📻 Stuff Every Ham Radio Operator Should Know: Training Guide

Electrical Quantities

Electric current is the flow of electrons through a circuit. Current is measured in amperes, often shortened to amps. Voltage is the push that makes electrons move, and it is measured in volts.

Resistance is the opposition to current flow and is measured in ohms. Frequency counts how many complete cycles happen each second and is measured in hertz. Electrical power is the rate of energy use and is measured in watts.

Metals are good conductors because they have many free electrons that can drift through the metal. Glass is a good insulator because its electrons are held tightly, so current cannot flow easily.

Alternating current reverses direction many times each second. Direct current keeps one direction. Radio frequency current is alternating current at a much higher frequency.

Metric Prefixes

Metric prefixes change the size of a unit. One ampere equals 1000 milliamperes. One thousand volts is one kilovolt, and 500 milliwatts is 0.5 watt.

One megahertz equals 1000 kilohertz. So 3.525 MHz is 3525 kHz, and 28400 kHz is 28.400 MHz.

For capacitance, one microfarad equals 1,000,000 picofarads. For frequency, one gigahertz equals 1000 megahertz, so 2425 MHz is 2.425 GHz.

Capitalization matters. kHz means kilohertz, but MHz means megahertz. A lowercase m means milli, so mHz would mean millihertz, which is a thousand times smaller than a hertz.

Ohm's Law and Power

Ohm's law links voltage, current, and resistance. Voltage equals current times resistance, E = I x R. Current equals voltage divided by resistance, I = E / R. Resistance equals voltage divided by current, R = E / I.

The DC power formula is P = I x E. Power in watts equals current in amperes times voltage in volts. For example, 13.8 volts at 10 amperes delivers 138 watts.

You can rearrange the formulas to find any missing value. A circuit with 12 volts and 2.5 amperes uses 30 watts. A circuit that needs 120 watts at 12 volts draws 10 amperes.

Decibels compare power levels. Doubling power is about plus 3 dB. Multiplying power by ten is plus 10 dB, so 20 watts to 200 watts is a 10 dB increase.

Practice example: if 90 volts pushes 3 amperes, the resistance is 30 ohms. If a 100-ohm resistor has 200 volts across it, the current is 2 amperes.

Units for Frequency, Power, Capacitance, and Inductance

Frequency counts complete cycles per second. One cycle per second is a hertz, so a faster cycle rate means a higher frequency. In ham radio we often switch between hertz, kilohertz, and megahertz.

Power tells how quickly electrical energy is used. It is measured in watts, not in volts or amperes. Volts measure potential and amperes measure current.

Prefixes change the size of a unit. Kilo means one thousand and milli means one thousandth. So 1,500,000 hertz equals 1500 kilohertz, or 1.5 MHz.

Capacitance describes the ability to store energy in an electric field. Its unit is the farad, but real capacitors often use microfarads or picofarads.

Inductance describes the ability to store energy in a magnetic field. Its unit is the henry, and smaller inductors are often labeled in millihenrys or microhenrys.

Impedance is the opposition a circuit gives to alternating current. It is measured in ohms, the same unit used for resistance. Impedance can change with frequency because it may include frequency-dependent effects.

Ohm's Law Calculations and Circuit Types

Use R equals E divided by I to find resistance when voltage and current are known. For 12 volts and 1.5 amperes, the resistance is 8 ohms. For 12 volts and 4 amperes, the resistance is 3 ohms.

Use E equals I times R to find voltage. For a 2-ohm resistor with 0.5 ampere of current, the voltage is 1 volt.

In a series circuit, parts connect one after another, so the same current flows through all of them. In a parallel circuit, every branch connects across the same two points, so the voltage is the same across all components.

More Electrical Units and Ohm's Law Examples

Inductance is the ability to store energy in a magnetic field. Coils of wire are common inductors because current through them creates a magnetic field.

Ohm's law finds current: I equals E divided by R. For 240 volts and 24 ohms, divide 240 by 24 to get 10 amperes.

Ohm's law also finds voltage: E equals I times R. One ampere through 10 ohms produces 10 volts.

Two amperes through the same 10-ohm resistor produce 20 volts, because doubling the current doubles the voltage drop.

Components and Their Jobs

A resistor opposes current flow. A potentiometer is an adjustable resistor, often used as a volume control. A variable resistor can also be called a rheostat.

