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Upgrading to Extra gives access to extra bandwidth on HF, for both Data, and Image modes.
Morse code, in the traditional CW form used on HF and in the low end of VHF bands can be termed on-off keying (OOK), or Amplitude Shift Keying (ASK). ASK can also use tones at a number of levels. ASK is not very robust in radio use, but is used for things like optical fibre. This is not on the exam, but comes into play later.
Many weak signal HF data modes use Frequency Shift Keying (FSK), or more usually, audio frequency shift keying (AFSK), switching between two or more frequencies. In effect, a suppressed carrier of 14010 kHz and an audio tone switching between 500 Hz and 700 Hz is the same as switching an RF signal between 14010.5 and 14010.7 kHz. Interestingly, one way to generate FSK is by commanding a DDS (Direct Digital Synthesis) module between two RF or IF frequencies rapidly.
It has been used for a great many years, for things like Radio Teletype, RTTY, to AX-25 Packet, to the latest modes added to WSJT and WSJT-X. The next few modes are built into one or both the latter two packages.
Gaussian Frequency Shift Keying (GFSK) uses a slower transition between the frequencies.
FT8 allows modest HF and VHF+ stations to exchange callsigns. It uses 8 tones. Each station transmits for (just under) 15 seconds. That said, in my limited experience of the mode, I have clicked on a callsign late in their receiving period, and it was still decoded.
This is one of the newer modes added to WSJT software. It is for weak signal chat and contest contacts. Stations take turns transmitting, for only 7.5 seconds each time. It uses 4 tones.
This is used for the LF and MF bands, and permits QSO operation. It is part of WSJT-X. It occupies a very narrow bandwidth.
It uses 4 tones (4-GFSK), seven different transmit periods and seven different tone spaces. This satisfies the "All these choices are correct" option.
You can read more here: Quick-Start Guide to FST4 and FST4W (PDF)
FST4W is used for beaconing. This is common, as many stations do not have a means to transmit on these bands, but may have an antenna of varying effectiveness.
Q65 appears to be developed beyond JT65, the latter previously used for EME. Both use 65 tones. Q65 uses averaging of multiple receive cycles. This means if the first transmission period fails to decode the information received in the first 30 second period, this data can be added to a second and third period, and so on, as necessary. The transmit period is variable, up to 300 seconds (10 minutes). See: Quick-Start Guide to Q65 (PDF)
Off the exam, Olivia is an example of an MFSK RTTY style mode, which can work well in poor conditions, including with auroral propagation, which is fluttery.
PSK is phase shift keying. BPSK uses a 180 degree shift. QPSK uses a 90 degree shift. In amateur radio the decoder references the previous element period for the phase shift. There are a bunch of variations, including CPSK using a reference tone. 8-PSK uses 45°, which is the practical limit.
Read more at Wikipedia:Phase-shift keying
PSK31 is a narrowband, 31 baud system. It uses either 180 or 90 degree shifts, forming sub-types BPSK31 or QPSK31. It also uses varicode, or variable length encoding, meaning a lowercase "e" is likely faster to send than an uppercase "Z". BPSK is more common, and better for poor conditions; QPSK faster in better conditions..
When audible, it sounds like a single tone with slight glitches or wobbles.
It is available is various free software packages, including fldigi.
QPSK doubles data throughput, providing 2 bits per baud in most cases. 8-PSK, one option with PACTOR IV below allows 3 bits per baud.
Can we mash up different modes at get more data through? In the words of a great man, "Yes we can!".
QAM stands for Quadrature Amplitude Modulation. A combination of level and phase angles forms a constellation of points forming a square. 16-QAM means 4 bits are sent for each element, 32-QAM means 5 bits. Higher numbers are used in things such as digital broadcast and cable TV. This was also used in various dial-up modems. There are some good graphics on: Wikipedia: QAM
It is / was used to transmit the L-R (difference) signal in C-QUAM ("Compatible QAM") AM stereo, and colour content (Chroma) in NTSC and PAL TV.
Off the exam, APSK, or Amplitude and Phase-Shift Keying is to some extent a super-set of this. It is used in DVB-S2 digital satellite TV. In most cases it uses a circular constellation pattern. See: Wikipedia: APSK
Under good conditions PACTOR IV has very good data throughput. It can be used for things such as keyboard to keyboard chat, email, and passing packet messages over long distances.
Under very difficult conditions it uses 2-tone chip, a form of FSK; then various PSK systems; then QAM, up to 32-QAM, allowing 5512.5 bits per second of actual data to be transmitted. The previous answer to this question was 300 bps packet, as the US had baud rate (or bps rate) limit of 300. This rate limit being removed was like a Suzuki Hayabusa and a 90 cc postal delivery bike riding side-by-side until they reach a ⊘ sign, and the big bike rapidly becomes a dot on the horizon (as it would to many Harley Davidson riders). Most other hams globally were only subject to a bandwidth limit, so were operating at high speed, as were sailors and professional users.
See: Signal ID Wiki: PACTOR IV
Hayabusa is Japanese for peregrine falcon, which predate blackbirds, the brand Honda uses on their slightly less speedy bike.
