Varicode is an encoding method where ASCII characters are represented by bit patterns ranging from 1 to 10 bits in length. Varicode is used for PSK31 ("Phase Shift Keying, 31 Baud"). ASCII (American Standard Code for Information Interchange) or Baudot (RTTY) rely on a precise number of evenly-timed bits. AX.25 is a protocol used for packet transmission.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Key words: TNC to COMPUTER INTERCONNECTION. Physical layer (for example, RS-232): the electrical, mechanical, procedural and functional specifications for moving data across a physical medium, including modulation, establishing and terminating connections. The Data Link layer packages data bits into frames, provides error-free transfer of frames including physical addressing, network topology, error notification. The Network layer (for example, Internetwork Protocol) uses logical addresses to route frames through a network of links. The Transport layer (for example, TCP Transmission Control Protocol) provides the end-to-end control, ensures that data is complete and properly sequenced ( e.g., retransmissions ).
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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"A cyclic redundancy check (CRC) is an error-detecting code commonly used in digital networks and storage devices to detect accidental changes to raw data" (Wikipedia). A CRC is computed at the originating end and sent with the message; the receiving end does the same calculation, a mismatch in the CRC indicates that the payload was damaged. The CRC manages error detection, other mechanisms can provide error correction.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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With 5 bits, Baudot can accommodate 32 combinations ( 2 exponent 5 ) per character set; one set represents uppercase letters A through Z, the other are figures 0 through 9 plus other symbols. The original ASCII (American Standard Code for Information Interchange) used seven bits to accommodate 128 combinations; enough for lowercase and uppercase letters, all digits and other symbols. So called "extended ASCII" uses 8 bits for a total of 256 combinations, this adds accented letters.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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AMTOR is similar to RTTY but with error correction added; a special 7-bit code is used. Amateur Teleprinting Over Radio (AMTOR) can run under two modes. Mode B ( FEC - Forward Error Correction ): characters are sent twice in groups of five in consecutive blocks. Mode A ( ARQ - Automatic Repeat reQuest ): characters are transmitted in blocks of 3, receiving station returns a positive acknowledgement or a request to resend. [ Frame Check Sequence is part of the AX.25 Packet protocol, no relation to AMTOR ]
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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AMTOR is similar to RTTY but with error correction added; a special 7-bit code is used. Amateur Teleprinting Over Radio (AMTOR) can run under two modes. Mode B ( FEC - Forward Error Correction ): characters are sent twice in groups of five in consecutive blocks. Mode A ( ARQ - Automatic Repeat reQuest ): characters are transmitted in blocks of 3, receiving station returns a positive acknowledgement or a request to resend. [ Frame Check Sequence is part of the AX.25 Packet protocol, no relation to AMTOR ]
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Key word: NOT. "APRS is a digital communications information channel for Ham radio. (...) As a single national channel (...), it gives the mobile ham a place to monitor for 10 to 30 minutes in any area, at any time to capture what is happening in ham radio in the surrounding area. Announcements, Bulletins, Messages, Alerts, Weather, and of course a map of all this activity including objects, satellites, nets, meetings, hamfests, etc. (...) APRS also supports global call sign-to-call sign messaging (...)" (www.aprs.org Bob Bruninga WB4APR). Automatic Link Establishment (ALE) is a standard for systems capable of automatically selecting a band and frequency from a list of channels for HF communications with a given similarly-equipped station.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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"A hash function is any algorithm that maps data of arbitrary length to data of a fixed length. (...) The values returned by a hash function are called hash values, hash codes, hash sums, checksums or simply hashes" (Wikipedia). A convolutional code is a type of error-correcting code (e.g., Viterbi or Reed-Solomon). Lempel-Ziv and Dynamic Huffman coding are lossless data compression algorithms.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Packet radio adheres to the AX.25 protocol. AX.25 is derived from the X.25 networking protocol: one notable difference is the use of call signs as addresses. AX.25 uses a Frame-Check Sequence for error detection. The Frame-Check sequence (FCS) is a sixteen-bit number calculated by both the sending and receiving stations of a frame. Comparing the received FCS with a locally computed one permits detecting corruption in transit.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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With 5 bits, Baudot can accommodate 32 combinations ( 2 exponent 5 ) per character set; one set represents uppercase letters A through Z, the other are figures 0 through 9 plus other symbols. The original ASCII (American Standard Code for Information Interchange) used seven bits to accommodate 128 combinations; enough for lowercase and uppercase letters, all digits and other symbols. So called "extended ASCII" uses 8 bits for a total of 256 combinations, this adds accented letters.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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With 5 bits, Baudot can accommodate 32 combinations ( 2 exponent 5 ) per character set; one set represents uppercase letters A through Z, the other are figures 0 through 9 plus other symbols. The original ASCII (American Standard Code for Information Interchange) used seven bits to accommodate 128 combinations; enough for lowercase and uppercase letters, all digits and other symbols. So called "extended ASCII" uses 8 bits for a total of 256 combinations, this adds accented letters.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Spread-spectrum transmission relies on a wide range of frequencies rather than a single one to reduce the effects of noise and interference. It requires several megahertz of bandwidth. Frequency-Hopping Spread-Spectrum changes the carrier frequency a number of times per second in a given pattern. Direct-Sequence Spread-Spectrum uses a pseudo-random bit pattern, many times faster than the data stream, to impress Phase Shift Keying on a carrier. For proper demodulation, the receiver must synchronize itself with the incoming stream. Noise and interference do not follow the same pre-agreed patterns and are thus effectively ignored.