Satellite Television

1
Satellite Television

• DBS
• TVRO
• CATV
• Uplink/Downlink
• Transponder (TX/RX)
• Repeater
• RF/Microwave

2
Satellite Television

• SIGNAL BEHAVIOURS
• Beam Shaping
• Parabolic Dish
• E field, H field
• Polarization Defined by ____ field.
• 1. Vertical (linear)
• 2. Horizontal (linear)
• 3.) Circular ( LHCP,
  RHCP)

3
Satellite Television

• Orientation at RX for polarizationA probe,
  resonant loop or printed element at LNA or LNB is
  physically or electrically adjusted to correct
  polarization.
• NOISE
• 1.Galactic Ex. 11 year sunspot cycle
• 2. Terrestrial Interference geothermal noise
• 
  electrical equipment

4
Satellite Television

• Noise contd.
• Harmonic noise from other transmitters
• Rain Fade
• Solar/satellite eclipse 2 times a year at each
  equinox

5
Satellite Television

• Why is a comsat TX power output low?
• FREQUENCY and BANDWIDTH
• C band 3.7 to 4.2 GHz
• KU band 11.7 to 12.7 GHz
• C band 24 transponders
• - BW 500 MHz for a channel
• - 12 channels at 36 MHz each 4 MHz
  gb.
• - 12 to 24 with V and H polarization

6
Satellite Television

• ORBITS
• Elliptical
• Geostationary or Geosynchronous ( parking orbit).
  Located in the Clarke Belt.
• -22,300 mi. (33,000km)
• - 17000 mi./hr.
• - balance centrifugal force
  gravitational
• pull (weightless)

7
Satellite Television

• FOOTPRINTS
• Boresight
• Kick thrusters
• 3 axis stabilization (pitch, yaw, and roll)
• 3 comsats at 120 degree separation can provide
  global coverage.
• Spectrum auctions and satellite spacings
• some 4 degrees and others up to 9 degrees.

8
Satellite Television

• DSS (digital)
• Uplink 13.7 to 14.2 GHz
• At satellite a transponder converts to 12.2 to
  12.7 GHz
• Castle Rock Colorado Earth station
• Boresight in Nebraska
• 1 channel has BW of 24 MHz
• 2 X 16 transponders 175 channels of A/V

9
Satellite Television

• DSS contd.
• Polarization adjustment achieved with pin diode
  switching. 18 Vdc for LH or 13 Vdc for RH.
• At RX the LNB develops 950 1450 MHZ signal

10
Satellite Television

• Targeting
• Elliptical orbits Keplerian mathematics
• - short windows
  of com.
• Geostationary orbits DBS systems
• - latitude, longitude of TVRO (RX)
• - azimuth and elevation calculated
• - position of azimuth referenced to
  north.
• - Z axis perpendicular to earths
  geocentre