A capacitor stores energy in an electric field. It has two conductive surfaces separated by an insulator called a dielectric. A capacitor can still hold dangerous charge after power is turned off.

An inductor stores energy in a magnetic field and is usually a coil of wire. Inductance is measured in henrys. A tuned circuit uses an inductor and capacitor together to respond strongly to one frequency.

A diode lets current flow in one direction. Its two electrodes are the anode and cathode, and a stripe often marks the cathode. A light emitting diode, or LED, glows when current flows through it.

A transistor can amplify a signal or act as an electronic switch. A bipolar junction transistor has emitter, base, and collector leads. A field effect transistor has gate, drain, and source leads.

A relay is an electrically controlled switch. An integrated circuit packs many components into one chip. A rectifier uses diodes to change alternating current into a varying direct current.

Schematic Symbols

A schematic uses standard symbols to show how components connect. It does not show actual wire lengths or physical appearance.

A resistor is drawn as a zigzag line. A battery is drawn with alternating long and short parallel lines. A capacitor is drawn as two separated plates.

An LED symbol is a diode symbol with arrows pointing outward. A variable resistor symbol is a resistor with an arrow contact on it. These symbols help identify components on a schematic.

A transformer symbol shows two coupled coils. A variable inductor symbol is a coil with an adjustable tap. An antenna symbol is a line topped by an upside-down triangle.

Transistor symbols show three leads with an arrow on one lead. NPN and PNP types have the emitter arrow pointing different ways.

Measurement and Soldering

A voltmeter measures voltage and connects in parallel with the component. A current meter connects in series so that the current flows through the meter.

An ohmmeter applies a small current and measures the resulting voltage. Never measure powered circuits on the resistance setting, and be careful around charged capacitors.

A basic multimeter measures voltage and resistance. Set the dial before touching the probes to live circuits, and use voltage-rated meter and leads for high voltage.

Use rosin-core solder for electronics. Acid-core solder is for plumbing and its acid flux can corrode parts. A good tin-lead solder joint looks smooth and shiny, while a cold joint looks rough or lumpy.

A dummy load is a 50-ohm non-inductive resistor that absorbs transmitter power as heat. Use it to test without radiating on the air.

An SWR meter should match the frequency and power level you will measure. A directional wattmeter compares forward and reflected power to determine SWR.

Battery Types and Diode Details

Some batteries can be recharged and some cannot. Nickel-metal hydride, lithium-ion, and lead-acid are all rechargeable chemistries. Charging must match the battery chemistry.

Carbon-zinc cells are made for single use and should not be recharged. They are different from nickel-cadmium, lead-acid, and lithium-ion, which can be recharged. Rapidly charging or discharging an unprotected battery can cause overheating or out-gassing.

A diode has two electrodes, anode and cathode, but the forward voltage drop is not the same for all diodes. Some diode materials and designs have a lower forward drop than others, which leaves more voltage for the load.

Switches

A single-pole single-throw switch, SPST, simply opens or closes one circuit. It has one on or off path for current.

A single-pole double-throw switch, SPDT, connects one common circuit to either of two other circuits. It is like a three-way household light switch.

More Components and Symbols

A transistor can provide power gain, meaning the output signal has more power than the input signal. In an amplifier, gain is simply the output compared with the input.

The schematic symbol for a lamp is a rounded bulb outline with a loop inside for the filament. It represents an indicator light.

Shielded wire has a metal braid or foil around the center conductor. This shield keeps outside signals from entering and keeps the wire's own signals from leaking out.

A meter is a device that measures an electrical quantity and displays it as a number. A digital meter shows the value directly on its screen.

A voltage regulator holds the output voltage of a power supply steady. Even when the input voltage or the load changes, the regulator keeps the voltage constant.

A transformer changes 120 V AC power to a lower AC voltage. It works only with alternating current, using two coils sharing a magnetic field.

Frequency Conversion and Ohmmeter Behavior

A mixer combines two signals and produces new frequencies from their sum and difference. Receivers use a mixer to move an incoming signal to a frequency that is easier to filter.

An oscillator generates a steady signal at a specific frequency. Transmitters and receivers depend on oscillators to know where they are on the dial.

