surface/space/sky Flashcards
Definition of surface wave
Surface wave propogation flows along the earths surface supported by the currents that have been induced into the ground by the transmitting antenna
Surface wave antennas (VHF)
VHF ground spike
VHF elevated ground spike (using freq below 70MHZ)
VHF vehicle mounted
Surface wave antennas (HF)
HF vehicle mounted
HF sloping wire
HF 12m co-site
Surface and sky wave antenna calculations - bowman braid
freq printed on the braid
Surface and sky wave antenna calculations - clansman braid
68.5 divided by the freq in use (round down)
Surface and sky wave antenna calculations - copper wire
71.3 divided by the freq in use (round down)
Best type of ground for surface waves (best to worst)
sea
moist arable land
poor arable land
desert
ice
jungle
Definition of space wave
radio waves follow a direct line-of-sight (LOS) path between transmit and receive antennas
Two components of space waves
direct waves
ground reflected waves
Minimum effective height (MEH) meaning
if the antenna is raised beyond a full wavelength above the ground (for the freq in use) we change from radiating surface wave to space wave propagation
MEH examples
30MHZ - 10M
50MHZ - 6M
75MHZ - 4M
Space wave antennas (VHF)
VHF elevated ground spike (when using freq above 70MHZ)
VHF monopole
VHF dipole
Space wave antennas (UHF)
UHF vehicle mounted
UHF elevated
Sky wave definition
sky wave is only used at HF, long ranges that are achieved by ‘bouncing’ the radio wave off a region of the upper atmosphere called the ionosphere
definitions-
1. skip distance
2. skip zone
3. refraction
- from transmitter to the point where the signal returns to earth
- area of no signal reception
- process by which an ionospheric layer bends a radio wave back towards earth
Short range of sky wave
0-300km (antenna 1/8λ off he ground)
Medium range of sky wave
300-1500km (antenna 1/4λ off the ground)
Long range of sky wave
1500-3000km (antenna 1/2λ off the ground)
Sky wave antennas (x4)
3/4 λ wave endfed
1/2 λ droopy dipole
1/2 λ wave horizontal dipole
HF Marlborough broadband (150w antenna)
Antenna calculation formula
c
f λ
c - velocity, value of 300,000,000Hz/300MHz
f - frequency, number of cycles per second, expressed in hz
λ - wavelength (lambda), measured in metres
Electromagnetic spectrum (HF, VHF, UHF) frequency
HF 3MHZ- 30MHz
VHF 30MHZ - 300MHz
UHF 300MHZ - 3GHz
3 main types of antennas
- resonant antennas
- wideband antennas
- travelling wave antennas
When does a resonant antenna perform at maximum effectiveness?
- when its length corresponds to the wavelength of the freq in use
- change the length of the antenna whenever you change freq
Freq efficiency and bandwidth of resonant antenna
- only efficient at one freq
- small bandwidth
Examples of resonant antennas (x3)
λ/2 dipole
λ/4 monopoles
λ/4 and 3/4λ endfeds
Freq efficiency and bandwidth of Wideband antennas
- designed to perform effectively over a range of freq
- greater bandwidth
- do not have to change length of antenna when you change freq
Examples of wideband antennas (x2)
VHF dipole
VHF monopole
Efficiency of travelling wave antennas
- construction and dimensions are determined by the freq and the ranges over which they are required to radiate
- terminated at the ends with resisters, makes them highly directional
Examples of travelling wave antennas (x3)
sloping v
para v
inverted v
GSA (ground spike antenna) - surface properties
Use, Range, Polarity,
Radiation pattern,
Propagation,
Advantages,
Disadvantages
Use: tactical VHF networking
Range: 0-20km
Polarity: vertical
Radiation pattern: omni-directional
Propagation: surface wave
Advantages: quickly erected, self-supporting
Disadvantages: inefficient
EGSA (elevated ground spike antenna) - surface
Use, Range, Polarity,
Radiation pattern,
Propagation,
Advantages,
Disadvantages
Use: tactical VHF networking
Range: 0-30km
Polarity: vertical
Radiation pattern: omni-directional
Propagation: surface wave (below 70MHz)
Advantages: quickly erected, can be remoted
Disadvantages: inefficient
HF/VHF vehicle whip - surface
Use, Range, Polarity,
Radiation pattern,
Propagation,
Advantages,
Disadvantages
Use: tactical HF/VHF networking
Range: HF 0-40KM, VHF 0-30KM
Polarity: vertical
Radiation pattern: omni-directional
Propagation: surface wave
Advantages: quickly erected, self-supporting
Disadvantages: inefficient
