Transcript Week 8

Digital communications
Hams have developed techniques
for transforming 1’s and 0’s into
tones into the same frequency
range as human voice.
So now a radio can transmit and
receive digital data.
The addition of information to a radio
wave is called modulation.
AM= Amplitude modulation
FM= Frequency modulation
The rules by which digital data is
packaged and exchanged is called
A modem (modulator-demodulator)
changes data signals to and from audio
If the modem combines computer
software that performs the protocol
rules and a soundcard, it is called a
terminal node controller (TNC)
The TNC is connected between the
transceiver and the computer in a
packet radio station. T4A06
Some examples of digital modesT8D01
On HF Bands
Radioteletype (uses 5-bit Baudot code)
Winlink 2000 (uses PACTOR or WINMOR protocols)
keyboard to keyboard
Packet radio
(uses AX.25 protocol)
(uses Morse code) (T8D09)
Since Radio signals experience many
disruptions as they travel from transmitter
to receiver; it is likely that errors may be
introduced into the stream of data.
This is measured by the bit error rate (BER)
Some protocol codes include elements
to allow the receiver to detect and
sometimes even correct the errors.
This special type of code is
called a parity bit (T8D11)
Packet radio is the most common digital
mode on VHF and UHF.
Packets are transmitted in noise-like bursts.
Frequency shift keying (FSK) is used to
transmit the individual characters as a
series of rapidly alternating tones.
The receiving TNC reassembles the data
from the packets.
Each “packet” contains a header with info
about the packet and the call sign of the
destination station The header also contains
checksum (the added element to allow the
receiver to check for errors)
If an error is detected, the receiver
automatically requested a retransmission.
This is called ARQ for automatic repeat
request. (T8D08)
Digital modes designed for real-time
person to person communication are
called keyboard to keyboard modes.
Most popular digital mode is PSK31
(phase shift keying, 31 baud) (T8D06);
even though it sends data at a low
rate, it works well in noisy conditions
The Automatic Position Reporting
System (APRS) uses packet radio to
transmit the location of a mobile or
portable station. (T8D02)
The portable station is basically a
packet radio station with a Global
Positioning System (GPS) receiver
attached to the TNC. (T8D03)
Traveling hams can send e-mail
“over the air” by using Winlink.
Winlink combines e-mail with a
digital modes.
The radio station that makes connection
between the traveling radio and the
internet is called a gateway. (T8C11)
What does the acronym “BER” mean
when applied to digital communications
A. Baud Enhancement Recovery
B. Baud Error Removal
C. Bit Error Rate
D. Bit Exponent Resource
Which of the following is an example of a
digital communications method?
A. Packet
B. PSK31
D. All of these choices are correct
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
What code is used when sending
CW in the amateur bands?
A. Baudot
B. Hamming
C. International Morse
D. Gray
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
What does the abbreviation PSK
A. Pulse Shift Keying
B. Phase Shift Keying
C. Packet Short Keying
D. Phased Slide Keying
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
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
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
D. A Global Positioning System receiver
Which of the following would be
connected between a transceiver and
computer in a packet radio station?
A. Transmatch
B. Mixer
C. Terminal node controller
D. Antenna
How is the computer’s sound card used when
conducting digital communications using a
A. The sound card communicates between the
computer CPU and the video display
B. The sound card records the audio frequency for
video display
C. The sound card provides audio to the
microphone input and converts received audio to
digital form
D. All of these choices are correct
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