When an ohmmeter is connected across a large, discharged capacitor, the reading starts low and increases over time. The capacitor charges from the meter's small current, so less current flows and the displayed resistance rises.

Radio Waves and Bands

A radio wave is an electromagnetic wave with electric and magnetic fields at right angles to each other and to the direction of travel. Radio waves travel at the speed of light in free space.

Wavelength in meters is about 300 divided by frequency in MHz. Higher frequency means shorter wavelength. A 150 MHz signal has about a 2 meter wavelength.

Amateur bands are often named by approximate wavelength. The 2 meter band covers 144 to 148 MHz. The 6 meter band covers 50 to 54 MHz. The 70 centimeter band covers 420 to 450 MHz.

Frequency ranges have names. VHF is 30 to 300 MHz. UHF is 300 to 3000 MHz. HF is 3 to 30 MHz. 6 meters and 2 meters are VHF bands.

Modulation and Modes

Modulation combines speech or data with an RF carrier signal. FM changes the carrier frequency, while AM changes its strength.

CW means continuous wave, but hams use it for Morse code. A CW signal has very narrow bandwidth, about 150 Hz.

Single sideband, or SSB, sends one sideband and no carrier. Its bandwidth is about 3 kHz. Hams use upper sideband on 10 meters, VHF, and UHF.

FM or phase modulation is used on most VHF and UHF voice repeaters. An FM voice signal is about 10 to 15 kHz wide.

SSB is better for weak, long-distance VHF and UHF contacts because it uses less bandwidth and puts power into a narrow signal. VHF packet radio also uses FM.

NTSC is an analog fast-scan color TV signal. PSK means Phase Shift Keying, which changes the phase of a carrier to carry data.

Receiver Characteristics

Sensitivity is a receiver's ability to detect weak signals. Selectivity is its ability to separate one signal from others nearby.

Squelch mutes the audio when no signal is present, so the radio does not hiss. To hear a very weak FM signal, set squelch so the audio stays on.

A receiver filter bandwidth should match the mode. A narrow CW filter can pull one Morse signal out of a crowded band, while a 2400 Hz filter works well for SSB.

On FM, being slightly off frequency distorts audio. On SSB, being off frequency changes voice pitch, and RIT or clarifier can fix receive pitch without moving transmit frequency.

An FM receiver has a capture effect: it locks onto the strongest signal and blocks weaker ones. With SSB you can sometimes hear two stations at once.

Band Names and Wavelength

Besides frequency, amateurs identify bands by their approximate wavelength in meters. A band like 2 meters or 70 centimeters is named from that approximate wavelength instead of always quoting the frequency.

Bandwidth and Frequency Control

Single sideband (SSB) has a narrower bandwidth than FM, so it takes up much less spectrum. That leaves room for more signals on the same band.

The VFO circuit in a transceiver sets the receive and transmit frequency. Turning the main tuning knob changes the VFO, moving the radio to a new frequency.

The FCC and Your License

The Federal Communications Commission, FCC, makes and enforces amateur radio rules in the United States. The rules are in Part 97 of Title 47 of the Code of Federal Regulations.

The FCC currently issues new licenses for three classes: Technician, General, and Amateur Extra. Older Novice and Advanced licenses can be renewed by existing holders, but no new ones are issued.

The Technician exam has 35 questions and requires 26 correct answers to pass. The license is normally granted for 10 years and can be renewed.

You may ask to renew your license up to 90 days before it expires. If it expires, you have a two-year grace period to renew without retesting, but you cannot transmit until the license is renewed.

After passing your first exam, you may start transmitting only when your license grant appears in the FCC Universal Licensing System database. The exam certificate alone is not enough.

Your license must show a current email address where the FCC can reach you. If the FCC cannot reach you, your license may be revoked or suspended.

Control Operator and Station Identification

Every amateur station that transmits must have a control operator. The control operator's license class determines the frequencies the station may use.

The station licensee designates the control operator. If the control operator is not the licensee, both are responsible for proper operation.

A Technician may not serve as control operator in an Amateur Extra-only segment, except during an emergency. The station owner's higher license class does not expand a Technician's privileges.

You must transmit your assigned call sign at least every 10 minutes during a contact and at the end. On phone, the identification must be given in English.

A station transmitting phone may identify by CW or phone. An on-air test transmission still requires station identification. Model-craft control may be transmitted without on-air identification, but the transmitter must be labeled.

