Transponder Mode A and C

Question 1

The ground radar consists of what?

Answer 1

Primary and SSR

Question 2

What does the primary radar do?

Answer 2

Gives back echo/reply. Gives us BEARING and DISTANCE in relation to time

Question 3

What does the Secondary Surveillance Radar do?

Answer 3

Moves around with the primary radar to interrogate the aircraft. (30miles) (P1,P3)

Question 4

How many MHz on the SSR?

Answer 4

1030MHz

Question 5

Mode A reply consists of what?

Answer 5

Code Reply

Question 6

If the reply contains ALTITUDE, which mode is it?

Answer 6

Mode C

Question 7

In a ground station interrogation, there are 500pps. How are they divided for each mode?

Answer 7

300 mode C
150 mode A
50 mode S

Question 8

Where does Flight Level come from?

Answer 8

Encoding Altimeter

Question 9

What is after the receiver and what does it do?

Answer 9

After the receiver is the mixer/oscillator which mixes the received 1030MHz with and 970MHz, thus resulting in an IF of 60MHz

Question 10

What does the DECODER do?

Answer 10

Wants to know whether if the signal is a mode A or C, then initiates the MODULATOR

Question 11

If we are using the CODE SELECTOR, what mode was decoded?

Answer 11

Mode A

Question 12

If a mode C was decoded, what does the pilot use for input?

Answer 12

Encoding Altimeter

Question 13

Aircraft Transponder transmission is how many MHz?

Answer 13

1090Mhz

Question 14

What does the suppression do?

Answer 14

For when the DME is transmitting and the aircraft doesn’t mistake it for an interrogation

Question 15

What is the pulse width for mode A and C interrogations?

Answer 15

0.8uS

Question 16

The distance from P1 and P3 in mode A is what?

Answer 16

8uS

Question 17

If the pulses are 21uS apart, what mode is the interrogation in?

Answer 17

Mode C

Question 18

With each transmission, we also send a second omnidirectional signal which equals the size of the ________ sidelobe

Answer 18

LARGEST

Question 19

How long after P1 do we send the P2 pulse?

Answer 19

2uS

Question 20

If P2 is large what does that mean and what will happen?

Answer 20

We are in a sidelobe and we will suppress (not reply)

Question 21

If we are in a main beam, how large will P2 be?

Answer 21

Small

Question 22

Is the side lobe suppression transmitted on the same antenna as the interrogation?

Answer 22

No it has its own OMNIDIRECTIONAL antenna

Question 23

Altitude encoding is based on what and what is it set to?

Answer 23

Based on BAROMETRIC PRESSURE, set to 29.92Hg

Question 24

What does the REPLY contain?

Answer 24

2 framing pulses, 12 pulses (octal) in between and the SPI

Question 25

How far are the framing pulses from each other?

Answer 25

20.3uS

Question 26

What is the maximum amount of pulses in a REPLY?

Answer 26

15 pulses

Question 27

What is the pulse width of the pulses on a REPLY?

Answer 27

0.45uS

Question 28

What is the SPI and what does it do?

Answer 28

Special Position Ident, can be activated by pressing the IDENT button. Only when ATC asks you to to SQWUAK IDENT.

Question 29

How long does the SPI stay for?

Answer 29

30s

Question 30

How many possible codes are there?

Answer 30

4096

Question 31

Why does the transponder not have an AGC?

Answer 31

Amplifiers go into saturation, one at a time

Question 32

What is the purpose of the AOC?

Answer 32

Feeds into the IF. CONTROLS THE GAIN OF THE VERY FIRST STAGE OF THE IF.

Question 33

How do you trigger the AOC? What is the result of this?

Answer 33

When too many replies, greater than 1200. Begins to reduce the IF gain = only strongest signals

Question 34

What is the purpose of a NOISE SUPPRESSION CIRCUIT?

Answer 34

Checks to see if pulse is valid or noise. Cuts the first 0.3uS of every pulse.

Question 35

What are the 4 conditions that prevents anything from going into the decoder?

Answer 35

Warm up, standby, Side lobe one-shot, reply

Question 36

What is the purpose of the DITCH DIGGER?

Answer 36

To see whether or not P2 is large. This sets up the ditch digger depth if P2 is greater than P1.

Question 37

What is the purpose of the one shot?

Answer 37

Stretches pulses depending on the transponder. 0.725 into 0.45uS

Question 38

What are the suppressor gates for?

Answer 38

Only allows pulses through if we have an appropriate lows on both sides

Question 39

What is the length of the LOW PASS FILTER to the BAND PASS FILTER?

Answer 39

1 23/32 inches

Question 40

What is the length of the Tx tube to the low pass filter?

Answer 40

11 inches (for duplexer)

Question 41

Where do interrogations come from?

Answer 41

Ground and TCAS

Question 42

What is the first thing you should check when troubleshooting a transponder?

Answer 42

Check all output voltages make sure they have correct values

Question 43

How long does the REPLY GATE GENERATOR last?

Answer 43

35uS

Question 44

What does code 7700 mean?

Answer 44

Emergency

Question 45

If there is a COMMUNICATION FAILURE, what code must be inputted?

Answer 45

7600

Question 46

If the code reads 7500, what does it mean?

Answer 46

Hijacking