D:\Edtech 2\Chapter34

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  • Examples of the different kinds of supplies would be helpful to illustrate the differences.
  • These are generally emergency or portable power sources.
  • Examples of the different kinds of batteries will help illustrate this point. Discuss how the different kinds of batteries are used.
  • Spend some time discussing how to get the most performance out of the HT (hold the HT vertical, speak across the mic, not into the mic, etc.) Also make sure that you cover that the rubber duck antenna actually has negative gain when compared to other antennas, that the trade-off for the convenience of a small, flexible antenna is reduced performance.
  • Point out that RFI can come from virtually any electronic device from overhead power lines, to electric can openers, to computers and TV sets.
  • Emphasize that filters can only attenuate the offending signal, they can not eliminate the signals. Discuss briefly the different kinds of filters and how they might be used. Have a high pass filter on hand that might be inserted into the feed line of a TV set to mitigate interfering signals and discuss how it might be installed.
  • Discuss briefly with the students these basic types of RFI, and how they might be able to distinguish between them. At the same time, discuss some techniques they might use to mitigate the effects of the interference. Direct detection usually affects consumer electronic devices (telephones and audio equipment). Can be mitigated by proper manufacture, installation, shielding, filters, ferrite bead chokes, etc. Actually very hard to deal with and generally not the fault of the ham radio operator, but try to convince your neighbor of that who just spent hundreds of dollars on their new equipment. Overload – generally is a problem in fringe reception areas of TV signals. Not as much a problem now days with satellite and cable TV. Usually the problem can be mitigated by reducing transmitter power or filtering. Harmonics – generally are a symptom of poor transmitter design or operation.
  • Discuss with the students other sources of interfering noise and give them techniques on how to seek out the source of the noise. In many cases of the fixed noise, simply turning off the potentially offending appliance will help identify the source. Power line noise mitigation is the responsibility of the power company. Motor vehicle noise is generally short lived unless it is coming from the hams vehicle. Grounding and filtering in many of these cases will mitigate the noise.
  • Discuss with the students that though the law is probably on their side, their neighbors will not understand that and they will hold the ham responsible for the interference. It takes diplomacy to deal with RFI complaints!!!!!
  • D:\Edtech 2\Chapter34

    1. 1. Power Supplies and Batteries Handheld Transceivers RF Interference (RFI)
    2. 2. Power Supplies <ul><li>Most modern radio equipment runs from 12 volts dc. </li></ul><ul><li>Household current is 120 volts ac. </li></ul><ul><li>Power supplies convert 120 volts ac to 12 volts dc. </li></ul><ul><ul><li>13.8 volts dc is the common voltage you will see. </li></ul></ul><ul><ul><li>This is the charging voltage for motorized vehicles. </li></ul></ul>
    3. 3. Power Supply Ratings Voltage and Current <ul><li>Continuous duty – how much current can be supplied over the long term. </li></ul><ul><li>Intermittent duty – how much surge current can be supplied over the short term. </li></ul><ul><li>Regulation – how well the power supply can handle rapid current changes. </li></ul>
    4. 4. Types of Power Supplies <ul><li>Linear: </li></ul><ul><ul><li>Transformers </li></ul></ul><ul><ul><li>Heavy (physically) </li></ul></ul><ul><ul><li>Heavy duty current </li></ul></ul><ul><ul><li>Expensive </li></ul></ul><ul><li>Switching: </li></ul><ul><ul><li>Electronics instead of transformers </li></ul></ul><ul><ul><li>Light weight and small </li></ul></ul><ul><ul><li>Not as robust </li></ul></ul><ul><ul><li>Less expensive </li></ul></ul>25 amp.Radio shack Switching type. About $70.00 A good reason for using a regulated power supply for communications equipment is to protect equipment from voltage fluctuations. Astron 15A linear low profile power supply, 15A ICS 12A continuous $116.00
