Term
|
Definition
| the measurement of one crest to another |
|
|
Term
|
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
a. Scientific
b. Engineering
c. Nato
d. Academic |
|
|
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 |
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Term
| 4. What are the advantages of the various signal polarities with regard to radar? |
|
Definition
a. Horizontal-used to detect low-level aircraft
b. Vertical-clutter rejection provided
c. 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 |
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Term
| 6. To escape cosmic noise, should we increase or decrease our operating frequency? |
|
Definition
a. Cosmic noise decreases as we increase operating frequency
b. They dramatically decrease as you approach 100 MHz |
|
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Term
| 7. To escape atmospheric attenuation, should we increase or decrease our operating frequency? |
|
Definition
a. Decrease our operating frequency
b. Negligible below 10GHz
c. 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) |
|
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Term
|
Definition
i. Occurs where warm air moves over a cool, dry landmass
ii. Conditions decrease wave propagation speed as altitude increases
1. Causes beams to bend upward |
|
|
Term
| 9. Define Super-refraction |
|
Definition
i. Occurs where warm ocean currents flow under cold air
1. Conditions extend the range of the beams
2. Not always welcome
a. Causes unwanted interference from other transmitters
b. Increases the amount of ground clutter the receiver must process and display |
|
|
Term
|
Definition
i. Super-refraction to the extreme
ii. Occurs when curvature of refraction > curvature of earth
iii. Wave is “trapped” in a narrow duct and extends longer than even super-refraction
iv. 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
|
|
Term
| 12. Which communications frequency band can operate over oceanic distances without the need of a relay? |
|
Definition
|
|
Term
| 13. VHF and UHF channels are spaced by how many megacycles? |
|
Definition
|
|
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
|
|
Term
16. Define:
a. Transponder: |
|
Definition
| i. Transmitter/Responder which receives signal and retransmits on a downlink frequency |
|
|
Term
|
Definition
| i. Signal sent to the satellite |
|
|
Term
|
Definition
| i. Signal sent from the satellite |
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|
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 problem
b. VC understood US’ comm plan very well
c. Able to jamm with precision |
|
|
Term
| 19. What changed about communications EA and EP after Vietnam? |
|
Definition
| a. Have quick was developed |
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Term
| 20. Using the challenge and reply authenticator in the text, authenticate A-B-C. Now try B-C-D. |
|
Definition
|
|
Term
| 21. Using the transmission authenticator from the text, authenticate a message for transmission at 2202Z. Now try 1359Z. |
|
Definition
|
|
Term
|
Definition
i. Airborne Intercept
ii. Sacrifice long range for light weight and close-in precision |
|
|
Term
|
Definition
i. Overcame the problem of detecting low flying targets by elevating the surveillance radar to well above the horizon
ii. Could detect wave skimming kamikaze at 40+ miles |
|
|
Term
|
Definition
i. Ground controlled intercept
ii. Combines long range of EW with precision of AI
iii. Max detection range close to 200 miles |
|
|
Term
| 23. Which devices can be used to generate microwaves? |
|
Definition
a. Klystrons
b. Twystrons
c. Magnetron
d. Microwave transistors |
|
|
Term
Characteristics of
a. Klystrons |
|
Definition
i. Very stable
ii. Long warm-up period
iii. Produces x-rays
iv. Very heavy |
|
|
Term
Characteristics of
b. Twystrons |
|
Definition
i. Very similar to Klystron
ii. Offers frequency agility |
|
|
Term
Characteristics of
c. Magnetron |
|
Definition
|
|
Term
Characteristics of
d. Microwave transistors |
|
Definition
i. Aren’t vacuum tubes
ii. Don’t need to warm up
iii. Don’t produce harmful x-rays
iv. Not very powerful
v. Need many to produce effective beam |
|
|
Term
| 24. What is a super-heterodyne receiver used for? |
|
Definition
a. Amplifies very weak returns without creating noise
i. 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
| 26. What are the advantages and disadvantages of low prf |
|
Definition
a. Low PRF
i. Advantages
1. Very limited second-bang targets
2. Simple
ii. Disadvantages
1. No Doppler capability |
|
|
Term
What are the advantages and disadvantages of
b. Medium PRF |
|
Definition
i. Advantages
1. Higher average power
2. Significant increase in range