The station licensee must allow FCC inspection of the station and records whenever an FCC representative requests it.

Allowed and Prohibited Communications

Hams may never willfully or maliciously interfere with any radio communication. Broadcasting, meaning transmissions intended for the general public, is prohibited.

Obscene or indecent language is prohibited. Music is generally prohibited on phone, except during an authorized retransmission from a crewed spacecraft.

Messages may not be encoded to hide their meaning, except for control of space stations or model craft. Business communications are generally not allowed, but an occasional on-air announcement of ham gear for sale is permitted when it is not regular.

Third-party communication is a message sent on behalf of another person. For a foreign third-party message, the foreign country needs a third-party agreement with the United States.

A control operator may be paid only when the amateur station is used as part of classroom instruction at an educational institution. Support for broadcasting or news gathering is allowed only for immediate safety of life or property when no other means is available.

In an emergency involving immediate danger to life or property, an amateur may use any means to get help, even outside normal privileges, when normal communication systems are not available. FCC Part 97 rules still apply during RACES or ARES operations.

Technician voice privileges on HF are only on 10 meters from 28.300 to 28.500 MHz. Technicians may use digital modes on portions of 10, 6, and 2 meters.

Secondary band segments require U.S. amateurs to avoid interfering with non-amateur stations. Secondary users also cannot claim protection from interference caused by primary stations.

Power Limits and Vanity Calls

A Technician may use up to 200 watts peak envelope power on permitted HF segments such as 10 meters. This limit applies to the Technician segments on 80, 40, 15 and 10 meters.

Above 30 MHz, a Technician may generally run up to 1500 watts PEP, which is the legal maximum for all hams. Some bands and situations have lower limits.

Any licensed amateur may apply for a vanity call sign under FCC rules. The license class only affects which shorter call sign groups are available.

Purpose, Coordination, and International Rules

One purpose of the Amateur Radio Service is advancing technical and communication radio skills. It is a voluntary and noncommercial service, not a personal radio service for everyone.

Volunteer frequency coordinators recommend channels for repeater and auxiliary stations. The coordinators are selected by eligible amateurs in the local or regional area.

A U.S. amateur may operate from a U.S.-documented vessel in international waters when the vessel's master permits it. No special maritime authorization is required.

FCC-licensed amateurs may not contact countries whose administrations have objected through the International Telecommunication Union. The ITU is a key part of that international notification process.

A club station license grant requires at least four club members. The club also needs a name, an organizing document, management, and a primary purpose devoted to amateur radio.

Control Points and Repeater Accountability

An amateur station's control point is the location where the control operator function is performed. It does not have to be at the antenna or the transmitting equipment, because remote control can move that function away from the radio.

If a repeater unknowingly relays a rule violation, the originating station's control operator remains accountable. The repeater did not knowingly create the content.

Repeaters and Direct Contacts

Simplex means transmitting and receiving on the same frequency. A repeater receives on one frequency and transmits on another. The difference between its input and output is the offset. On 2 meters, the common offset is plus or minus 600 kHz. On 70 centimeters, it is plus or minus 5 MHz.

The national FM simplex calling frequency on 2 meters is 146.520 MHz. On 70 centimeters the national simplex frequency is 446.000 MHz. Call there, then move to another frequency to chat.

To answer a station calling CQ, say the other station's call sign first, then your call sign. CQ means calling any station. To call a specific station on a repeater, give their call sign, then yours.

Many repeaters require a CTCSS sub-audible tone to open squelch. DTMF uses two audio tones at the same time for keypad commands. The reverse function lets you listen on a repeater's input frequency.

Q signals are short codes. QSY means changing frequency. QSL means I acknowledge receipt. QRZ asks who is calling me. QRM means interference from other stations.

Band plans are voluntary guidelines, not FCC rules. Leave room inside a band edge because display error, modulation sidebands, and drift can push your signal outside authorized frequencies.

Nets, Traffic, and Public Service

In a radio net, net control runs the net. Transmit only when net control directs you, unless you have an emergency. Typical net control duties include calling the net to order and directing communications between stations.

In ham radio, traffic means formal messages exchanged by net stations. The preamble of a traffic message has information needed to track the message, such as message number and origin. The check is the number of words in the message text.

