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By Joe Seibert AL1F

Bandwidth & Interference. By Joe Seibert AL1F. What is bandwidth?. Bandwidth is the amount of radio spectrum a signal occupies. Why is bandwidth important? Hams have a limited amount of bandwidth to use and we must avoid interfering with each other.

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By Joe Seibert AL1F

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  1. Bandwidth & Interference By Joe Seibert AL1F

  2. What is bandwidth? • Bandwidth is the amount of radio spectrum a signal occupies. • Why is bandwidth important? • Hams have a limited amount of bandwidth to use and we must avoid interfering with each other.

  3. Different modes of operation utilize different bandwidths. • Example: • CW- 20 Hz (Continuous Wave = Morse Code) • PSK 31- 31 Hz (digital) • RTTY- 250 Hz (digital) • SSB- 2-3 KHz (single sideband telephony) • FM (N)-5 KHz (telephony) • FM (W)- 15 KHz (telephony) • SCTV- 2.5 MHz (Image) • FSTV- 6 MHz (Image)

  4. SSB Signal 2 - 3 kHz wide FM Signal 5 - 15 kHz wide UHF Fast-Scan TV ~ 6 MHz Bandwidth

  5. Example of limited space… • 2 meter band = 144-48 MHz, or 4 MHz bandwidth • A n FM repeater requires an input & output frequency. Each signal is FM and occupies 15 KHz of space for a total of 30KHz/repeater. • You can fit 12 repeaters in the 4 MHz bandwidth allotted to ham radio. But the band plan does not allow repeaters over the entire 4 MHz bandwidth!

  6. Bandplan- A general agreement of what modes will be used in certain portions of each band. • Each band has a specific bandplan that helps us avoid interfering with each other. And make the best use of the available spectrum. Generally the lower portion of the band is designated for CW & data, the upper portion for phone and image communications. • Example- 20 meter band = 14.000 to 14.350 MHz, or a 350 KHz bandwidth. • 20 meter Bandplan= • 14.000 – 14.150= CW & data • 14.150 – 14.350= phone & image

  7. ARRL 10 Meter Bandplan (28-29.7 MHz):28.000-28.070 CW28.070-28.150 RTTY28.150-28.190 CW28.200-28.300 Beacons28.300-29.300 Phone28.680 SSTV29.000-29.200 AM29.300-29.510 Satellite Downlinks29.520-29.590 Repeater Inputs29.600 FM Simplex29.610-29.700 Repeater Outputs

  8. Two Common Types of Modulation • AM- amplitude- the amplitude of the signal varies up and down • FM- frequency- the amplitude stays the same but the frequency varies

  9. Amplitude Modulation An unmodulated RF carrier requires narrow Bandwidth (on and off is CW) Modulation of the carrier creates sidebands. This requires more bandwidth. Transmitter power is spread across this bandwidth

  10. AM and SSB The carrier contains no audio information. The sidebands contain duplicate audio information By filtering out the carrier and one sideband, we save spectrum and concentrate our RF energy into a narrower bandwidth. SSB is therefore more efficient.

  11. INTERFEENCE • Recognition and correction of problems • A logical first step when attempting to cure a radio frequency interference problem in a nearby telephone is to install an RF filter at the telephone. • The most likely cause of telephone interference from a nearby transmitter is the transmitter's signals are causing the telephone to act like a radio receiver. • 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

  12. Recognition and correction of problems • If someone tells you that your transmissions are interfering with their TV reception: • First make sure that your station is operating properly and; • That it does not cause interference to your own television. • When a neighbor reports that your radio signals are interfering with something in his home: • The proper course of action to take is to check your station and make sure it meets the standards of good amateur practice.