λ/4 sloping wire - surface
Use, Range, Polarity,
Radiation pattern,
Propagation,
Advantages,
Disadvantages
Use: tactical HF networking
Range: 0-100KM
Polarity: vertical
Radiation pattern: omni-directional with a slight gain to the coupler
Propagation: surface wave
Advantages: quickly erected, self-supporting
Disadvantages: narrow band
12m co-site - surface
Use, Range, Polarity,
Radiation pattern,
Propagation,
Advantages,
Disadvantages
Use: tactical HF networking
Range: 0-100km
Polarity: vertical
Radiation pattern: omni-directional
Propagation: surface wave
Advantages: quick, wide band
Disadvantages: inefficient, fragile
EGSA (elevated ground spike antenna) - space
Use, Range, Polarity,
Radiation pattern,
Propagation,
Advantages,
Disadvantages
Use: tactical VHF networking
Range: 0-30km
Polarity: vertical
Radiation pattern: omni-directional
Propagation: space wave (above 70MHz)
Advantages: quickly erected, can be remoted
Disadvantages: inefficient
VHF elevated monopole - space
Use, Range, Polarity,
Radiation pattern,
Propagation,
Advantages,
Disadvantages
Use: tactical VHF networking
Range: 0-50km
Polarity: vertical
Radiation pattern: omni-directional
Propagation: space wave
Advantages: quickly erected, can be remoted
Disadvantages: inefficient
VHF elevated dipole - space
Use, Range, Polarity,
Radiation pattern,
Propagation,
Advantages,
Disadvantages
Use: tactical VHF networking
Range: 0-60km
Polarity: vertical
Radiation pattern: omni-directional
Propagation: space wave
Advantages: quickly erected, can be remoted
Disadvantages: inefficient
Elevated UHF (HCDR) antenna - space
Use, Range, Polarity,
Radiation pattern,
Propagation,
Advantages,
Disadvantages
Use: tactical UHF networking
Range: 0-30km (0-12km vehicle mounted)
Polarity: vertical
Radiation pattern: omni-directional
Propagation: space wave
Advantages: quickly erected, can be remoted
Disadvantages: inefficient
3/4λ enfed antenna - sky
Use, Range, Polarity,
Radiation pattern,
Propagation,
Advantages,
Disadvantages
Use: HF static, scattered networking
Range: 0-300km
Polarity: horizontal and vertical
Radiation pattern: omni directional
Propagation: sky wave and surface
Advantages: efficient, can be remoted
Disadvantages: narrowband, greater time/space required
λ/2 horizontal dipole - sky
Use, Range, Polarity,
Radiation pattern,
Propagation,
Advantages,
Disadvantages
Use: static HF sky wave working
Range: 0-3000km
Polarity: horizontal
Radiation pattern: omni-directional up to 300km, broadside above
Propagation: sky wave
Advantages: efficient, can be remoted
Disadvantages: narrowband, greater time/space required
λ/2 droopy dipole - sky
Use, Range, Polarity,
Radiation pattern,
Propagation,
Advantages,
Disadvantages
Use: tactical HF sky wave working
Range: 0-1500km
Polarity: horizontal
Radiation pattern: omni-directional up to 300km then broadside
Propagation: sky wave
Advantages: quickly erected, can be remoted
Disadvantages: narrow band, not as efficient
Marlborough broadband (20W and 50W) antenna - sky
Use, Range, Polarity,
Radiation pattern,
Propagation,
Advantages,
Disadvantages
Use: tactical HF sky wave networking
Range: 0-300km (20W) 0-600km (50W)
Polarity: horizontal
Radiation pattern: omni-directional up to 300km, broadside above
Propagation: sky wave
Advantages: quickly erected, can be remoted
Disadvantages: inefficient, not as efficient as other sky wave antennas
Predictable ionospheric variations (x4)
day/night variations
seasonal
geographical
the sunspot cycle
ionisation intensity in order of ascending height
D
E
F1
F2
(F1 AND F2 combine at night)
2 important effects of the D layer on sky wave communications
- during the day, the d layer absorbs power but has the beneficial effect of reducing noise and interference
- at night noise and interference will increase
Unpredictable ionospheric variations (x3)
- sporadic E
- sudden ionospheric disturbances (SID)
- ionospheric storms
Why is coaxial cable preferred
robust
flexible
easily matched to dipoles and end-fed antennas
What is modulation
when the audio freq (AF) is mixed with a Radio freq (RF) signal within a modulator.
(RF signal is also called the carrier wave)
How are the 2 ways that a signal can be outputted as after modulation
Depends how they are mixed or modulated, determines whether the output is amplitude modulation (AM), or freq modulation (FM)