RACES is the Radio Amateur Civil Emergency Service. RACES operators must be certified by a civil defense agency. ARES is made up of volunteer hams who register for public service and does not require that certification.

In a true emergency where life or property is in immediate danger, a control operator may use any means to get help, even outside normal privileges. Part 97 rules still apply in RACES and ARES operations.

Interference, Tuning, and Problem Solving

If two stations interfere with each other on the same frequency, they should negotiate continued use of the frequency. No one owns a frequency. Listen first and ask if the frequency is in use.

If your FM audio is reported over-deviating, talk farther away from the microphone. Wide FM is about 5 kHz deviation and narrow FM is about 2.5 kHz. Too much microphone gain on SSB distorts transmitted audio.

Use a standard phonetic alphabet to spell unusual words, such as Alpha, Bravo, Charlie. That helps when letters sound alike over noise.

In a contest, you try to contact as many stations as possible in a set time. Send only the required identification and exchange. A grid locator is a letter-number designator for an area.

Radio direction finding uses a directional antenna to locate a noise source or hidden transmitter. Hidden transmitter hunts are often called fox hunts.

An electronic keyer helps send clean Morse code. You set a transceiver frequency with the keypad or VFO knob. The scanning function tunes through frequencies to check for activity.

If an SSB voice answering your CQ sounds too high or too low, use RIT or clarifier to adjust receive frequency without moving transmit frequency. To hear a weak FM signal, open the squelch so audio stays on.

Auxiliary Stations and Control Methods

An auxiliary station can send one-way transmissions linking a remote repeater receiver to the main transmitter. It supports another amateur station rather than serving as a general backup radio.

Automatic control means the station can transmit without a control operator making each decision. A repeater is a common example because it retransmits signals on its own.

Any amateur station may be remotely controlled when operated lawfully. Remote control means the control operator operates the station through a control link, such as over the internet.

Phone Calls, Identification, and Repeaters

To seek any phone contact without a repeater, repeat CQ, give your call sign, then listen. The pause lets another station answer before you call again.

When adding a self-assigned indicator on phone, you may say stroke, slant, or slash between call sign parts. All three are acceptable separators.

A repeater station receives another amateur station and simultaneously retransmits its signal on a different channel. The separate input and output channels let it receive and transmit at the same time.

In a linked repeater network, each repeater retransmits what any one of them receives. Linking lets a small handheld radio cover far more ground than one repeater alone.

Transceiver Controls and Interference Basics

PTT means push to talk. Grounding the PTT input switches the radio from receiver to transmit, so you can send your voice.

A strong ham signal can overwhelm a broadcast radio even if the ham is on a different frequency. This is called fundamental overload, and it happens because the broadcast receiver cannot reject strong out-of-band signals.

Fundamental overload, harmonics, and spurious emissions can all cause radio frequency interference. Harmonics fall on multiples of your frequency, and spurious emissions are stray signals outside your intended band.

A filter at the antenna input of a neighbor's receiver can reduce out-of-band overload. The filter blocks your strong signal while letting the receiver's own stations through.

If a neighbor says your transmissions interfere with their TV, first check whether your own TV has the same problem. This helps confirm whether your station is the source.

A band-reject filter can reduce interference to a 2-meter radio from a nearby commercial FM station. It blocks a narrow range of frequencies while passing others.

Resolving Interference and Audio Problems

If a device in a neighbor's home causes harmful interference to your station, work with your neighbor to find the device. Politely explain the FCC rules and make sure your station follows good practice.

For cable TV interference from your ham transmissions (not fiber optic), check that all TV coax connectors are installed properly. Loose connectors let your signal leak into the cable system.

Distorted audio through an FM repeater can be caused by being slightly off frequency, talking too close to the microphone, or a poor location. Check each one to fix the problem.

Antenna Types and Polarization

Polarization tells the orientation of the electric field. A vertical antenna makes vertically polarized waves. If one antenna is vertical and the other horizontal, they are cross-polarized and the signal is much weaker.

A half-wave dipole radiates strongest broadside to the wire, like the sides of a figure eight. Very little signal goes off the ends.

A 19-inch vertical antenna is common on 2 meters because it is a resonant quarter-wave. A full wavelength on 2 meters is a bit under 7 feet, and a quarter of that is about 19 inches.