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Spread-spectrum transmission relies on a wide range of frequencies rather than a single one to reduce the effects of noise and interference. It requires several megahertz of bandwidth. Frequency-Hopping Spread-Spectrum changes the carrier frequency a number of times per second in a given pattern. Direct-Sequence Spread-Spectrum uses a pseudo-random bit pattern, many times faster than the data stream, to impress Phase Shift Keying on a carrier. For proper demodulation, the receiver must synchronize itself with the incoming stream. Noise and interference do not follow the same pre-agreed patterns and are thus effectively ignored.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Spread-spectrum transmission relies on a wide range of frequencies rather than a single one to reduce the effects of noise and interference. It requires several megahertz of bandwidth. Frequency-Hopping Spread-Spectrum changes the carrier frequency a number of times per second in a given pattern. Direct-Sequence Spread-Spectrum uses a pseudo-random bit pattern, many times faster than the data stream, to impress Phase Shift Keying on a carrier. For proper demodulation, the receiver must synchronize itself with the incoming stream. Noise and interference do not follow the same pre-agreed patterns and are thus effectively ignored.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Spread-spectrum transmission relies on a wide range of frequencies rather than a single one to reduce the effects of noise and interference. It requires several megahertz of bandwidth. Frequency-Hopping Spread-Spectrum changes the carrier frequency a number of times per second in a given pattern. Direct-Sequence Spread-Spectrum uses a pseudo-random bit pattern, many times faster than the data stream, to impress Phase Shift Keying on a carrier. For proper demodulation, the receiver must synchronize itself with the incoming stream. Noise and interference do not follow the same pre-agreed patterns and are thus effectively ignored.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Spread-spectrum transmission relies on a wide range of frequencies rather than a single one to reduce the effects of noise and interference. It requires several megahertz of bandwidth. Frequency-Hopping Spread-Spectrum changes the carrier frequency a number of times per second in a given pattern. Direct-Sequence Spread-Spectrum uses a pseudo-random bit pattern, many times faster than the data stream, to impress Phase Shift Keying on a carrier. For proper demodulation, the receiver must synchronize itself with the incoming stream. Noise and interference do not follow the same pre-agreed patterns and are thus effectively ignored.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Spread-spectrum transmission relies on a wide range of frequencies rather than a single one to reduce the effects of noise and interference. It requires several megahertz of bandwidth. Frequency-Hopping Spread-Spectrum changes the carrier frequency a number of times per second in a given pattern. Direct-Sequence Spread-Spectrum uses a pseudo-random bit pattern, many times faster than the data stream, to impress Phase Shift Keying on a carrier. For proper demodulation, the receiver must synchronize itself with the incoming stream. Noise and interference do not follow the same pre-agreed patterns and are thus effectively ignored.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Spread-spectrum transmission relies on a wide range of frequencies rather than a single one to reduce the effects of noise and interference. It requires several megahertz of bandwidth. Frequency-Hopping Spread-Spectrum changes the carrier frequency a number of times per second in a given pattern. Direct-Sequence Spread-Spectrum uses a pseudo-random bit pattern, many times faster than the data stream, to impress Phase Shift Keying on a carrier. For proper demodulation, the receiver must synchronize itself with the incoming stream. Noise and interference do not follow the same pre-agreed patterns and are thus effectively ignored.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Spread-spectrum transmission relies on a wide range of frequencies rather than a single one to reduce the effects of noise and interference. It requires several megahertz of bandwidth. Frequency-Hopping Spread-Spectrum changes the carrier frequency a number of times per second in a given pattern. Direct-Sequence Spread-Spectrum uses a pseudo-random bit pattern, many times faster than the data stream, to impress Phase Shift Keying on a carrier. For proper demodulation, the receiver must synchronize itself with the incoming stream. Noise and interference do not follow the same pre-agreed patterns and are thus effectively ignored.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
Spread-spectrum transmission relies on a wide range of frequencies rather than a single one to reduce the effects of noise and interference. It requires several megahertz of bandwidth. Frequency-Hopping Spread-Spectrum changes the carrier frequency a number of times per second in a given pattern. Direct-Sequence Spread-Spectrum uses a pseudo-random bit pattern, many times faster than the data stream, to impress Phase Shift Keying on a carrier. For proper demodulation, the receiver must synchronize itself with the incoming stream. Noise and interference do not follow the same pre-agreed patterns and are thus effectively ignored.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
Spread-spectrum transmission relies on a wide range of frequencies rather than a single one to reduce the effects of noise and interference. It requires several megahertz of bandwidth. Frequency-Hopping Spread-Spectrum changes the carrier frequency a number of times per second in a given pattern. Direct-Sequence Spread-Spectrum uses a pseudo-random bit pattern, many times faster than the data stream, to impress Phase Shift Keying on a carrier. For proper demodulation, the receiver must synchronize itself with the incoming stream. Noise and interference do not follow the same pre-agreed patterns and are thus effectively ignored.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
Spread-spectrum transmission relies on a wide range of frequencies rather than a single one to reduce the effects of noise and interference. It requires several megahertz of bandwidth. Frequency-Hopping Spread-Spectrum changes the carrier frequency a number of times per second in a given pattern. Direct-Sequence Spread-Spectrum uses a pseudo-random bit pattern, many times faster than the data stream, to impress Phase Shift Keying on a carrier. For proper demodulation, the receiver must synchronize itself with the incoming stream. Noise and interference do not follow the same pre-agreed patterns and are thus effectively ignored.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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