GARTHWILSON wrote:
If you can think of simple inexpensive ways to get around these cassette problems and get some faster data rates without losing reliability, I'd like to hear them.
Steve Wozniak(sp?), IIRC, created a cassette interface that got all the way up to 3000bps. It didn't use audio tones, but rather, nonsinusoidal waves. What was basically recorded on the tape was a raw NRZI signal. Due to the AC coupling to the tape, what came back was an AMI (Alternate Mark Inversion) signal. That is, the reader would get a pulse (alternating between positive and negative; hence the modulation name) every time a logic 1 was "received."
Using an encoding system like MFM, you could get pretty high data rates that way.
If I'm not mistaken, data recorded on floppy disks is done the same way: MFM-encoded NRZI out, MFM-encoded AMI back in.
Of course, we can get away with this with cassettes, because we don't have FCC requirements or splatter to worry about. After all, this technique is essentially UWB, but on recorded media instead of RF.
Quote:
The phone modem constellations of amplitude and phase modulation that allow 56kbps on a phone connection whose frequency response is limited to a few kHz are not useful without a solid, clean transmission medium with good S/N ratio, no signifficant jitter (since it really fowls up the phase), etc..
This is why I advocate using pure phase shift or frequency shift keying. Amplitude shift keying, in any form, is too unreliable on the amateur radio bands. BPSK and QPSK are fine modulation methods, and I would love to employ them on the 2m band to achieve 12000bps and 24000bps throughputs, though the latter does require a better connection path. Imagine, on the 70cm band, BPSK can be used to easily achieve 80 to 160kbps, rivaling many people's DSL connections in real-world performance!
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I also have a 4mm tape drive in my Windows XP machine.