John Smith wrote:
Dee:

Will you agree that a 56K phone modem, does indeed, transmit this data
rate with an audio bandwidth of ~300Hz to ~5000K, and if you do so
agree, how can you argue this cannot fit in a HF AM RF signal which
only goes 2.5K each side of center frequency??????????

Of course it can.

The question is whether the RF path will have characteristics
comparable to those of the telephone line.

Are you NOT imposing an audio frequency of AT LEAST a 5K bandwidth on
the rf carrier with normal speech?

No. Typical ham transceivers only need about 2.5 kHz of audio
bandwidth.

(actually, most quality
transceivers have a wider audio bandwidth than this which can be set
+/-) and if you agree you are indeed, how can you argue that 5K
bandwidth can carry a 56K data rate over a phone line--and NOT a hf rf
signal???? That looks insane to me?

It's a question of the characteristics of the RF path. Certainly there
are some paths that will support the amplitude- and phase- stable
requirements of the 56K modem - and some paths that won't.

On top of that is the fact that most RF paths aren't full duplex. How
fast is the 56K modem in half-duplex with transmit-receive switching?

The modem is NOT using the whole 5K bandwidth--necessarily, there is
compression into a narrower bandwidth which can and is generally
software controlled--if necessary (the modems software is a LOT
smarter than most give it credit for, especially in the case of the
old "onboard processor" and "hardware logic" USRobotics external
modems.

You need to explain to me why it even begins to look difficult to you
for me to be able to understand what you are asking?

As, I have to be missing something here...

You are. Do you think HF offers the same transmission characteristics
as a telephone line?

You know, I have not even looked to see on the web, but aren't tons of
people doing this right now as we newsgroup?

On telephone wires or HF radio?

I suppose you could actually use the rf signal as data carrier itself
and modulate it directly through on/off switching, as opposed to
modulating the rf carrier with the audio data carrier... but that
would take some heavy duty equip mods/revamps, if it didn't wipe out
the neighbors cable tv! grin

Think about this:
at 100 mhz if you can precisely control the EXACT amplitude of each
and every cycle of rf out the back end of the xmitter, you have a
virtual 100mbs data carrier... most are working here... 450 MHz?
1Ghz? 12Ghz?

Think about the stability of the RF path at HF.

... and of course, the receiver has to be able to decipher the
amplitudes of each cycle back to a data stream for the video card...

... this is the land where dreamers are...

John

"Dee Flint" wrote in message
...

"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.

Dee D. Flint, N8UZE