🗼 Stuff Every Extra Class Ham Should Know: Training Guide

Low-frequency bands and antenna limits

On the 630 m amateur band, the maximum radiated power outside Alaska is 5 W EIRP. Stations in Alaska within 800 km of Russia are limited to 1 W EIRP, and the neighboring 2200 m band has a 1 W EIRP limit.

Antennas used to transmit on the 2200 m and 630 m bands must not be taller than 60 meters above ground. The general antenna structure rule triggers FAA notification and FCC registration for structures higher than 60.96 meters, which is 200 feet.

Amateur emissions on the 60 m band may not occupy more than 2.8 kHz, about the width of one SSB voice signal. Power is limited to 100 W ERP on the four main 60 m channels and to 9.15 W ERP in the 5351.5 to 5366.5 kHz segment.

Before operating on 630 m or 2200 m, you must notify the Utilities Telecom Council and wait 30 days unless it flags a nearby power line carrier system. Stations on those bands may operate only from fixed locations at least 1 km from power lines carrying PLC signals.

Amateurs may not transmit north of Line A in the UHF segment from 420 to 430 MHz. In that range, amateurs must also accept interference from FCC land mobile stations within 80.5 km of Buffalo, Cleveland, and Detroit.

Remote control and telecommand

A remotely controlled station that loses its control link must stop transmitting after no more than 3 minutes. The station must have a copy of its license and contact details for the licensee and a control operator posted at the station.

A model craft telecommand transmitter may run at most 1 W. It must carry a label with your call sign, name, and address, and station identification is waived for transmissions aimed only at the model craft.

To operate an amateur station aboard a ship or aircraft, you need approval from the ship's master or the pilot in command. An amateur station on an aircraft may not be used while the aircraft is flying IFR unless it meets FAA rules.

An amateur space telecommand station may use special codes to obscure the meaning of its telecommand messages to protect the satellite from unauthorized commands. A space telecommand station may also transmit one-way communications.

An automatically controlled data station answering an interrogation may use at most 500 Hz bandwidth outside the listed segments. This rule does not apply to beacon, repeater, auxiliary, earth, space, or space telecommand stations.

Other FCC obligations

For transmitters installed after January 1, 2003 and operating below 30 MHz, spurious emissions must be at least 43 dB below the mean power of the fundamental. Transmitters built before April 15, 1977 or first marketed before January 1, 1978 are exempt from this rule.

A RACES control operator needs an FCC amateur license and enrollment in a civil defense organization, but no separate RACES license exists. Under normal conditions RACES stations may use the bands, segments, and emissions authorized to the control operator.

An amateur radio exam session requires a team of at least three volunteer examiners coordinated by a VEC. A VE may not administer an exam to close family such as a spouse, children, parents, or siblings.

WSJT digital modes

FT8 uses 15 second transmit and receive cycles, which keeps contacts fast but gives a few dB less sensitivity than slower modes. FT4 is faster with 7.5 second cycles and works well for contesting.

WSPR transmitting periods last 2 minutes and happen randomly in time. It is a weak signal beacon mode used to check propagation with very low power.

MSK144 meteor scatter on VHF can make contacts up to about 2100 km, or 1300 miles. Signals bounce off ionized meteor trails in the E region.

JT65 was designed for EME, also called moonbounce, on VHF and higher bands. Its decode threshold is about minus 25 dB signal to noise ratio.

Q65 is designed for fast fading paths such as tropospheric, rain, and ionospheric scatter. It can average several repeated transmissions to decode signals too weak for a single try.

ARRL band plans

The ARRL 20 m band plan assigns RTTY to 14.070 to 14.095 MHz. A band plan is a voluntary division that keeps incompatible modes apart.

The ARRL 20 m plan lists 14.100 MHz for NCDXF beacons. Hams listen there to see if the band is open without calling anyone.

The ARRL 2 m band plan lists 146.52 MHz as the national simplex calling frequency. It also lists 144.200 MHz as the national SSB calling frequency.

