Glossar
Technical terms explained
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Hertz (Hz)
Unit for the frequency of an oscillation
It has been named after the German physicist
Heinrich Rudolf Hertz
who managed to experimentally prove the existence of the radio waves that have
previously been postulated by
James Clerk Maxwell.
High frequency (HF)
This denotes any frequencies beyond 30 kHz that serve as a carrier for for low-frequency signals to be transmitted. At 30 kHz furthermore starts the range of the long waves.
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Low frequency (LF)
This denotes frequencies below 30 kHz that are modulated onto another signal of high frequency as a data signal. Some methods of signal transmission use frequencies below 30 kHz (so-called VLF waves) as a carrier for data transmission.
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Power Line Communication (PLC)
This procedure uses existing power lines to transmit signals. The nature of
these signals depends of the appliance using PLC.
The generally best known use of PLC can be found in the information technology
by setting up a LAN across the in-house power grid. The advantage of this is
obvious: You don't have to install any cables nor set up any Wifi networks. All
in all one could think that everything is totally unproblematic.
However, in reality everything looks entirely different: First of all, the
signal doesn't stop at the outer wall of the house or apartment, but, depending
on the transmission speed, can travel more or less a distance through the
cable so that other stations in range can pick up the signals, and secondly the
electric lead isn't shielded at all, thus transforming the entire power grid
into a gigantic antenna that happily emits any signals traveling across it into
the adjacent space.
Another annoyance that can be caused by PLC is that it interferes with any
other appliances connected to the power grid by the PLC signals, thereby
causing them to malfuction or disrupting their operation altogether.
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QRM
Interferences by other stations or appliances.
This phenomenon occurs anytime multiple stations share the same radio
frequency. As long as only one station transmits, everything is fine. However,
when multiple stations attempt to transmit, the signals interfere with each
other and thereby cause disruptions on the receiving side.
Another reason for QRM very often is caused by insuffichently shielded
devices that work with high frequencies themselves that are radiated into the
adjacent space due to insufficient or missing shielding and can be picked up by
other devices. Switch-mode power supplies can also cause significant
interferences that are propagated across the power grid and interfere with
other appliances.
Another nuisance is the PLC that causes
significant interference in some regions.
QRN
Atmospheric interferences
This phenomenon is based on the natural background noise that can adversely
affect any radio traffic, caused, for example, by thunderstorms.
Try it out and set your radio to medium wave in an upcoming thunderstorm: The
noise that you are hearing is mostly caused by the thunderstorm.
However, thunderstorms are not the only factors for radiointerference.
QSB
Signal fade
Depending on daytime, season, and meteorological conditions the propagation
conditions can change and thereby influence the signal strength. Interferences
that occur (especially when both the surface wave and the sky wave can reach
the same spot) can cause the signal to be amplified or canceled out, and
atmospheric absorption and scattering can cause additional adverse effects.
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to the topUnits and magnitudes
Unit | Symbol | Meaning | Calculation |
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Designator | Symbol | Magnitude (power) | Magnitude (decimal fraction) |
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yotta- | Y | 10²⁴ | 1,000,000,000,000,000,000,000,000 |
zetta- | Z | 10²¹ | 1,000,000,000,000,000,000,000 |
exa- | E | 10¹⁸ | 1,000,000,000,000,000,000 |
peta- | P | 10¹⁵ | 1,000,000,000,000,000 |
tera- | T | 10¹² | 1,000,000,000,000 |
giga- | G | 10⁹ | 1,000,000,000 |
mega- | M | 10⁶ | 1,000,000 |
kilo- | k | 10³ | 1,000 |
hecto- | h | 10² | 100 |
deca- | da | 10 | 10 |
deci- | d | 10⁻¹ | 0.1 |
centi- | c | 10⁻² | 0.01 |
milli- | m | 10⁻³ | 0.001 |
micro- | µ | 10⁻⁶ | 0.000,001 |
nano- | n | 10⁻⁹ | 0.000,000,001 |
pico- | p | 10⁻¹² | 0.000,000,000,001 |
femto- | f | 10⁻¹⁵ | 0.000,000,000,000,001 |
atto- | a | 10⁻¹⁸ | 0.000,000,000,000,000,001 |
zepto- | z | 10⁻²¹ | 0.000,000,000,000,000,000,001 |
yocto- | y | 10⁻²⁴ | 0.000,000,000,000,000,000,000,001 |
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