Microwave QSOs with the aid of airplane reflection

29 Pages·2007·1.68 MB·English

Microwave QSOs
with the aid
of airplane reflection
Wolf-Henning Rech
DF9IC in JN48iw
http://www.df9ic.de
Content
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Some theory
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Observations on beacons
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Experience from QSOs
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Airplane tracking with ADS-B
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A propagation test
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Conclusion
28. Nordic VHF Meeting 2006
Sletten Wolf-Henning Rech DF9IC 2
Reflection or scatter?
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Reflection:
ִ
like a mirror: angle of incidence = angle of reflection
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reflective area must be:
large - smooth - plane
e. g. dish reflector
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Scatter:
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mostly omnidirectional (with varying power density)
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from either a rough surface
or from a large number
of small particles
e. g. moon (EME)
e. g. rain (RS)
28. Nordic VHF Meeting 2006
Sletten Wolf-Henning Rech DF9IC 3
Geometry of DX via airplane
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Large passenger and freight airplanes use a
height of FL300 - FL400 (30.000 - 40.000 ft)
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the airplane is close to the horizon for maximum
range (very low elevation 0...1°)
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then the angle of incidence of the wave on the
aircraft is around 3°
28. Nordic VHF Meeting 2006
Sletten Wolf-Henning Rech DF9IC 4
Maximum range via airplane
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Maximum range by airplane at FL400 at the
right position and radio LOS path including
refraction in the atmosphere is 1040 km
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Experimental limit on 1296 and 2320 is 800 km
for good probability and duration (from DF9IC
SK7MW 777 km easy, SM7ECM 809 km difficult)
28. Nordic VHF Meeting 2006
Sletten Wolf-Henning Rech DF9IC 5
Geometry of DX via airplane
Top View
LOS range
Station B
Station A
Airplane location
28. Nordic VHF Meeting 2006
Sletten Wolf-Henning Rech DF9IC 6
Path attenuation
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Reflection:
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Scatter:
with A : effective reflective area
s
: radar cross section
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Example:
d = d = 390 km, f = 1296 MHz, g = 32 dBi,
1 2 TX
P = 51 dBm, g = 24 dBi, P = -130 dBm
TX RX RX
s
results in A = 2.7 m2 = 5000 m2
28. Nordic VHF Meeting 2006
Sletten Wolf-Henning Rech DF9IC 7
Duration and Doppler shift
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Airplane speed = 900 km/h = 15 km/min
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typical duration of one reflection is between few
seconds to few minutes
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Doppler shift occurs because of difference in
aircraft speed perpendicular to both stations
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Different Doppler shifts from various airplanes
allow to differentiate between them (only CW)
28. Nordic VHF Meeting 2006
Sletten Wolf-Henning Rech DF9IC 8
Which is the best frequency?
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Path attenuation is frequency independent
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Pro lower frequencies:
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wide beamwidth of antennas
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curvature of reflecting planes is less harmful
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angle condition (incident = reflected) is less stringent
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we use more TX power (but microwave will QRO in
future)
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Pro higher frequencies:
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more antenna gain
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Conclusion: we should try more on microwave!
28. Nordic VHF Meeting 2006
Sletten Wolf-Henning Rech DF9IC 9
Observations on beacons
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Use of SPECTRAN or similar programs for audio
analysis (spectrogram, waterfall display)
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Airplane reflection is Doppler-shifted; frequency
depends on its speed relative to both stations
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Example:
GB3MHL
1296.830
at DF9IC
d = 630 km
28. Nordic VHF Meeting 2006
Sletten Wolf-Henning Rech DF9IC 10