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Subelement T8
Modulation modes: amateur satellite operation; operating activities; non-voice and digital communications
Section T8A
Modulation modes: bandwidth of various signals; choice of emission type
Which of the following is a form of amplitude modulation?
  • Spread spectrum
  • Packet radio
  • Single sideband
  • Phase shift keying (PSK)

Single Sideband is a modulation mode commonly used with HF operation and can be essentially described as a variant of amplitude modulation (AM) that only uses half of the signal and no carrier. Because of this, it is easier to use over a long distance where the reduced bandwidth usage results in less interference and the lack of carrier makes it more likely that the signal will be copyable despite any interference.

Spread-spectrum is not in and of itself a form of modulation, but rather is a technique (or a family of techniques, actually) that spreads a signal out on a wide range of frequencies in order to reduce interference, avoid detection, etc.

Packet Radio could probably be used with Amplitude Modulation, but itself can be used with many different modulations.

Phase Shift Keying is a modulation mode, but it is a digital modulation mode and has nothing to do with Amplitude Modulation.

Last edited by rjstone. Register to edit

Tags: ssb amplitude modulation arrl chapter 2 arrl module 3

What type of modulation is most commonly used for VHF packet radio transmissions?
  • FM
  • SSB
  • AM
  • PSK

Since packet radio benefits from good bandwidth and minimal audio amplitude variations, both of which are advantages of FM; and because FM is an allowed modulation method on VHF, FM is the most commonly used modulation for packet.

Last edited by spuder. Register to edit

Tags: frequency modulation digital modes vhf arrl chapter 2 arrl module 3

Which type of voice mode is most often used for long-distance (weak signal) contacts on the VHF and UHF bands?
  • FM
  • DRM
  • SSB
  • PM

The listed choices are: Frequency Modulation (FM), Single Side-Band (SSB), DRM, and Phase Modulation (PM). All of these have their own advantages and disadvantages, but of them Single Side-Band is unique in that it does not transmit a carrier and requires approximately half of the bandwidth of an FM signal; these two characteristics make it ideal for long- distance and weak signal contacts in nearly any band because less of the signal needs to make it through for the receiver to correctly copy the transmission.

For comparison, consider your AM/FM car radio; when you are too far from the tower, the signal begins to fuzz making it uncopyable. With SSB the signal would fade but you would have less "white noise" in the faded signal and more of it would be just the voice part that you are interested in. The downside to this mode is that without a carrier, even when the signal is strong it may not be as clear as an AM or FM signal.

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Tags: ssb uhf vhf arrl chapter 2 arrl module 3

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

FM (Frequency Modulation) is the same modulation used by the FM radio in your car, which makes it easier to remember. Note that regular FM radio broadcast stations (music, talk radio, etc) use what is commonly known as Wide FM, whereas ham radio generally uses Narrow FM which uses less bandwidth (about 5-15kHz).

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Tags: vhf uhf frequency modulation arrl chapter 2 arrl module 3

Which of the following types of emission has the narrowest bandwidth?
  • FM voice
  • SSB voice
  • CW
  • Slow-scan TV

CW or "Continuous Wave" is also known as "Morse Code". This consists of turning the RF carrier "on" and "off". Since the signal only has to be strong enough to detect if the transmitter is on or not, it requires very little bandwidth.

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Tags: morse code bandwidth radio operation arrl chapter 2 arrl module 3

Which sideband is normally used for 10 meter HF, VHF, and UHF single-sideband communications?
  • Upper sideband
  • Lower sideband
  • Suppressed sideband
  • Inverted sideband

As a convention agreed upon, the Upper Sideband is used for SSB on 10M HF, VHF and UHF bands. You will need to just remember upper sideband for the upper frequency bands.

Last edited by hutch. Register to edit

Tags: 10 meter ssb vhf hf uhf arrl chapter 2 arrl module 3

What is an advantage of single sideband (SSB) over FM for voice transmissions?
  • SSB signals are easier to tune
  • SSB signals are less susceptible to interference
  • SSB signals have narrower bandwidth
  • All of these choices are correct

A rough way of understanding single sideband is to consider that AM voice transmissions have two sidebands -- upper and lower, with each sideband being approximately half of the bandwidth of the signal. With Single Sideband there is no carrier and only one of the sidebands is used, either Upper or Lower, and as a result SSB has a much narrower bandwidth.

It is true that SSB signals are more likely to be heard than FM signals when the signal is weak, but this does not imply that they are less susceptible to interference or that they are easier to tune -- they are simply still copyable if a smaller portion of the signal makes it through.

Last edited by bdengle32@yahoo.com. Register to edit

Tags: ssb frequency modulation bandwidth arrl chapter 2 arrl module 3

What is the approximate bandwidth of a single sideband (SSB) voice signal?
  • 1 kHz
  • 3 kHz
  • 6 kHz
  • 15 kHz

Single Sideband is a form of modified Amplitude Modulation (AM). Whereas AM normally uses twice the bandwidth of the original carrier, Single Sideband avoids that issue and also does not waste power on a carrier.

The bandwidth used by a single sideband voice signal varries between 300 and 3400 Hz, or .3 to 3.4 kHz. The approximate bandwidth, therefore, is the rough maximum used, which is approximately 3kHz.

Last edited by aust. Register to edit

Tags: bandwidth ssb hf arrl chapter 2 arrl module 3

What is the approximate bandwidth of a VHF repeater FM phone signal?
  • Less than 500 Hz
  • About 150 kHz
  • Between 10 and 15 kHz
  • Between 50 and 125 kHz

This can be demonstrated on a 2 meter handheld radio if you have an interest to see it; if you transmit on 146.520MHz and listen on 146.525MHz you will likely still be able to hear the signal. If you can't (or barely can) then the bandwidth is closer to 5kHz (standard for FRS radios, for example) and if you can hear it strongly it may be closer to 10 or 15kHz. The further away you get the wider the bandwidth would need to be for you to still be able to hear it.

Remember that if the bandwidth is 5kHz you will only hear them at the transmit frequency +/- 2.5Khz, because the transmit frequency is the middle so half will be above and half below. Most handheld radios seem to use 10kHz, but some support "half deviation" mode which uses 5kHz.

Last edited by bdengle32@yahoo.com. Register to edit

Tags: frequency modulation vhf repeater arrl chapter 2 arrl module 3

What is the typical bandwidth of analog fast-scan TV transmissions on the 70 centimeter band?
  • More than 10 MHz
  • About 6 MHz
  • About 3 MHz
  • About 1 MHz

Analog fast-scan TV transmissions use a lot of bandwidth compared to voice and other modes because of how much information is attached to the minorities that need to be transmitted. The approximate bandwidth is about 6 MHz.

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Tags: amateur television (atv) bandwidth 70 cm arrl chapter 2 arrl module 3

What is the approximate maximum bandwidth required to transmit a CW signal?
  • 2.4 kHz
  • 150 Hz
  • 1000 Hz
  • 15 kHz

CW uses the least bandwidth of all commonly used modes; all you really need to get across clearly is a single tone so that the receiving station can hear when it is "on" or "off".

A good rule of thumb for CW (Continuous Wave, Morse Code) is that when it asks about bandwidth it's probably the smallest value listed.

Last edited by jdblakey. Register to edit

Tags: arrl chapter 2 arrl module 3 morse code

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