Technician License Class Gordon West Technician Class Manual Pages Bandwidth & Interference Presented by Heart Of Texas Amateur Radio Club (HOTARC)

Bandwidth & Interference 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 Common Signal Bandwidths 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: 6 MHz !! FM: Over twice SSB

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

Bandwidth & Interference 5 T6A01 (pg 132) What are phone transmissions? A.The use of telephones to set up an amateur radio contact B.A phone patch between amateur radio and the telephone system C.Voice transmissions by radio D.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? A.AM B.SSB C.PSK D.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? A.Less than 500 Hz B.About 150 kHz C.Between 5 and 15 kHz D.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? A.More than 10 MHz B.About 6 MHz C.About 3 MHz D.About 1 MHz Not just 6 kHz, but 6000 kHz!!

Bandwidth & Interference 9 T6 C04 (pg 133) What type of transmission is indicated by the term NTSC? A.A Normal Transmission mode in Static Circuit B.A special mode for earth satellite uplink C.A standard fast scan color television signal D.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? A.Frequency modulation B.Phase modulation C.Single sideband D.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? A.1 kHz B.2 kHz C.Between 3 and 6 kHz D.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? A.SSB signals are easier to tune in than FM signals B.SSB signals are less likely to be bothered by noise interference than FM signals. C.SSB signals use much less bandwidth than FM signals D.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.A break cannot affect amateur communications B.Harmonic radiation from the TV may cause the amateur transmitter to transmit off-frequency C.TV interference may result when the amateur station is transmitting, or interference may occur to the amateur receiver D.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? A.You are not required to do anything B.Contact the FCC to see if other interference reports have been filed C.Check your station and make sure it meets the standards of good amateur practice D.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? A.Make sure that your station is operating properly and that it does not cause interference to your own television B.Immediately turn off your transmitter and contact the nearest FCC office for assistance C.Tell them that your license gives you the right to trans- mit and nothing can be done to reduce the interference D.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? A.You alone are responsible, since your transmitter is causing the problem B.Both you and the owner of the television receiver share the responsibility C.The FCC must decide if you or the owner of the television receiver is responsible D.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? A.Work with your neighbor to identify the offending device B.Politely inform your neighbor about the rules that require him to stop using the device if it causes interference C.Check your station and make sure it meets the standards of good amateur practice D.All of these answers are correct

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

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

Bandwidth & Interference 21 Notch (Band Stop) Filter Stop Band High Frequency Low Frequency 40 dB 0 dB fcfc fcfc -3 dB Pass Band 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. Want to “stop” (be deaf to) nearby transmitter on this frequency

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? A.Low-pass filter B.High-pass filter C.Band pass filter D.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 T3 D03 (pg 138) What is the major cause of telephone interference? A.The telephone wiring is inadequate B.Tropospheric ducting at UHF frequencies C.The telephone was not equipped with adequate interference protection when manufactured. D.Improper location of the telephone in the home Poorly designed?

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

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

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? A.Snap-on ferrite chokes B.Low-pass and high-pass filters C.Notch and band-pass filters D.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? A.Fundamental overload B.Doppler shift C.Spurious emissions D.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? A.Your microphone is picking up noise from an open window B.You have the volume on your receiver set too high C.You need to adjust your squelch control D.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? A.The batteries in your transceiver are failing B.Strong signals are overloading the receiver and causing undesired signals to be heard C.The receiver is picking up low orbit satellites D.A nearby broadcast station is having transmitter problems

Bandwidth & Interference 31 T3 D11 (pg 140) What is meant by receiver front-end overload? A.Too much voltage from the power supply B.Too much current from the power supply C.Interference caused by strong signals from a nearby source D.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? A.Too much voltage from the power supply B.Too much current from the power supply C.Interference caused by very strong signals from a nearby source D.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? A.Increase transmit power B.Change mode of transmission C.Report the interference to the equipment manufacturer D.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? A.At the transmitter B.At the receiver C.At the station power supply D.At the microphone

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