In this section, the question pool committee removed nearly all of the questions about PSK31 and replaced them with questions about PACTOR. This is really puzzling to me as there are many more hams using PSK31, and are likely to use PSK31, than are using, or are likely to use PACTOR.
In recent years, operating what’s known as the “digital modes” has become popular. They are known by this name because you can’t operate them without a computer. RTTY, PSK31, JT65, and PACTOR are examples of digital modes.
When operating the digital modes, amateurs connect the audio output of their transceivers into the input of a computer sound card and the output of the sound card to the audio input of the transceiver. The computer does all the heavy lifting, decoding the tones on the input and generating the tones to be transmitted.
Amateurs operate these modes in specific sub-bands. 14.070 – 14.100 MHz is the segment of the 20 meter band that is most often used for data transmissions. (G2E04) Below the RTTY segment, near 14.070 MHz is the segment of the 20 meter band where most PSK31 operations are commonly found. (G2E08) 3585 – 3600 kHz is the segment of the 80 meter band most commonly used for digital transmissions. (G2E07)
Amateurs have actually been operating RTTY for a long time, but it has become a lot more popular in recent years because amateurs can now operate this mode using a computer and not a clunky, mechanical teletype machine. RTTY signals shift between two frequencies. That’s why this mode is called frequency shift keying. One frequency denotes a “1,” while another denotes a “0.” The difference between those two frequencies is called the frequency shift. 170 Hz is the most common frequency shift for RTTY emissions in the amateur HF bands. (G2E06)
Using a computer sound card to generate audio tones that shift the frequency of a transmitted signal is called audio frequency shift keying (AFSK). LSB is the mode normally used when sending an RTTY signal via AFSK with an SSB transmitter. (G2E01) USB is the standard sideband used to generate a JT65 or JT9 digital signal when using AFSK in any amateur band. (G2E15)
RTTY uses a code called the Baudot code to encode characters. Baudot code is a 5-bit code, with additional start and stop bits. (G2E05)
To tune and decode digital signals, amateur radio operators use computer programs that display signals in a portion of an amateur radio band in what is called a waterfall display. In a waterfall display, frequency is horizontal, signal strength is intensity, time is vertical. (G2E12) When an operator selects one of the signals being displayed, the computer will then begin to decode that signal.
Properly tuning a digital signal is important. All of these choices are correct when talking about What could be wrong if you cannot decode an RTTY or other FSK signal even though it is apparently tuned in properly: (G2E14)
- The mark and space frequencies may be reversed
- You may have selected the wrong baud rate
- You may be listening on the wrong sideband
Many digital modes, such as RTTY and PSK31, have no error correction. Occasionally, there are errors receiving these signals, but generally, that’s not a problem, as operators can generally fill in the blanks.
If errors cannot be tolerated, you might want to consider using a mode called PACTOR. PACTOR uses the ARQ protocol for error correction, and a network of stations running PACTOR has been set up to relay data between radio stations and the Internet. This communication system, called Winlink, sometimes uses the Internet to transfer messages. (G2E13)
Stations that are connected to the Internet are called gateways. To establish contact with a digital messaging system gateway station, transmit a connect message on the station’s published frequency. (G2E10) Be aware that there is no way to join a contact between two stations using the PACTOR protocol. Joining an existing contact is not possible, PACTOR connections are limited to two stations. (G2E09)
Like any amateur radio communications, you should make sure that a frequency is not in use before starting a PACTOR transmission. To do this, put the modem or controller in a mode which allows monitoring communications without a connection to determine if the channel is in use by other PACTOR stations. (G2E02)
Even though the PACTOR protocol includes error correction, it’s still a good idea to choose a clear frequency so that there is no interference. All of these choices are correct when talking about symptoms that may result from other signals interfering with a PACTOR or WINMOR transmission (G2E03):
- Frequent retries or timeouts
- Long pauses in message transmission
- Failure to establish a connection between stations
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