LESSON 6

SUBELEMENT T8 – Modulation modes; amateur satellite operation, operating activities, non-voice communications – [4 Exam Questions - 4 Groups]

Lesson 6a
T8A – Modulation modes; bandwidth of various signals.






Intelligence (voice or data) is placed on a radio carrier by a process known as Modulation. For the purpose of this test you only need to be acquainted with three types of modulation, CW, AM, and FM. I did not mention Single Sideband (SSB) because SSB is a form of Amplitude Modulation (AM).

With CW (continuous wave) the carrier is either all the way on or all the way off and by turning the carrier on and off Morse code can be sent.

Amplitude Modulation is accomplished by changing the amplitude of the carrier by increasing and decreasing the RF signal (carrier frequency) with an audio signal. The increase and decrease is proportional to the positive and negative peaks of the AF signal. If an AM transmitter is operating properly the power output, as read on a wattmeter, should increase as the AF signal increases up to a maximum of half again the un-modulated transmitted power. The power increase is not an increase in the carrier power but in two sidebands that are formed beside the carrier.

The upper sideband is equal to the carrier frequency plus the audio frequency and the lower sideband is equal to the carrier frequency minus the audio frequency. So if a transmitter is operating on 4,000 KHz and has a 1 KHz tone modulating it then the output of the transmitter would have a carrier of 4,000 KHz, a upper sideband of 4,001 KHz, and a lower sideband of 3,998 KHz.

The carrier does not carry any actual intelligence and the upper sideband and the lower sideband both carry the same information. So if the carrier and one sideband is removed the other sideband can be sent with all the intelligence contained in a standard AM signal with all the power being transmitted in the signal with the intelligence. Because all of the power is included in the intelligence part of the signal SSB is the most common voice communications used for long-distance or weak signal contacts on the VHF and UHF bands.

The carrier of an AM signal does act as a reference necessary for the sideband to heterodyne against to make it intelligible. The product detector reinserts the carrier by mixing the incoming SSB signal with the Beat Frequency Oscillator’s output frequency thus reproducing the audio contained in that sideband.

About all you really need to remember out of all that above for the test is that Single sideband is a form of amplitude modulation, and the type of voice modulation most often used for long-distance or weak signal contact on the VHF and UHF bands is SSB.

Frequency Modulation differs from Amplitude Modulation in that the carrier’s frequency is changed with the amplitude of the modulating signal while the power remains constant. A wattmeter attached at the output of an FM transmitter should not change with modulation. The stronger the modulating signal the further the FM carrier will shift off the center frequency. The carrier should shift evenly up and down from the center frequency.

FM is the most common type of modulation used for VHF and UHF voice repeaters.

The primary advantage of single sideband over FM for voice communications is SSB has a much narrower bandwidth. The bandwidth of an amateur radio VHF FM repeater phone signal is approximately between 5 and 15 KHz. Single sideband has a bandwidth of approximately 3 KHz.

CW has the narrowest band width of all with a bandwidth of approximately 150 Hz.

Back in the early days of SSB a gentleman’s agreement was established that stations using SSB on 40 meters and frequencies below the 40 meter band would use lower sideband and stations operating with SSB on frequencies above 40 meters would use USB. Thus the most common sideband used for 10 meters, VHF, and UHF amateur radio communications is upper sideband.

During the 1980’s when home computers started to become popular packet radio also became popular on VHF amateur radio bands. The type of modulation most commonly used for VHF packet radio transmission is FM.

As a technician class amateur radio operator you will be able to run a fast-scan TV station on the 70 cm band if you desire. The typical bandwidth of analog fast-scan TV transmission on the 70 cm band is about 6 MHz.

