Unit 4. Tactical Airfield Systems

Question 1

Transportable Tactical Air Navigation System, AN/TRN–41

417. Capabilities and limitations
418. What is the AN/TRN–41 designed to do?

Answer 1

It’s designed to provide a combat control team with a NAVAIDS to assist aircraft in locating landing zones, drop zones, or extraction zones in deployed locations.

Question 2

2. What are the seven major units of the AN/TRN–41?

Answer 2

(1) A radio receiver-transmitter. (2) Antenna.
(3) Support assembly.
(4) DC filter.
(5) Azimuth monitor.
(6) Radio frequency amplifier.
(7) Monitor support assembly.

Question 3

3. How does the aircraft determine azimuth information?

Answer 3

By comparing the phase angle between the detected modulation envelope and the reference burst signals transmitted by the TRN–41.

Question 4

4. What is the function of the radio receiver-transmitter?

Answer 4

To detect and decode weak interrogations at one frequency and generate high-power replies at another frequency.

Question 5

5. What functions does the antenna perform?

Answer 5

Receives interrogation signals from airborne TACAN transponders and delivers them to the receiver portion of the receiver-transmitter. It also modulates and radiates the RF energy delivered by the transmitter portion of the RT.

Question 6

6. What component does the RMA interfaces with to obtain power and provide information for RF transmission?

Answer 6

The AN/PRC–77 Radio Set.

Question 7

418. Block diagram theory of operation

1. What is the primary power source of the AN/TRN–41?

Answer 7

A battery or a generator.

Question 8

2. What are the three modes of operation of the AN/TRN–41?

Answer 8

(1) Standby or demand only mode.
(2) TACAN and DME only mode.
(3) Normal operation.

Question 9

3. How does the RT maintain constant average transmit power?

Answer 9

The RT automatically inserts random squitter pulses between the reply transmissions in sufficient quantity to hold the average output power constant.

Question 10

4. What is the overall reply delay for X and Y channel transmissions?

Answer 10

50 +- 1 us for X,56+- 1 us for Y.

Question 11

5. How does the anti-CW jamming circuit compensate for CW jamming?

Answer 11

It reduces the gain of the IF amplifier under conditions of CW jamming.

Question 12

6. What benefits does the receiver section’s logarithmic amplifier offer?

Answer 12

Much wider dynamic range without losing essential timing information.

Question 13

7. What does the echo suppression circuit do after detecting a relatively high-level interrogation?

Answer 13

Increases the deadtime, thus eliminating the relatively low level echoes to these interrogations.

Question 14

8. What happens to the RF signal in the transmitter’s 100-watt amplifier?

Answer 14

The RF signal gets modulated with a Gaussian shaped pulse and amplified to a level of approximately 150 watts.

Question 15

9. The Morse code identification burst may consist of up to how many characters every 37.5 seconds?

Answer 15

Four.

Question 16

10. How long must a monitored parameter exceed its alarm limit for an RT alarm condition to exist?

Answer 16

Five seconds.

Question 17

11. What function is performed by the antenna reference trigger sensor assembly, 2A2?

Answer 17

It generates the 15-, 135-, and 1350-Hz sensor triggers which produce the reference trigger pulses sent to the RT.

Question 18

4–2. Mobile Microwave Landing System, AN/TRN–45

419. Capabilities and limitations
420. What three types of guidance are supplied by the AN/TRN–45?

Answer 18

(1) AZ.
(2) EL.
(3) Range (distance) guidance.

Question 19

2. What is meant by a split site configuration when installing an AN/TRN–45?

Answer 19

The elevation station and azimuth station are installed on opposite ends of the runway.

Question 20

3. For optimum reception, at what distance in front of the equipment antennas do you place the monitor antennas?

Answer 20

90 to 110 feet from the equipment antennas.

Question 21

4. On how many channels can the AZ/EL equipment operate?

Answer 21

200.

Question 22

420. Block diagram theory of operation

1. Briefly describe how the DME/P equipment supplies distance information to an aircraft.

Answer 22

The DME/P equipment replies to double coded interrogations from inbound aircraft, delays them, processes replies, and sends them back into space to the aircraft. The aircraft equipment calculates distance from the overall time elapsed from interrogation to reply.

Question 23

2. If an aircraft MLS receiver receives a TO and FRO sweep from the AZ station with no difference in sweep times, where in the coverage area is the aircraft located?

Answer 23

Runway centerline.

Question 24

3. When setting up an AN/TRN–45 EL station, how can you avoid interference and shadowing?

Answer 24

The scan area can be reduced during installation to avoid scanning lower elevations.

Question 25

4. What is the purpose of a “preamble period” prior to a beam sweep in the EL or AZ station?

Answer 25

It allows the aircraft receiver to acquire the elevation (EL) or azimuth (AZ) stations.

Question 26

5. What parameter is checked when MEAN GLIDEPATH is monitored in the EL station?

Answer 26

The station is being monitored to ensure the proper glide angle is being transmitted.

Question 27

6. Name the four operating modes for the AN/TRN–45.

Answer 27

(1) Off Air (standby). (2) On. (3) Maintenance. (4) Service Demand.

Question 28

7. How long will the EL or AZ station batteries last in the Service Demand mode?

Answer 28

8 hours.

Question 29

8. How often is a BIT automatically done?

Answer 29

Every 30 minutes.

Question 30

4–3. Tactical Control Tower, AN/MSN–7 421. Capabilities and limitations 1. What six functional groups make up the AN/MSN–7?

Answer 30

(1) Power Distribution. (2) Meteorological. (3) Communications. (4) ECU. (5) LON/MCP . (6) Shelter.

Question 31

2. What four pieces of information does the meteorological functional group of the AN/MSN–7 provide?

Answer 31

(1) Wind speed and direction. (2) Temperature. (3) Altitude data. (4) Current time.

Question 32

3. What functional group monitors and displays the current status of the other functional groups in the AN/MSN–7?

Answer 32

LON/MCP .

Question 33

4. How fast can the AN/MSN–7 be driven on improved roads?

Answer 33

50 MPH.

Question 34

422. Block diagram theory of operation | 1. When can utility power be used to power the facility?

Answer 34

When within acceptable limits.

Question 35

2. What electrical/mechanical relay automatically switches either generator power or utility power from the auto-transformer?

Answer 35

AC power contactor A15K1.

Question 36

3. How many wind sensors are found in the Meteorological Functional Group?

Answer 36

2

Question 37

4. Describe the LMR antennas in the AN/MSN–7.

Answer 37

The LMR Antennas consist of a total of two vertical omni-directional unity gain elements that provide G/G transceiver communications from a single collinear antenna. The antenna consists of two VHF elements (136 to 174 MHz), capable of handling up to 50W of RF power. Antennas are connected directly to the LMRs via the antenna entry panel.

Question 38

5. What is the purpose of the CCU?

Answer 38

The CCU provides overall control of shelter communications, interfaces the audio and control of the two LMRs, seven G/A transceivers, 12 landlines, six external radios, VRS A8A2, and three CAUs from one central location.

Question 39

6. How many channels are used in the VRS System in the AN/MSN–7?

Answer 39

The VRS has 32-channels but only 30 channels are used.

Question 40

7. What is used to program frequencies in the LMR?

Answer 40

The MCP.

Question 41

8. What switch allows the operator to manually select either generator or utility power?

Answer 41

The power override switch.

Question 42

9. What are the two hazard detectors on the AN/MSN–7?

Answer 42

The CO and smoke detectors.