# Shared Flashcard Set

## Details

Review Questions
Review questions in the back
81
Aviation
Not Applicable
03/27/2012

Term
 Define wavelength
Definition
 the measurement of one crest to another
Term
 Define Frequency
Definition
 how many waves occur in a given amount of time
Term
 Is there a relationship between wavelength and frequency
Definition
 W*F=C (velocity equation) W and F are inversely related
Term
 What are the frequency band designators
Definition
Term
 3. What is the sum of two sine waves that are 180 degrees out of phase?
Definition
 a. 0. They eliminate each other through destructive interference
Term
 4. What are the advantages of the various signal polarities with regard to radar?
Definition
 a. Horizontal-used to detect low-level aircraftb. Vertical-clutter rejection providedc. Circular-penetrates all but the heaviest precipitation
Term
 5. What is the Doppler shift for an approaching object?
Definition
 a. Pitch of an audio tone is higher when an object is approaching and lower when it’s moving away from the radar
Term
 6. To escape cosmic noise, should we increase or decrease our operating frequency?
Definition
 a. Cosmic noise decreases as we increase operating frequencyb. They dramatically decrease as you approach 100 MHz
Term
 7. To escape atmospheric attenuation, should we increase or decrease our operating frequency?
Definition
 a. Decrease our operating frequencyb. Negligible below 10GHzc. 22.24 GHz is the “water line”
Term
 8. To maximize refraction, should we increase or decrease our frequency?
Definition
 a. Decrease the frequency (as frequency increases refraction decreases)
Term
 9. Define sub-refraction
Definition
 i. Occurs where warm air moves over a cool, dry landmassii. Conditions decrease wave propagation speed as altitude increases1. Causes beams to bend upward
Term
 9. Define Super-refraction
Definition
 i. Occurs where warm ocean currents flow under cold air1. Conditions extend the range of the beams2. Not always welcomea. Causes unwanted interference from other transmittersb. Increases the amount of ground clutter the receiver must process and display
Term
 9. Define ducting
Definition
 i. Super-refraction to the extremeii. Occurs when curvature of refraction > curvature of earthiii. Wave is “trapped” in a narrow duct and extends longer than even super-refractioniv. Can cause “second-time around” echoes
Term
 10. What are the upper and lower limits of each communication frequency band?
Definition
 a. HF-2 (2-30 MHZ)b. VHF AM (116-152 MHz)c. VHF FM (30-80 MHz)d. UHF (225-400 MHz)
Term
 11. Which communication frequency bands are shared with civil users?
Definition
 a. HF (CB and Ham)b. VHF
Term
 12. Which communications frequency band can operate over oceanic distances without the need of a relay?
Definition
 a. HF
Term
 13. VHF and UHF channels are spaced by how many megacycles?
Definition
 a. Every .025 MHZ
Term
 14. Arthur C. Clark invented satellite communications to overcome which limitation of VHF/UHF radio?
Definition
 a. It’s line-of-sight limitation
Term
 15. Military SATCOM is based on which communications frequency?
Definition
 a. UHF
Term
 16. Define:a. Transponder:
Definition
Term
Definition
 i. Signal sent to the satellite
Term
Definition
 i. Signal sent from the satellite
Term
 17. How did the staff of Bletchly Park “break” the Luftwaffe’s Enigma Code?
Definition
 a. Went through messages and worked backwards with the same limerick
Term
 18. Explain EA and EP during the Vietnam Conflict
Definition
 a. Chattermark became a problemb. VC understood US’ comm plan very wellc. Able to jamm with precision
Term
 19. What changed about communications EA and EP after Vietnam?
Definition
 a. Have quick was developed
Term
 20. Using the challenge and reply authenticator in the text, authenticate A-B-C. Now try B-C-D.
Definition
 a. Kilob. Papa
Term
 21. Using the transmission authenticator from the text, authenticate a message for transmission at 2202Z. Now try 1359Z.
Definition
 a. HA b. GW
Term
 22. Define AI
Definition
 i. Airborne Interceptii. Sacrifice long range for light weight and close-in precision
Term
 Define AEW
Definition
 i. Overcame the problem of detecting low flying targets by elevating the surveillance radar to well above the horizonii. Could detect wave skimming kamikaze at 40+ miles
Term
 Define GCI
Definition
 i. Ground controlled interceptii. Combines long range of EW with precision of AIiii. Max detection range close to 200 miles
