By Joe Seibert AL1F

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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. - PowerPoint PPT Presentation

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  • Bandwidth & Interference

  • 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.

  • 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)

  • Bandwidth

  • Example of limited space2 meter band = 144-48 MHz, or 4 MHz bandwidthA 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!

  • 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 & data14.150 14.350= phone & image

  • 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

  • Two Common Types of ModulationAM- amplitude- the amplitude of the signal varies up and downFM- frequency- the amplitude stays the same but the frequency varies

  • *Amplitude ModulationAn unmodulated RFcarrier requires narrowBandwidthModulation of the carriercreates sidebands. Thisrequires more bandwidth.Transmitter power is spread across this bandwidth(on and off is CW)

  • *AM and SSBThe carrier contains noaudio information.

    The sidebands containduplicate audio informationBy filtering out the carrier and one sideband, we save spectrum and concentrate our RF energy into a narrower bandwidth. SSB is therefore more efficient.

  • *INTERFEENCE Recognition and correction of problemsA 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

  • * 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.

  • * 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: (youve seen these before)Snap-on ferrite chokesLow-pass and high-pass filtersNotch and band-pass filtersAll of these answers are correct

  • * Recognition and correction of problems (cont)

    If a "Part 15" device in your neighbors home is causing harmful interference..

  • * 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 neighbors home is causing harmful interference to your amateur station you should:Work with your neighbor to identify the offending devicePolitely inform your neighbor about the rules that require him to stop using the device if it causes interferenceCheck your station and make sure it meets the standards of good amateur practiceAll of these answers are correct

  • * Fundamental overloadSymptoms 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.

  • * DistortionIf 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

  • Bandwidth and Interference Questions

  • *Which emission type has the narrowest bandwidth?FM voiceSSB voiceCWSlow-scan TV

  • *Which emission type has the narrowest bandwidth?

    C. CW

  • *What are phone transmissions?The use of telephones to set up an amateur radio contactA phone patch between amateur radio and the telephone systemVoice transmissions by radioPlacing the telephone handset near a radio transceiver's microphone and speaker to relay a telephone call

  • *What are phone transmissions?

    C. Voice transmissions by radio

  • * Which type of modulation is most commonly used for VHF and UHF voice repeaters?

    AMSSBPSKFM

  • * Which type of modulation is most commonly used for VHF and UHF voice repeaters?

    D. FM

  • * What is the approximate bandwidth of a frequency-modulated voice signal?Less than 500 Hz About 150 kHzBetween 5 and 15 kHzMore than 30 kHz

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

  • * 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 MHzAbout 6 MHzAbout 3 MHzAbout 1 MHz

  • * 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

  • What type of signal is indicated by the term NTSC?A. Normal Transmission Mode in a Static CircuitB. Never Twice the Same ColorC. Standard fast scan color TV signalD. A frame compression scheme for TV signals

  • What type of signal is indicated by the term NTSC?

    C. A standard fast scan color TV signal

  • *Which of the following is a form of amplitude modulation? Frequency modulationPhase modulationSingle sidebandPhase shift keying

  • *Which of the following is a form of amplitude modulation?

    C. Single sideband

  • *What is the approximate bandwidth of a single-sideband voice signal?1 kHz2 kHzBetween 3 and 6 kHzBetween 2 and 3 kHz

  • *What is the approximate bandwidth of a single-sideband voice signal?

    D. Between 2 and 3 kHz

  • * 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 signalsSSB signals have no advantages at all in comparison to other modes.

  • * What is the primary advantage of single sideband over FM for voice transmissions?

    C. SSB signals use much less bandwidth than FM signals

  • This is the appearance of an AM signal on a spectrum scope. There is a carrier in the center that uses power but contains no information (it can be used for tuning). Each of the two sidebands (upper and lower) are identical but inverted. HF amateur communications are generally on a single sideband (SSB) by suppressing the carrier and opposite sideband. This is more efficient by using less bandwidth and power is not wasted transmitting a dead carrier and duplicate sideband.

    Because of radio design simplicity, the convention has been to use lower sideband (LSB) below 14 MHz and upper sideband (USB) above 14 MHz.