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HRDF ( H igh R esolution D irection F inder) Purpose, Principles & Aerial System

HRDF ( H igh R esolution D irection F inder) Purpose, Principles & Aerial System. Doppler. A change in frequency of an RF signal caused by the relative motion between the source and the observer Doppler is a natural phenomenon. Squeeze. Stretch. Doppler.

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HRDF ( H igh R esolution D irection F inder) Purpose, Principles & Aerial System

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  1. HRDF(High Resolution Direction Finder)Purpose, Principles & Aerial System

  2. Doppler • A change in frequency of an RF signal caused by the relative motion between the source and the observer • Doppler is a natural phenomenon

  3. Squeeze Stretch Doppler • Relative movement of a sound source towards and away from a fixed point causes frequency modulation or a Doppler effect • This is a natural phenomenon

  4. D A B C Doppler

  5. Squeeze Stretch Doppler

  6. Doppler

  7. Doppler

  8. +fm fc 6 5 7 10 6 15 1 8 4 -fm 9 3 1 10 2 1 11 12 18 17 13 16 14 15 6 10 1 15

  9. +fm fc 6 5 7 10 6 15 1 8 4 -fm 9 3 1 10 2 1 11 12 18 17 13 16 14 15 6 10 1 15

  10. +fm fc 6 5 7 10 6 15 1 8 4 -fm 9 3 1 10 2 1 11 12 18 17 13 16 14 15 6 10 1 15

  11. +fm fc 6 5 7 10 6 15 1 8 4 -fm 9 3 1 10 2 1 11 12 18 17 13 16 14 15 6 10 1 15

  12. Pseudo Doppler • The man made frequency modulation induced by the electronic rotation of the HRDF aerial array is what we will now refer to as Pseudo Doppler • It is the phase of this Pseudo Doppler that will ultimately determine the bearing of the aircraft

  13. UHF Aerial Array • 18 unipole aerials, 1.67m in diameter • 7.62m diameter counterpoise 3m above the ground • fm is ± 33 Hz @ 225MHz • fm is ± 60Hz @ 400 MHz

  14. Auxiliary Aerial • It is the phase of the Pseudo Doppler induced by the electronic rotation of the HRDF aerial array that will ultimately determine the bearing of the aircraft • We need to ensure that Aircraft Doppler (frequency modulation produced by the aircraft movement) is not considered in bearing calculation process

  15. 10 9 11 12 8 13 7 14 6 5 15 16 4 3 17 2 18 1 Auxiliary Aerial • Pseudo Doppler • + • Aircraft Doppler Aux Aircraft Doppler only

  16. Advantages • Low Operating Cost • Requires little aircraft equipment • Interface with Console

  17. Any Questions?

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