    5. 5. Inverters and Generators <ul><li>Inverters convert dc into ac. </li></ul><ul><ul><li>Square, triangle, sine-wave inverters. </li></ul></ul><ul><li>Generators create ac. </li></ul><ul><ul><li>Gas powered. </li></ul></ul><ul><ul><li>Various voltage and current ratings. </li></ul></ul><ul><ul><li>Special precautions. </li></ul></ul>
    6. 6. Aims 300 watt Pure sine Power inverter $134.00 Modified sine inverters fall into the following four groups: 300 watts ($40-$60): For household appliances, TVs (up to 27&quot;), VCR, desktop computers, other mobile office equipment. Most of these connect via a 12-Volt plug. 600 watts ($100-$120): For household appliances, large screen TVs, 5-amp power tools, and bread machines. Most such inverters are connected directly to the 12-volt battery and have three or more grounded outlets for powering several products at the same time. 1750 watts ($199-$380): For household appliances, larger power tools, microwave ovens, toasters, and hair dryers. All of theses inverters are designed for direct connection to the battery network and can generally supply 1500 watts of continuous power. 3000 watts ($395-$750): With output power generally rated at 2500 watts for continuous load, these inverters can power virtually all household appliances and office equipment. For loads of this magnitude, special wiring and battery banks. a few devices which could have problems when they are connected to an inverter producing a modified-sine wave signal: oxygen concentrators, fax machines, laser printers, high voltage cordless tool chargers, equipment with variable speed motors, electric shavers, Large screen Plasma TV and garage door openers. Modified Sine AIMS 400 Watt Power Inverter with cable 12 volt Only $ 34.00
    7. 7. Batteries <ul><li>Create current through a chemical reaction. </li></ul><ul><ul><li>Made up of individual cells (approximately 1.5 volts per cell) connected in series or parallel. </li></ul></ul><ul><li>Battery types. </li></ul><ul><ul><li>Disposable. </li></ul></ul><ul><ul><li>Rechargeable. </li></ul></ul><ul><ul><li>Storage. </li></ul></ul><ul><li>Power capabilities rated in Ampere-hours. </li></ul><ul><ul><li>Amps X time. </li></ul></ul>
    8. 8. On the large deep cycle battery, they are rated at how many amps for 20 hours. A 120AH battery will do 120/20 or 6 Amps for 20 hours. <ul><li>Carbon-Zinc & Alkaline </li></ul><ul><ul><ul><li>Typically 1.5 volts or 9 volts per cell </li></ul></ul></ul><ul><ul><ul><li>Not rechargeable </li></ul></ul></ul><ul><li>Nickel-Cadmium (NiCd) </li></ul><ul><ul><ul><li>Typically 1.2 volts per cell </li></ul></ul></ul><ul><ul><ul><li>Rechargeable </li></ul></ul></ul><ul><li>Nickel-Metal Hydride (NiMH) </li></ul><ul><ul><ul><li>Typically 1.2 volts per cell </li></ul></ul></ul><ul><ul><ul><li>Rechargeable </li></ul></ul></ul><ul><li>Lithium Ion </li></ul><ul><ul><ul><li>Typically 3.3 – 3.6 volts per cell </li></ul></ul></ul><ul><ul><ul><li>Rechargeable </li></ul></ul></ul><ul><ul><ul><li>Longest life by size of any of these batteries </li></ul></ul></ul>
    9. 9. Battery Charging <ul><li>Some batteries can be recharged, some cannot. </li></ul><ul><li>Use the proper charger for the battery being charged. </li></ul><ul><li>Batteries will wear out over time. </li></ul><ul><li>Best if batteries are maintained fully charged. </li></ul><ul><ul><li>Over-charging will cause heating and could damage the battery. </li></ul></ul><ul><li>Some batteries (lead-acid) will release toxic fumes during charging so require ventilation. </li></ul>
    10. 10. Handheld Transceivers <ul><li>Single, dual and multi-band versions (with increasing cost and complexity). </li></ul><ul><ul><li>Some have expanded receiver coverage (wide-band receive). </li></ul></ul><ul><li>Very portable and self-contained. </li></ul><ul><ul><li>Internal microphone and speaker. </li></ul></ul><ul><ul><li>Rubber duck antenna. </li></ul></ul><ul><ul><li>Battery powered. </li></ul></ul>
    11. 11. What type of control is being used when transmitting using a handheld radio? D. Local control
    12. 12. If you are going into an emergency area, carry: <ul><li>Extra battery packs. </li></ul><ul><li>Drop-in, fast charger. </li></ul><ul><li>Extended antenna. </li></ul><ul><li>External microphone and speaker. </li></ul><ul><li>Headset. </li></ul>
