AircraftScatterSharp New Features

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3 Aircraft Scatter Is using aircraft to redirect or scatter RF that would otherwise be lost in space Increases Communications Distance Has increasing advantage over troposcatter as frequency increases Has increasing advantage as distance increases, up to ~ 900 km (560 miles) Truly a weak-signal mode

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5 AircraftScatterSharp New Features Doppler Calculations (value and rate of change) Radar Cross Section modeling with estimated RCS for more than 100 aircraft Optionally, program will automatically assign RCS to selected aircraft using this model Adjustable lower limits for altitude and RCS below which planes will not be displayed Planes not meeting these limits will be removed from display Plane icon size and color indexed to RCS More extensive Manual Parameter Entry options including both static and dynamic modeling Rolling terrain elevation reporting

6 Aircraft Scatter is Bistatic Radar

7 Bistatic Radar Bistatic Radar Equation for Path Loss (db): L = 10 log((lambda**2)*s/(((rt**2)*(rr)**2))) 153 L = total loss (db) Rt = distance from transmitter to reflector (km) Rr = distance from receiver to reflector (km) Lambda = wavelength (m) S = radar cross section of aircraft (sq m) For lambda = 2M and Rt = Rr = 450km and S = 63 (B747): AS Path Loss = db Free Space -135; Troposcatter -241; EME -252 db

8 Radar Cross Section meters2 B-1 bomber 0.01 Radar Cross Sections Advanced tactical fighter Small single engine aircraft 1* Small fighter or 4-passenger jet (LearJet) 2*# Douglas DC-9 8# Boeing # Medium bomber or medium jet airliner 20 * Large bomber or large jet airliner 40 * Boeing # Jumbo jet 100* Bird 0.01 Man F-117 fighter B-2 bomber Automobile * Skolnik # ARRL UHF/Microwave Experime nter s Manual

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10 Estimated Radar Cross Sections A B B B B A A B B777-VIP 67 B B B A B A A A B B B

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12 Bistatic Radar Signal Loss is proportional to: Log((Frequency)2) = 20 (Log(Frequency)) db Log((Distance)4) = 40 Log(Distance) db Signal Loss is inversely proportional to: Log(Radar Cross Section) = 10 Log(RCS) db

13 Aircraft Scatter s Competition Troposcatter Frequency dependence of loss (db) 30 log(frequency) Distance dependence of loss ~9 db / 100km Meteor Scatter Loss (db) proportional to 30 Log(Frequency) Best at distances of km Aircraft scatter loss in db is proportional to: 20 Log(Frequency) and 40 Log(Distance) Which mode has best chance of success for a particular choice of frequency and distance?

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15 LearJet RCS = 2 B747 RCS = * Log(2/63) = -15 db

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19 Troposcatter s Achilles Heel

20 If we subtract 10 db of signal from Tropo for Take Off Angle of only 1 degree or add 20 db of signal to AS for Forward Scatter Enhancement, Balance shifts in favor of AS even for lower frequencies and shorter distances! But if the aircraft s RCS is lower than expected, then balance shifts in favor of troposcatter

21 Forward Scatter Enhancement Aircraft Scattering Angle

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24 Aircraft Scattering Angle

25 Remember, AS Angle depends on the SUM of your skew angle PLUS your partner s skew angle Take-home message: Keep YOUR skew angle less than 3-5 degrees to keep FSE within 10 db of maximum possible value There is also a distance effect, but it is weaker than the skew-angle effect

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28 FSE 144 MHz Beamwidth = * λ / radius FSE 10 GHz

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30 Theory vs Reality - VK7MO 144 thru 1296 MHz 12/13 results were within 10 db Moncur R. Aircraft Enhancement Some Insights from Bistatic Radar Theory. CQ VHF Magazine Fall 2003.

