Presentation on theme: "Accelerated Technician Class Session #2. Propagation How radio waves get there… and back. Right is Jeff Cram KI4VZQ testing the TSA Network Satellite."— Presentation transcript:
Accelerated Technician Class Session #2
Propagation How radio waves get there… and back. Right is Jeff Cram KI4VZQ testing the TSA Network Satellite
HF Propagation It is the unpredictable nature of HF propagation that makes the HF bands so much fun. Long distance communication (DX) is accomplished by the reflection of radio waves by the ionosphere, the upper layers of the atmosphere ionized by ultraviolet radiation from the sun.
Ionospheric Protection The ionosphere and magnetosphere protect us from harmful radiation from the sun.
How the Ionosphere is Formed
The Ionosphere F2 Layer (Reflecting) F1 Layer (Reflecting) E Layer (Reflecting) D Layer (Absorbing)
Layers of the Ionosphere D Layer, Absorbing, Disappears at night E Layer, Reflecting, Disappears at night F1 and F2 Layers, Reflecting, combine into a single F layer at night. The reflective layers are responsible for sky wave propagation.
Line of Sight Propagation Worldwidecommunications by line of sight is not possible due to the curvature of the Earth
Sky wave Propagation Over the horizon communication is possible by sky- wave propagation, bouncing signals off the ionosphere.
Sunspots Sunspots peak during 11-year cycles. The higher the sunspot count, the more the atmosphere is ionized. Thus, higher sunspot counts support a higher Maximum Usable Frequency (MUF).
VHF/UHF Propagation Generally line of sight can be blocked by and/or reflected off mountains and large buildings – even the Moon! Temperature inversions in the troposphere can cause “ducting,” and a path will open briefly for miles. VHF/UHF will penetrate the Ionosphere, making these frequencies ideal for satellite, and Earth-Moon-Earth (EME) operations.
VHF/UHF signals travel only in straight lines. We call this “line of sight” propagation Direct communications are not possible because of the mountain VHF/UHF Propagation
What is the cause or irregular fading of signals from distant stations during times of generally good reception? A. Absorption of signals by the “D” layer of the ionosphere B. Absorption of signals by the “E” layer of the ionosphere C. Random combining of signals arriving via different path lengths D. Intermodulation distortion in local receiver
What part of the atmosphere enables the propagation of radio signals around the world? A. The stratosphere B. The troposphere C. The ionosphere D. The magnetosphere
How does the wavelength of a radio wave relate to its frequency? A. The wavelength gets longer as its frequency increases B. The wavelength gets shorter as the frequency increases C. There is no relationship between wavelength and frequency D. The wavelength depends on the bandwidth of the signal
What property of radio waves is often used to identify the different frequency bands? A. The approximate wavelength B. The magnet intensity of waves C. The times it takes the waves to travel one mile D. The voltage standing wave ratio of waves
What is the formula for converting frequency to wavelength in meters? A. Wavelength in meters equals frequency in hertz multiplied by 300 B. Wavelength in meters equals frequency in hertz divided by 300 C. Wavelength in meters equals frequency in megahertz divided by 300 D. Wavelength in meters equals 300 divided by frequency in megahertz
Amateur Radio Practice Doing things right. Right: KC9OKC Scott Teerlinck, Moline, IL
Safety Amateur Radio is a relatively safe hobby. There are only a few ways to get hurt or killed being a ham radio operator: 1. Electrocute yourself. 2. Fall off a tower, or the inverse, have someone/something fall on you from a tower. 3. Slowly cook yourself with RF energy.
It Just Kills Me... People have been killed by as little as 30 Volts. As little as 1/10 of an amp (100 milliamps) can be fatal. AC is more dangerous than DC, as it interferes with heart rhythm. The path electric current takes across the body is important. Therefore, always keep one hand in your pocket when working near dangerous voltages.
High Voltage Safety Ground all the equipment cases. Make sure your power outlets are grounded. Do not defeat safety interlocks on equipment that contain lethal voltages. Remember, capacitors can store a charge for a really long time. Care should be taken to discharge them.
Antenna Safety Don’t put antennas. where they could fall across power lines Don’t climb towers without a safety belt. Don’t do tower work without a ground crew. If you’re working under the tower, wear a hard hat.
Lightning Ground antennas when not in use. Ground the tower structure itself. Ground rods should be copper or copper clad steel and 8 ft. long. Disconnect AC power mains during storms, or use line conditioners or surge suppressors. GET OFF THE AIR DURING SEVERE STORMS!!