Shortening a dipole raises its resonant frequency. Lengthening it or adding loading coils lowers the resonant frequency. A short handheld antenna has low efficiency, so some transmitter power is lost.

A Yagi antenna concentrates energy in one direction and has more gain than a vertical or J-pole. Antenna gain means stronger signal in one direction compared with a reference, with less in other directions.

Handheld VHF radios often work poorly inside a vehicle because the metal body shields signals. Mounting an antenna outside, such as on the roof, can improve both transmitted and received signals.

Feed Lines and Connectors

Coaxial cable is the most common amateur feed line because it is easy to install and use. Most ham coax has a characteristic impedance of 50 ohms, matching many radios and antennas.

Coax loses more power as frequency increases. RG-213 has less loss than RG-58 at the same frequency. Air-insulated hardline has the lowest loss of common feed lines.

Moisture contamination inside coax causes failure over time. Sun damage to the jacket can crack it and let water in. Feed line loss is converted into heat.

PL-259 connectors are common on HF and VHF. Type N connectors are better for frequencies above 400 MHz. Outdoor connectors should be carefully taped or weatherproofed.

A high SWR increases effective feed-line loss. Sources of coax loss include water intrusion, high SWR, and adding many connectors.

SWR and Antenna Problems

SWR compares forward and reflected power on a feed line. A perfect impedance match gives a reading of 1:1. A high reading, such as 4:1, means there is an impedance mismatch.

A directional wattmeter measures forward and reflected power and can determine SWR. An antenna analyzer checks whether an antenna is resonant at a desired frequency.

Most solid-state transmitters reduce output power as SWR rises, called SWR foldback, to protect the final amplifier transistors. If your FM radio output is low, check the antenna and feed line for high SWR.

Erratic changes in SWR often come from a loose antenna or feed-line connection. A loose connection changes the impedance path unpredictably.

An antenna tuner, also called an antenna coupler, matches the impedance between the antenna system and the transceiver. It does not physically retune the antenna.

Feed-line loss affects both transmitted and received signals. Using shorter, lower-loss cable and weatherproofing connectors helps keep more signal on the air.

Ionosphere and Skywave

The ionosphere is a charged layer high in the atmosphere that can bend HF radio waves back to Earth. This allows long-distance contacts. Long-distance ionospheric propagation is much more common on HF than VHF.

Sporadic E happens when patches of the ionosphere's E region become dense enough to reflect higher frequencies. It can bring occasional strong signals on 10, 6, and 2 meters from beyond the horizon.

The sunspot cycle runs about 11 years from peak to peak. At high sunspot numbers, 10 meters is best for long-distance F region propagation from dawn to just after sunset. At sunspot peak, 6 and 10 meters may open via the F region.

Ionospheric signals become elliptically polarized, so vertical or horizontal antennas both work for skywave contacts. Irregular fading can happen when multiple signal paths combine randomly.

Auroral backscatter can reflect VHF signals, but they sound distorted with a raspy or buzzing sound. Meteor scatter works best on 6 meters and contacts often last only seconds.

VHF, UHF, and Line-of-Sight

Multipath propagation happens when signals bounce off buildings and hills and reach the receiver by different paths. Depending on antenna position, those copies add together or cancel. Moving a VHF antenna a few feet can change signal strength a lot.

Picket fencing is rapid flutter on mobile signals caused by multipath. As a car moves, it passes through spots where reflected signals add and cancel.

The radio horizon is farther than the visual horizon because the atmosphere bends radio waves slightly. UHF signals are rarely heard beyond the radio horizon because the ionosphere usually does not carry them.

Tropospheric ducting is caused by temperature inversions, warm air over cooler air. It can trap VHF and UHF signals in a duct and carry them about 300 miles.

Cross-polarization on a line-of-sight VHF or UHF path reduces received signal strength. Holding a handheld radio sideways can cross-polarize it with a repeater's vertical antenna.

Weather and Obstacles

Trees and plants absorb UHF and microwave signals. Shooting a signal through thick trees can make a weak signal disappear, so hams try to get UHF antennas up above the treetops.

Precipitation, such as rain, absorbs and scatters microwave signals and can shorten a microwave link. However, rain and fog have little effect on 10-meter and 6-meter band signals.

