Radio Wave Propagation Teach you enough to get all right during the VE Session Learn a few things from you Have fun Finish everything on time (if the propagation questions about your experiences not a little early) Bob, KA9BH Eric, K9VIC
Radio Wave Propagation But first some leftovers from last week...
The Smith Chart Dr. Zachary Smith
The Smith Chart Resistance/conductance component at the center. Zero resistance at left Infinite resistancee at right Reactance arcs above/below the center. Inductive above (+1j Ω at top center) Capacitive below (-1j Ω at bottom center) Standard (normalized) resistance at center of the chart. SWR circles around center.
What's it good for? The Smith Chart Used to portray complex impedances graphically Can be used to solve for impedances when transformed through feedlines, etc. Move clockwise around the chart from a load to the source One wavelength is twice around the chart (e.g., ¼ wavelength would be ½ way around the circle) Can be used for the open/shorted feedline questions.
The Smith Chart Open/Shorted Feedline Questions: Shorted feedline, 1/8 wavelength long A shorted feedline (at the load) has essentially zero resistance Moving ¼ turn clockwise (toward the source) we arive at +1j Ω, an inductive load viewed from the source. Open feedline, 1/ /4 wavelength long An open feedline (at the load) has essentially an infinite resistance Moving 1/2 turn clockwise (toward the source) we arive at zero Ω, a low impedance load viewed from the source.
VE Exam Three Exam questions, one each from three groups: Earth-Moon-Earth (EME) communications; meteor scatter. Transequetorial propagation; long path; gray line; multi-path propagation. Aural propagation; selective fading; radio-path horizon; take-off angle over flat or sloping terrain(covered last session); earth effects on propagation (also covered last session); less common propagation modes.
HF Propagation Ground Wave (160 10 meters) 50 miles maximum Polarization dependent Vertical better than horizontal Remember most horizontal antennas have a small vertical componant (next slide) Frequency dependent Lower Frequency better than higher Due to refraction along the earth's
Ground Wave HF Propagation
Ground Wave HF Propagation
HF Propagation Ionosphere
HF Propagation Ionosphere
HF Propagation Ionosphere
Critical Frequency Critical Angle HF Propagation Ionosphere The highest frequency that will be returned to the earth when transmitted vertically under given ionospheric conditions The highest angle with respect to a vertical line at which a radio wave of a specified frequency can be propagated and still returned to the earth from the ionosphere
HF Propagation Ionosphere Maximum Usable Frequency (MUF) The upper frequency limit that can be used for transmissions between two points independent of transmitter power.
HF Propagation Ionosphere
HF Propagation Ionosphere Ionospheric Layer and Height (miles) D Layer 30-60 E Layer 60-90 F1 Layer 140 F2 Layer 160-200 F Layer 160-200 Maximum Skip Distance (miles) Absorbtive 1,400 Minimal Skip Affect 2,500 2,500
Long Path HF Propagation Ionosphere Signal takes the longer of two great circle paths Long path is 180 opposite short path May hear both paths (echo) Works on all HF bands (160 thru 10- meters) Very consistent on 20-meters
HF Propagation Ionosphere
Sporadic E HF Propagation Ionosphere Applies to VHF (or 10-meters) 50 MHz: 6000+ miles 144 MHz: 1900 miles Strong cycle May, June, July Lesser cycle December, early January Independent of Solar Cycle
Sporadic E HF Propagation Ionosphere When 28 MHz goes short (250 300 miles), 50 MHz goes long (1,400 miles) When 50 MHz shortens (400 miles), 144 MHz goes long (1,400 miles) HF may seem dead as the F-layers are blocked (or the E-layer is the top reflector) Not the same as a Pedersen Ray (F 2 phenomina)
HF Propagation NVIS (Near Vertial Incident Skywave)
HF Propagation Ionosphere (backscatter)
HF Propagation Ionosphere Grayline Propagation Occurs at daytime/nighttime terminator (twilight, sunset, sunrise) D-layer quickly disappears or hasn't yet formed F-layer is present Skip is 8-10,0000 miles on 3 or 4 HF bands Always along Grayline (NOT one station in twilight, the other in darkness or light)
HF Propagation Trans-equatorial propagation Best late afternoon/early evening Reflection height suggests bulged F- layer 3100-5000 miles over magnetic equator (add frequencies) Why do we care? Chicago to magnetic equator is more than 2500 miles (south of 'real' equator)
Selective Fading HF Propagation Phase difference between components of a signal combine and cancel (generally due to multipath) Large bandwidth are more effected Phase band modes (even narrow band) are very succeptible
Meteor Scatter Propagation Ionosphere Transmit using 15 second intervals Popular modes: Fast CW (100+ WPM) WSJT JT6 Best during meteor showers, and in the morning (heading into the shower) Can be used any time with JT-modes
EME Earth-Moon-Earth Theoretically works for any two stations that can both see the moon (12,000 miles) Frequencies Used: 144.000-144.1000 432.000-432.1000 Transmit 'schedule' 2-meters: 2 minutes on, 2 minutes listening 70-cm: 2.5 minutes on, 2.5 minutes listening
EME Considerations Distance (2-week cycle) Perigee (closest to earth) = 359,000 km Apogee (farthest from earth) = 404,510 km Why do we care, they're both pretty far? Apogee is about 1.127 X perigee Signal increase is (1.127) 2 =1.270 (~30%) DB = 10 log 1.3/1 = 1.14 db
EME Considerations Moon's orbit is eliptical and tilted re: earth Velocity not constant relative to earth Allows 59% of the moon to be seen 41% of the far side (not dark) never seen Libration Fading Fluttery, irregular fading
Considerations EME How do we increase s+n/n? Bandwidth (cw, WSJT, JT65, etc.) ERP (amps, lots of aluminum) Rx noise level (low noise rx a must)
VHF/UHFPropagation Troposhperic Ducting Troposphere 0 6 miles in height Ducting products potential contacts of 500 miles Due to radio horizon Horizon =( (2h) 1/2 h = haat horizon in miles Radio horizon ~15% farther than geometric horizon Six miles = 31,,680 feet, Horizon = 251.7 miles (double for two stations)
VHF/UHF Propagation Aural Propagation Think Aurora Borealis (Australis) Charged particle from the sun create ions E-layer ionization layer SSB rarely readable CW best option (with fluttery tones) Both stations point antennas north (in the northern hemisphere)
VHF/UHF Propagation Meteor Scatter Meteor creates 12-mile ion trail at E-layer height Propagation 500 1400 miles Works on 28 to 144 MHz (50 MHz best bet) Short lived: 30 seconds on 50 MHz 3 seconds on 144 MHz <1 second on 432 MHz
Radio Wave Propagation Questions?