*T8A01
Which of the following is a form of amplitude modulation?
A. Spread-spectrum
B. Packet radio
C. Single sideband
D. Phase shift keying
~~

*T8A02
What type of modulation is most commonly used for VHF packet radio transmissions?
A. FM
B. SSB
C. AM
D. Spread Spectrum
~~

*T8A03
Which type of voice modulation is most often used for long-distance or weak signal contacts on the VHF and UHF bands?
A. FM
B. AM
C. SSB
D. PM
~~

*T8A04
Which type of modulation is most commonly used for VHF and UHF voice repeaters?
A. AM
B. SSB
C. PSK
D. FM
~~

*T8A05
Which of the following types of emission has the narrowest bandwidth?
A. FM voice
B. SSB voice
C. CW
D. Slow-scan TV
~~

*T8A06
Which sideband is normally used for 10 meter HF, VHF and UHF single-sideband communications?
A. Upper sideband
B. Lower sideband
C. Suppressed sideband
D. Inverted sideband
~~

*T8A07
What is the primary advantage of single sideband over FM for voice transmissions?
A. SSB signals are easier to tune
B. SSB signals are less susceptible to interference
C. SSB signals have narrower bandwidth
D. All of these choices are correct
~~

*T8A08
What is the approximate bandwidth of a single sideband voice signal?
A. 1 kHz
B. 3 kHz
C. 6 kHz
D. 15 kHz
~~

*T8A09
What is the approximate bandwidth of a VHF repeater FM phone signal?
A. Less than 500 Hz
B. About 150 kHz
C. Between 5 and 15 kHz
D. Between 50 and 125 kHz
~~

*T8A10
What is the typical bandwidth of analog fast-scan TV transmissions on the 70 cm band?
A. More than 10 MHz
B. About 6 MHz
C. About 3 MHz
D. About 1 MHz
~~

*T8A11
What is the approximate maximum bandwidth required to transmit a CW signal?
A. 2.4 kHz
B. 150 Hz
C. 1000 Hz
D. 15 kHz
~~

Answers:
C, A, C, D, C, A, C, B, C, B, B

Lesson 6b

T8B - Amateur satellite operation; Doppler shift, basic orbits, operating protocols

Space communications offers the ham radio operators an exciting opportunity. Space communications included talking to the International Space Station and working other ham stations via satellites. Amateur operators whose license privileges allow them to transmit on the satellite uplink frequency may be the control operator of a station communicating through an amateur satellite or space station. The same holds true when operating the International Space station using 2 meter and 70 cm amateur radio band frequencies, any amateur holding a Technician or higher class license is allowed to participate it that type of operation.

Amateur radio satellites are not used to get global positioning information nor are they used to make telephone calls. An amateur radio satellite may be used to talk to amateur radio operators in other countries.

The following is true of all amateur radio communications but the question in this section deals with space communications. The maximum transmitter power that should be used on the uplink frequency of an amateur satellite or space station is the minimum amount of power needed to complete the contact.

Available satellite tracking programs can help to determine the time period during which an amateur satellite or space station can be accessed. Amateur radio satellites have beacons or transmissions from them that contains information about a satellite. Listening for a satellite beacon may also assist in determining the time period a satellite may be used.

Some satellites operate in a digital mode. The most commonly used method of sending signals to and from a digital satellite is FM packet.

“Doppler shift” and “Spin fading” can affect communications via satellite. Any operator wanting to use amateur radio satellites should acquaint themselves with these two phenomena.

Doppler Effect happens when either or both the receiving station and the transmitting station move towards each other or away from each other. When the two stations are coming closer together the frequency of the transmitted signal will appear higher and if they are moving apart the frequency will appear lower. Most mobile do not have sufficient speed for Doppler shift to made noticeable change in a radio frequency but considering the speed of the rotation of the earth and the speed of the moving satellites space communications can Doppler shift can have a very noticeable effect on frequency of the transmitted signal. So in regards to satellite communications “Doppler shift” is an observed change in signal frequency caused by relative motion between the satellite and the earth station.

Because of their height above the earth’s surface satellites greatly extend the range of line of sight communications so just as with other types of line of site communications antenna polarization can greatly effect the signal strength. Satellite antennas do not remain in a fixed angle in respect to the earth stations. “Spin fading” is caused by the rotation of the satellite and its antennas.

