Mike:

The clock in a ~4GHz computer and DDR memory makes modem data xfr look
incredibly s-l-o-w.... with spaces miles long between marker bits...

100Mbs nic cards are not even close to a challenge to that clock
speed...

John

"Mike Coslo" wrote in message
...
wrote:
Mike Coslo wrote:

wrote:

Mike Coslo wrote:

Dave Heil wrote:
LenAnderson@ieeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee eeeeeeeeeeeeeeeeeeeeeeeeee.org
wrote:


How we be gonna scale those pictures and live video to fit
into 2.5 KHz?


Two steps:


1) Convert the pictures and video into highly-compressed
digital formats for transmission.

Oooh, there could be a problem there! There are limits to the
compression, and we have exceeded them in some forms already.


Of course! But it all depends what you consider "acceptable
quality"...

I'm assuming it has to be better than a very high quality SSTV image
in the case of stills, and present day OTA video signals....


Check to
see how many vertical pans there are on video signals lately.
The
compression on the digital signals (note that even if you are
getting
your feed via analog cable, you are still almost certainly
looking at a
digital signal) already calls for some major aliasing.


OTOH, if all you want is B&W ~CGA video....

Comes pre-aliased! ;^)


There are limits, and there are limits. How much more are we
going to throw away?


Always a tradeoff. Hams routinely use 1.8 kHz wide SSB filters for
"communications quality". Hardly hi-fi but it can make the
difference
between QSO and QRJ.


2) Use different modes/modulations/protocols

Shannon's Theorem tells us that we can get very high data
rates through
very narrow bandwidths *if* we have adequate signal-to-noise
ratio.
Note that "noise" takes many forms, not just the thermal
noise we're used to.

What're we going to do when the data rate that we need is darn
near(or above) frequency in use?

Use modes designed for the purpose. See below.

And a high enough frequency to handle the BW requirements.



For example, PSK has an advantage over OOK when dealing with
thermal
noise. But when dealing with other types of noise, OOK can
have an
advantage. It all depends on the transmission medium. What
works on a
telephone line may not work on an HF path of the same apparent
bandwidth.


I thought that we were going to be able to send live video
and digital images on HF?


You can do that now - just need enough S/N.


Always?


No mode always gets through.

But if you have enough S/N, all sorts of things are possible.

Remember though that we are talking about our favorite playground -
HF. A high S/N is not often the case here.


Here's one way. I apologize if you are way beyond this simplified
example:

Consider how PSK31 works in BPSK mode. There are just two basic
modulation states - 0 degrees and 180 degrees. One bit per unit
time.

But in QPSK mode, there are four basic modulation states - 0
degrees,
90 degrees, 180 degrees and 270 degrees. Two bits per unit time,
but
the bandwidth is no greater than with BPSK. Only problem is that
you
need a transmitter, receiver and transmission medium whose total
distortion is low enough that you can accurately tell the four
states
apart.

Now consider a theoretical "256PSK" mode, in which there are 256
states: 0 degrees, 360/256 degree, 720/256 degrees, etc., all the
way
to ~359 degrees. 8 bits in one unit time, in the same bandwidth!
But
you need a transmitter, receiver and transmission medium whose
total
distortion is low enough that you can accurately tell the 256
states
apart.

The error rate would be fantastic!

You can see that if we just keep increasing the number of states,
the
number of bits per unit time in the same bandwidth keeps going up.
But
you need more and more accurate modulator/medium/demodulator - IOW,
better and better signal-to-noise. Or to look at it another way,
the
mode carries huge amounts of data in a tiny bandwidth but has very
little tolerance for noise that takes the form of phase distortion.

Now for this system to be practical, there would have to be a way to
correct for all that phase distortion

Now imagine multiple spaced carriers in the 2.5 kHz bandwidth all
carrying data - lotta bits, huh?

Now yer cheatin! ;^) That is increased bandwidth


Of course you may find that in practice it's not that easy to get a
modulator/medium/demodulator setup that meets the requirements -
particularly if the medium is HF RF with relatively low power.

I have to imagine that there must be a lot of power, despite the
sensitivity being to phase distortion. When I look at my phase
display, there is a lot of noise showing up that can become bogus
phase noise.


Simply by hooking our computers to our rigs via the
proper interfaces.


And software.

I really didn't think it was all that simple.


Nobody said it was simple!

Mr. Smith did!

Why don't we get together
and pop off a live video system for say the 160 meter band. The
video
would be real time, 30 fps, and otherwise like broadcast video.
Better
yet, Why don't we do it at computer resolution?


Ask the PROFESSIONALS, Mike. Remember, ham radio is a HOBBY,
according
to them....

SNORT!


Now it seems that the *idea* is that we are going to use
DRM, and we're
going to need to get more spectrum in which to use.


There are all sorts of solutions. But there's a world of
difference between people talking theory and actual
application.

I did hear that DRM was capable of doing imagery. I couldn't find
any
examples tho'. And they were very vague about it.


Most of all, some folks confuse the journey and the destination.

The journey beats all.....


Exactly.

Does complex and newer equal better?

Sometimes. Not always.


Is analog simpler than digital?

Sometimes!

Does having a computer that attaches to the Internet
make a person a digital expert?


Some folks think so! I don't. And besides - "digital expert"
doesn't
mean someone knows much about radio.

Ain't that the truff?


I ask for enlightenment, I get invective.

Are you surprised?

Nope. It doesn't make for a very good discussion tho'.


Discussion is not what the invective-hurlers want, Mike.

You're right. Your multi-angle psk is the closest thing to
possibility that I have seen yet. For Satellites and other UHF
applications, it starts to become possible/practical:

http://www.tech-faq.com/qpsk.shtml

They also write about 8psk. Note that link degradation is an issue.


Here on HF, we just don't have the proper conditions. I can do
quadrature mode, but almost no one does. I've done some QSO's using
BPSK63, but of course that uses more BW.

But imagine! Someone (you) writing about something with a real
possibility, not just calling me stupid or ignorant, etc!!!!

Sunnavagun (with apologies to Hans)
BTW, 20 meters is going to town tonight!

- Mike KB3EIA -