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Waves > surface/space/sky > Flashcards

surface/space/sky Flashcards

1
Q

Definition of surface wave

A

Surface wave propogation flows along the earths surface supported by the currents that have been induced into the ground by the transmitting antenna

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2
Q

Surface wave antennas (VHF)

A

VHF ground spike
VHF elevated ground spike (using freq below 70MHZ)
VHF vehicle mounted

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3
Q

Surface wave antennas (HF)

A

HF vehicle mounted
HF sloping wire
HF 12m co-site

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4
Q

Surface and sky wave antenna calculations - bowman braid

A

freq printed on the braid

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5
Q

Surface and sky wave antenna calculations - clansman braid

A

68.5 divided by the freq in use (round down)

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6
Q

Surface and sky wave antenna calculations - copper wire

A

71.3 divided by the freq in use (round down)

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7
Q

Best type of ground for surface waves (best to worst)

A

sea
moist arable land
poor arable land
desert
ice
jungle

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8
Q

Definition of space wave

A

radio waves follow a direct line-of-sight (LOS) path between transmit and receive antennas

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9
Q

Two components of space waves

A

direct waves
ground reflected waves

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10
Q

Minimum effective height (MEH) meaning

A

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

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11
Q

MEH examples

A

30MHZ - 10M
50MHZ - 6M
75MHZ - 4M

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12
Q

Space wave antennas (VHF)

A

VHF elevated ground spike (when using freq above 70MHZ)
VHF monopole
VHF dipole

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13
Q

Space wave antennas (UHF)

A

UHF vehicle mounted
UHF elevated

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14
Q

Sky wave definition

A

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

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15
Q

definitions-
1. skip distance
2. skip zone
3. refraction

A
  1. from transmitter to the point where the signal returns to earth
  2. area of no signal reception
  3. process by which an ionospheric layer bends a radio wave back towards earth
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16
Q

Short range of sky wave

A

0-300km (antenna 1/8λ off he ground)

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17
Q

Medium range of sky wave

A

300-1500km (antenna 1/4λ off the ground)

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18
Q

Long range of sky wave

A

1500-3000km (antenna 1/2λ off the ground)

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19
Q

Sky wave antennas (x4)

A

3/4 λ wave endfed
1/2 λ droopy dipole
1/2 λ wave horizontal dipole
HF Marlborough broadband (150w antenna)

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20
Q

Antenna calculation formula

A

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

21
Q

Electromagnetic spectrum (HF, VHF, UHF) frequency

A

HF 3MHZ- 30MHz
VHF 30MHZ - 300MHz
UHF 300MHZ - 3GHz

22
Q

3 main types of antennas

A
  1. resonant antennas
  2. wideband antennas
  3. travelling wave antennas
23
Q

When does a resonant antenna perform at maximum effectiveness?

A
  • when its length corresponds to the wavelength of the freq in use
  • change the length of the antenna whenever you change freq
24
Q

Freq efficiency and bandwidth of resonant antenna

A
  • only efficient at one freq
  • small bandwidth
25
Q

Examples of resonant antennas (x3)

A

λ/2 dipole
λ/4 monopoles
λ/4 and 3/4λ endfeds

26
Q

Freq efficiency and bandwidth of Wideband antennas

A
  • designed to perform effectively over a range of freq
  • greater bandwidth
  • do not have to change length of antenna when you change freq
27
Q

Examples of wideband antennas (x2)

A

VHF dipole
VHF monopole

28
Q

Efficiency of travelling wave antennas

A
  • 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
29
Q

Examples of travelling wave antennas (x3)

A

sloping v
para v
inverted v

30
Q

GSA (ground spike antenna) - surface properties
Use, Range, Polarity,
Radiation pattern,
Propagation,
Advantages,
Disadvantages

A

Use: tactical VHF networking
Range: 0-20km
Polarity: vertical
Radiation pattern: omni-directional
Propagation: surface wave
Advantages: quickly erected, self-supporting
Disadvantages: inefficient

31
Q

EGSA (elevated ground spike antenna) - surface
Use, Range, Polarity,
Radiation pattern,
Propagation,
Advantages,
Disadvantages

A

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

32
Q

HF/VHF vehicle whip - surface
Use, Range, Polarity,
Radiation pattern,
Propagation,
Advantages,
Disadvantages

A

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

33
Q

λ/4 sloping wire - surface
Use, Range, Polarity,
Radiation pattern,
Propagation,
Advantages,
Disadvantages

A

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

34
Q

12m co-site - surface
Use, Range, Polarity,
Radiation pattern,
Propagation,
Advantages,
Disadvantages

A

Use: tactical HF networking
Range: 0-100km
Polarity: vertical
Radiation pattern: omni-directional
Propagation: surface wave
Advantages: quick, wide band
Disadvantages: inefficient, fragile

35
Q

EGSA (elevated ground spike antenna) - space
Use, Range, Polarity,
Radiation pattern,
Propagation,
Advantages,
Disadvantages

A

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

36
Q

VHF elevated monopole - space
Use, Range, Polarity,
Radiation pattern,
Propagation,
Advantages,
Disadvantages

A

Use: tactical VHF networking
Range: 0-50km
Polarity: vertical
Radiation pattern: omni-directional
Propagation: space wave
Advantages: quickly erected, can be remoted
Disadvantages: inefficient

37
Q

VHF elevated dipole - space
Use, Range, Polarity,
Radiation pattern,
Propagation,
Advantages,
Disadvantages

A

Use: tactical VHF networking
Range: 0-60km
Polarity: vertical
Radiation pattern: omni-directional
Propagation: space wave
Advantages: quickly erected, can be remoted
Disadvantages: inefficient

38
Q

Elevated UHF (HCDR) antenna - space
Use, Range, Polarity,
Radiation pattern,
Propagation,
Advantages,
Disadvantages

A

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

39
Q

3/4λ enfed antenna - sky
Use, Range, Polarity,
Radiation pattern,
Propagation,
Advantages,
Disadvantages

A

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

40
Q

λ/2 horizontal dipole - sky
Use, Range, Polarity,
Radiation pattern,
Propagation,
Advantages,
Disadvantages

A

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

41
Q

λ/2 droopy dipole - sky
Use, Range, Polarity,
Radiation pattern,
Propagation,
Advantages,
Disadvantages

A

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

42
Q

Marlborough broadband (20W and 50W) antenna - sky
Use, Range, Polarity,
Radiation pattern,
Propagation,
Advantages,
Disadvantages

A

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

43
Q

Predictable ionospheric variations (x4)

A

day/night variations
seasonal
geographical
the sunspot cycle

44
Q

ionisation intensity in order of ascending height

A

D
E
F1
F2
(F1 AND F2 combine at night)

45
Q

2 important effects of the D layer on sky wave communications

A
  • 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
46
Q

Unpredictable ionospheric variations (x3)

A
  • sporadic E
  • sudden ionospheric disturbances (SID)
  • ionospheric storms
47
Q

Why is coaxial cable preferred

A

robust
flexible
easily matched to dipoles and end-fed antennas

48
Q

What is modulation

A

when the audio freq (AF) is mixed with a Radio freq (RF) signal within a modulator.
(RF signal is also called the carrier wave)

49
Q

How are the 2 ways that a signal can be outputted as after modulation

A

Depends how they are mixed or modulated, determines whether the output is amplitude modulation (AM), or freq modulation (FM)

Waves (1 decks)

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