Presented by Heart Of Texas Amateur Radio Club (HOTARC)

1. Technician License ClassGordon West Technician Class ManualPages 132-141Bandwidth & Interference Presented by Heart Of Texas Amateur Radio Club (HOTARC)

2. Bandwidth and Types of Modulation • See pages 132 – 135… • Key words: • CW, phone, FM, fast-scan TV • Single sideband • First, let’s look at the big picture… Bandwidth & Interference

3. CW: 5-10 Hz Digital PSK31: 31 Hz RTTY: 250 Hz Phone (Voice) SSB: 2-3 kHz AM: 4-6 kHz FM: 5-15 kHz Slow Scan TV:3 kHz Fast Scan TV: FM: Over twice SSB Common Signal Bandwidths 6 MHz !! Bandwidth & Interference

4. T6 A06 (pg 132) • Which emission type has the narrowest bandwidth? • FM voice • SSB voice • CW • Slow-scan TV Bandwidth & Interference

5. T6A01 (pg 132) 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 Bandwidth & Interference

6. T6 A05 (pg 132) • Which type of modulation is most commonly used for VHF and UHF voice repeaters? • AM • SSB • PSK • FM Think of the quiet quality of “FM broadcast radio.” We mainly use SSB (narrower) on the HF bands, where the spectrum is so “precious.” Bandwidth & Interference

7. T6 A10 (pg 132) • 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 Again, think of FM signals as over twice the width of SSB (which is 2-3 kHz). 2 × 2.5 kHz = 5 kHz Bandwidth & Interference

8. T6 A11 (pg 133) • 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 Not just 6 kHz, but6000 kHz!! Bandwidth & Interference

9. T6 C04 (pg 133) • What type of transmission is indicated by the term NTSC? • A Normal Transmission mode in Static Circuit • A special mode for earth satellite uplink • A standard fast scan color television signal • A frame compression scheme for TV signal Just remember that NTSC is what we all grew up watching! Today’s kids will only know digital TV! Bandwidth & Interference

10. T6 A02 (pg 134) • Which of the following is a form of amplitude modulation? • Frequency modulation • Phase modulation • Single sideband • Phase shift keying Remember that SSB is just half of an AM signal (amplitude modulation). Bandwidth & Interference

11. T6 A09 (pg 135) • 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 Have you got it yet? A SSB signal is about 3 kHz wide. Bandwidth & Interference

12. T6 A08 (pg 135) • 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. Bandwidth & Interference

13. Interference: A Very Dirty Word! • See pages 135 – 141… • Key words: • Interference! • Your station • Your neighbors • Telephones are often poorly designed • Strong signals Bandwidth & Interference

14. T3 D07 (pg 135) • What effect might a break in a cable television transmission line have on amateur communications? • A break cannot affect amateur communications • Harmonic radiation from the TV may cause the amateur transmitter to transmit off-frequency • TV interference may result when the amateur station is transmitting, or interference may occur to the amateur receiver • The broken cable may pick up very high voltages when the amateur station is transmitting Think of it as a “leak”—unwanted signals either leak out or leak in. Bandwidth & Interference

15. T5 D08 (pg 136) • What is the proper course of action to take when a neighbor reports that your radio signals are interfering with something in his home? • You are not required to do anything • Contact the FCC to see if other interference reports have been filed • Check your station and make sure it meets the standards of good amateur practice • Change your antenna polarization from vertical to horizontal Bandwidth & Interference

16. T5 D05 (pg 136) • What should you do first if someone tells you that your transmissions are interfering with their TV reception? • Make sure that your station is operating properly and that it does not cause interference to your own television • Immediately turn off your transmitter and contact the nearest FCC office for assistance • Tell them that your license gives you the right to trans-mit and nothing can be done to reduce the interference • Continue operating normally because your equipment cannot possibly cause any interference Bandwidth & Interference

17. T3 D02 (pg 137) • 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? • You alone are responsible, since your transmitter is causing the problem • Both you and the owner of the television receiver share the responsibility • The FCC must decide if you or the owner of the television receiver is responsible • The owner of the television receiver is responsible Note Gordon’s comments on this question. Bandwidth & Interference

18. T5 D09 (pg 137) • What should you do if a "Part 15" device in your neighbor’s home is causing harmful interference to your amateur station? • 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 Bandwidth & Interference

