Mod 10

1
Mod 10

• Radio Systems

2
Radio Based Systems

• Fiber Optics (as it relates to radio)
• Satellite
• Microwave
• Tropospheric Scatter (Tropo)
• High Frequency (HF)
• Terms

3
Fiber Optics

• Has taken the majority of business away from
  radio systems.
• Radio systems are still useful.
• Emergencies
• Places fiber cannot go
• You get fiber optics in Networking classes and
  the physics class.

4
Satellite

• Uses microwave transmission system
• Uses radio for broadcast
• Good for long distances
• Earth station (uplink/downlink)
• Geosynchronous orbit - above equator 22,300 miles
• bent pipe

5

• Can use fixed or mobile antenna
• Transponder - rx signal at satellite and converts
  it to another frequency (downlink) for reception
  at another earth terminal.
• 17 degree beam used. Creates a footprint.
• Three birds can provide global coverage.
• Equipment - Xmtr/Rcvr/waveguides antenna (fixed
  or tracking)
• What is a waveguide? How is it sealed? Why is it
  sealed? What does it look like?

6
The Frequency Band

• C
• Ku
• Ka
• All in the GHz range
• Range for uplink and downlink frequencies
• The frequency band is part of the RF spectrum (a
  chart)
• Get more info at next PTC and AFCEA

7
Advantages of Satellites

• Distance insensitivity.
• Single-hop transmission.
• Remote areas and maritime use.
• Good error rate for data. 1 x 10-11
• Broadcast technology. (covers the footprint)
• Large bandwidth. Bird has 24 transponders
  (rx/tx) each at 36 MHz of BW. (3.4Gbps)

8
Disadvantages of Satellites

• One-way propagation delay. Bad for voice and
  asynchronous data protocols (ACKs and NAK).
  Delay is .25 to .5 seconds.
• Multihops. Increases delay. Aka double
  satellite hop. Voice almost unusable. The
  protocols for data can be spoofed so the data
  appears to have arrived sooner.

9
Disadvantages continued

• High path loss in transmission to satellite. May
  need more power. Monitor S/N levels.
• Rain absorption affects path loss. Rain absorbs
  signal strength.
• Congestion buildup. If satellites are too close
  together, interference occurs.

10
VSAT

• Very Small Aperture Terminal - mid 1980s
• Dish size - 1 to 2 meters
• Good for data applications (not vox/video)
• Cheaper prices
• Remote sites
• Relate this to your group project (is it possible
  to build a network?)

11
Microwave

• Used to be the main technology for telcos long
  haul communication (Mainland HI)
• Rights-of-way and natural barriers
• 1 radio channel 30 MHz b/w 6,000 vox
• Radio frequency spectrum is limited
• Analog M/W uses amplitude or freq. mod.
• Digital M/W uses PSK or QAM (crypto)
• Can interface with T1 and T3 if digital.

12
Microwave (continued)

• Range of transmission varies
• 20 to 25 miles at one watt or less
• To get more distance
• use a high gain antenna
• increase power (need FCC authorization)

13
To Build a M/W Site

• Line of Sight
• Path Coordination
• Frequency and Licensing
• FCC-trained personnel
• Tower and antenna location
• Power and backup power
• Time requirement

14
Tropospheric Scatter

• aka tropo
• huge antennas
• power transmitter
• sensitive receivers
• signal bounces off the troposphere
• a small amount of the signal returns to earth
• Good for long distances has high capacity
• Dead technology

15
High Frequency

• Not a dead technology (Hilo CC uses HF)
• Low channel capacity
• Can send vox and data
• You need a separate transmitter and receiver
  station/location (no waveguide)
• Used in emergency situations/disasters
• Requires constant frequency changes (QSY)

16
Diversity

• Frequency Diversity 2 freq 1 antenna
• Space Diversity 2 antennas 1 freq
• Polarization Diversity vertical or horizontal
  off the antenna (propagates)

17
Terms

• RF Spectrum
• RSL receive signal level
• bird
• Line of sight
• Transponder - a receiver and transmitter
• Diversity - a means of affecting redundancy
• Footprint

18
continued

• Knife edge effect
• Bent Pipe
• Low Boy
• IRIG B
• GPS
• AGC
• AFC
• s/n

19
Other Telecommunications Terms

• Mission Critical (circuit/system)
• Mission Essential
• Dual Homing
• Diverse Routing
• Alternate Routing

20
Module 10 Quiz

• What is the difference between analog and digital
  M/W?
• What are the benefits of using M/W?
• What are some problems with M/W?
• Why did M/W fall out of favor?
• How far can you transmit a signal over a M/W
  system with 1 watt of power?

21

• Name the frequency bands in satellites?
• What are the advantages and disadvantages of
  satcom?
• Are satellite antennas fixed or can they move
  (i.e., tracking)?
• What is GPS?
• How do you build a M/W station? List the steps.
• What is RSL? Why is it important?
• Questions on PPT and textbook.

22
Finances for Telecommunications

• Benefits (hard and soft)
• Costs
• Cost/Benefit Calculations
• Life Cycles
• Break Even Analysis and ROI
• The decision making process