Term
 23. Which devices can be used to generate microwaves?
Definition
 a. Klystronsb. Twystronsc. Magnetrond. Microwave transistors
Term
 Characteristics of a. Klystrons
Definition
 i. Very stableii. Long warm-up periodiii. Produces x-raysiv. Very heavy
Term
 Characteristics of b. Twystrons
Definition
 i. Very similar to Klystron ii. Offers frequency agility
Term
 Characteristics of c. Magnetron
Definition
 i. Smallii. Not precise
Term
 Characteristics of d. Microwave transistors
Definition
 i. Aren’t vacuum tubesii. Don’t need to warm upiii. Don’t produce harmful x-raysiv. Not very powerfulv. Need many to produce effective beam
Term
 24. What is a super-heterodyne receiver used for?
Definition
 a. Amplifies very weak returns without creating noisei. Combines weak return with strong-stable, known frequency
Term
 25. What determines a radar’s range resolution?
Definition
 a. Determined by the duration of the transmitted pulse (pulse width)
Term
Definition
 a. Low PRFi. Advantages1. Very limited second-bang targets2. Simpleii. Disadvantages1. No Doppler capability
Term
Definition
 i. Advantages1. Higher average power2. Significant increase in range3. True look-down Doppler capability4. Doppler blind speeds are further outii. Disadvantages1. More complex2. Creates second-bang targets
Term
Definition
 i. Advantages1. Great effective range2. Doppler blind speeds even more spread out3. Unambiguous Doppler processingii. Disadvantages1. Very complex2. Very severe second-bang target (can’t sort wanted from unwanted targets)
Term
 27. Define: a. Beamwidth:
Definition
 The angular measure of the main lobe
Term
 b. Main lobe:
Definition
 i. The lobe in which we want to receive information
Term
 c. Back lobe:
Definition
 i. Same amplitude as the main lobe ii. Unwanted area of potential receptioniii. Wasted energy
Term
 d. Side lobe:
Definition
 i. Unwanted lobes of potential receptionii. Smaller than main and back lobes
Term
 28. Write a brief description Parabolic reflector
Definition
 i. Round dishii. Creates and receives pencil beamiii. Useful for AI and target tracking
Term
 Write a brief description b. Squat antennas
Definition
 i. Thick antennas (wider than they are tall)1. Fan-shaped beama. Useful for EW and AEWb. Used to find azimuth of targetii. Thin long antennas (taller than they are wide)1. Fan-shaped beama. Great for searching a target’s altitude
Term
 Write a brief description iii. Square antennas
Definition
 1. Can estimate target’s height2. Useful for GCI
Term
 29. Which type of radar might employ a Raster scan?
Definition
 a. Round antennas
Term
 30. Which type of antenna might employ a fan beam?
Definition
 a. Squat antenna
Term
 31. Why are the side lobes and back lobes unwanted? What are some of the fixes for these problems?
Definition
 a. Unwanted because they introduce ambiguity to out measurement of the target’s azimuthb. Reduce amplification of echoes that are in close proximity to the radarc. Side lobe cancellationi. Using two antennas simultaneously1. Directional and dipoleii. CPU only displays those signals that are closer to the main lobe
Term
Definition
 a. Advantagesi. Significant reduction in back and side lobesii. b. Disadvantagesi. Does produce side and back lobesii. Very precise constructioniii. Very hard to manufactureiv. Expensivev. Very big1. Takes very big hits when ac is maneuvering
Term
Definition
 a. Advantagesi. Rigidly mountedii. No movement of antennaiii. Can change beam shapeiv. Multiple directional receptionv. Only limited by CPU processing powerb. Disadvantagesi. None listed
Term
 34. Why do most GCI radars operate in the L-Band?
Definition
 a. The L-Band is the “sweet spot” in which Solar noise is decreased and atmospheric attenuation is minimal (1-2 GHz)
Term
 35. Explain the importance of pulse compression
Definition
 a. Pulse compression will give the same range resolution as before however, it will be four times as high; four times as likely to detect an object at a given range