Some satellites orbit in a Low Earth Orbit which is abbreviated “LEO.”

A satellite operating in the “mode U/V” has an uplink in the 70 cm band (UHF) and a downlink in the 2 meter band (VHF).

*T8B01
Who may be the control operator of a station communicating through an amateur satellite or space station?
A. Only an Amateur Extra Class operator
B. A General Class licensee or higher licensee who has a satellite operator certification
C. Only an Amateur Extra Class operator who is also an AMSAT member
D. Any amateur whose license privileges allow them to transmit on the satellite uplink frequency.
~~

*T8B02 [97.313(a)]
How much transmitter power should be used on the uplink frequency of an amateur satellite or space station?
A. The maximum power of your transmitter
B. The minimum amount of power needed to complete the contact
C. No more than half the rating of your linear amplifier
D. Never more than 1 watt
~~

*T8B03
Which of the following can be done using an amateur radio satellite?
A. Talk to amateur radio operators in other countries
B. Get global positioning information
C. Make telephone calls
D. All of these choices are correct
~~

*T8B04
Which amateur stations may make contact with an amateur station on the International Space Station using 2 meter and 70 cm band amateur radio frequencies?
A. Only members of amateur radio clubs at NASA facilities
B. Any amateur holding a Technician or higher class license
C. Only the astronaut's family members who are hams
D. You cannot talk to the ISS on amateur radio frequencies
~~

*T8B05
What is a satellite beacon?
A. The primary transmit antenna on the satellite
B. An indicator light that that shows where to point your antenna
C. A reflective surface on the satellite
D. A transmission from a space station that contains information about a satellite
~~

*T8B06
What can be used to determine the time period during which an amateur satellite or space station can be accessed?
A. A GPS receiver
B. A field strength meter
C. A telescope
D. A satellite tracking program
~~

*T8B07
With regard to satellite communications, what is Doppler shift?
A. A change in the satellite orbit
B. A mode where the satellite receives signals on one band and transmits on another
C. An observed change in signal frequency caused by relative motion between the satellite and the earth station
D. A special digital communications mode for some satellites
~~

*T8B08
What is meant by the statement that a satellite is operating in "mode U/V"?
A. The satellite uplink is in the 15 meter band and the downlink is in the 10 meter band
B. The satellite uplink is in the 70 cm band and the downlink is in the 2 meter band
C. The satellite operates using ultraviolet frequencies
D. The satellite frequencies are usually variable
~~

*T8B09
What causes "spin fading" when referring to satellite signals?
A. Circular polarized noise interference radiated from the sun
B. Rotation of the satellite and its antennas
C. Doppler shift of the received signal
D. Interfering signals within the satellite uplink band
~~

*T8B10
What do the initials LEO tell you about an amateur satellite?
A. The satellite battery is in Low Energy Operation mode
B. The satellite is performing a Lunar Ejection Orbit maneuver
C. The satellite is in a Low Earth Orbit
D. The satellite uses Light Emitting Optics
~~

*T8B11
What is a commonly used method of sending signals to and from a digital satellite?
A. USB AFSK
B. PSK31
C. FM Packet
D. WSJT
~~

Answers:
D, B, A, B, D, D, C, B, B, C, C

Lesson 6c

T8C – Operating activities; radio direction finding, radio control, contests, special event stations, basic linking over Internet

Sometimes fun activities can serve to prepare you for more serious projects later. Hidden transmitter hunts help hams learn how to find sources of radio interference. A directional antenna will indicate the direction from which the signal source is coming and will serve as a very useful tool in a hidden transmitter hunt. Radio direction finding is a method used to locate sources of noise interference or jamming stations.

Many hams enjoy contesting. The object of most contests is usually to try to establish as many contacts as possible with in a certain time period. When making a contact during contests do not send unnecessary information. Send only the minimum information needed for proper identification and the contest exchange.

