System 3 DATA LINK

Question 1

How many epochs are in day?

Answer 1

112.5 epochs

Question 2

How long is an epoch?

Answer 2

12.8 minutes

Question 3

How many frames in an epoch?

Answer 3

64 frames in an epoch

Question 4

How long is a frame?

Answer 4

12 sec or 1536 time slots

Question 5

How many time slots are there per second?

Answer 5

128 time slots

Question 6

How long is a time slot (msec)?

Answer 6

7.8125 msec

Question 7

How many simultaneous nets can link 16 support

Answer 7

127 simultaneous nets

Question 8

What frequency range does link 16 operate in

Answer 8

960 MHz to 1215 MHz

Question 9

List 3 items for Link 16 frequency agility (frequency hopping)

Answer 9

• Hops between 51 freqs spaced 3 MHz apart
• Hop rate in excess of 70,000 hops per sec
• Hop pattern based on net number
• Avoids IFF freqs 1030 & 1090 MHz

Question 10

What Security and Interference Protection Features does link 16 have?

Answer 10

Security:

• Error Detection And Correction (EDAC): Helps protect info from being corrupted by jamming or interference
• Pseudorandom Noise: The transmission signal is masked with noise within the Link 16 signal; transmitted data appears as incoherent noise

Interference Protection:
Link 16 terminals monitor their own transmissions in several areas, and if authorized levels are exceeded the Interference Protection Feature (IPF) automatically disables transmission

Question 11

What are the 4 types of link 16 messages?

Answer 11

Fixed format: J-series msgs.
Variable message format (VMF): user-defined msgs.
Round-trip timing (RTT): Used for net sync.
Free text: digital voice or video

Question 12

How many possible fixed-format J-series messages are there? What are the 2 general types of J-series messages?

Answer 12

256 possible fixed-format messages: 32 categories (e.g. J12), 8 subcategories (e.g. J12.6)
2 General Types:
1. Addressed messages: sent to specific JU.
2 .Broadcast messages: sent to everyone.

Question 13

What is the J-Series message structure?

Answer 13

Jitter
Sync
Time refinement
Header
Data
Propagation

Question 14

What are stacked nets in link 16?

Answer 14

Separate units performing the same function within one NPG. Same time slot, NPG, and function; Different hopping patterns.

Question 15

What are multinetting in link 16?

Answer 15

Allows different NPGs to utilize a single time slot for different functions. Different crypto variables or net numbers, hopping patterns, NPG, and functions

Question 16

What is dedicated access mode in link 16?

Answer 16

Each JU is positively assigned a unique allocation of time slots. The normal mode for most NPGs. No transmission conflicts for optimum data fidelity.

Question 17

What is contention access mode in link 16?

Answer 17

Groups of JU’s share a pool of time slots.

Question 18

Explain time quality in link 16

Answer 18

The highest time quality is 15 and reserved for the NTR;

Units joining must be within 6 sec of NTR and once sync’d with NTR they remain sync’d

Question 19

What is the Standard Double Pulse (STD-DP) data packing

Answer 19

3 words x 2 transmission of 258 Pulses

Question 20

On the EPLRS radio what are the 4 lights

Answer 20

ALM = on when there is no crypto
OUT OF NET= pulse every 4 sec in a net; pulse every 2 sec searching for a net
PWR = power
KAB = on when 9V battery is low or failed

Question 21

What are the four power levels of the EPLRS radio, and what in the normal level

Answer 21

• low (.4 W), med low (3 W), med high (20 W), and high (100 W).
• Med high (20 watts) is normal operating power

Question 22

What is dedicated access in SADL

Answer 22

exclusive transmit slot assignment to each terminal.

Question 23

What is contention access in SADL

Answer 23

All members of a group are assigned a common pool of time slots

Question 24

What are the Host Interfaces in SADL

Answer 24

SCU
Generic
Gateway

Question 25

Define Guard Channel in SADL

Answer 25

The physical RF Channel required to enter the network

Question 26

Define Secondary Channel in SADL

Answer 26

Defines the allowable frequency set the radio will use for hopping

Question 27

Define Net Shape (4:4) for SADL

Answer 27

Digit 1 is number of flights in the Air key (1 - 4)

Digit 2 is number of aircraft per flight (1 - 4)

Question 28

Define Net Position (4:4) for SADL

Answer 28

Digit 1 is flight # that ownship is in (1 - 4)

Digit 2 is ownship’s position in the flight (1 - 4)

Question 29

How is an extended Data Net created and how many aircraft can it support

Answer 29

Possible by using Air key number 90 - 94, and can support up to 80 aircraft.

Question 30

Explain Link 16 TDMA timing

Answer 30

24 hour day divided into 112.5 epochs
Epoch = 12.8 minutes = 64 frames
Frame = 12 seconds
128 time slots per second
1536 time slots per frame

Question 31

How many J series message possibilities are there?

Answer 31

256 possible fixed=format J-series messages

Question 32

Explain Pack 4 Single Pulse data packing

Answer 32

12 words x 1 transmission, 444 pulses. No jitter scheduled in time slot