Hi:
What waveform[s] of FSK do[es] the EDT [European Deaf Telephone] protocol use?
FSK = Frequency Shift Keying
Quote from
"EDT Operational Mode -- The modulation is frequency shift keyed modulation (i.e. carrier is 10 ms before a character is transmitted and removed 1s after the last character) using Recommendation V.21(1) frequencies. The data signalling rate is 110 bits/s."
Quote from
"European Deaf Telephone (or EDT), which is used in Germany, Austria, Switzerland, Malta, Spain and Italy, uses ITU-T V.21 Channel 1 modulation at a signaling rate of 110 bps. ITU-T V.21 Channel 1 modulation has a mark frequency at 980 Hz and a space frequency at
1080 Hz. In EDT, the mark frequency is transmitted for 300 ms before a character is transmitted, and the mark frequency is transmitted for up to one (1) second after the last character. EDT has a character format of one (1) start bit, seven (7) data bits, one (1) even parity bit and two (2) stop bits. The first EDT character can be detected using the present invention, as described below. For example, at step 506 of FIG. 5, the mark frequency that precedes the start bit is used for the detection of the first EDT character. At step 508, tone detector 420 starts looking for the mark frequency, i.e. 980 Hz, and at step 510, it is determined whether the 980 Hz mark frequency is detected for a pre-determined amount of time. In one embodiment, detection of 10-20 ms of the mark frequency can be sufficient at step 510."According to the above links, EDT uses FSK in which the two are frequencies are 980 Hz [representing a "1"] and 1080 Hz [representing a "0"].
What are the shapes of the 980 Hz and 1080 Hz tones? Are they sine waves, square waves, sawtooth waves, triangle waves??
Would an EDT-demodulator recognize only certain wave-shapes while ignoring others?
Thanks