Topics in Propagation

Transcription

1 Topics in Propagation Extra Class Course Spring 2013 Andy Durbin k3wyc

2 Propagation The magic that allows a signal to travel between the transmitting antenna and the receiving antenna. This course is limited to a brief discussion of the topics covered in the Extra class test pool

3 Propagation Subject areas: HF VHF, UHF, and microwave

4 HF Propagation Ground-wave Sky-wave Long path Gray line Much more information on line e.g.

5 Ground Wave Signals that propagate by traveling along the surface of the Earth All radio waves influenced by diffraction and refraction Vertically polarized HF and lower frequencies subject to a special case of diffraction Wave is tilted due to slowing of lower part and follows Earth curvature Ground wave can travel much further than straight line of sight The lower the frequency the longer the ground wave path

6 Ground Wave

7 Ground Wave

8 Ground Wave Course book Fig 10-1 is a very simplified depiction Very detailed plots for various ground types here:

9 Ground Wave How does the maximum distance of ground-wave propagation change when the signal frequency in increased? A It stays the same B It increases C It decreases D It peaks at roughly 14MHz

10 How does the maximum distance of ground-wave propagation change when the signal frequency in increased? A It stays the same B It increases C It decreases D It peaks at roughly 14MHz

11 What type of polarization is best for ground-wave propagation? A Vertical B Horizontal C Circular D Elliptical

12 What type of polarization is best for ground-wave propagation? A Vertical B Horizontal C Circular D Elliptical

13 THE IONOSPHERE The region above the Earth from 30 miles to 260 miles. Above 260 miles it s the vacuum of space. (no air) Oxygen and Nitrogen in the Ionosphere is exposed to intense ultraviolet radiation from the Sun which knocks off electrons creating positively charged Ions. Regions (layers) of differing charge density are formed. D E F.

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15 Sky Wave Any signal that travels away from the surface of the Earth and is returned by the ionosphere Hop The path of a wave that returns to Earth after being bent by the ionosphere Skip Distance The distance between the transmitter and the closest point that the sky-wave returns to the Earth Low takeoff angle normally gives greatest skip distance

16 Pedersen Ray

17 Pedersen Ray Pedersen wave is a special case of sky wave propagation Medium takeoff angle signal returned to Earth at a greater distance than for a lower takeoff angle Signal travels long distance in F2 region Lower signal loss for multiple hops covering same distance

18 What is the name of the high-angle wave in HF propagation that travels some distance within the F2 region? A Oblique angle ray B Pedersen ray C Ordinary ray D Heaviside ray

19 What is the name of the high-angle wave in HF propagation that travels some distance within the F2 region? A Oblique angle ray B Pedersen ray C Ordinary ray D Heaviside ray

20 D Layer Absorption Lowest of ionosphere s layers is the D layer Dense compared to other layers Only active when illuminated by sun Strongest at noon and disappears quickly after sunset Longer wavelengths have greater absorption Eliminates long distance sky wave propagation on 1.8 and 3.5MHz

21 Long Path Shortest distance between any two points on the Earth s surface is called great circle Normal propagation path is by the shortest distance Long path is the portion of the great circle that is not the short path (Earth s circumference approx 25,000 miles) Normally requires beam antennas to be pointed 180 degrees from the short path bearing Long path signal may be heard as an echo of the short path signal Sometimes long path will give better propagation than short path

22 Long Path

23 What type of propagation is probably occurring if an HF beam antenna must be pointed in a direction 180 degrees from the station in order to receive the strongest signals? A Long path B Sporadic-E C Transequatorial D Auroral

24 What type of propagation is probably occurring if an HF beam antenna must be pointed in a direction 180 degrees from the station in order to receive the strongest signals? A Long path B Sporadic-E C Transequatorial D Auroral

25 Gray Line

26 Gray Line Gray line is the region between night and day As sunset approaches the sun stops illuminating the lower D layer while it still illuminates the higher E and F layers Similarly, as sunrise approaches the E and F layers become active before the D layer attenuation starts. For a short time have the advantage of good E and F layer without the disadvantage of D layer attenuation Long distance contacts possible along the gray line in short and long path directions

27 Path of Gray line varies Depends on time of day Depends of time of year Gray Line Over poles only at Equinox (March 21, Sept 21) Several software tools depict the gray line current position on a world map (N1MM, PSK Reporter, Google Earth)

