Power SuppliesSection 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 radio’s sensitive circuits ( T4A03).

A mobile transceiver can run off of the car’s regular 12 volt battery. (T5A06)

For safety reasons:the negative connection of the transceiver should connect to the battery’s negative terminal or to the engine’s 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

T4A03Which is a good reason to use a regulated power supply for communications equipment?A. It prevents voltage fluctuations from reaching sensitive circuitsB. A regulated power supply has FCC approvalC. A fuse or circuit breaker regulates the powerD. Power consumption is independent of load

T4A10What is the source of a high-pitched whine that varies with engine speed in a mobile transceiver’sreceive audio?A. The ignition systemB. The alternatorC. The electric fuel pumpD. Anti-lock braking system controllers

T4A11Where should a mobile transceiver’s power negative connection be made?A. At the battery or engine block ground strapB. At the antenna mountC. To any metal part of the vehicleD. Through the transceiver’s mounting bracket

T5A06How much voltage does a mobile transceiver usually require?A. About 12 voltsB. About 30 voltsC. About 120 voltsD. About 240 volts

T6D05What type of circuit controls the amount of voltage from a power supply?A. RegulatorB. OscillatorC. FilterD. 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 windowB. You have the volume on your receiver set too highC. You need to adjust your squelch controlD. Noise on the vehicle’s 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 vehicle’s 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!

T6A10What is the nominal voltage of a fully charged nickel-cadmium cell?A. 1.0 voltsB. 1.2 voltsC. 1.5 voltsD. 2.2 volts

T6A11Which battery type is not rechargeable?A. Nickel-cadmiumB. Carbon-zincC. Lead-acidD. Lithium-ion

T0A08What 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 hoursB. Add acid to the batteryC. Connect the battery to a car’s battery and run the engineD. All of these choices are correct

T0A09What kind of hazard is presented by a conventional 12-volt storage battery?A. It emits ozone which can be harmful to the atmosphereB. Shock hazard due to high voltageC. Explosive gas can collect if not properly ventedD. All of these choices are correct

T0A10What 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 explodeB. The voltage can become reversedC. The “memory effect” will reduce the capacity of the batteryD. 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 transmitter’s 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 transmitter’s 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 receiver’s 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 problem—the problem is with the receiver (TV)

Sometimes the interfering signal’s 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 can’t cause a licensed station a problem2. 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 properlyMake 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.

T4A04Where must a filter be installed to reduce harmonic emissions?A. Between the transmitter and the antennaB. Between the receiver and the transmitterC. At the station power supplyD. At the microphone

T4A05What 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 filterB. High-pass filterC. Band-pass filterD. Band-reject filter

T4A09Which would you use to reduce RF current flowing on the shield of an audio cable?A. Band-pass filterB. Low-pass filterC. PreamplifierD. Ferrite choke

T7B02What is meant by fundamental overload in reference to a receiver?A. Too much voltage from the power supplyB. Too much current from the power supplyC. Interference caused by very strong signalsD. Interference caused by turning the volume up too high

T7B03Which of the following may be a cause of radio frequency interference?A. Fundamental overloadB. HarmonicsC. Spurious emissionsD. All of these choices are correct

T7B04What is the most likely cause of interference to a non-cordless telephone from a nearby transmitter?A. Harmonics from the transmitterB. The telephone is inadvertently acting as a radio receiverC. Poor station groundingD. Improper transmitter adjustment

T7B05What 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 transmitterB. Install a high-pass filter at the transmitterC. Install an RF filter at the telephoneD. Improve station grounding

T7B06What should you do first if someone tells you that your station’s 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 toyour own televisionB. Immediately turn off your transmitter and contact the nearest FCC office for assistanceC. Tell them that your license gives you the right to transmit and nothing can be done to reduce theinterferenceD. Continue operating normally because your equipment cannot possibly cause any interference

T7B07Which of the following may be useful in correcting a radio frequency interference problem?A. Snap-on ferrite chokesB. Low-pass and high-pass filtersC. Band-reject and band-pass filtersD. All of these choices are correct

T7B08What should you do if a “Part 15” device in your neighbor’s home is causing harmful interferenceto your amateur station?A. Work with your neighbor to identify the offending deviceB. Politely inform your neighbor about the rules that require him to stop using the device if it causes interferenceC. Check your station and make sure it meets the standards of good amateur practiceD. All of these choices are correct

RF GroundingSection 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.

T4A08Which type of conductor is best to use for RF grounding?A. Round stranded wireB. Round copper-clad steel wireC. Twisted-pair cableD. Flat strap

T7B11What is a symptom of RF feedback in a transmitter or transceiver?A. Excessive SWR at the antenna connectionB. The transmitter will not stay on the desired frequencyC. Reports of garbled, distorted, or unintelligible transmissionsD. Frequent blowing of power supply fuses