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Upgrading to Extra gives access to extra bandwidth on HF, for both Data, and Image modes.
Many 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.
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.
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.
Under good conditions packet radio has good data throughput, at 300 baud it is higher than the weak signal modes such as PSK31; and than RTTY, which is often 45.45 baud. It is used for sending messages and bulletins, just as VHF packet is. Messages originated from VHF stations to distant stations may be passed through an HF gateway station.
These are the actual questions from the Extra licence exam pool, as published by the NCVEC.E2E01
Frequency shift keying (FSK) or AFSK are common, answer B.
Pulse modulation and spread spectrum are for high VHF and up only.E2E02
Forward Error Correction, answer A.E2E03
Stations take turns transmitting at 7.5 second intervals, answer C.E2E04
This is indicating selective fading, answer A.E2E05
Winlink is an email forwarding system, not a live chat systems, answer AE2E06
300 baud, answer C.E2E07
All of the above, answer D.E2E08
This is PACTOR, answer B.
Hellschreiber is a graphical text messaging system; and RTTY and AMTOR are text modes.E2E09
PSK31 uses "varicode", variable length coding, for efficiency, answer D.E2E10
With just 31 baud, PSK31 has narrow bandwidth, answer C.E2E11
Direct FSK varies the VFO's frequency; AFSK sends audio tones to the microphone input, answer A.E2E12
This system scans the ALE frequency for each band, looking for ALE link establishment signals, which sound like a turkey gobbling, answer A.E2E13
300 baud packet is faster than the others, answer D.
PSK 31 is 31 baud, RTTY 45.45 baud, much less than 300. AMTOR is a development of RTTY.
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, May 2022.
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