    13. 13. Radio Frequency Interference (RFI) <ul><li>Unwanted, unintentional signals from some electronic device that interferes with radio wave reception. </li></ul><ul><li>You can prevent creating RFI by operating your transmitting equipment properly. </li></ul>What should you do if you receive a report that your transmissions are causing splatter or interference on nearby frequencies? D. Check transmitter for off frequency operation or spurious emissions
    14. 14. Who is responsible for taking care of the interference if signals from your transmitter are causing front end overload in your neighbor's television receiver? D. The owner of the television receiver is responsible What is the major cause of telephone interference? C. The telephone was not equipped with adequate interference protection when manufactured.
    15. 15. RFI Mitigation Filters -attenuate (reduce) interfering signals – but do not totally eliminate them. High-pass –generally on the receive side. Low-pass – generally on the transmit side. Band-pass – used within most radio equipment. Phone RF filter Snap-on ferrite Chokes may be attached to speaker wires, telephone wires, AC line cords Where must a filter be installed to reduce spurious emissions? A. At the transmitter
    16. 16. Low Pass Filter Reduces harmonic radiation Band Pass Filter Blocks RF above and below a certain frequency a filter that passes all frequencies except those in a stop band centered on a center frequency Notch Filter What type of filter should be connected to a TV receiver as the first step in trying to prevent RF overload from a nearby 2-meter transmitter? D. Notch filter
    17. 17. Types of RFI <ul><li>Direct detection – offending signals get into the electronics circuits to cause interference. </li></ul><ul><li>Overload – strong signal that overwhelms the weaker, wanted signal. </li></ul><ul><li>Harmonics – even multiples of the offending signal that coincide with the wanted signal. </li></ul>It is exactly two, or three, or more times the desired frequency
    18. 18. Cable TV Interference <ul><li>Usually the result of broken shielding somewhere in the cable. </li></ul><ul><ul><li>Loose connections. </li></ul></ul><ul><ul><li>Broken connections. </li></ul></ul><ul><ul><li>Corroded connections. </li></ul></ul><ul><li>Usually solved by proper cable maintenance by cable supplier. </li></ul><ul><ul><li>If the subscriber is a legitimate subscriber. </li></ul></ul>What effect might a break in a cable television transmission line have on amateur communications? C. TV interference may result when the amateur station is transmitting, or interference may occur to the amateur receiver
    19. 19. Noise Sources <ul><li>Electrical arcs (motors, thermostats, electric fences, neon signs). </li></ul><ul><li>Power lines. </li></ul><ul><li>Motor vehicle ignitions. </li></ul><ul><li>Motor vehicle alternators. </li></ul><ul><ul><li>If another operator tells you he is hearing a variable high-pitched whine on the signals from your mobile transmitter, the power wiring for your radio could be picking up noise from the vehicle's electrical system. </li></ul></ul><ul><li>Switching power supplies. </li></ul><ul><li>Computers, networks, and TV sets. </li></ul>Doppler shift is NOT a cause of radio frequency interference. Ignition noise in car…Turn on noise blanker on radio
    20. 20. Dealing with RFI <ul><li>Make sure you operate your equipment properly. </li></ul><ul><li>Eliminate interference in your own home first. </li></ul>
    21. 21. Dealing with RFI <ul><li>Take interference complaints seriously. </li></ul><ul><li>Make sure that you’re really not the cause (demonstrate that you don’t interfere within your own home). </li></ul><ul><li>Offer to help eliminate the RFI, even if you are not at fault. </li></ul><ul><li>Consult ARRL RFI Resources for help and assistance. </li></ul>
    22. 22. <ul><li>For RFI to an amateur station you can use direction finding techniques to locate the noise and, hopefully, eliminate it. </li></ul><ul><li>If it's a “Part 15” device in your neighbours home you can: </li></ul><ul><ul><ul><li>Work with your neighbour to identify the device </li></ul></ul></ul><ul><ul><ul><li>Politely inform your neighbour about the rules </li></ul></ul></ul><ul><ul><ul><li>Check your station </li></ul></ul></ul><ul><ul><li>Radio direction finding is a method used to locate sources of noise interference or jamming. </li></ul></ul>A directional antenna would be the most useful for a hidden transmitter hunt.