28 Gray Line

29 Sunrise April

30 Mid morning April

31 Sunset April

32 At what time of day is gray line propagation most likely to occur? A At sunrise and sunset B When the sun is directly over the location of the transmitting station C When the sun is directly overhead at the middle of the communications path between the two stations D When the sun is directly above the location of the receiving station

33 At what time of day is gray line propagation most likely to occur? A At sunrise and sunset B When the sun is directly over the location of the transmitting station C When the sun is directly overhead at the middle of the communications path between the two stations D When the sun is directly above the location of the receiving station

34 Fading General term to describe variation in strength of a received signal Multiple causes ionospheric variation (layer heights, absorption, polarization); reflections from passing aircraft (flutter); etc Selective fading is fading that varies across the frequency range of the signal being received The narrower the signal the less the impact of selective fading For an AM signal the upper and lower sidebands may have different propagations paths and arrive at the receiver at different times

35 Which if the following describes selective fading? A Variability of signal strength with beam heading B Partial cancellation of some frequencies within the received pass band C Sideband inversion within the ionosphere D Degradation of signal strength due to back scatter

36 Which if the following describes selective fading? A Variability of signal strength with beam heading B Partial cancellation of some frequencies within the received pass band C Sideband inversion within the ionosphere D Degradation of signal strength due to back scatter

37 VHF/UHF/Microwave Radio horizon Tropospheric and trans-equatorial Aurora and meteor scatter Earth-Moon-Earth

38 Radio Horizon Radio horizon is the farthest distance from the transmitter that radio waves will travel by space wave propagation VHF and UHF signals can be received beyond the direct line of sight path Radio path horizon exceeds geometric horizon Signal path is extended by tropospheric bending Distance increase approximately 15%

39 Radio Horizon

40 By how much does the VHF/UHF radio path horizon distance exceed the geometric horizon? A By approximately 15% of the distance B By approximately twice the distance C By approximately one-half the distance D By approximately four times the distance

41 By how much does the VHF/UHF radio path horizon distance exceed the geometric horizon? A By approximately 15% of the distance B By approximately twice the distance C By approximately one-half the distance D By approximately four times the distance

42 Multipath Moving transmitter, moving receiver, or moving signal reflector, may cause fading as reflected path interferes with direct path Ham mobile is typical moving receiver or transmitter Over-flying aircraft act as signal reflector and induce multipath fading Picket fencing or flutter

43 Multipath

44 Tropospheric Ducting What is the troposphere? Source: parison_us_standard_atmosphere_1962.sv g?qsrc=3044

45 Tropospheric Ducting VHF radio waves may be trapped between the edges of a warm air layer and travel great distances Requires sharp transition in temperature between the warm air layer and the surrounding colder air Thickness of the layer controls the maximum frequency for which ducting will be supported Thicker layers support lower frequencies.

46 Tropospheric Ducting

47 Tropospheric Ducting

48 Which of the following is usually responsible for causing VHF signals to propagate for hundreds of miles? A D region adsorption B Faraday rotation C Tropospheric ducting D Ground wave

49 Which of the following is usually responsible for causing VHF signals to propagate for hundreds of miles? A D region adsorption B Faraday rotation C Tropospheric ducting D Ground wave

50 Transequatorial Propagation A form of F layer ionospheric propagation discovered by amateurs in 1940 s Observed on various North-South paths on 50MHz when expected MUF was 40MHz Two regions of peak ionization form at the time of the spring and fall equinox Regions are located between 10 and 15 deg either side of the Earth magnetic equator Propagation best in afternoon and early evening Maximum distances approximately 5000 miles

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52 Transequatorial Propagation Source -

53 What is the best time for transequatorial propagation? A Morning B Noon C Afternoon or early evening D Late at night

54 What is the best time for transequatorial propagation? A Morning B Noon C Afternoon or early evening D Late at night

55 Auroral Propagation Aurora results from large scale interaction between ionosphere, Earth s magnetic field, and the electrically charged particles of the solar wind Auroral curtain may act as a reflector for signals above 20MHz Ionization happens in the E layer about 70 miles altitude Most frequent close to spring and fall equinox Most commonly used on 10, 6, and 2m bands Signals may be badly distorted and fluttery favoring CW mode but it may be subject to white noise modulation Transmit and receive station point antennas toward the aurora (North in Northern hemisphere)

56 Northern Lights Aurora Borealis

57 Auroral Propagation Not much chance in AZ

58 Where in the ionosphere does Aurora activity occur? A In the F1 region B In the F2 region C In the D region D In the E region

59 Where in the ionosphere does Aurora activity occur? A In the F1 region B In the F2 region C In the D region D In the E region