Knife-edge diffraction lets some radio signal bend around a sharp edge, like a ridge or building top. This can let VHF signals reach places just behind a hill.

Buildings can block a path to a repeater, but a directional antenna may still work by aiming at a building or surface that reflects signals to the repeater. Sometimes the best direction is not directly toward the repeater.

Electrical Safety

In US three-wire 120 volt AC cable, black insulation means hot, white means neutral, and green or bare is ground. Fuses and breakers in 120 volt circuits go in series with the hot wire only.

Electrical current through the body can cause heating, cell disruption, and muscle contractions. The path current takes through the body affects the risk. Use three-wire grounded cords, grounding, and discharged capacitors to guard against shock.

When measuring high voltage, use a meter and leads that are voltage-rated for the expected voltage. An inadequate rating can allow insulation breakdown or arcing.

Install an antenna so that if it falls, no part comes within 10 feet of power lines. Never attach an antenna to a utility pole.

RF Exposure

Radio signals are non-ionizing radiation. They do not have enough energy to cause chemical changes in cells or damage DNA, unlike X-rays and gamma rays.

The station licensee is responsible for making sure no one is exposed to RF energy above FCC limits. This includes re-evaluating the station whenever the transmitter, antenna, or feed line changes.

Touching an antenna while it is transmitting can cause an RF burn to the skin. Keep antennas where people cannot reach them, and move antennas farther from people to reduce exposure.

RF exposure depends on frequency, power, distance from the antenna, and the antenna's radiation pattern. Compliance can be checked by calculations, computer modeling, or calibrated measurements.

Duty cycle is the percentage of time transmitting during the RF exposure averaging time. A 50 percent duty cycle transmits half the time, so allowable power density can be two times higher than at 100 percent.

Among the choices on the exam, 50 MHz has the lowest maximum permissible RF exposure. A lower exposure limit means less field strength or power density is permitted.

Battery and Circuit Protection

Shorting an unprotected 12-volt battery can cause burns, fire, or an explosion. Low voltage does not mean low short-circuit current.

A fuse removes power during an overload. Do not replace a 5-amp fuse with a 20-amp fuse, because wiring designed for 5 amps could overheat and cause a fire before the bigger fuse reacts.

Some capacitors can hold a dangerous charge after equipment is switched off. Discharge high-voltage capacitors safely before working on equipment.

Guard against electric shock by using three-wire power cords, a common safety ground, and discharged capacitors. These methods help carry fault current safely and reduce dangerous touch voltages.

Duty Cycle and RF Exposure

Duty cycle matters for RF safety because it affects average radiation exposure. A transmitter that is on less often contributes less total energy during the averaging period.

Duty cycle is the percentage of time the transmitter is on during the RF exposure averaging time. For example, transmitting for one minute in a ten-minute interval gives a 10 percent duty cycle.

Tower Safety

Never climb a tower without a helper or observer. Safe tower work requires training, staying tied off, and an approved harness.

Before putting up an antenna tower, look for overhead electrical wires. Plan the location so no part of the tower, antenna, or guy lines can fall within 10 feet of power lines.

A crank-up tower may be climbed only when it is retracted or mechanically locked. The lifting cable alone is not a safe mechanical lock.

Put a safety wire through a guy-line turnbuckle to prevent vibration from loosening it. Wind can slowly rotate a turnbuckle and change guy-line tension.

Grounding and Bonding

Tower grounding conductors should be short and direct. Avoid sharp bends, because lightning current changes quickly and sharp bends add impedance.

A proper tower grounding method uses bonded eight-foot ground rods at each tower leg. Bonding all rods and the tower together creates one connected grounding system.

Local electrical codes establish grounding requirements for an amateur tower or antenna. FCC Part 97 rules and FAA lighting rules do not set tower grounding requirements.

For RF bonding of station equipment, use flat copper strap. RF current flows mostly along the surface of a conductor, and flat strap has more surface than round wire.

Bonding keeps grounded parts at similar electrical potential. This helps reduce RF problems and improves safety.

Station Power and Accessories

Use short, heavy-gauge wires for a radio's DC power connection to minimize voltage drop when transmitting. A typical 50-watt mobile radio needs about 13.8 volts at 12 amps.

In a vehicle, connect a mobile radio's negative power lead at the 12-volt battery chassis ground. Random metal or a mounting bracket can give poor connections and noise.

