Mode S Transponder

Question 1

What does the PRIMARY radar give us?

Answer 1

Range and Position/ Bearing and Distance

Question 2

What is the main reason for Mode S?

Answer 2

Collision Avoidance and Synchronous Garble

Question 3

What additional info does Mode S give us?

Answer 3

Aircraft Identity, ATC instructions, Traffic Info Service, Weather info

Question 4

What is the major improvement of Mode S?

Answer 4

Interrogate a single aircraft at a time

Question 5

What is Mode S?

Answer 5

Discrete Selective Interrogation

Question 6

When a mode S transponder is being interrogated with an address that is not its own unique code, what happens?

Answer 6

They ignore the interrogation, reduces channel congestion

Question 7

Does the mode S have an AOC?

Answer 7

No it does not because AOC is involved when an aircraft is replying 1200pps or more.

Question 8

What is the ADS-B?

Answer 8

Automatic Dependent Surveillance Broadcast (gives a lot of information)

Question 9

The mode S includes what?

Answer 9

Call sign/24bit ICAO address in the form of a hex code (broadcast on squitter)

Question 10

During a mode S ATCRBS ALL CALL how long should P4 be and who replies?

Answer 10

1.6uS

Everyone replies, ATCRBS aircraft with mode A or C, mode S with their 24bit address

Question 11

What does the DF11 squitter give ATC?

Answer 11

Gives ATC the address for all the aircrafts in the zone

Question 12

What is the purpose of the ALL CALL?

Answer 12

To get the bearing and distance of an aircraft using the PSR in combination with the SSR to give aircraft ID

Question 13

In a mode S Discrete ALL CALL who replies?

Answer 13

One specific aircraft using the correct address

Question 14

How many bits is a short surveillance interrogation?

Answer 14

56bits

Question 15

How many bits is a comm-A long interrogation?

Answer 15

112bits

Question 16

How many bits is a comm-C long interrogation?

Answer 16

1280bits (16x112bits)

Question 17

The first 5 bits tells us what?

Answer 17

The type of interrogation/format

Question 18

How many bits is the address and parity?

Answer 18

Last 24bits

Question 19

DF17, 18, and 19 are all what?

Answer 19

Squitters

Question 20

Which DF is EXTENDED SQUITTER?

Answer 20

DF17 (10001)

Question 21

If P4 is only 0.8uS, what type of interrogation is it and who replies?

Answer 21

It would be during an ATCRBS ALL CALL, modes A and C will reply, mode S will not

Question 22

What pulses are sent during a mode S interrogation format?

Answer 22

P1, P2, P6 at 1030MHz

Question 23

In mode S which pulse acts as the side lobe suppression?

Answer 23

P5

Question 24

What is the distance between P1 and P5?

Answer 24

4.5uS

Question 25

What is DPSK?

Answer 25

Differential Phase Shift Keying, a specific modulation used for the interrogation

Question 26

How long is P6?

Answer 26

16.25uS or 30.25uS

Question 27

How long is each chip?

Answer 27

0.25uS

Question 28

When you want to change the 0.25uS chips from LO to HI what do you do?

Answer 28

Change the phase of the 1030MHz by 0.25uS

Question 29

The Sync Phase Reversal Pulse is superimposed with what?

Answer 29

P5

Question 30

What pulse is mandatory in order to go through to the decoder?

Answer 30

Sync Phase Reversal Pulse

Question 31

If we are in a side lobe how big is P5?

Answer 31

P5 is as big or covers the sync phase reversal pulse, hence we are in a side lobe therefore we will not be decoding

Question 32

How long is the PREABMLE and what does it contain?

Answer 32

3.5uS and contains P1 and P2

Question 33

How long from P6 to the Sync Phase Reversal Pulse?

Answer 33

1.25uS

Question 34

How long from the Sync Phase Reversal Pulse to the beginning of the data?

Answer 34

0.5uS

Question 35

In a MODE S reply, what are the pulse widths?

Answer 35

0.5uS

Question 36

How long is the REPLY PREAMBLE?

Answer 36

8uS

Question 37

After the reply preamble what are we getting?

Answer 37

56 or 112 PPM pulse pairs

Question 38

How long is each bit?

Answer 38

1uS (early 0, late 1)

Question 39

What is the total reply length for a mode S reply?

Answer 39

Short is 64uS (8uS + 56uS) | Long is 120uS (112+8)

Question 40

When clicking the VFR button, what channel does it auto set the transponder to?

Answer 40

1200