Frequently, especially on VHF and UHF, when a distant contact is established the operators will pass their grid locater to designate their location. A grid locator is a letter-number designator assigned to a geographic location.

The FCC allows for special event stations that are operated in conjunction with an activity of special significance to the amateur community to apply for a temporary “1 by 1” format (letter-number-letter) call sign.

Radio controlled models are allowed to use amateur radio bands if they are operated by licensed amateur radio operators. The maximum power allowed when transmitting telecommand signals to radio controlled models is 1 watt. In place of on-air station identification when sending signals to a radio control model using amateur frequencies a label indicating the licensee’s name, call sign and address must be affixed to the transmitter.

A repeater directory might be used to obtain a list of active nodes that use VoIP. To select a specific IRLP (Internet Radio Linking Project) node when using a portable transceiver use a keypad to transmit the IRLP node ID. (Information not needed for test but hopefully helpful to understand what I just said: A node is a point where a base station or a repeater can interface with the internet. VoIP is the abbreviation for Voice over Internet Protocol. Amateur radio operators are using VoIP to extend the range of base stations or repeaters.)

A gateway is the term used to identify an amateur radio station that is used to connect another amateur station to the internet.


*T8C01
Which of the following methods is used to locate sources of noise interference or jamming?
A. Echolocation
B. Doppler radar
C. Radio direction finding
D. Phase locking
~~


*T8C02
Which of these items would be useful for a hidden transmitter hunt?
A. Calibrated SWR meter
B. A directional antenna
C. A calibrated noise bridge
D. All of these choices are correct
~~


*T8C03
What popular operating activity involves contacting as many stations as possible during a specified period of time?
A. Contesting
B. Net operations
C. Public service events
D. Simulated emergency exercises
~~


*T8C04
Which of the following is good procedure when contacting another station in a radio contest?
A. Be sure to sign only the last two letters of your call if there is a pileup calling the station
B. Work the station twice to be sure that you are in his log
C. Send only the minimum information needed for proper identification and the contest exchange
D. All of these choices are correct
~~


*T8C05
What is a grid locator?
A. A letter-number designator assigned to a geographic location
B. A letter-number designator assigned to an azimuth and elevation
C. An instrument for neutralizing a final amplifier
D. An instrument for radio direction finding
~~


*T8C06
For what purpose is a temporary "1 by 1" format (letter-number-letter) call sign assigned?
A. To designate an experimental station
B. To honor a deceased relative who was a radio amateur
C. For operations in conjunction with an activity of special significance to the amateur community
D. All of these choices are correct
~~


*T8C07 [97.215(c)]
What is the maximum power allowed when transmitting telecommand signals to radio controlled models?
A. 500 milliwatts
B. 1 watt
C. 25 watts
D. 1500 watts
~~


*T8C08 [97.215(a)]
What is required in place of on-air station identification when sending signals to a radio control model using amateur frequencies?
A. Voice identification must be transmitted every 10 minutes
B. Morse code ID must be sent once per hour
C. A label indicating the licensee’s name, call sign and address must be affixed to the transmitter
D. A flag must be affixed to the transmitter antenna with the station call sign in 1 inch high letters or larger
~~


*T8C09
How might you obtain a list of active nodes that use VoIP?
A. From the FCC Rulebook
B. From your local emergency coordinator
C. From a repeater directory
D. From the local repeater frequency coordinator
~~


*T8C10
How do you select a specific IRLP node when using a portable transceiver?
A. Choose a specific CTCSS tone
B. Choose the correct DSC tone
C. Access the repeater autopatch
D. Use the keypad to transmit the IRLP node ID
~~


*T8C11
What name is given to an amateur radio station that is used to connect other amateur stations to the Internet?
A. A gateway
B. A repeater
C. A digipeater
D. A beacon
~~

Answers:
C, B, A, C, A, C, B, C, C, D, A

Lesson 6d

T8D – Non-voice communications; image data, digital modes, CW, packet, PSK31

Packet, PSK31, and MFSK, are all examples of digital communications method.