  13. Recognition and correction of problems • The most likely cause of telephone interference from a nearby transmitter is the transmitter's signals are causing the telephone to act like a radio receiver. • If someone tells you that your transmissions are interfering with their TV reception you should first make sure that your station is operating properly and that it does not cause interference to your own television. • The following may be useful in correcting a radio frequency interference problem: (you’ve seen these before) • Snap-on ferrite chokes • Low-pass and high-pass filters • Notch and band-pass filters All of these answers are correct

  14. Recognition and correction of problems(cont) • If a "Part 15" device in your neighbor’s home is causing harmful interference…..

  15. Recognition and correction of problems • When a neighbor reports that your radio signals are interfering with something in his home the proper course of action to take is to check your station and make sure it meets the standards of good amateur practice. • A logical first step when attempting to cure a radio frequency interference problem in a nearby telephone is to install an RF filter at the telephone. • If a "Part 15" device in your neighbor’s home is causing harmful interference to your amateur station you should: • Work with your neighbor to identify the offending device • Politely inform your neighbor about the rules that require him to stop using the device if it causes interference • Check your station and make sure it meets the standards of good amateur practice All of these answers are correct

  16. Fundamental overload • Symptoms of overload and overdrive • A fundamental overload, in reference to a receiver, is interference caused by very strong signals from a nearby source. • Receiver front-end overload is the result of interference caused by strong signals from a nearby source.

  17. Distortion • If you receive a report that your signal through the repeater is distorted or weak, the problem may be any of the following: Your transmitter may be slightly off frequency Your batteries may be running low You could be in a bad location

  18. Bandwidth and Interference Questions

  19. Which emission type has the narrowest bandwidth? • FM voice • SSB voice • CW • Slow-scan TV

  20. Which emission type has the narrowest bandwidth? C. CW

  21. What are phone transmissions? • The use of telephones to set up an amateur radio contact • A phone patch between amateur radio and the telephone system • Voice transmissions by radio • Placing the telephone handset near a radio transceiver's microphone and speaker to relay a telephone call

  22. What are phone transmissions? C. Voice transmissions by radio

  23. Which type of modulation is most commonly used for VHF and UHF voice repeaters? • AM • SSB • PSK • FM

  24. Which type of modulation is most commonly used for VHF and UHF voice repeaters? D. FM

  25. What is the approximate bandwidth of a frequency-modulated voice signal? • Less than 500 Hz • About 150 kHz • Between 5 and 15 kHz • More than 30 kHz

  26. What is the approximate bandwidth of a frequency-modulated voice signal? C. Between 5 and 15 kHz

  27. What is the normal bandwidth required for a conventional fast-scan TV transmission using combined video and audio on the 70-centimeter band? • More than 10 MHz • About 6 MHz • About 3 MHz • About 1 MHz

  28. What is the normal bandwidth required for a conventional fast-scan TV transmission using combined video and audio on the 70-centimeter band? B. About 6 MHz

  29. What type of signal is indicated by the term NTSC? • A. Normal Transmission Mode in a Static Circuit • B. Never Twice the Same Color • C. Standard fast scan color TV signal • D. A frame compression scheme for TV signals

  30. What type of signal is indicated by the term NTSC? • C. A standard fast scan color TV signal

  31. Which of the following is a form of amplitude modulation? • Frequency modulation • Phase modulation • Single sideband • Phase shift keying

  32. Which of the following is a form of amplitude modulation? C. Single sideband

  33. What is the approximate bandwidth of a single-sideband voice signal? • 1 kHz • 2 kHz • Between 3 and 6 kHz • Between 2 and 3 kHz

  34. What is the approximate bandwidth of a single-sideband voice signal? D. Between 2 and 3 kHz

  35. What is the primary advantage of single sideband over FM for voice transmissions? • SSB signals are easier to tune in than FM signals • SSB signals are less likely to be bothered by noise interference than FM signals. • SSB signals use much less bandwidth than FM signals • SSB signals have no advantages at all in comparison to other modes.

  36. What is the primary advantage of single sideband over FM for voice transmissions? C. SSB signals use much less bandwidth than FM signals

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