MOD 9 UNIT 1A

• UHF, SHF, and EHF SATCOM keep military connected to cyberspace domain 

• Can be locate on ground, in air, or on ship

INFORMATION

REFLECTOR

• Used for TRANSMITTING and RECEIVING MICROWAVE FREQUENCIES TO AND FROM SPACE

• Comprised of parabolic dish

• Parabolic shape results in higher gain than other antennas 

• Size of reflector is INVERSELY PROPORTIONATE to Frequency being used 

• When transmitting, signal will leave feed horn, strike the dish, focusing into concentrated beam 

• When receiving downlink, signal will reflect off dish into feed horn

FEED HORN (KNOW THE WHOLE PARAGRAPH)

• Offers conveying signals to and from the dish

• Attached to waveguides

• General purpose is to deliver signals between transmitter/receiver and parabolic dish 

• Feed horn can focus outgoing RF into beam where it’ll reflect off parabolic dish

• During receive, signal is reflected off parabolic dish and collected into feed horn so it can be relayed 

• Feed Horn is capable of adjusting different types of polarization 

• Linear Polarization can be adjusted for either horizontal or vertical

• Circular polarization can be adjusted to right hand or left hand

• SPECIFIC TO THEIR BAND

• If switching from X band to Ka, must switch out feed horn to match

SATELLITE MODEM

• Modem stands for modulate - demodulate 

• Job is to convert digital data to usable electromagnetic waves during transmit and vice versa during receive 

• During transmit, DTE sends info to modem to be delivered 

• Information will be in digital format and known as baseband 

• Modem modulates info, turning baseband into analog Intermediate Frequency 

• IF is sent to Up converter for final translation to it’s transmit frequency 

• When receiving, order is reversed 

• Down converted signal is sent to modem, and demodulated to extract info for the DTE 

• Attributes to assist modem are:

  • FORWARD ERROR CORRECTION (FEC) 

    • Assists with sub optimal signal to nose level often received at modem

    • Adds artificial redundancy to data stream

    • Uses redundancy to fix errors caused by noise and interference 

    • Multiple copies of message are sent to the distant end 

    • Receiving end will take multiple copies and recreate more error free messages 

    • Multiple FEC rates to choose from 

  • SCRAMBLING

    • Ability to obfuscate analog data to make it difficult to read without proper key 

    • Protects data steam, not to be confused with encryption 

    • Scrambling only randomizes data 

    • Encryption uses mathematical algorithms to protect info 

  • DATA INTERFACES

    • Important distinction is medium in which its transmitted/received to the DTE

  • ACCESS METHODS

    • In order to efficiently use satellites bandwidth, we employ FDMA, TDMA, CDMA, WCDMA, and DAMA

    • Modems typically designed with only one in mind 

    • More modems can use multiple methods

  • COAXIAL CABLES

    • Need to have medium to pass signal so we use coaxial cable

    • Has grounded outer conducting shield

    • Inner conductor (known as center conductor), less vulnerable to EMI