Automatic Position Reporting System abbreviated APRS combines GPS, amateur radio and the Internet to produce real-time position reports. The location of home stations, moving vehicles, weather, and more is displayed on a map. A Global Positioning System Receiver is normally used when sending automatic location reports via amateur radio.

Because of the wide bandwidth (6 MHz) no band below the 420 MHz (70 cm) band allows fast scan TV. The type of transmission indicated by the term NTSC (National Television System Committee) is fast scan color TV.

The question is asked, “Which of the following emission modes may be used by a Technician Class operator between 219 and 220 MHz?” The answer is B. Data. That answer is correct but read the section below from Part 97 of the FCC regulations before trying to operate in that portion of the 1.25 meter band. A lot more information is also needed before operating there see FCC Part 97.303(e).
FCC Part 97.303(e) In the 1.25 m band:
(1) Use of the 219-220 MHz segment is limited to amateur stations participating, as forwarding stations, in point-to-point fixed digital message forwarding systems, including intercity packet backbone networks. It is not available for other purposes.
PSK31 is a low-rate data transmission mode. The abbreviation PSK means Phase Shift Keying.

A packet transmission may include a check sum which permits error detection, a header which contains the call sign of the station to which the information is being sent, and an automatic repeater request in case of error. Packet uses digapeters (short for digital repeater) which unlike voice repeaters use the same input frequency and output frequency.

Continuous Wave transmission, usually shortened to CW transmission, more properly should be called Interrupted Continuous Wave (ICW) because the CW operator uses International Morse code to communicate on the amateur bands. A straight key, electronic keyer, or computer keyboard are all used to sent CW signals. (Other devices used to send CW are not asked for here so they are not mentioned.)

The simplest form of error detection code is the “parity” bit format. A “parity” bit is an extra code element used to detect errors in receives data.

*T8D01
Which of the following is an example of a digital communications method?
A. Packet
B. PSK31
C. MFSK
D. All of these choices are correct
~~

*T8D02
What does the term APRS mean?
A. Automatic Position Reporting System
B. Associated Public Radio Station
C. Auto Planning Radio Set-up
D. Advanced Polar Radio System
~~

*T8D03
Which of the following is normally used when sending automatic location reports via amateur radio?
A. A connection to the vehicle speedometer
B. A WWV receiver
C. A connection to a broadcast FM sub-carrier receiver
D. A Global Positioning System receiver
~~

*T8D04
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. An analog fast scan color TV signal
D. A frame compression scheme for TV signals
~~

*T8D05
Which of the following emission modes may be used by a Technician Class operator between 219 and 220 MHz?
A. Spread spectrum
B. Data
C. SSB voice
D. Fast-scan television
~~

*T8D06
What does the abbreviation PSK mean?
A. Pulse Shift Keying
B. Phase Shift Keying
C. Packet Short Keying
D. Phased Slide Keying
~~

*T8D07
What is PSK31?
A. A high-rate data transmission mode
B. A method of reducing noise interference to FM signals
C. A method of compressing digital television signal
D. A low-rate data transmission mode
~~

*T8D08
Which of the following may be included in packet transmissions?
A. A check sum which permits error detection
B. A header which contains the call sign of the station to which the information is being sent
C. Automatic repeat request in case of error
D. All of these choices are correct
~~

*T8D09
What code is used when sending CW in the amateur bands?
A. Baudot
B. Hamming
C. International Morse
D. Gray
~~

*T8D10
Which of the following can be used to transmit CW in the amateur bands?
A. Straight Key
B. Electronic Keyer
C. Computer Keyboard
D. All of these choices are correct
~~

*T8D11
What is a "parity" bit?
A. A control code required for automatic position reporting
B. A timing bit used to ensure equal sharing of a frequency
C. An extra code element used to detect errors in received data
D. A "triple width" bit used to signal the end of a character
~~

Answers:
D, A, D, C, B, B, D, D, C, D, C