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32 What Do We Know So Far? Relative benefit of AS increases with frequency and with distance Must be along the interstation path or within about 3 degrees to get db Forward Scattering Enhancement Longer distances ( km or miles) will give greater FSE than shorter distances Path loss is high, generally above 200 db for 144 MHz and up, even with maximum Forward Scattering Enhancement The RCS is never precisely known for any particular case, so exact prediction of signal strengths is not possible. The calculations should be considered to be order of magnitude

33 Complications Antenna Pointing Doppler Shift

34 Is Pointing at the Aircraft Necessary? Consider both Elevation and Horizontal Skew compared with beamwidth of antenna array Elevation and Scattering Angle vs Distance for Aircraft Altitude 10,000 meters QSO Distance 200 km 400 km 600 km 800 km 1000 km Distance to Aircraft 100 km 200 km 300 km 400 km 500 km Elevation Scattering Angle * Maximum Forward Scattering Enhancement *

35 Complications: Doppler Shift Aircraft speeds km/h ( mph) Δf = (1/λ) * (VTx + VRx) λ = wavelength VTx = Plane s Velocity component along path from aircraft to Tx station VRx = Plane s Velocity component along path from aircraft to Rx station When plane is moving along the direct path between Tx and Rx stations, the two Doppler Velocities cancel out When plane is moving perpendicular to the direct path between the Tx and Rx stations, the two Doppler Velocities ADD This is another HUGE reason why it is GREAT when you can make use of a plane traveling along the direct path between your station and your QSO partner s station

36 Maximum Doppler Shift (Hz) Flight Perpendicular to Interstation Path (Single Station Component) MHz km/h

37 Maximum Doppler Shift Single Station Component

38 Doppler Shift (Hz) Flight Perpendicular to Interstation Path (Both Station Components) MHz km/h

39 Maximum Doppler Shift Both Station Components

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41 16.48 Hz/second change in Doppler Shift is 247 Hz during a single 15 second ISCAT-A cycle Compare to Hz/ second for parallel flight path example just shown which gives change of 0.09 Hz over 15 second cycle

42 Doppler shift at 10 GHz for 1000 km/h = 9260 Hz * 2 = 18,530 Hz Change speed by 1% to 1010 km/h and Doppler changes by 1%, or 185 Hz!

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48 Manual Calculations and Calculations on SQLite Database Aircraft Examples for RF Calculations, Max FSE,Tropo Angle, Doppler

49 Digital Modes and AS

50 Reasons to use Digital Modes for Aircraft Scatter Pull weak signals out of the noise Short chopped signal segments on upper bands Because it s cool

51 Complications to using Digital Modes with Aircraft Scatter Doppler shift Short chopped up signal blocks Short period to complete QSO if plane flying perpendicular to interstation path

52 Which Digital Mode to Use? Mode Spacing BW (Hz) Baud rate) Duration (s) S/N (db) JT4A JT9A JT65A QRA64A ISCAT-A * ISCAT-B * JT9E JT9F JT9G JT9H MSK /-8# MSK144 Sh & For Microwaves, ISCAT is preferred due to its tolerance for Doppler shifts, its 15 second periods and ability to cope with short bursts. MSK144 can t handle the Doppler shifts and JT65 is too slow and can t handle bursts. *with 30s average #for 70/500 ms burst &20 ms burst

53 Summary Try to use aircraft with minimal skew (< 3-5 degrees) to maximize FSE Try to use aircraft flying along interstation path to maximize QSO time, maximize FSE, minimize Doppler shift and its rate of change Use a program like Aircraft Scatter Sharp to track aircraft in real time Digital modes greatly increase your likelihood of completing QSOs (path losses greater than 200 db); ISCAT preferred for uwaves Whether or not you need to point at aircraft rather than at remote station depends on your beamwidth, skew angle, aircraft elevation Aircraft Scatter Sharp will track aircraft, allow you to estimate signal levels, compare with tropo signal levels, and see Doppler shift all in real time

54 Preferred Mode vs Band / Distance MHz km 300 or less T T/M M M 144 T A M/A M 222 T A A A# 432 T A A A# 903 T / A* A A A# 1296 and up T / A* A A A# T = TS, A=AS, M = MS. * TS will be favored over AS for high aircraft elevation angles # AS will be useful if the aircraft is above the horizon for both stations

55 Questions? Mach 9.6 (11,850 km/h)

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57 Not just any Magic, but Physics Magic When the forward scattering angle is 180 degrees: We get constructive interference of the scattered radiation, called Diffractive Scattering which gives us Forward scatter enhancement = 4*Pi* A/(lambda**2) For 1296 MHz, if there is db enhancement, then 8 db signal margin becomes db signal margin

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59 Something for Nothing? Beamwidth (in degrees) = (14.32 * lambda) / (radius) Frequency MHz G 5G 10G 1 meter 3 db beamwidth deg meters 3 db beamwidth deg meters 3 db beamwidth deg Radius