19. Low Pass 0 dB -3 dB Pass Band Stop Band 40 dB fc Frequency High Pass 0 dB -3 dB Stop Band Pass Band 40 dB fc Frequency Low Pass, High Pass Filters Bandwidth & Interference

20. 0 dB -3 dB Stop Band Pass Band Stop Band 40 dB Low Frequency fc fc High Frequency Band Pass Filter Bandwidth & Interference

21. 0 dB -3 dB Pass Band Stop Band Pass Band 40 dB Want to “stop” (be deaf to) nearby transmitter on this frequency fc fc Low Frequency High Frequency Notch (Band Stop) Filter Repeaters use cavity notch filters that have very sharp skirts to keep the transmitter from interfering with the receiver, since they’re both active at the same time on very close frequencies. Bandwidth & Interference

22. T5 A07 (pg 137) • 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? • Low-pass filter • High-pass filter • Band pass filter • Notch filter Just like those notch filters used for repeaters, this sends the unwanted frequencies to ground. Note Gordon’s caution on pg 138. Bandwidth & Interference

23. Poorly designed? T3 D03 (pg 138) • What is the major cause of telephone interference? • The telephone wiring is inadequate • Tropospheric ducting at UHF frequencies • The telephone was not equipped with adequate interference protection when manufactured. • Improper location of the telephone in the home Bandwidth & Interference

24. Poorly designed? T5 D03 (pg 138) • What is the most likely cause of telephone interference from a nearby transmitter? • Harmonics from the transmitter • The transmitter's signals are causing the telephone to act like a radio receiver • Poor station grounding • Improper transmitter adjustment Bandwidth & Interference

25. Poorly designed? T5 D04 (pg 138) • What is a logical first step when attempting to cure a radio frequency interference problem in a nearby telephone? • Install a low-pass filter at the transmitter • Install a high-pass filter at the transmitter • Install an RF filter at the telephone • Improve station grounding Bandwidth & Interference

26. Telephone Filter These filters are only effective if the signal is coming through the phone line. If it is being picked up by the telephone’s circuitry directly, there is no filter that can remove it. Bandwidth & Interference

27. T5 D07 (pg139) • Which of 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 The FCC likes filters, filters, filters! Bandwidth & Interference

28. T5 D02 (pg 139) • Which of the following is NOT a cause of radio frequency interference? • Fundamental overload • Doppler shift • Spurious emissions • Harmonics Bandwidth & Interference

29. T5 D10 (pg 139) • What could be happening if another operator tells you he is hearing a variable high-pitched whine on the signals from your mobile transmitter? • Your microphone is picking up noise from an open window • You have the volume on your receiver set too high • You need to adjust your squelch control • The power wiring for your radio is picking up noise from the vehicle's electrical system Bandwidth & Interference

30. T9 B03 (pg 140) • What is the most likely cause of sudden bursts of tones or fragments of different conversations that interfere with VHF or UHF signals? • The batteries in your transceiver are failing • Strong signals are overloading the receiver and causing undesired signals to be heard • The receiver is picking up low orbit satellites • A nearby broadcast station is having transmitter problems Bandwidth & Interference

31. T3 D11 (pg 140) • What is meant by receiver front-end overload? • Too much voltage from the power supply • Too much current from the power supply • Interference caused by strong signals from a nearby source • Interference caused by turning the volume up too high Bandwidth & Interference

32. T5 D01 (pg 140) • What is meant by fundamental overload in reference to a receiver? • Too much voltage from the power supply • Too much current from the power supply • Interference caused by very strong signals from a nearby source • Interference caused by turning the volume up too high Bandwidth & Interference

33. T3 D01 (pg 140) • What should you do if you receive a report that your transmissions are causing splatter or interference on nearby frequencies? • Increase transmit power • Change mode of transmission • Report the interference to the equipment manufacturer • Check transmitter for off frequency operation or spurious emissions Bandwidth & Interference

34. T5 A06 (pg 141) • Where must a filter be installed to reduce spurious emissions? • At the transmitter • At the receiver • At the station power supply • At the microphone Bandwidth & Interference

35. T7 A05 (pg 141) • What is a method used to locate sources of noise interference or jamming? • Echolocation • Doppler radar • Radio direction finding • Phase locking Also known as “RDF.” We stage “fox hunts” to practice this skill. Bandwidth & Interference