General/Chapter 6 Study Guide - Revision history

Admin: /* Section 6.6: Operating Procedures */

2016-06-21T05:08:30Z

Section 6.6: Operating Procedures

← Older revision		Revision as of 05:08, 21 June 2016
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	<pre>		<pre>
			Call:

	CQ CQ CQ DE KC7DBU KC7DBU		CQ CQ CQ DE KC7DBU KC7DBU

	CQ CQ CQ DE KC7DBU KC7DBU K		CQ CQ CQ DE KC7DBU KC7DBU K

			Response:

	KC7DBU KC7DBU DE N6QU N6QU K		KC7DBU KC7DBU DE N6QU N6QU K

Admin: /* Section 6.5: Summary */

2016-06-21T05:08:02Z

Section 6.5: Summary

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Admin: /* Section 6.2: Summary */

2016-06-21T04:52:41Z

Section 6.2: Summary

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	* Rapid changes in phase sound like buzzing		* Rapid changes in phase sound like buzzing

	==Section 6.2: Summary==		===Section 6.2: Summary===

	* An FSK signal is generated by changing an oscillator's frequency directly with a digital control signal		* An FSK signal is generated by changing an oscillator's frequency directly with a digital control signal

Admin: /* Section 6.2: Summary */

2016-06-21T04:52:30Z

Section 6.2: Summary

← Older revision		Revision as of 04:52, 21 June 2016
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	* An FSK signal is generated by changing an oscillator's frequency directly with a digital control signal		* An FSK signal is generated by changing an oscillator's frequency directly with a digital control signal
			* The two separate FSK frequencies are identified by "mark" and "space"

	==Section 6.3: Character Based Modes==		==Section 6.3: Character Based Modes==

Admin: /* Section 6.1 Summary */

2016-06-21T04:50:49Z

Section 6.1 Summary

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	* The digital mode that is designed to operate at extremely low signal levels is JT9 and JT65		* The digital mode that is designed to operate at extremely low signal levels is JT9 and JT65

	===Section 6.~~1 Summary=~~==		==Section 6.2: Digital Basics==

	Definitions:		Definitions:

Admin: /* Section 6.3: Character Based Modes */

2016-06-15T09:54:41Z

Section 6.3: Character Based Modes

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 * 1 symbol = 2 transmission intervals
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Admin: /* Section 6.3: Character Based Modes */

2016-06-15T09:30:41Z

Section 6.3: Character Based Modes

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	* Reversal = 0, no reversal = 1		* Reversal = 0, no reversal = 1
	* 1 symbol = 2 transmission intervals		* 1 symbol = 2 transmission intervals


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Admin: Created page with "=Chapter 6: Digital Modes= ==Section 6.1: Intro to Digital Modes== Where to find digital: * digital modes restricted to CW/data band allocation * Calling frequencies are at..."

2016-06-15T09:25:15Z

Created page with "=Chapter 6: Digital Modes= ==Section 6.1: Intro to Digital Modes== Where to find digital: * digital modes restricted to CW/data band allocation * Calling frequencies are at..."

New page

=Chapter 6: Digital Modes=

==Section 6.1: Intro to Digital Modes==

Where to find digital:
* digital modes restricted to CW/data band allocation
* Calling frequencies are at lowest end, move up with activity
* On 20 m: PSK31 at 14.070 MHz, RTTY and other modes above that
* Table: Bands vs Frequency Ranges
* For the exam:
** 20 m segment for digital:
*** 14.070 - 14.100 MHz
** 20 m segment for PSK31: below RTTY segment, near 14.070 MHz
** 80 m segment for digital: 3.570 - 3.600 MHz
** 40 m segment for digital: 7.070 - 7.125 MHz
* Digital modes regulated as voice emissions by FCC
* Maximum bandwidth and data rates set by FCC to limit signal bandwidth
* Digital codes must be publicly specified and must comply with bandwidth/signal rate restrictions
* Rules may change to be based on bandwidth

