Gorgon said:mstechca said:_3iMaJ said:The receiver simply uses a PLL to make the appropriate decision on what data was sent.
I know that, but what are the frequencies for the "Mark" and "space" tones?
300/300 Bd (All number in Hz)
Bell 103 calling: 1270(1)/1070(0) answer: 2225(1)/ 2025(0)
V21 calling: 980(1)/1180(0) answer: 1650(1)/1850(0)
75/1200Bd
Bell 202 Calling:387(1)/487(0) answer: 1200(1)/2200(0)
V23 Calling: 390(1)/450(0) answer: 1300(1)/2100(0)
This is taken form the K-series design manual from Silicon Systems.
TOK
mstechca said:Is the difference between FSK and AFSK just the way data is handled?
and what are the frequencies (in hertz, kilohertz, whatever) of the mark and space tones?
mstechca said:Is the difference between FSK and AFSK just the way data is handled?
and what are the frequencies (in hertz, kilohertz, whatever) of the mark and space tones?
thats what I thought. and how do I determine these two different frequencies FSK uses? I can't just go random.Nigel Goodwin said:FSK is just a carrier, and you switch the carrier between two different frequencies.
mstechca said:Packet radio has a universal frequency of about 144Mhz, so what is it for FSK?
mstechca said:thats what I thought. and how do I determine these two different frequencies FSK uses? I can't just go random.Nigel Goodwin said:FSK is just a carrier, and you switch the carrier between two different frequencies.
FSK is just a carrier, and you switch the carrier between two different frequencies. AFSK uses a single carrier frequency and you modulate it with one of two audio tones, one for mark and one for space - commonly used frequencies have been posted previously in this thread.
FSK is two audio tones that modulate a single carrier, you can hear it. 1200Hz and 2200Hz are low frequencies that were used at 300 (up to 2400?) baud over low-bandwidth and noisy telephone lines. All kinds of improvements in modulation allows 56k over telephone lines and transmitters. They use data-compression, error-correction and phase modulation. They use a lot more than only two audio tones.
mstechca said:Nigel says:
FSK is just a carrier, and you switch the carrier between two different frequencies. AFSK uses a single carrier frequency and you modulate it with one of two audio tones, one for mark and one for space - commonly used frequencies have been posted previously in this thread.
Audiogurusays:
FSK is two audio tones that modulate a single carrier, you can hear it. 1200Hz and 2200Hz are low frequencies that were used at 300 (up to 2400?) baud over low-bandwidth and noisy telephone lines. All kinds of improvements in modulation allows 56k over telephone lines and transmitters. They use data-compression, error-correction and phase modulation. They use a lot more than only two audio tones.
I'm very confused, because Nigel says with FSK, you switch the carrier between 2 frequencies. Audioguru says that FSK is equivalent to what Nigel said about AFSK (two tones modulating a single carrier).
Who is right?
Frequency-shift keying
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Frequency-shift keying (FSK) is a form of frequency modulation in which the modulating signal shifts the output frequency between predetermined values.
Usually, the instantaneous frequency is shifted between two discrete values termed the mark frequency and the space frequency. This is a noncoherent form of FSK.
Audio frequency-shift keying
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Audio frequency-shift keying (AFSK) is a modulation technique by which digital data is represented as changes in the frequency (pitch) of an audio tone, yielding an encoded signal suitable for transmission via radio or telephone. Normally, the transmitted audio alternates between two tones: one, the "mark", represents a binary one; the other, the "space", represents a binary zero.
AFSK differs from regular frequency-shift keying in that the modulation is performed at baseband frequencies. In radio applications, the AFSK-modulated signal is normally used to modulate an RF carrier (using a conventional technique, such as AM FM or ACSSB(R)(LM Mode(R)) for transmission.
AFSK is not generally used for high-speed data communications, as it is less efficient than other modulation modes. In addition to its simplicity, however, AFSK has the advantage that encoded signals will pass through AC-coupled links, including most equipment originally designed to carry music or speech.
Applications
Most early telephone-line modems used audio frequency-shift keying to send and receive data, up to rates of about 300 bits per second. The common Bell 103 modem used this technique, for example. Some early microcomputers used a specific form of AFSK modulation, the Kansas City standard, to store data on audio cassettes. AFSK is still widely used in amateur radio, as it allows data transmission through unmodified voiceband equipment.
I haven't read a single book about radio. I think the prof in university talked a little about radios. Many magazines I read in the library taught me stuff about radios.mstechca said:audioguru, I suppose you go through 100's and 100's of books related to radio.
so this becomes equivalent to an FM signal , where the carrier freq is changed WRT to i/p signal.Frequency-shift keying (FSK) is a form of frequency modulation in which the modulating signal shifts the output frequency between predetermined values.
Good point!akg said:so this becomes equivalent to an FM signal , where the carrier freq is changed WRT to i/p signal.
audioguru said:FM is a very simple way to make FSK. But how would you detect it, it is DC modulation, isn't it? I guess you could scale down its frequencies with a counter then detect them with a PLL.
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