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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
Examples of resonant antennas (x3)
λ/2 dipole λ/4 monopoles λ/4 and 3/4λ endfeds
26
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
27
Examples of wideband antennas (x2)
VHF dipole VHF monopole
28
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
29
Examples of travelling wave antennas (x3)
sloping v para v inverted v
30
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
31
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
32
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
33
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
34
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
35
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
36
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
37
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
38
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
39
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
40
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
41
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
42
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
43
Predictable ionospheric variations (x4)
day/night variations seasonal geographical the sunspot cycle
44
ionisation intensity in order of ascending height
D E F1 F2 (F1 AND F2 combine at night)
45
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
46
Unpredictable ionospheric variations (x3)
- sporadic E - sudden ionospheric disturbances (SID) - ionospheric storms
47
Why is coaxial cable preferred
robust flexible easily matched to dipoles and end-fed antennas
48
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)
49
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)

Waves (1 decks)

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