doppler radar
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doppler radar
Q.An 8800MHZ tranmitter is moving directly away from receiver at 291kt.calculate:
the frequency received in MHZ...
ans: 8799.9956MHZ......
Plz shed some light how to solve this problem......
thanks
the frequency received in MHZ...
ans: 8799.9956MHZ......
Plz shed some light how to solve this problem......
thanks
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You asked for it!
The principle of Doppler radar works on a device emitting a set frequency and that same device measuring the return frequency to establish if motion is occurring.
So how?
Radio waves act in similar ways to sound waves. So think of an F1 car. As it speeds towards you the engine sounds high pitched and once it passes by the engine takes on a lower sound. Right?
What's happening? As the car comes towards you the sound waves are being compressed by the car's motion in your direction. Thus the Hz (Cycles per second) increases which has a direct effect on the pitch of the sound, a higher pitch.
Once the car passes the opposite effect occurs with the car's motion being away from you. The same applies to radio waves.
Now the maths.
You are travelling away, thus stretching the radar wave, hence the lower frequency. The speeds you travel away at has a protional effect on the radio wave.
As it is a radio wave we are talking about they travel at the speed of light which is 1,079,252,849 km/h
As we fly in knots we want it that way as well so times by 0.53997 to get knots = 582,749,918kts.
What is the speed of the aircraft relative to the speed of light in terms of a factor?
Aircraft speed divided by speed of radio wave (Speed of light, warp 1... Whatever)
291kts / 582,749,918kts = 0.0000004994
and we can now apply the effect of the aircraft's speed on the radar's frequency.
What's the reduction in frequency, Hz?
Radar Frequency times relative speed factor.
Btw. 8800MHz = 8,800,000,000Hz
8,800,000,000Hz x 0.0000004994 = 4394Hz
and now minus from the original frequency which equals...
8,800,000,000Hz - 4394Hz = 8,799,995,606Hz = 8799.9956MHz
Ta da!
The principle of Doppler radar works on a device emitting a set frequency and that same device measuring the return frequency to establish if motion is occurring.
So how?
Radio waves act in similar ways to sound waves. So think of an F1 car. As it speeds towards you the engine sounds high pitched and once it passes by the engine takes on a lower sound. Right?
What's happening? As the car comes towards you the sound waves are being compressed by the car's motion in your direction. Thus the Hz (Cycles per second) increases which has a direct effect on the pitch of the sound, a higher pitch.
Once the car passes the opposite effect occurs with the car's motion being away from you. The same applies to radio waves.
Now the maths.
You are travelling away, thus stretching the radar wave, hence the lower frequency. The speeds you travel away at has a protional effect on the radio wave.
As it is a radio wave we are talking about they travel at the speed of light which is 1,079,252,849 km/h
As we fly in knots we want it that way as well so times by 0.53997 to get knots = 582,749,918kts.
What is the speed of the aircraft relative to the speed of light in terms of a factor?
Aircraft speed divided by speed of radio wave (Speed of light, warp 1... Whatever)
291kts / 582,749,918kts = 0.0000004994
and we can now apply the effect of the aircraft's speed on the radar's frequency.
What's the reduction in frequency, Hz?
Radar Frequency times relative speed factor.
Btw. 8800MHz = 8,800,000,000Hz
8,800,000,000Hz x 0.0000004994 = 4394Hz
and now minus from the original frequency which equals...
8,800,000,000Hz - 4394Hz = 8,799,995,606Hz = 8799.9956MHz
Ta da!
Last edited by Touch'n'oops; 29th Aug 2011 at 04:09. Reason: Was tired and ment to say factor not percentage