Digital conversion and data codes

To accurately reproduce an analog signal, you must sample at least twice the highest frequency component. This is the Nyquist rule, and sampling slower folds high frequencies into false lower ones.

To sample a 1 volt range at 1 millivolt resolution you need at least 10 bits. Nine bits give only 512 levels, while 10 bits give 1024 levels.

An 8 bit analog to digital converter encodes 256 different input levels because each added bit doubles the number of levels. Adding a small amount of noise called dither can reduce quantization noise.

An FT8 signal occupies about 50 Hz, so dozens fit inside one SSB voice channel. Using sinusoidal data pulses minimizes the bandwidth of a PSK31 signal.

ARQ stands for automatic repeat request. The receiver checks for errors and asks the sender to retransmit if something is wrong, and symbol rate and baud are the same thing.

Gray code allows only one bit to change between sequential code values, which avoids glitches. Baudot uses 5 data bits per character, while ASCII uses 7 or 8.

Radio signals and bandwidth

An unprocessed SSB phone signal has a peak envelope power to average power ratio of about 2.5 to 1 because speech has loud peaks but a much lower average.

FM modulation index is the frequency deviation divided by the highest modulating frequency. If an FM signal deviates 3000 Hz each side with a 1000 Hz modulating frequency, the index is 3.

A CW signal takes roughly 4 Hz of bandwidth for each word per minute of speed, so a 13 WPM signal occupies about 52 Hz. Keying speed and rise and fall times affect the bandwidth.

Spread spectrum frequency hopping rapidly changes the transmit frequency in a pseudorandom sequence that the receiver also knows, so interference only hits a small part of the message.

The most common way to reduce CW key clicks is to increase the keying waveform rise and fall times, making the edges softer. Too much transmit audio is a common cause of overmodulated AFSK digital signals.

Ionosphere basics

The maximum usable frequency, or MUF, is the highest frequency that works reliably over a given path by ionospheric refraction. Going above the MUF makes your signal pass through the ionosphere into space.

Sporadic E is made of transient, localized patches of high electron density in the E region. These patches come and go with little warning and are most likely between sunrise and sunset.

During a polar cap absorption event, HF and VHF radio waves are absorbed over the polar ionosphere. Solar radiation storms can block HF radio at high latitudes.

The D region exists in daytime from about 40 to 90 km altitude. Solar flare X-rays enhance the D region, which can block HF on the sunlit side of Earth.

Solar flares and radio blackouts

Solar flare X-ray classes A, B, C, M, and X each step up by a factor of 10. An X flare reaches 10 to the minus 4 watts per square meter, and an M flare is one tenth of that.

An X1 solar flare triggers an R3 strong radio blackout, with wide area HF loss for about an hour on the sunlit side. An X20 flare gives an R5 extreme blackout for several hours.

Geomagnetic activity and aurora

The Kp index runs from 0 to 9, and a value of 5 or higher indicates a geomagnetic storm. G1 minor storms begin at Kp 5, and G5 extreme storms are Kp 9. The planetary Kp averages readings from 13 observatories.

The best aurora viewing is under an oval between about 60 and 75 degrees latitude. Electrons produce bright aurora, while protons make only a faint, diffuse glow.

Solar cycle, CMEs, and path clearance

The number of sunspots varies on an about 11 year cycle called the solar cycle. HF band conditions improve and fade along with it, and Solar Cycle 24 began in December 2008 and ended in December 2019.

The fastest Earth directed coronal mass ejections, or CMEs, can reach Earth in as little as 15 to 18 hours. A sustained southward magnetic field in a CME makes geomagnetic storming stronger.

The first Fresnel zone gets narrower as frequency goes up. Of common bands, 5.8 GHz has the smallest first Fresnel zone, so it needs the least path clearance.

RC circuits and resonance

The time constant of an RC circuit is the resistance times the capacitance. After one time constant, a charging capacitor holds about 63 percent, or 0.632, of its full charge. When discharging, the charge falls to about 0.368 of its starting value.

