On Sun, 14 Jun 2009 10:17:20 -0500, Rich Griffiths
wrote:

Shannon's equations provide most of the answers:
http://www.st-andrews.ac.uk/~www_pa/...rt8/page1.html

Shannon's equations don't actually tell you much that's useful, as a
Ham.

This would presume that the Ham is rather indifferent or incapable.
Shannon's work is exceedingly useful, and at the core, quite simple to
perceive which further illuminates those mediocre qualities of your
Ham. It is unfortunate that the link above offers no graphs by which
Shannon's points would become startling apparent.

For instance:
http://www.aero.org/publications/cro...ages/04_04.gif
shows how signal to noise ratio has a vast effect over bit error in
digital transmission. In the face of equal powers (noise and bit
level), you would run the odds of 1 bit in 10 being mistaken (pretty
good odds, actually). If you were to raise the power in the bit by
10dB, that would fall to 1 bit in a million being mistaken.

In the same graph, Shannon reveals how, if you code your bits (I will
leave it to the student to discover the meaning of that), you could
achieve the same 1:1000000 advantage with the addition of less than 1
dB of power boost.

73's
Richard Clark, KB7QHC

On Jun 14, 10:03*am, Richard Clark wrote:

In the same graph, Shannon reveals how, if you code your bits (I will
leave it to the student to discover the meaning of that), you could
achieve the same 1:1000000 advantage with the addition of less than 1
dB of power boost.

73's
Richard Clark, KB7QHC

Until fairly recently, hams didn't do much coding, for a variety of
reasons. Computational horsepower is probably a big reason. Coding's
easy, decoding not so easy, at least in a "parts readily available
from Radio Shack" sort of sense. Obviously, today, one could do all
sorts of coding on a laptop PC, particularly at low bit rates, but
you'd still need to have an unusual convergence of someone who knows
how to implement the coding algorithms who's also interested in
amateur microwave operating. It's not anything like a turnkey thing,
or even a "go get gnuradio" thing. Where you see coding in common ham
use, it's buried in an application (PSK31, JT65, and the like)

The other problem is the frequency control issue. If you want low
rates and ragged edge of Shannon, you need good frequency stability
and control (and to a lesser extent, good phase noise). Until
recently (with GPS disciplined oscillators and surplus Rb sources)
this was a real challenge. As Rich commented with respect to antenna
pointing, you also have to be right on for frequency, and that's hard,
especially in a field situation. Tuning to 10Hz accuracy at 10GHz
implies 1E-9 frequency accuracy, which is challenging. To a certain
extent, processing power in a PC helps (get close, do parallel
demodulation, find the signal), but just like for coding, it requires
finding a person (or small group) who can deal with building low phase
noise stable oscillators AND with developing software that is somewhat
complex, compared to the usual "whack it out in a weekend of coding"
stuff.

I suspect there ARE hams experimenting with this, but it's a long way
from critical mass wide acceptance. You need something that you can
write an article in QST, and offer $100 widgets to make that
happen. There's not much cheap surplus gear either, since commercial
equipment these days tends to be more specialized and isn't as
amenable to hackery.

There are also proprietary rights issues with some coding techniques
(e.g. Turbo) but I suspect that legal issues aren't what's holding
hams back. For things like LDPC, there are published software
implementations that are free to use. I haven't looked but I imagine
that various convolutional codes and decoders are also publicly
available, along with Viterbi soft-decision decoders.

On Sun, 14 Jun 2009 11:08:36 -0700 (PDT), Jim Lux
wrote:

Until fairly recently, hams didn't do much coding, for a variety of
reasons.

This neither negates the specific issues of signal to noise in their
relationship, a matter that is quite in the power of the Ham to
control to some extent; nor does it invalidate the simplicity of that
relationship revealed through one graphic that serves to reduce the
obscurity of a lot of math.

As for the variety of reasons, computation power would seem to be in
abundance (the first mythical Cray is a door stop today). That as an
excuse is a croak.
It's not anything like a turnkey thing,
Like I said, an indifferent or incapable individual in the guise of
"Ham." I am amazed how that Lid is raised on a pedestal.
or even a "go get gnuradio" thing. Where you see coding in common ham
use, it's buried in an application (PSK31, JT65, and the like)
So, let me get this straight, because it is available (a seeming
contradiction from the tenor of your response), it is not accessible?
Or it is not useful? Or it is not understood? Or Shannon has been
rendered obsolete?

Your objections are answered with your own solutions and yet the sense
of what you say is shove Shannon out the window and whine about the
noise.

73's
Richard Clark, KB7QHC

On Sun, 14 Jun 2009 10:03:29 -0700, Richard Clark wrote:

On Sun, 14 Jun 2009 10:03:29 -0700, Richard Clark wrote:

On Sun, 14 Jun 2009 10:17:20 -0500, Rich Griffiths
wrote:


Shannon's equations don't actually tell you much that's useful, as a
Ham.

This would presume that the Ham is rather indifferent or incapable.
Shannon's work is exceedingly useful
snip

Well, I do admit that I went overboard there! Probably shouldn't speak
too quickly about moonbounce, meteor scatter, etc. I do think, however,
that for many Hams (me, at least :-) ) the applicable word is
"indifferent" rather than "incapable".

If you can genuinely find useful application to what microwave rovers do
-- or most microwave operators, for that matter -- that would be a special
contribution. I expect that would be even less likely for most HF and VHF
operations.

I'd characterize Shannon's work as more of academic interest (for most Ham
radio) than practical interest. In most of what most Hams do, there are
just too many other issues to deal with.

Please note the use of the word "most". I'm sure there are exceptions,
but I expect they're a small part of hamdom (as is microwaving, sigh).

--
Rich W2RG

I'd characterize Shannon's work as more of academic interest (for most Ham
radio) than practical interest. *In most of what most Hams do, there are
just too many other issues to deal with.

Please note the use of the word "most". *I'm sure there are exceptions,
but I expect they're a small part of hamdom (as is microwaving, sigh).

--
Rich * W2RG

I think you've hit the nail on the head..

If you're communicating with deep space probes, you've probably
already eked out the last tenth of dB everywhere else in the system,
so you can worry about coding and how close you are to the Shannon
limit.

If you're a ham, especially microwave rovering, then getting the last
couple dB is the least of your problems. It's easier for the ham to
get 3dB by some other means than, say, implementing coding.

Where some kind soul has made using coding easy, it's used (e.g.
JT65).