117 Volt AC Outlet Ground Hot Neutral For safety and fire protection, each outlet in your home should be wired exactly this way. Match the colored wires to the colored screws on the outlet.
Multimeter (Analog) These meters will measure Voltage, Resistance and Current. The handiest piece of test equipment any ham could own.
Digital Multimeter These modern multimeters are easier to use and harder to break than older analog meters. The higher input impedance makes them more accurate. Many include extra features like diode and transistor test functions.
S - Meter The S-meter gives a relative signal strength reading of a received signal. No manufacturer claims their S-meters are calibrated. (Exception: FlexRadio Systems)
SWR Meter Measures transmitter output power and reflected power from the antenna system
Reflectometer The reflectometer is a fancy SWR meter showing forward power, reflected power and SWR all at once. They require no set up or calibration to use.
Dummy Load Use a dummy load to tune your transmitter. This is good practice as it reduces QRM and gives the transmitter a near perfect 50Ω load. Note: Dummy loads get hot.
Low-Pass Filter A low-pass filter goes between your transmitter and antenna. It removes harmonic radiation from your signals. Your neighbors’ TV sets will thank you.
What is considered to be a proper grounding method for a tower? A. A single four-foot ground rod, driven into the ground no more than 12 inches from the base B. A ferrite-core RF choke connected between the tower and ground C. Separate eight-foot long ground rods for each tower leg, bonded to the tower and each other D. A connection between the tower base and a cold water pipe
What reading on an SWR meter indicates a perfect impedance match between the antenna and the feedline? A. 2 to 1 B. 1 to 3 C. 1 to 1 D. 10 to 1
Where must a filter be installed to reduce harmonic emissions? A. Between the transmitter and the antenna B. Between the receiver and the transmitter C. At the station power supply D. At the microphone
What is connected to the green wire in a three- wire electrical AC plug? A. Neutral B. Hot C. Safety ground D. The white wire
Which of the following might damage a multimeter? A. Measuring a voltage too small for the chosen scale B. Leaving the meter in the milliamps position overnight C. Attempting to measure voltage when using the resistance setting D. Not allowing it to warm up properly
Electrical Principles A battery, a bulb and some wire… and a little math. Right is W4ZH Jeff Smith “Go Kit” Prototype in a Car/Truck
Units of Measurement HertzFrequency (cycles per second) VoltsElectromotive Force AmperesElectrical Current OhmsResistance (to current flow) FaradsCapacitance HenriesInductors Watts Power (the ‘work’ being done)
Ohms Law Ohms Law is applicable to all electrical circuits. Ohms Law is a mathematical expression of the relationship between Voltage (EMF), Current (the flow of electrons in a circuit), and Resistance (to current flow). Expressed as E = I x R
Voltage and Current? + - It is possible to have voltage without current, as in the case of a battery by itself. In order to have current, there must be an electrical path (circuit) from the positive to the negative terminal of the voltage source. A E I R
Ohms Law E IR Resistance to current flow (Ohms) The flow of electrons(Amperes) Electromotive Force (Volts)
Ohms Law A ohms 3 ohms 2 ohms 12 volts As we substitute the values shown, what happens to the current flow in the circuit? E/R = I 12/4 = 3 12/3 = 4 12/2 = 6
Power P IE ElectromotiveForce(Volts) The flow of electrons(Amperes) Energy Expended (Watts)
Volts, Amps and Watts A ohms 12 volts The current in this circuit = _________ Amps The power in this circuit = _________ Watts 3 36
System of Metric Units gigaG10 9 1,000,000,000 megaM10 6 1,000,000 kilok10 3 1,000 Basic Unit millim microµ nanon picop
Which is a commonly accepted value for the lowest voltage that can cause a dangerous electric shock? A. 12 volts B. 30 volts C. 120 volts D. 300 volts
If an ammeter calibrated in amperes is used to measure a 3000-milliampere current, what reading would it show? A amperes B. 0.3 amperes C. 3 amperes D. 3,000,000 amperes
Which of the following is a good electrical conductor? A.Glass B.Wood C.Copper D.Rubber
Which instrument would you use to measure electric potential or electromotive force? A. An ammeter B. A voltmeter C. A wavemeter D. An ohmmeter
Electrical power is measured in which of the following units? A.Volts B.Watts C.Ohms D.Amperes