Radio Frequencies Flashcards
1
Q
Very Low Frequency (VLF)
A
- 3 kHz - 30 kHz
- 10 km - 100 km
- Propagation - Surface wave
2
Q
VLF Uses
A
- Band not used much for communications in general; difficulties in building efficient antenna for long wavelengths used (10-100km)
- band used for submarine communications
- also been used for global navigation systems with ground based transmitters
3
Q
Low Frequency (LF)
A
- 30 kHz - 300 kHz
- 1 km - 10 km
- Propagation - mainly surface wave
4
Q
LF Uses
A
- long wave radio broadcasting using amplitude modulation (AM)
- surface wave allows large region coverage with single high power antenna
- bandwidth limited
- large band area needed for effective broadcasting transmitting antenna
- Navigation systems using ground based transmitters operate in LF; provide backup to GPS
- LF used in some territories for broadcasting time signals
5
Q
Medium Frequency (MF)
A
- 300 kHz - 3 MHz
- 100m - 1 km
- Propagation - surface wave; sky wave at night
6
Q
MF Uses
A
- medium-wave radio broadcasting using AM
- reception range increased at night by sky-wave propagation; can result in interference from unwanted transmissions
- transmitting antenna may be quarter-wavelength monopole
7
Q
High Frequency (HF)
A
- 3 MHz - 30 MHz
- 10 m - 100 m
- Propagation - sky-wave
8
Q
HF Uses
A
- amateur radio; global distances can be covered by sky wave, often with modest transmitter power
- propagation of HF dependent on ionosphere
- HF used for short-wave radio broadcasting, also for variety of government, military, aviation and maritime purposes
9
Q
Very High Frequency (VHF)
A
- 30 MHz - 300 MHz- 1 m - 10 m
- Propagation - line of sight, contributions from reflected, diffracted and scattered waves
10
Q
VHF Uses
A
- wider bandwidth services accommodated than possible at HF, MF or LF
- shorter wavelength of VHF also means antennas more compact
- FM radio and DAB situated in this band
- used for aviation and some private mobile radio
11
Q
Ultra High Frequency (UHF)
A
- 300 MHz - 3 GHz
- 100mm - 1 m
- Propagation - line of sight, contributions from reflected, diffracted and scattered waves
12
Q
UHF Uses
A
- terrestrial TV broadcasting done in UHF
- some (not all) channels of 8 MHz bandwidth in range 470-790 MHz used; each channel carrying digital multiplex
- antennas compact enough to fit in mobile devices
- huge variety of applications found in this band; mobile phones, WiFi, Bluetooth, GPS; some radar applications
- microwave ovens work at 2.45 GHz which is also in this band
13
Q
Super High Frequency (SHF)
A
- 3 GHz - 30 GHz
- 10mm - 100mm
- Propagation - Line of sight, contributions from reflected, diffracted and scattered waves
14
Q
SHF Uses
A
- satellite broadcasting operates in this band
- able to take advantage of wider bandwidths available
- atmospheric absorption relatively low
- congestion in UHF encouraged move to higher frequencies for WiFi in particular 5 GHz Standard
- SHF used by many radar applications
15
Q
Extremely High Frequency (EHF)
A
- 30 GHz - 300 GHz
- 1 mm - 10 mm
- Propagation - line of sight, contributions from reflected, diffracted and scattered waves