Term
 36. What two things does a staggered PRF achieve?
Definition
 a. It helps eliminate second bang targets by displaying only the ones that line up in both beams b. Protects against range ambiguity
Term
 37. What is chaff and how can it be defeated?
Definition
 a. Large number of dipole elements designed to match half the wavelength of the victim radar’s RFb. Can be defeated with true Doppler processing using Medium or High PRF
Term
 38. What are decoys and how are they used?
Definition
 a. Expendable aircraft-like vehicle used to provide deception and create saturation in the networkb. Use corner reflectors and small radios to fool the enemy and take fire away from the strike aircraft
Term
 39. Define spot jamming and list the EP
Definition
 i. Fool some of the people all of the timeii. EPs are:1. frequency agility2. Frequency diversity
Term
 Define sweep jamming and list the EP
Definition
 i. Fool all of the people some of the timeii. Less severe than spotiii. EPs are:1. Patience and persistence
Term
 Define barrage jamming and list the EP
Definition
 i. Fool all of the people all of the timeii. Power is spread thin due to all the freq’s being jammediii. EP is:1. Pulse Compression
Term
 40. Explain range jamming and list the EP
Definition
 i. Records one of the victim’s radar pulses and continually repeats it after a time delay creating strobes on displayii. Staggered PRF defeats this
Term
 Explain azimuth jamming and list the EP
Definition
 i. Exploits radar’s side and back lobesii. Repeats radar pulse at a time when the victim’s side lobes are trained on the jammeriii. Fix- ultra low side lobes
Term
 41. Which radio frequencies are used by the Mark XII and Mode S IFF/SIF systems?
Definition
 a. AC is Interrogated at 1030 MHzb. AC replies at 1090 MHz
Term
 42. Which of the six different modes of the Mk XII IFF/SIF system are shared with civil aviation?
Definition
 a. Mode 3A,B,Cb. Mode S
Term
 43. Which IFF/SIF modes are selectable in flight?
Definition
 a. Mode 1b. Mode 3
Term
 44. What are the permissible digit values for the various IFF/SIF modes?
Definition
 a. Mode 1-two digits; octal and 0-3b. Mode 2-four digits; Octalc. Mode 3A- four digits; octald. Mode 3C-three digits, Not octale. Mode 4 -Encryptedf. Mode S-twenty four digits, octal; plus alt and spdg. Mode 5-Encrypted version of Mode S
Term
 45. Do the naval ships carry IFF/SIF transponders?
Definition
 a. Yes
Term
 46. How does Mode S differ from MK XII?
Definition
 a. Mode S eliminates FRUIT by only responding to one radar at a time instead of all of them like MK XII
Term
 47. How do SAR sensors achieve their precise range and azimuth resolution?
Definition
 a. By using shorter pulse widths and extreme pulse compression
Term
 48. What do the shadows on a SAR image reveal?
Definition
 a. The true perspective of the radar
Term
 49. How do moving objects appear on the SAR image?
Definition
 a. They will be a blur or completely Doppler shifted right out of the image
Term
Definition
Term
 51. How does structural attenuation work? What are the limitations of this approach?
Definition
 a. By carefully arranging the AC’s internal structures, the radio frequencies can be attenuated as much as RAMb. Effectiveness decreases as wavelength increases
Term
 52. What is impedance matching? How is it achieved?
Definition
 a. The use of materials in aircraft construction that don’t reflect radio waves very wellb. Achieved by matching the aircraft structure to that of the atmosphere using materials such as fiberglass, carbon fiber or ceramics
Term
 53. Define diffusion. What shapes are effective diffusers?
Definition
 a. To deflect incident radar beams in every direction except back to the transmitting radarb. Gaussian Curves
Term
 54. What is the vulnerability of diffusion?
Definition
 a. Vulnerable to detection by multi-static radars
Term
 55. List some of the LPI sensors
Definition
 a. AESA
Term
 56. Define Cloaking
Definition
 a. Combining LO and LPI with simple noise jamming
Term
 57. How do OTH radars achieve their great range?
Definition
 a. By leaving the transmitter on (Max PRF) and bringing the frequency down to the HF region
Term
 58. In which frequency band do OTH radar operate?
Definition
 a. HF
Term