| |
PA2AGA > HDDIG 26.09.00 21:00l 159 Lines 7209 Bytes #999 (0) @ EU
BID : HD_2000_261A
Read: GUEST
Subj: HamDigitalDigest 2000/261A
Path: DB0AAB<DB0ZKA<DB0ABH<DB0SRS<DB0CWS<DB0ZDF<DB0AIS<DB0NDK<DB0ACH<PI8JOP<
PI8ZAA<PI8WFL<PE1NMB<PI8HGL
Sent: 000926/1825Z @:PI8HGL.#ZH1.NLD.EU #:18329 [Den Haag] FBB $:HD_2000_261A
From: PA2AGA@PI8HGL.#ZH1.NLD.EU
To : HDDIG@EU
Date: Tue, 26 Sep 00 19:50:23 MET
Message-Id: <hd_2000_261A>
From: pa2aga@pe1mvx.ampr.org
To: hd_broadcast@pa2aga.ampr.org
X-BBS-Msg-Type: B
Ham-Digital Digest Sun, 24 Sep 2000 Volume 2000 : Issue 261
Today's Topics:
ACARS software for PK900
Compression et all (11 msgs)
THIS REALLY WORKS!!!!!!!!!!!! (9/6/00 04:40 PM EDT) (2 msgs)
Send Replies or notes for publication to: <Ham-Digital@UCSD.Edu>
Send subscription requests to: <Ham-Digital-REQUEST@UCSD.Edu>
Problems you can't solve otherwise to brian@ucsd.edu.
Archives of past issues of the Ham-Digital Digest are available
(by FTP only) from ftp.UCSD.Edu in directory "mailarchives/ham-digital".
We trust that readers are intelligent enough to realize that all text
herein consists of personal comments and does not represent the official
policies or positions of any party. Your mileage may vary. So there.
Loop-Detect: Ham-Digital:2000/261
----------------------------------------------------------------------
Date: Sat, 23 Sep 2000 23:24:39 -0400
From: "Timmins" <timmins@penn.NOSPAM.com>
Subject: ACARS software for PK900
At one point there was a software that would run with the PK900 to provide
ACARS reception, as the decoder was buuilt in.
Anyone remember what that was??
Bill, N3DDY
------------------------------
Date: Sat, 23 Sep 2000 09:38:28 -0400
From: Gary Coffman <ke4zv@bellsouth.net>
Subject: Compression et all
On Thu, 21 Sep 2000 16:07:51 -0700, Scott Moore <samiam@cisco.com> wrote:
>Since I lost track of ham, there have been at least two developments
>that should hit ham radio like a bombshell, namely digital voice
>compression (mpeg) and also digital video compression (mpeg again).
>Voice compression should allow voice traffic to go to very narrow
>channel modes, with a resulting dramatic increase on the number
>of people able to get on a given band, plus the greater accuracies
>and longer range receiption afforded by digital error correction.
>Digital video, mpeg-1 style, should change ATV entirely, allowing
>ATV work in much narrower bandwidth, and much lower frequencies.
>Could it even allow DX ATV ? I don't see why mpegs cannot completely
>replace slow scan.
>I know some of this technology is pretty new, but is anyone doing this/
>working on this ?
Yeah, some people are working on it. We did digital voice here back in
1990, high fidelity at 56 kb in a 100 kHz channel. Since then there has
been much progress with codecs to the point where the required data
rates for toll grade speech have fallen 10 fold. That takes it out of the
special RF modem range and down into the range where the digital
signal can be crammed through an ordinary FM voice grade radio
occupying a 15 kHz channel. But guess what, we've been putting toll
quality speech through voice grade FM radios for over half a century.
Nothing new here. No savings in occupied bandwidth, little or no
improvement in range. Etc.
Now if the average amateur didn't insist on doing digital through his
Yaekencom FM voice radio, we could build special RF modems that
would occupy less bandwidth than a FM analog voice signal. We could
squeeze it into as little as 600 Hz of occupied bandwidth. But don't
hold your breath waiting for that to happen. It has as little chance as
the widespread adoption of the 56 kb MSK RF modem we've had
available since 1989. Most amateurs won't buy it if it doesn't come
from Japan ready to plug and play (and the plugs better be prewired,
see Rigblaster).
Now there are some real benefits to digitized voice. We can route it,
for example, over a digital network to give us linked systems such as
we never dreamed were possible a few years ago. We can use FEC
to push it through noisy links. Etc. But the chance that it will conserve
occupied bandwidth is practically nil. Amateurs will still be using voice
grade FM radios to carry the digital audio signals. (Hell, people are
actually running PSK31 through voice grade FM radios on VHF. That
makes a 31 Hz wide signal tie up a 15 kHz channel.)
Digital TV, well understand that the HDTV signal has a data rate of
1.2 Gbit/sec. Even at microwave that's a stretch. We're using GPS
synchronized external clocking in order to try to fit it into current
40 MHz STL channel allocations to get it out to the transmitter site.
(Removing the clock signal lets us stuff the data bits more tightly.)
Compressing it with MPEG and then modulating it 8VSB can fit it
into a 6 MHz channel. That's the system broadcasters are moving
toward right now. But that on the fly MPEG conversion requires a
rack full of equipment that costs over $100,000. (Doing the reverse
conversion from MPEG back to straight video is a much easier
task, fortunately, or DTV receivers would be totally out of reach of
the average viewer.)
SDTV has one fourth the data rate, but the on the fly MPEG converter
still costs $100,000, and 8VSB still occupies 6 MHz even if we're only
using it at one fourth capacity. So there's no occupied spectrum savings
there either. We already have analog SDTV in a 6 MHz bandwidth.
If we were to rate reduce 8VSB, we could fit a SDTV signal in 1.5 MHz.
That's still too wide for any amateur band below 70 cm, and we're already
doing ATV on 70 cm. We could have more channels there it is true, but
to do it we'd have to have special equipment at both ends of the link.
Today, a cable tuner and ordinary TV can be used to receive ATV. With
this special signal, not even the new DTV receivers would be able to decode
it (because it is running at a different rate than they are designed to
decode).
We'd have to build everything ourselves all the way to the CRT. Is that likely
to happen in anything like a large scale way in the amateur community?
Having observed amateurs for 35 years, I think not. If it can't be added
as a simple accessory to their analog radios, they aren't going to do it.
I'm sorry to be so down here, but this is the reality we've been facing
in digital amateur radio. Enough people won't get off the dime to let
anything better than what we've been doing for the last 20 years achieve
a critical mass unless it is a pure plug and play that they can use with
their existing Japanese analog radios.
We aren't radio amateurs anymore, we're just radio users, not much
different from CBers. Even Hank and Charles, who moan so much,
are just radio users, stuffing bits through their Japanese radios instead
of through a Taiwanese telephone modem. If they started building and
using high performance RF modems, then they might be able to say that
they're putting the radio back into radio amateur.
Gary
Gary Coffman KE4ZV | You make it |mail to ke4zv@bellsouth.net
534 Shannon Way | We break it |
Lawrenceville, GA | Guaranteed |
------------------------------
Date: Sat, 23 Sep 2000 14:51:08 GMT
From: "Hank Oredson" <horedson@att.net>
Subject: Compression et all
"Gary Coffman" <ke4zv@bellsouth.net> wrote in message
news:us7pssgkl7e154a642iu4kscrpuha943hi@4ax.com...
Again taking the argument over to "Hams can't do anything useful
To be continued in digest: hd_2000_261B
Read previous mail | Read next mail
| |
