From: "Dee Flint" on Mon 4 Jul 2005 21:04


"John Smith" wrote in message
...
Mike:

300 baud is ridiculous, in Dee's first post mentioning 300 baud I tossed
it out the window--that was fine up to about 1985, then only the mentally
challenged continued to run 300 baud modems!

Please show me and everyone else how we can run more than 300 baud on HF
without exceeding reasonable band widths. There are a whole lot of things,
not just video, that would be nice to do.

How can we do it? Bandwidth is directly related to baud rate.

Not DIRECTLY related. :-) Look to the 56K modem that most folks
use to connect to the ISPs now. Those work over about a 3 KHz
bandwidth limit.

That 56K modem is capable of 56,000 bits per second. If that was
carried on an AM carrier, then it would require 112 KHz bandwidth
minimum. Using SSB techniques it would be 56 KHz bandwidth
minimum. Yet it works in THREE KILOHERTZ BANDWIDTH. HOW?

You are "in the engineering profession." You explain it to
yourself. Then you, as an amateur extra can explain it to
these other radio experts in here.

Here's a hint: Those 56K modems use a combination of amplitude
and phase modulation of a carrier...and do it at at least 8
discrete levels of amplitude and phase. Obviously it works.
All you need to do is rid yourself of the old AM double SB
concepts (even the SSB concepts) and look deeper.

John Carson of AT&T showed the basic mathematics for AM, PM, and
FM way back in 1915. All you need to do is work with some
basic series equations and solve the combination of AM and PM.
That sort of thing is done "in the engineering profession."
Where you are.

"300 Baud" (or 300 bits per second) is way slow by comparison.
Ordinary LSB AM of an audio carrier can do it within the 3 KHz
telco lines. Yet the 56K modems are wayyyyy faster.

Once, you, as "in the engineering profession," solve it, you
will have AN answer, one of several possibilities for
increasing throughput rate in a very limited bandwidth. Aid your
ham compadres with your answer when you get done. Comprende?

de nada...

bit bit