Digital modes:
* RTTY - popular, mechanical teleprinters
* PSK31 - narrow bandwidth, weak signal, cheap hardware
* PACTOR - packet teletype over radio, improvement on RTTY, data transmitted as packets, PACTOR is proprietary mode
* Packet radio - common on VHF/UHF, not as common on HF due to higher error rates/sensitivity to noise
* Miscellaneous other modes:
** MFSK16, GTOR, JT9, JT65, CLOVER, ALE, WSPR

===Section 6.1: Summary===

* 20 m band segment used for digital modes is 14.070 - 14.100
* The band segment on 80 m used for digital modes is 3.570 - 3.600 MHz
* The 20 m segment with PSK31 operations is below RTTY, around 14.070 MHz
* The communication system that sometimes uses the internet to transfer messages is WINLINK
* The digital mode that is designed to operate at extremely low signal levels is JT9 and JT65

===Section 6.1 Summary===

Definitions:
* Air link - the part of the communication system involving RX/TX of radio signals
* Bit - 0 and 1, fundamental unit of data
* Bit rate - number of bits per second sent between 2 computers
* Baud - number of symbols per second
* Duty cycle - ratio of time spent transmitting to total time on/offline
* Protocol - rules controlling the data exchange method
* Mode - combination of protocol and modulation method
* Modem - translates bits into tones and back again

Bit rate vs baud rate:
* Modern modems can use complex audio signals to encode multiple pieces of information into single character
* As more information is packed into characters, the bit rate becomes faster than the baud rate
* Digital mode combines protocol (how information and characters are encoded) with modulation method
* OOK = on/off keying
* FSK = frequency shift keying
* PSK = phase shift keying
* I/Q = 2 phase-shifted AM signals

Frequency shift keying FSK:
* Bits of data encoded as tones; tone frequencies are represented by different bits
* Two-tone FSK signal: "mark" and "space"
* True, direct FSK: digital data controls VFO
* AFSK = audio frequency shift keying - convenient, uses mic/SSB, but prone to distortion
* More symbols means more frequencies means more time to differentiate between signals

Phase shift keying PSK:
* data is encoded as phase relationship between tones
* Rapid changes in phase sound like buzzing

==Section 6.2: Summary==

* An FSK signal is generated by changing an oscillator's frequency directly with a digital control signal

==Section 6.3: Character Based Modes==

RTTY:
* RTTY - oldest, most popular, narrow band
* RTTY uses baudot code - 5 bits per character
* Stop/start bits to sync transmission
* 5 bits = 2^5 = 32 characters
* Letters and figures codes to get 62+2 characters
* Standard mark/space frequencies are 2125 Hz (mark), 2295 Hz (space)
* Difference between mark and space tones is called shift
* HF, most common speeds are 60, 75, 100 WPM corresponding to 45, 56, 75 baud
* Most conversations on HF are 45 baud, most common shift is 170 Hz

MFSK:
* MFSK - multiple-frequency shift keying, uses more than two tones to encode data
* MFSK16 - uses 16 separate tones, all 15.625 Hz apart
* This allows entire signal to be received with a 500 Hz CW filter
* Thru signal shaping and tone control, can sustain contacts through fading and distortion better than two-tone signals

DominoEX:
* DominoEX - modification of MFSK, uses differences betweeen successive tones
* Less sensitive to tuning error sand drift
* Data rates go from 4 baud to 21.5 baud, bandwidths up to 524 Hz

OLIVIA:
* wider bandwidth MFSK mode, 125-1000 Hz bandwidth, variable number of tones
* Uses forward error correction, can be used at low signal levels

Others:
* MT63: Multi-tone, data has 64 tones, advanced DSP techniques allow it to perform well under noisy conditions
* PSK31: Phase shift keying, 31 is the symbol rate (31.25 baud)
** Variable-length character codes (like Morse code)
** PSK63 at 63.5 baud also popular
** Very narrow bandwidth, so usually close to calling frequency
* PSK31 sends single tone, reversals of phase sent at regular intervals
* Reversal = 0, no reversal = 1
* 1 symbol = 2 transmission intervals