A dummy load is a 50-ohm non-inductive resistor mounted on a heat sink. It absorbs transmitter power as heat so you can test without radiating on the air.

A transverter shifts both the transmit and receive signals of a transceiver to another band. This lets one radio work bands it was not built for.

A clip-on ferrite choke on a microphone cable can stop distorted voice transmissions caused by your own RF feeding back into the transmitter.

An RF power amplifier goes between the transceiver output and the antenna to increase transmitted power. It must be set correctly for the mode, such as SSB or CW-FM.

Satellites and Space

Part 97 defines an amateur space station as an amateur station located more than 50 kilometers above Earth's surface. That is about 31 miles.

LEO means Low Earth Orbit. LEO satellites circle Earth roughly every 100 minutes. The International Space Station orbits about every 90 minutes, and Technician licensees or higher may contact it on amateur VHF frequencies.

Doppler shift is a frequency change caused by relative motion between the satellite and your station. The signal appears higher as the satellite approaches and lower as it moves away.

Satellite tracking programs use Keplerian elements to predict a satellite's position and pass times. They also provide pointing directions and the Doppler-corrected frequency.

U/V mode means uplink on 70 centimeters and downlink on 2 meters. V/U mode is the reverse. Amateur satellites commonly use SSB, FM, and CW/data modes.

A satellite beacon transmits health and status telemetry. Anyone may receive telemetry from an amateur satellite. When using a linear transponder, adjust uplink power so your downlink signal is about as strong as the beacon.

Satellite spin can cause spin fading as antennas rotate. Using circularly polarized antennas can help smooth out this fading. Too much uplink power can block other users on a shared satellite.

Digital Voice and Data Modes

FT8 is a digital mode designed for very weak signals. It uses 15-second transmit and receive cycles, and your computer clock must be accurate. The radio's audio connects to a computer running FT8 software.

A digital mode interface carries receive audio, transmit audio, and transmitter keying. The computer's line input connects to the transceiver speaker output, and the computer's line output connects to the radio's audio input.

APRS, the Automatic Packet Reporting System, sends short data packets such as GPS positions, text messages, and weather. Most US APRS activity is on 2 meters at 144.390 MHz.

DMR, Digital Mobile Radio, splits a 12.5 kHz channel into two time slots for two digital voice conversations. To use a DMR repeater, program the correct color code, which is a number, not a color. A talkgroup ID sorts traffic so you hear only your group.

A DMR code plug is the configuration data loaded into a radio for repeaters and talkgroups. D-STAR requires your call sign to be programmed into the radio before transmitting.

Packet radio includes a checksum for error detection, a destination header, and automatic repeat request, or ARQ, for retransmitting damaged data. PSK means Phase Shift Keying.

Internet Linking and Advanced Data

Voice Over Internet Protocol, or VoIP, carries digital voice over the internet. IRLP, the Internet Radio Linking Project, connects amateur radio systems through the internet. A gateway connects amateur stations to internet resources.

EchoLink can initiate a repeater transmission without using a radio, but you must register your call sign and prove you are licensed. A Technician license is enough for EchoLink.

Winlink sends email over amateur radio using addresses based on ham call signs. It can work over HF, VHF, and UHF links.

A digital mode hotspot is a low-power box that connects nearby digital radios to a digital voice or data network over the internet. It is useful where no digital repeater is nearby.

An amateur radio mesh network uses commercial Wi-Fi gear with modified firmware. Nodes can relay data through other nodes without one central access point.

WSJT-X software supports weak-signal activities including Earth-Moon-Earth, propagation beacons, and meteor scatter. Technician digital privileges include portions of 10 meters, 6 meters, and 2 meters.

Satellite Control and DMR Talkgroups

To control a station using an amateur satellite, you need only be allowed on the satellite's uplink frequency. Any amateur whose license permits transmission there may serve as control operator.

In DMR, a talkgroup is an ID that sorts traffic so you hear only your group. To join a talkgroup, you program your radio with the group's ID or code.

Digital Modes and Error Correction

Packet radio, IEEE 802.11, and FT8 are all digital communication modes. They represent information with coded symbols rather than a continuously varying analog signal.

ARQ stands for Automatic Repeat reQuest. The receiving station checks incoming data for errors and asks the sender to transmit again when an error is found.