60 Which of the following effects does Aurora activity have on radio communication? A SSB signals are raspy B Signals propagating through the Aurora are fluttery C CW signals appear to be modulated by white noise D All of these choices are correct

61 Which of the following effects does Aurora activity have on radio communication? A SSB signals are raspy B Signals propagating through the Aurora are fluttery C CW signals appear to be modulated by white noise D All of these choices are correct

62 Meteor Scatter Meteoroids are the smallest members of the solar system, ranging in size from large fragments of asteroids or comets, to extremely small micrometeoroids Meteor is a meteoroid that passes into Earth atmosphere creating brief flash of light moving across the sky. Creates a trail of free electrons and positively charged ions Meteorite refers to any parts of the meteorite than reach the Earth s surface

63 Meteor Scatter Ionized trail of a meteor will reflect radio waves Best reflections for frequencies between 28 and 148MHz (10m, 6, and 2m bands) Meteor trails form miles above Earth (similar to E layer) Maximum distance for single hop approximately 1200 miles For a single meteor propagation duration may be as short as 12 seconds depending on frequency in use and size or meteor QSO chances much better if more than one meteor

64 Meteor Scatter Want more meteors? Wait for a shower! Check the meteor shower calendar and mark yours Typical best time between midnight and noon Typical QSO is standard format and quick Each minute may be divided into 15 sec segments with Westerly station allocated first and third period and Easterly station allocated second and fourth period FSK441 designed for meteor scatter by Joe Taylor W1JT (also originator of JT65 and JT9) High speed CW also used ( wpm computer generated and decoded)

65 When a meteor strikes the Earth s atmosphere, a cylindrical region of free electrons is formed at which layer of the ionosphere? A The E layer B The F1 layer C The F2 layer D The D layer

66 When a meteor strikes the Earth s atmosphere, a cylindrical region of free electrons is formed at which layer of the ionosphere? A The E layer B The F1 layer C The F2 layer D The D layer

67 Which of the following is a good technique for making meteor scatter contacts? A 15 second timed transmission sequences with stations alternating based on location B Use of high speed CW or digital modes C Short transmissions with rapidly repeated call signs and signal reports D All of these choices are correct

68 Which of the following is a good technique for making meteor scatter contacts? A 15 second timed transmission sequences with stations alternating based on location B Use of high speed CW or digital modes C Short transmissions with rapidly repeated call signs and signal reports D All of these choices are correct

69 EME or Moon-Bounce If two stations can see the moon then moon bounce QSO may be possible Stations may be separated by nearly half the circumference of the Earth (nearly 12,000 miles) Signal path very long (2 x 239,000 miles average) Requires low noise receivers and digital mode software that decodes signal close to the noise floor. JT65 (K1JT - Joe Taylor again)

70 EME or Moon-Bounce Best chance for QSO when moon is closest to Earth (perigee) Apogee is farthest point so that s the worst time However moon orbit only slightly elliptical so not a major factor Avoid moon low on horizon Avoid moon close to sun Best QSO chances when moon at high elevation angle

71 EME or Moon-Bounce Apparent size difference for apogee and perigee

72 EME Procedures and Scheduling Select date and time for best moon position Most operation on 2m and 70cm 2m cm JT65 is time synchronous mode with 1 minute blocks All station require accurate time sync (within 1 second is preferred but mode can work with up to 4 sec split) SSB and CW use 2 minute blocks on 2m and 2.5 minute blocks on 70cm Apparent size difference for apogee and perigee

73 EME - Libration Fading Fluttery, rapid, irregular, deep fading. Special case of multi-path fading Moon surface is irregular Earth and moon are continuously but slowly changing relative position Apparent size difference for apogee and perigee

74 When scheduling EME contacts, which of these conditions will generally result in the least path loss? A When the moon is at perigee B When the moon is full C When the moon is at apogee D When the MUF is above 30MHz

75 When scheduling EME contacts, which of these conditions will generally result in the least path loss? A When the moon is at perigee B When the moon is full C When the moon is at apogee D When the MUF is above 30MHz

76 Which of the following describes a method of establishing EME contacts? A Time synchronous transmission with each station alternating B Storing and forwarding digital messages C Judging optimum transmission times by monitoring beacons from the moon D High speed CW identification to avoid fading

77 Which of the following describes a method of establishing EME contacts? A Time synchronous transmission with each station alternating B Storing and forwarding digital messages C Judging optimum transmission times by monitoring beacons from the moon D High speed CW identification to avoid fading