3. True look-down Doppler capability
4. Doppler blind speeds are further out
ii. Disadvantages
1. More complex
2. Creates second-bang targets |
|
|
Term
What are the advantages and disadvantages of
c. High PRF |
|
Definition
i. Advantages
1. Great effective range
2. Doppler blind speeds even more spread out
3. Unambiguous Doppler processing
ii. Disadvantages
1. Very complex
2. 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
|
Definition
| i. The lobe in which we want to receive information |
|
|
Term
|
Definition
i. Same amplitude as the main lobe
ii. Unwanted area of potential reception
iii. Wasted energy |
|
|
Term
|
Definition
i. Unwanted lobes of potential reception
ii. Smaller than main and back lobes |
|
|
Term
| 28. Write a brief description Parabolic reflector |
|
Definition
i. Round dish
ii. Creates and receives pencil beam
iii. 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 beam
a. Useful for EW and AEW
b. Used to find azimuth of target
ii. Thin long antennas (taller than they are wide)
1. Fan-shaped beam
a. Great for searching a target’s altitude |
|
|
Term
Write a brief description
iii. Square antennas |
|
Definition
1. Can estimate target’s height
2. Useful for GCI |
|
|
Term
| 29. Which type of radar might employ a Raster scan? |
|
Definition
|
|
Term
| 30. Which type of antenna might employ a fan beam? |
|
Definition
|
|
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 azimuth
b. Reduce amplification of echoes that are in close proximity to the radar
c. Side lobe cancellation
i. Using two antennas simultaneously
1. Directional and dipole
ii. CPU only displays those signals that are closer to the main lobe |
|
|
Term
| 32. Advantages and disadvantages of the planar array? |
|
Definition
a. Advantages
i. Significant reduction in back and side lobes
ii.
b. Disadvantages
i. Does produce side and back lobes
ii. Very precise construction
iii. Very hard to manufacture
iv. Expensive
v. Very big
1. Takes very big hits when ac is maneuvering |
|
|
Term
| 33. Advantages and disadvantages of the active array? |
|
Definition
a. Advantages
i. Rigidly mounted
ii. No movement of antenna
iii. Can change beam shape
iv. Multiple directional reception
v. Only limited by CPU processing power
b. Disadvantages
i. 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 RF
b. 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 network
b. 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 time
ii. EPs are:
1. frequency agility
2. Frequency diversity |
|
|
Term
| Define sweep jamming and list the EP |
|
Definition
i. Fool all of the people some of the time
ii. Less severe than spot
iii. EPs are:
1. Patience and persistence |
|
|
Term
| Define barrage jamming and list the EP |
|
Definition
i. Fool all of the people all of the time
ii. Power is spread thin due to all the freq’s being jammed
iii. 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 display
ii. Staggered PRF defeats this |
|
|
Term
| Explain azimuth jamming and list the EP |
|
Definition
i. Exploits radar’s side and back lobes
ii. Repeats radar pulse at a time when the victim’s side lobes are trained on the jammer
iii. 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 MHz
b. 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
|
|
Term
| 43. Which IFF/SIF modes are selectable in flight? |
|
Definition
|
|
Term
| 44. What are the permissible digit values for the various IFF/SIF modes? |
|
Definition
a. Mode 1-two digits; octal and 0-3
b. Mode 2-four digits; Octal
c. Mode 3A- four digits; octal
d. Mode 3C-three digits, Not octal
e. Mode 4 -Encrypted
f. Mode S-twenty four digits, octal; plus alt and spd
g. Mode 5-Encrypted version of Mode S |
|
|
Term
| 45. Do the naval ships carry IFF/SIF transponders? |
|
Definition
|
|
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
| 50. What are the advantages and disadvantages of surface attenuation? |
|
Definition
a. Advantages:
i. Can be useful against GCI, AEW and AI radars
b. Disadvantages:
i. Heavy
1. Reduced payload and fuel load
ii. Toxic
iii. Maintenance nightmare
iv. Needed hangars |
|
|
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 RAM
b. 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 well
b. 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 radar
b. 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
|
|
Term
|
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
|
|
Term
| 59. List some advantages and disadvantages of the OTH radar |
|
Definition
a. Advantages:
i. Very long range
ii. B-2 and B-52 look the same (stealth is marginalized)
b. Disadvantages
i. Huge
ii. Lose pulse-echo ranging
iii. Need second antenna (receiver) |
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