| |
PA2AGA > HDDIG 26.09.00 22:58l 148 Lines 6438 Bytes #999 (0) @ EU
BID : HD_2000_262A
Read: GUEST
Subj: HamDigitalDigest 2000/262A
Path: DB0AAB<DB0ZKA<DB0ABH<DB0SRS<DB0ZDF<DB0AIS<DB0NDK<DB0ACH<PI8JOP<PI8ZAA<
PI8HGL
Sent: 000926/2007Z @:PI8HGL.#ZH1.NLD.EU #:18354 [Den Haag] FBB $:HD_2000_262A
From: PA2AGA@PI8HGL.#ZH1.NLD.EU
To : HDDIG@EU
Date: Tue, 26 Sep 00 19:50:44 MET
Message-Id: <hd_2000_262A>
From: pa2aga@pe1mvx.ampr.org
To: hd_broadcast@pa2aga.ampr.org
X-BBS-Msg-Type: B
Ham-Digital Digest Mon, 25 Sep 2000 Volume 2000 : Issue 262
Today's Topics:
Compression et all (5 msgs)
NTSB and SUV
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:2000/262
----------------------------------------------------------------------
Date: Sun, 24 Sep 2000 11:58:49 -0500
From: "Steve Sampson \(K5OKC\)" <ssampson@nospam.radio-link.net>
Subject: Compression et all
"Gary Coffman" wrote
>
> 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.
I forget the mans name, but he developed a packet radio digital voice
application back in the late 80's. It was kind of neat. Many old timers
will recall a program for the PC that played voice over the speaker and
sang "Daisy." This was a 1 bit software A/D and with compression
was easily transported by even 1200 baud. I used the same software
idea (PC 8 kHz software interrupt), only I sampled an 8 bit A/D. I wasn't
very good with Op-Amps back then, and bought a Covox card that
had an 8 bit A/D with a very nice audio section.
I found that once you had audio in a sampled digital form, that you
could do many things with it. First of which, is block it up into 20 ms
segments, and second to wrap it with other digital information.
> 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.
I don't think getting digital voice below 5 kHz is the issue. In my
opinion, getting digital voice down to 5 kHz that sounds good is
the issue.
Bandwidth right now is chopped up in frequency domain slices,
and legal entities must be incorporated to assign these channels
(as we call them). We also have the time domain to consider. If
we could get digital audio that fits in a 5 kHz bandwidth (and we
can now) then other coding schemes can be used.
Take a simple TDMA coding scheme. With TDMA you could
easily have 4 channels of voice (or voice and data) in one 5 kHz
channel quite easily, and there is aslo CDMA.
Both of these take the same "channel" and use it for four things.
Therefore we have 5 kHz divided by four in a digital setting, and
5 kHz divided by one in an analog setting.
> 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.
Wouldn't increasing the channel occupancy do the same thing?
> We could squeeze it into as little as 600 Hz of occupied bandwidth.
> But don't hold your breath waiting for that to happen.
Then you're offering the group here a solution that even you don't
believe will ever happen. How valuable is that?
> 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).
Everything gets down to personalities. If the 56 k modem was any
good, then it would have been marketed. Failure in marketing kills
more businesses than financial mismanagement. You can fix the
later, but once you miss your target on the first, you are ready to
stick a fork in it (dead meat). If you could have got a real distributor
to put it out, instead of a mom and pop operation, then the modem
might have made some real money. Wide band modems is not where
terrestrial communications are headed. The P3 satellite might
support that waste of bandwidth, but it has a time domain as well
(called an orbit).
> 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.
I disagree for the reasons I gave above.
> Amateurs will still be using voice grade FM radios to carry the
> digital audio signals.
However, it is multiplexed with other digital signals (callsign, smart
squelch, etc).
> 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.
The issue isn't if three people do it, it is if two people will. That's how
any new mode gets started. If it is fun, then two will increase at an
exponential rate, and then at some future date, as people get bored,
a linear brick wall type of free-fall occurs as everyone sells thier junk
at a swap meet in Dayton...
> 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.
You keep blaming the Japanese, but I haven't seen any 4 color ad's out
of PacComm, so I don't expect wideband modems to begin selling like
hot-cakes, especially since they don't have little buttons that go beep,
or video displays that have your callsign in them...
Marketing...
> We aren't radio amateurs anymore, we're just radio users, not much
To be continued in digest: hd_2000_262B
Read previous mail | Read next mail
| |