A higher Q makes a resonant circuit's bandwidth narrower because bandwidth equals center frequency divided by Q. A high Q circuit is more selective, and raising Q also narrows the matching bandwidth of an impedance matching network.

At resonance, a series RLC circuit has minimum impedance equal to its resistance because the inductive and capacitive reactances cancel. Current is therefore at its maximum at that frequency.

A parallel LC circuit has maximum impedance at resonance, opposite of a series circuit. The inductor and capacitor effectively cancel, so almost no current is drawn from the source, and with a constant current source the voltage is maximum.

At the half power points of a resonant circuit, the current is about 0.707 of its maximum. Power scales with the square of current, so 0.707 squared gives one half.

Reactance and phase

In an ideal inductor, voltage leads current by 90 degrees, or one fourth of a cycle. Inductive reactance is 2 pi f L, so doubling the frequency doubles the reactance.

A capacitor's reactance falls as frequency rises because capacitive reactance is 1 divided by 2 pi f C. Doubling the frequency cuts the reactance in half.

Power and energy

Maximum load power occurs when the load resistance equals the source's internal resistance, but efficiency at that point is only 50 percent. At maximum power transfer, the load voltage and current are each half of their maximums.

Reactive power is measured in volt amps reactive, or VAR, instead of watts. True power uses watts, apparent power uses volt amps, and the math symbol for reactive power is the capital letter Q.

Ideal inductors and capacitors dissipate zero power. They store energy and send it back to the circuit, so only the resistance does real work. Reactive power is often called wattless or nonproductive power.

Battery operating time is capacity in amp hours divided by average current. A 10 amp hour battery feeding a steady 2 amps lasts about 5 hours.

A series linear voltage regulator dissipates power equal to the input to output voltage difference times the output current. The regulator burns off the extra voltage as heat, and dropout voltage is the minimum input to output difference needed to regulate.

Semiconductors and diodes

Gallium arsenide is a semiconductor used mainly in microwave circuits because electrons move faster in it than in silicon. Gallium nitride beats silicon materials for the highest operating frequency in MMIC chips.

A field effect transistor, or FET, has higher DC input impedance at its gate than a bipolar transistor. A depletion mode FET conducts between source and drain even with no gate voltage applied.

Zener diodes are sometimes connected between a MOSFET gate and its source or drain to protect the gate from static damage. A small static charge can punch through the thin gate insulation, but a Zener clamps the voltage first.

The most useful characteristic of a Zener diode is a constant voltage drop while current varies in reverse breakdown. A switchmode voltage regulator works by varying the duty cycle of pulses fed into a filter.

A varactor diode is designed to act as a voltage controlled capacitor. Reverse bias changes its junction capacitance, and radios use it to tune oscillators and filters without moving parts. A Schottky barrier diode is a metal semiconductor junction.

A PIN diode is useful as an RF switch because its low junction capacitance when reverse biased blocks RF. Forward DC bias controls how much it attenuates RF.

The most common optoisolator is an LED and a phototransistor. The signal crosses by light instead of wire, so the two sides stay electrically isolated.

Logic and amplifiers

Tri-state logic has output states of 0, 1, and high impedance. The high impedance state is like disconnected, allowing many devices to share one bus without fighting.

Four flip flops are needed to divide a signal's frequency by 16 because each flip flop divides by 2. One flip flop alone divides by 2.

An astable multivibrator keeps switching between two states with no external clock, so it is a simple oscillator. A monostable multivibrator switches temporarily for a set time.

A Class D amplifier uses switching for high efficiency. Its output devices are fully on or fully off most of the time, and an RF switching amplifier needs an output filter to remove harmonic content.

Switching amplifiers are more efficient than linear amplifiers because the device is saturated or cut off most of the time, wasting little power as heat. Using a Class C amplifier on a single sideband signal causes distortion and excessive bandwidth.

Filters and magnetic parts

Inductor and transformer cores are sometimes built from thin layers to reduce power loss from eddy currents. Thin insulated layers break up the swirling currents, keeping the core cooler and more efficient.

