Austria Theory AM flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

ITU Region 1

The ITU radio region containing Europe, Africa, the former Soviet Union and the Middle East; Austria operates under Region 1 allocations, including the 144–146 MHz amateur band.

Callsign identification rule

The full callsign must be transmitted at the beginning and end of each contact and at intervals not exceeding ten minutes during the contact, using the station's assigned identifier.

CQ call format

The letters CQ followed by the station's own callsign, repeated at most three times per call; the reply consists of the other station's callsign followed by the caller's callsign.

Harmful interference duty

A licensed operator must immediately eliminate any harmful interference caused by the station, even when the transmission otherwise complies with the licence conditions and band plan.

Station log contents

Each entry records date, time in UTC, frequency or band, mode, and the callsign of the correspondent, and the log is retained for the period required by the national authority.

Ohm's law and power

Voltage equals current times resistance (U = I·R); power equals voltage times current, equivalently I²R or U²/R, valid for purely resistive circuits at DC and low frequency.

Parallel resistance formula

The reciprocal of the total resistance equals the sum of the reciprocals of the individual resistors; two equal resistors in parallel give half the value of one resistor.

Capacitive reactance

XC = 1/(2πfC), so reactance falls as frequency or capacitance rises; a capacitor blocks DC and passes high frequencies, behaving as a short at very high frequency.

LC resonance

A series or parallel LC circuit resonates at f = 1/(2π√(LC)), where inductive and capacitive reactances cancel; the bandwidth B equals f/Q, with Q the quality factor.

Decibel power ratio

Power ratio in decibels equals 10·log10(P2/P1); a doubling of power is +3 dB, a tenfold increase is +10 dB, and halving is −3 dB.

Decibel voltage ratio

Voltage ratio in decibels equals 20·log10(U2/U1); doubling the voltage is +6 dB, and a tenfold voltage increase is +20 dB, assuming equal impedances.

Silicon diode forward voltage

A silicon junction diode begins to conduct appreciably when the anode is about 0.6 to 0.7 volts positive with respect to the cathode; germanium diodes conduct at about 0.3 volts.

Carson's bandwidth rule

The occupied bandwidth of an FM signal is approximately twice the sum of the peak deviation and the highest modulating frequency, giving about 11 kHz for 2.5 kHz deviation and 3 kHz audio.

Half-wave dipole length

The physical length in metres is approximately 143 divided by the frequency in megahertz, the constant including the end-effect shortening factor of about 0.95.

Quarter-wave vertical length

The physical length in metres is approximately 71.5 divided by the frequency in megahertz; such a vertical requires a ground plane or radials to provide the return current path.

Dipole feed impedance

A centre-fed half-wave dipole in free space presents about 73 ohms at resonance; lowering it toward ground reduces this value, and off-centre feeding raises it.

Balun purpose

A balun converts between balanced and unbalanced lines; a 1:1 choke balun at the dipole feed point prevents common-mode current on the coaxial shield, reducing pattern distortion and interference.

Coaxial cable impedance

Characteristic impedance depends on the inner and outer conductor diameters and the dielectric constant; 50 ohms is standard for radio equipment and 75 ohms for television and video.

SWR formula

SWR equals (1 + |Γ|) divided by (1 − |Γ|), where Γ is the reflection coefficient (ZL − Z0)/(ZL + Z0); an SWR of 2:1 corresponds to about 11 percent reflected power.

Velocity factor

The ratio of propagation speed in a cable or antenna wire to the speed of light; physical length equals free-space length multiplied by the velocity factor, about 0.66 for solid polyethylene coax.

Ionospheric sky wave

HF signals refract from the ionosphere, chiefly the F layer, enabling worldwide communication; the maximum usable frequency rises with solar activity and varies with time of day.

Radio horizon distance

For line-of-sight VHF and UHF paths, the horizon in kilometres is approximately 4.12 times the square root of the antenna height in metres above ground.

Spurious emission limits

Transmitters must keep harmonics and other spurious products below the limits set for the licence class; a low-pass filter after the final amplifier attenuates harmonics before the antenna.

Class C amplifier use

Class C stages are efficient but strongly non-linear and generate harmonics, so they suit only constant-envelope modes such as CW and FM; SSB needs linear Class AB amplification.

Receiver sensitivity

The minimum input signal level that produces a specified signal-to-noise ratio at the receiver output; it depends on front-end noise figure and IF bandwidth.

Receiver selectivity

The ability of a receiver to reject signals outside the desired passband; it is determined mainly by the intermediate-frequency filter shape and the number of IF stages.

Mixer image rejection

The mixer converts RF to the intermediate frequency; signals at the image frequency are also converted, and rejection depends on the RF preselector and the choice of first IF.

Dummy load rating

A 50-ohm resistive load that absorbs transmitter power without radiation; it must be rated for the full peak envelope power and present low reactance across the operating band.

SWR meter reading

An instrument inserted between transmitter and antenna that displays the ratio of forward to reflected power; 1:1 indicates a matched load, while an infinite reading indicates an open or short circuit.

Common-mode choke

Ferrite beads or a choke balun on the feed line suppress common-mode current on the cable shield, which otherwise causes interference and distorts the antenna radiation pattern.

Switching supply noise

Differential-mode noise from a switching power supply is reduced with an LC filter at the source, while the supply leads are kept short and twisted to limit radiated interference.

Power meter calibration

A power meter calibrated for one frequency band may read low on another because of detector response and mismatch; measurements are valid only within the meter's specified frequency range.