    23. 23. What the Rules Say <ul><li>RFI from and to unlicensed devices is the responsibility of the users of such devices </li></ul><ul><li>Bottom line – If your station is operating properly, you are protected against interference complaints </li></ul><ul><li>BUT – Be a good neighbor because they may (probably) not be familiar with Part 15 rules and regulations </li></ul>
    24. 25. What are the three types of station control permitted and recognized by FCC rule? A. Local, remote and automatic control B. Local, distant and automatic control C. Remote, distant and unauthorized control D. All of the choices are correct Who is accountable if a repeater station inadvertently retransmits communications that violate FCC rules? A. The repeater trustee B. The repeater control operator C. The transmitting station D. All of these answers are correct What is one way to select a frequency on which to operate? A. Use the keypad or VFO knob to enter the correct frequency B. Turn on the CTCSS encoder C. Adjust the power supply ripple frequency D. All of these answers are correct On these questions; all of the above is not correct.
    25. 26. The following may be useful in correcting a radio frequency interference problem: Snap-on ferrite chokes Low-pass and high-pass filters Notch and band-pass filters All of these answers are correct <ul><ul><ul><li>Work with your neighbor to identify the offending device </li></ul></ul></ul><ul><ul><ul><li>Politely inform your neighbor about the rules that require him to stop using the device if it causes interference </li></ul></ul></ul><ul><ul><ul><li>Check your station and make sure it meets the standards of good amateur practice </li></ul></ul></ul><ul><li>All of these answers are correct </li></ul><ul><li>What are the penalties for making a false emergency call? </li></ul><ul><li>You could have your license revoked </li></ul><ul><li>You could be fined a large sum of money </li></ul><ul><li>You could be sent to prison </li></ul><ul><li>All of these answers are correct </li></ul>
    26. 27. What is a good way to guard against electrical shock at your station? A. Use 3-wire cords and plugs for all AC powered equipment B. Connect all AC powered station equipment to a common ground C. Use a ground-fault interrupter at each electrical outlet D. All of these answers are correct What precautions should be taken when a lightning storm is expected? A. Disconnect the antenna cables from your station and move them away from your radio equipment B. Unplug all power cords from AC outlets C. Stop using your radio equipment and move to another room until the storm passes D. All of these answers are correct What kind of hazard is presented by a conventional 12-volt storage battery? A. It contains dangerous acid that can spill and cause injury B. Short circuits can damage wiring and possibly cause a fire C. Explosive gas can collect if not properly vented D. All of these answers are correct
    27. 28. What factors affect the RF exposure of people near an amateur transmitter? A. Frequency and power level of the RF field B. Distance from the antenna to a person C. Radiation pattern of the antenna D. All of these answers are correct How can you determine that your station complies with FCC RF exposure regulations? A. By calculation based on FCC OET Bulletin 65 B. By calculation based on computer modeling C. By measurement of field strength using calibrated equipment D. All of these choices are correct What action might amateur operators take to prevent exposure to RF radiation in excess of FCC supplied limits? A. Alter antenna patterns B. Relocate antennas C. Change station parameters such as frequency or power D. All of these answers are correct

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