Transcript Technician License Class

Technician
License Class
Gordon West
Technician Class Manual
Pages 132-141
Bandwidth & Interference
Presented by
Heart Of Texas
Amateur Radio Club
(HOTARC)
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
2
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: Over
– FM: 5-15 kHz twice SSB
Slow Scan TV: 3 kHz
Fast Scan TV: 6 MHz !!
Bandwidth & Interference
3
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
4
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
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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
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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
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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
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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
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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
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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
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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
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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
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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
Thinkcommunications
of it as a “leak”—
B. Harmonic radiation from the
TV maysignals
causeeither
the
unwanted
amateur transmitter to transmit
off-frequency
leak out
or leak in.
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
Bandwidth & Interference
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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
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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 transmit and nothing can be done to reduce the interference
D. Continue operating normally because your equipment
cannot possibly cause any interference
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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
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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
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Low Pass, High Pass Filters
Low Pass
0 dB
-3 dB
Pass
Band
Stop
Band
40 dB
fc
Frequency
High Pass
0 dB
-3 dB
Stop
Band
40 dB
Bandwidth & Interference
Pass
Band
fc
Frequency
19
Band Pass Filter
0 dB
-3 dB
Stop
Band
40 dB
Low
Frequency
Pass
Band
fc
Stop
Band
fc
High
Frequency
Bandwidth & Interference
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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.
0 dB
-3 dB
Pass
Band
40 dB
Low
Frequency
Bandwidth & Interference
Stop
Band
fc
Pass
Band
fc
High
Frequency
Want to “stop” (be deaf to)
nearby transmitter on this
frequency
21
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
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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
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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
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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
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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.
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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!
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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
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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
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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
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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
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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
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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
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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
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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.
Bandwidth & Interference
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