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Special Modes and Techniques

Special Modes and Techniques. Chapter 4 Section 6. Extending Communication Range with Satellites. Higher VHF and UHF frequencies pass through the atmosphere without bouncing This makes them suitable for satellite contact

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Special Modes and Techniques

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  1. Special Modes and Techniques Chapter 4 Section 6

  2. Extending Communication Range with Satellites • Higher VHF and UHF frequencies pass through the atmosphere without bouncing • This makes them suitable for satellite contact • You can use satellites like repeaters to talk to amateurs in other countries (T7B03) • Any amateur who’s license allows them to transmit on the satellites uplink frequency may use the satellite (T7B01) • The group that has coordinated the building and launching of the largest number of amateur satellites is AMSAT (T7B08) • Many amateur satellites are called LEOs which stands for Low Earth Orbit (T7B11)

  3. Satellite Frequencies • Band plans designate certain frequencies for satellite communication • The Satellite Sub-band is the portion of the band where satellite operations are permitted (T7B09) • The Satellite Sub-band for 70 cm is 435-438 mghrtz (T7B10)

  4. Special Satellite Problems • Satellites are moving fast over the horizon • One impact of moving is Doppler Shift • A Doppler Shift is a change in signal frequency caused by movement through space (T7B07) • Most common example is change in sound of a train’s horn as it is coming and then passes • Problem is that frequency to contact a satellite may not be the exact frequency it is suppose to uplink on • Satellites send out Beacon Messages • A satellite beacon is a signal then carries information about a satellite (T7B05) • To determine when you can contact a satellite use a satellite tracking program (T7B06) • As always when contacting a satellite you should use the minimum power needed to make the contact (T7B02)

  5. Other Spacey Activities • Amateur Radio can be used to contact the international space station • Most of the time one or more of the astronauts are amateur operators • Have to use programs to know when it will pass over • Many people also use directional tracking antennas to confirm when range is just right • Any amateur with a technician or higher class license can call the space station (T7B04)

  6. Up in the Air About Other Things • Radio controlled model planes use amateur radio frequencies • To legally run them you need an amateur radio license • The transmitter must be labeled with the licenses call sign and address (T7A12) • The maximum amount of power allowed in transmitting control commands is 1 watt (T7A11)

  7. Special Events and Contests • Amateur radio may support a local event • River to River relay run • Parades • A special event station is a temporary station that operates in conjunction with an event of special significance (T7A10) • Often get a special event call sign to be used in conjunction with the event. • They have contests to see who can contact the most stations in a given period of time • An activity that involves contacting as many stations as possible is contesting (T7A07)

  8. Fox Hunts • Have a hidden transmitter or station and people have contest to see who can track it down first • A directional antenna is the most useful device for finding a hidden transmitter (T7A06) • Signal is strongest when you are aiming at the target • If you get a direction from several positions the lines will cross at the transmitter location • The method of radio direction finding can be used to locate sources of noise, interference or jamming (T7A05) • People who pull stunts on amateur radio often don’t fully realize that amateurs guard their privileges and often know how to track down violators

  9. Where its At • Operators may send out a signal with their location along with transmissions • APRS stands for Automatic Position Reporting System (T6C02) • Works on 144.39 Mghrtz • You need a global positioning system receiver in addition to your radio to send out a location report (T6C03)

  10. Digital Communication • Oldest form is Morse Code – simple, requires only operator skill, and telegraph key, get through interference and noise when voice can’t • One of the reasons to use digital communication instead of analog to communicate with another station is because many digital methods automatically correct for errors caused by noise or interference (T5D13) • Packet Radio is an example of a digital communication method (T6C01)

  11. Digital Modes • PSK31 is a low speed data transmission mode that works well under noisy conditions (T6C07) • PSK stands for Phase Shift Keying (T6C06)

  12. Efficient Use of Spectrum • Radio voice communication on FM uses about 15 khrtz • Digital transmissions can be in the 3 khrtz range • Contrast with Analog Television Station • NTSC refers to the US standard fast scan color television signal (T6C04) • The Normal Bandwidth for a conventional fast scan television transmission is 6 Mhrtz (T6A11) • That is 150% the size of the whole 2 meter amateur band

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