Mode S Transponder Flashcards
What does the PRIMARY radar give us?
Range and Position/ Bearing and Distance
What is the main reason for Mode S?
Collision Avoidance and Synchronous Garble
What additional info does Mode S give us?
Aircraft Identity, ATC instructions, Traffic Info Service, Weather info
What is the major improvement of Mode S?
Interrogate a single aircraft at a time
What is Mode S?
Discrete Selective Interrogation
When a mode S transponder is being interrogated with an address that is not its own unique code, what happens?
They ignore the interrogation, reduces channel congestion
Does the mode S have an AOC?
No it does not because AOC is involved when an aircraft is replying 1200pps or more.
What is the ADS-B?
Automatic Dependent Surveillance Broadcast (gives a lot of information)
The mode S includes what?
Call sign/24bit ICAO address in the form of a hex code (broadcast on squitter)
During a mode S ATCRBS ALL CALL how long should P4 be and who replies?
1.6uS
Everyone replies, ATCRBS aircraft with mode A or C, mode S with their 24bit address
What does the DF11 squitter give ATC?
Gives ATC the address for all the aircrafts in the zone
What is the purpose of the ALL CALL?
To get the bearing and distance of an aircraft using the PSR in combination with the SSR to give aircraft ID
In a mode S Discrete ALL CALL who replies?
One specific aircraft using the correct address
How many bits is a short surveillance interrogation?
56bits
How many bits is a comm-A long interrogation?
112bits
How many bits is a comm-C long interrogation?
1280bits (16x112bits)
The first 5 bits tells us what?
The type of interrogation/format
How many bits is the address and parity?
Last 24bits
DF17, 18, and 19 are all what?
Squitters
Which DF is EXTENDED SQUITTER?
DF17 (10001)
If P4 is only 0.8uS, what type of interrogation is it and who replies?
It would be during an ATCRBS ALL CALL, modes A and C will reply, mode S will not
What pulses are sent during a mode S interrogation format?
P1, P2, P6 at 1030MHz
In mode S which pulse acts as the side lobe suppression?
P5
What is the distance between P1 and P5?
4.5uS
What is DPSK?
Differential Phase Shift Keying, a specific modulation used for the interrogation
How long is P6?
16.25uS or 30.25uS
How long is each chip?
0.25uS
When you want to change the 0.25uS chips from LO to HI what do you do?
Change the phase of the 1030MHz by 0.25uS
The Sync Phase Reversal Pulse is superimposed with what?
P5
What pulse is mandatory in order to go through to the decoder?
Sync Phase Reversal Pulse
If we are in a side lobe how big is P5?
P5 is as big or covers the sync phase reversal pulse, hence we are in a side lobe therefore we will not be decoding
How long is the PREABMLE and what does it contain?
3.5uS and contains P1 and P2
How long from P6 to the Sync Phase Reversal Pulse?
1.25uS
How long from the Sync Phase Reversal Pulse to the beginning of the data?
0.5uS
In a MODE S reply, what are the pulse widths?
0.5uS
How long is the REPLY PREAMBLE?
8uS
After the reply preamble what are we getting?
56 or 112 PPM pulse pairs
How long is each bit?
1uS (early 0, late 1)
What is the total reply length for a mode S reply?
Short is 64uS (8uS + 56uS)
Long is 120uS (112+8)
When clicking the VFR button, what channel does it auto set the transponder to?
1200
