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2016 Extra Class study guide: E2D - VHF and UHF operating methods

Posted: 21 Mar 2016 08:27 AM PDT
http://feedproxy.google.com/~r/kb6nu...m_medium=email


E2D Operating methods: VHF and UHF digital modes and procedures; APRS; EME
procedures, meteor scatter procedures

One of the most commonly misunderstood concepts in digital communications
is the baud. A baud is not equal to a bit per second, except for very
simple systems. Rather, the definition of baud is the number of data
symbols transmitted per second, and a data symbol may represent multiple
bits.

While modern Internet digital communication techniques can send and receive
digital data at MBps speeds, digital communications over amateur radio
links is much slower. Under clear communications conditions, 300-baud
packet is the digital communication mode that has the fastest data
throughput. (E2D09)

In the past ten years or so, we’ve had an explosion of digital modes become
available. JT65 is one example. The type of modulation used for JT65
contactsis multi-tone AFSK. (E2D13) One advantage of using JT65 coding is
the ability to decode signals which have a very low signal to noise ratio.
(E2D14)

JT65 is a digital mode especially useful for EME communications. (E2D03)
JT65 improves EME communications because it can decode signals many dB
below the noise floor using FEC.(E2D12) One of the reasons that JT65 is
such and effective method of establishing EME contacts is because it uses
time synchronous transmissions alternately from each station. (E2D06) JT65
software organizes the timing of contacts by alternating transmissions at 1
minute intervals. (E2E03)

APRS

One of the most popular digital modes is the Automatic Packet Reporting
System, or APRS. Most APRS operation takes place on the 2 m band around
144.39 MHz.

AX.25 is the digital protocol used by APRS. (E2D07) AX.25 is more commonly
known as packet radio. Unnumbered Information is the type of packet frame
used to transmit APRS beacon data. (E2D08)

APRS stations can be used to help support a public service communications
activity. An APRS station with a GPS unit can automatically transmit
information to show a mobile stations position during the event. (E2D10)
Latitude and longitude are used by the APRS network to communicate your
location. (E2D11)

Amateurs that enjoy satellite communications also use digital modes. For
example, store-and-forward is a technique normally used by low Earth
orbiting digital satellites to relay messages around the world. (E2D05) The
purpose of digital store-and-forward functions on an Amateur Radio
satellite is to store digital messages in the satellite for later download
by other stations. (E2D04)

Meteor scatter

Digital modes can also be used to make meteor scatter contacts. FSK441 is a
digital mode especially designed for use for meteor scatter signals.
(E2D01) All of these choices are correct when talking about good techniques
for making meteor scatter contacts: (E2D02)

15 second timed transmission sequences with stations alternating based on
location
Use of high speed CW or digital modes
Short transmission with rapidly repeated call signs and signal reports


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