Automatic Link Establishment steps through a list of HF frequencies to find other stations to establish communication(s) to establish with. They transmit a sequence of tones which sound like a gobbling turkey, which includes a callsign.
These are or were also used commercially, and by the military.
As always, these are the actual questions from the Extra licence exam pool, as published by the NCVEC.
E2E01
Which type of modulation is common for data emissions below 30 MHz?
A. DTMF tones modulating an FM signal
B. FSK
C. Pulse modulation
D. Spread spectrum
Frequency shift keying (FSK) or AFSK are common, answer B.
Pulse modulation and spread spectrum are for high VHF and up only.
E2E02
Which of the following synchronizes WSJT-X digital mode transmit/receive timing?
A. Alignment of frequency shifts
B. Synchronization of computer clocks
C. Sync-field transmission
D. Sync-pulse timing
Clocks on PCs, Pis, etc should be set by the Internet or GPS, answer B.
E2E03
To what does the "4" in FT4 refer?
A. Multiples of 4 bits of user information
B. Four-tone continuous-phase frequency shift keying
C. Four transmit/receive cycles per minute
D. All these choices are correct
It is named for the four-tone FSK, answer B.
The truth or otherwise of other statements does not alter the naming convention, with the 8 modes using 8 tones, the 65 ones 65 tones.
E2E04
Which of the following is characteristic of the FST4 mode?
A. Four-tone Gaussian frequency shift keying
B. Variable transmit/receive periods
C. Seven different tone spacings
D. All these choices are correct
All are true, answer D.
E2E05
Which of these digital modes does not support keyboard-to-keyboard operation?
A. WSPR
B. RTTY
C. PSK31
D. MFSK16
WSPR is a weak signal beaconing and propagation evaluation mode, not a live chat system, answer A
E2E06
What is the length of an FT8 transmission cycle?1
A. It varies with the amount of data
B. 8 seconds
C. 15 seconds
D. 30 seconds
The transmit period for each stations is 15 seconds, answer C.
E2E07
How does Q65 differ from JT65?
A. Keyboard-to keyboard operation is supported
B. Quadrature modulation is used
C. Multiple receive cycles are averaged
D. All these choices are correct
Q65, used for EME, allows multiple receive cycles to be averaged, answer C.
E2E08
Which of the following HF digital modes can be used to transfer binary files?
A. PSK31
B. PACTOR
C. RTTY
D. AMTOR
This is PACTOR, answer B.
The others are text modes.
E2E09
Which of the following HF digital modes uses variable-length character coding?
A. RTTY
B. PACTOR
C. MT63
D. PSK31
PSK31 uses "varicode", variable length coding, which improves efficiency, answer D.
E2E10
Which of these digital modes has the narrowest bandwidth?
A. MFSK16
B. 170 Hz shift, 45 baud RTTY
C. FT8
D. PACTOR IV
Each FT8 emission has a very narrow bandwidth, answer C.
E2E11
What is the difference between direct FSK and audio FSK?
A. Direct FSK applies the data signal to the transmitter VFO
B. Direct FSK occupies less bandwidth
C. Direct FSK can transmit faster baud rates
D. Only direct FSK can be decoded by computer
Direct FSK varies the VFO's frequency, answer A.
AFSK sends audio tones to the microphone or similar input.
E2E12
How do ALE stations establish contact?
A. ALE constantly scans a list of frequencies, activating the radio when the designated call sign is received
B. ALE radios monitor an internet site for the frequency they are being paged on
C. ALE radios send a constant tone code to establish a frequency for future use
D. ALE radios activate when they hear their signal echoed by back scatter
This system scans the ALE frequency for each band, looking for ALE link establishment signals, which sound like a turkey gobbling, answer A.
E2E13
Which of these digital modes has the fastest data throughput under clear communication conditions?
A. MFSK16
B. 170 Hz shift, 45 baud RTTY
C. FT8
D. PACTOR IV
PACTOR IV is faster than the others, by a very large margin, answer D.
Forward Error Correction, FEC, is a system where additional data is sent in the data-stream, increasing the likelihood that the message will be decoded, without needing to request retransmission.
Your TV likely uses it, and clearly it is unable to request retransmission of corrupted packets. This is discussed in a later section.
A deleted question asked for a possible reason that attempts to initiate contact with a digital station on a clear frequency were unsuccessful. The use of the incorrect transmit frequency, that the protocol version used is not supported by the station, and that another station you are unable to hear is using the frequency, were all correct.
Named for its inventor, Hellschreiber generates an image of the transmitted text, in a small strip. It is based on an old military technology. While now on screen, it originally printed to a paper tape. There are a range of tone based (MFSK) and on-off keying modes. There is a club: Feld Hell Club
The on-off version shows CW is not only used to carry Morse, likewise as Morse can also be an interrupted tone on an AM, FM, or digital carrier.
On to: Propagation 1 - EME, Meteors, Microwaves, TEP, Grey-line
You can find links to lots more on the Learning Material page.
Written by Julian Sortland, VK2YJS & AG6LE, August 2025.
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