. The transmitter will not stay on the desired frequency C. Reports of garbled, distorted, or unintelligible transmissions D. Frequent blowing of power supply fuses