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Subel. L14b
11 questions
Subelement L14b

Digital Modes.

Section L14b

What does "connected" mean in an AX.25 packet-radio link?

  • A telephone link is working between two stations
  • A message has reached an amateur station for local delivery
  • A transmitting and receiving station are using a digipeater, so no other contacts can take place until they are finished
  • Correct Answer
    A transmitting station is sending data to only one receiving station; it replies that the data is being received correctly

When two PACKET stations are "connected", the receiving station acknowledges each received packet as valid. A "connection" involves only two stations; each acknowledging the packets from the other. Concurrent "connections" can share the same frequency. A 'Terminal-Node Controller' (TNC) is the key component in a packet station. The TNC is a specialized MODEM which assembles/de-assembles data packets and performs error checking.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

What does "monitoring" mean on a packet-radio frequency?

  • A member of the Amateur Auxiliary is copying all messages
  • A receiving station is displaying all messages sent to it, and replying that the messages are being received correctly
  • Innovation, Science and Economic Development Canada is monitoring all messages
  • Correct Answer
    A receiving station is displaying messages that may not be sent to it, and is not replying to any message

A 'Terminal-Node Controller' (TNC) is the key component in a packet station. The TNC is a specialized MODEM which assembles/de-assembles data packets and performs error checking. A TNC in "Monitor" mode will display the packets heard but not attempt to acknowledge any.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

What is a digipeater?

  • A repeater that changes audio signals to digital data
  • A station that retransmits any data that it receives
  • Correct Answer
    A station that retransmits only data that is marked to be retransmitted
  • A repeater built using only digital electronics parts

A 'Digipeater' (contraction of 'digital repeater') only repeats packets specifically addressed for routing through that digipeater: i.e., marked with its call sign. Unlike duplex voice repeaters using two frequencies, the digipeater receives, temporarily stores and retransmits the data packets on a single frequency.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

What does "network" mean in packet radio?

  • Correct Answer
    A way of connecting packet-radio stations so data can be sent over long distances
  • A way of connecting terminal-node controllers by telephone so data can be sent over long distances
  • The connections on terminal-node controllers
  • The programming in a terminal-node controller that rejects other callers if a station is already connected

In packet radio operation, a 'network' is a succession of digipeaters (or normal packet stations which can also 'digipeat') used to connect to a station normally not within range of the originating station.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

In AX.25 packet-radio operation, what equipment connects to a terminal-node controller?

  • A transceiver and a modem
  • A DTMF keypad, a monitor and a transceiver
  • A DTMF microphone, a monitor and a transceiver
  • Correct Answer
    A transceiver, a computer and possibly a GPS receiver

An amateur packet station would comprise a computer, a terminal-node controller and a transceiver. A GPS (Global Positioning System) receiver may be used if geographical coordinates need to be transmitted.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

How would you modulate a 2 meter FM transceiver to produce packet-radio emissions?

  • Connect a keyboard to the transceiver's microphone input
  • Connect a DTMF key pad to the transceiver's microphone input
  • Correct Answer
    Connect a terminal-node controller to the transceiver's microphone input
  • Connect a terminal-node controller to interrupt the transceiver's carrier wave

The Digital Station block diagram: Input/Output, Computer, MODEM, Transceiver, Antenna. In a packet station, the TNC is the specialized modem (i.e., it incorporates a modem) used to assemble/disassemble data packets.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

When selecting a RTTY transmitting frequency, what minimum frequency separation from a contact in progress should you allow (center to center) to minimize interference?

  • 60 Hz
  • Correct Answer
    250 to 500 Hz
  • Approximately 6 kHz
  • Approximately 3 kHz

In order of bandwidth requirements: CW = about 100 Hz, RTTY = about 600 Hz, SSB = 2 to 3 kHz, FM = 10 to 20 kHz. Minimum frequency separation: CW = 150 to 500 Hz, RTTY = 250 to 500 Hz, SSB = 3 kHz to 5 kHz. [ The 'Mark' and 'Space' states are represented by two discrete frequencies normally 170 Hz apart from one another. ]

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

Digital transmissions use signals called __________ to transmit the states 1 and 0:

  • Correct Answer
    mark and space
  • packet and AMTOR
  • Baudot and ASCII
  • dot and dash

The terms 'Mark' (on) and 'Space' (off) date back to the days of land-line telegraph where dots and dashes corresponding to the incoming pulses were inked or embossed on paper ribbon. When the telegraph circuit was energized, the receiving machine would mark the paper, otherwise blank space appeared on the paper. [ Samuel F. B. Morse perfected a "Telegraph Register" which could mark dots and dashes on a moving strip of paper in the years 1832 to 1844. US Patent 000006420 ]

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

Which of the following terms does not apply to packet radio?

  • Automatic Packet Reporting System (APRS)
  • AX.25
  • Correct Answer
    Baudot
  • ASCII

Key word: NOT. 'Baudot' is the encoding used for RTTY (Radioteletype). On packet, the computer exchanges ASCII (American Standard Code for Information Interchange) with the TNC (terminal-node controller). The TNC packages packets per the AX.25 protocol. Automatic Packet Reporting System (APRS) is one application of packet radio.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

When using AMTOR transmissions, there are two modes that may be utilized. Mode A uses Automatic Repeat Request (ARQ) protocol and is normally used:

  • Correct Answer
    for communications after contact has been established
  • at all times. Mode B is for test purposes only
  • only when communications have been completed
  • when making a general call

AMTOR (Amateur Teleprinting Over Radio). Mode 'B' [Forward Error Correction, groups of 5 characters are sent twice] used for CQ (call to any station), bulletins or nets where no acknowledgements are exchanged. Mode 'A' [Automatic Repeat Request, characters sent by groups of three must be acknowledged] used when two stations are in contact (similar to the "connection" in packet).

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

With a digital communication mode based on a computer sound card, what is the result of feeding too much audio in the transceiver?

  • Lower error rate
  • Power amplifier overheating
  • Correct Answer
    Splatter or out-of-channel emissions
  • Higher signal-to-noise ratio

'Overdeviation (FM)' or 'Overmodulation (SSB)' results in excessive bandwidth on the air (splatter) and interfering with stations using adjacent frequencies ('out-of-channel emissions').

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

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