A toroidal core confines most of the magnetic field inside the core, so the coil couples less to nearby parts. Ferrite beads are often used as VHF and UHF parasitic suppressors on HF transistor amplifiers.

A Chebyshev filter has ripple in the passband and a sharp cutoff. An elliptical filter has an even sharper cutoff with one or more notches in the stop band.

A cavity filter is used in a 2 meter repeater duplexer because it handles power and has sharp, high Q response at VHF. Helical filters are often used as band pass or notch filters in VHF and UHF transceivers.

Analog building blocks

A mixer outputs the two input frequencies plus their sum and difference frequencies. High mixer input levels can generate spurious mixer products.

An SSB signal has no carrier, so a product detector is used to mix the signal with a local carrier and recover audio. A frequency discriminator is a circuit for detecting FM signals.

An inverting op amp circuit with a 1800 ohm input resistor and a 68 kilohm feedback resistor has an absolute voltage gain of about 38 because 68000 divided by 1800 is about 37.8. A typical op amp has very low output impedance.

A phase locked loop is a servo loop with a phase detector, filter, VCO, and reference. The phase detector compares the VCO with the reference, and the filtered error steers the VCO until it locks. A PLL can do frequency synthesis and FM demodulation.

Antenna gain and patterns

An isotropic radiator is a hypothetical lossless antenna that radiates equally in all directions. No real antenna is isotropic, but engineers use it as a reference for dBi gain.

An antenna with 6 dB gain over isotropic has 3.85 dB gain over a half wave dipole because a dipole already has 2.15 dB gain over isotropic. Antenna efficiency is radiation resistance divided by total resistance.

Adding a terminating resistor to a rhombic or long wire antenna changes the pattern from bidirectional to unidirectional by absorbing energy that would reflect back. An unterminated long wire develops more lobes closer to the wire axis as it gets longer.

An ideal parabolic dish's gain increases 6 dB when the operating frequency doubles because the dish is twice as big in wavelengths. Top loading an electrically short HF vertical improves radiation efficiency.

As the Q of an antenna increases, the SWR bandwidth decreases. A high Q antenna is sharply tuned and works only over a narrow range. A loading coil resonates an electrically short antenna by cancelling its capacitive reactance.

Feed point impedance and matching

The approximate feed point impedance at the center of a two wire half wave folded dipole is 300 ohms, about four times a simple half wave dipole. This matches well to 300 ohm line.

A gamma match connects the coax shield to the antenna center and the center conductor a fraction of a wavelength to one side. It is common on Yagi antennas and can shunt feed a grounded tower at its base.

The velocity factor of a transmission line depends mostly on the insulating dielectric material. Foam dielectric coax has lower loss per unit length than solid dielectric coax of the same size.

An air insulated parallel conductor line that is electrically a half wavelength at 14.10 MHz is about 10.6 meters long because its velocity factor is near 1. Coax is electrically longer than its physical length because waves move more slowly in it.

A quarter wavelength transmission line shorted at the far end presents a very high impedance at the generator. This happens because a quarter wave line turns impedance upside down. A half wave line shorted at the far end looks like a very low impedance.

A Smith chart calculates impedance along transmission lines. It plots resistance circles and reactance arcs to track impedance changes and design matching stubs.

A Beverage antenna uses a termination resistor to absorb signals from the reverse direction, keeping the antenna directional. A Beverage should be at least one wavelength long for good performance.

RF exposure and tower safety

The FCC human body RF exposure limits are most restrictive from 30 to 300 MHz because the body absorbs RF energy most readily there. When evaluating exposure at a neighbor's home, you must stay under uncontrolled MPE limits.

SAR measures the rate RF energy is absorbed by the body. Handheld radios have SAR limits, and high gain antennas at microwave frequencies can create high exposure levels.

One hundred percent tie-off means at least one lanyard is attached to the tower at all times, even while moving. While climbing, lanyards should be attached to the tower legs.

A shock absorbing lanyard should be attached above the climber's head level when working above ground. This keeps slack short and reduces fall distance. An external earth connection or ground rod primarily dissipates lightning charge.