RadioBanter - View Single Post - Echos from the past, code a hinderence to a ticket

August 9th 05, 09:48 PM

wrote:

Michael Coslo wrote:

I just had to snip some...

I can see the needed s/n ratio going up with each addition.

Exactly! Point is, if you can get the S/N high enough, you can put lots
more data through the same bandwidth.

There's no one answer to "how much data can I put through a bandwidth
of X Hz",
because it's related to things like S/N and modulation method.
Tradeoffs,
ES101 stuff.

But there is an answer that fits with practical useage.

more snippage

Telephone line modems make use of the predictable stability and
characteristics of the telephone lines. HF radio is a bit less
stable.

And yet even here, I can remember paying extra for a modem line, which
was quieter than a regular phone line. I don't know if there are such
things any more - its been a long time since I've used dial-up.
Otherwise you slow to a crawl, as error checking struggles to keep up
with line noise s/n.

The 'phone companies have cleaned up their act so much that most lines
will not only support 56k dialup, they'll also support DSL. Such improvements
are almost invisible to the unsuspecting public. They happen over periods of
years.

Just as an exercise, how much information can be carried by a 1.8 MHz
signal?

As much as the S/N allows! See above.

Of course! As a practical matter though, we have to assume amateur
radio conditions. A real limitation there.

Which is why you'll not see the pundits doing any of what they talk
about.

When all is said and done, much more is said than done....

One of the things that I wonder about with the need for huge s/n
handling ratios is that we obviously want a quiet reciever, with a
impressive noise floor. This means all of the "oomph" must be on the
strong signal handling side. We need an exquisitely sensitive and quiet
reciever, with exceptional strong signal handling capacity.

Not really.

In most situations, HF radio reception is limited by the noise picked
up by the antenna,
not internal receiver noise. Been that way since at least the 1930s. It
does no good to
have an HF receiver with, say, .05 uV for 10 dB S/N sensitivity if the
antenna picks up .5 uV of noise in the same bandwidth.

You don't need a noise generator, lab full of gear or an EE to know if
your receiver is sensitive enough. Just do this simple test:

1) Tune the rx to an unoccupied frequency, using the mode and bandwidth
you intend to use.

2) Turn off the AGC and turn up the gain until you hear the background
noise roaring away.

3) Disconnect the antenna.

If the noise drops way down, or disappears, you have all the
sensitivity you can use in that application.

Did I forget to say we had to have quiet RF conditions?

I don't doubt that we can increase the s/n ratio by all the methods we
spoke about, but isn't there some limit there? Or is there no limit, in
that we could get ~infinite bandwidth out of any frequency if we had
~infinite power?

some more snippage

Faith based electronics.

Yes - those who dare to even like modes such as Morse Code
are cursed as infidels who do not understand the Word that
"newer is always better" and "the PROFESSIONALS know best"

If newer is always better, I wonder why these vanguards of the brave
new world aren't typing to us stodgy mortals in leet? After all, it's
newer.

Because it's not about that at all.

One of the biggest flaws of many people is that they have no
appreciation of mature technology and people.

Heck, some of them don't have any apparent maturity themselves...

snort...

They choose to concentrate
on the limitations and foibles of both, not realizing that they are
themselves full of their own foibles and limitations.

You have to remember that in some folks' minds, newer *is* better,
regardless
of the reality. It's almost an ideology of constant change as being
morally
superior.

Remember Red China's "cultural revolution" in the 1960s? One of their
main ideas was that there would be a constant, continuing revolution in everything
- that all the old ideas would be tossed aside, to be replaced by the New.

Sounds like some people here!

In the process, however, they were unable to do even simple things like
feed themselves, and large numbers of people died because of it.

The largest famine in history, and we hardly heard anything about it IIRC.

Here in the West, the ideology of constant change has to do with
selling things.
Fads and fashions. In the process, all sorts of bad stuff and waste
come and go.
Worst of all, there's a sort of addiction to the quick fix rather than
real solutions.

They create for
themselves great effort and even harm in their rush to discard the old,
simply to reinvent it.

See my post about the Space Shuttle in a different thread.

I wonder how that tremendous antenna from the UofD is coming along? You
know, the one that is going to revolutionize radio? HF antennas a few
feet long that outperform anything we have today.
The one that was so "efficient" that it melted when the inventor
powered it with 100 watts. And I'm not the one who used the word
efficient, *they* did.

It *is* efficient, Mike! It's very efficient at turning HF RF energy
into heat.

I've seen better! ;^)

Not much better!

Don't expect it from "John Smith", Len, "b.b.", or even "an
old friend".
You won't get it.

That's really what it comes down to.

73 de Jim, N2EY