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PA2AGA > HDDIG 26.09.00 22:49l 182 Lines 7230 Bytes #999 (0) @ EU
BID : HD_2000_261C
Read: GUEST
Subj: HamDigitalDigest 2000/261C
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Sent: 000926/1847Z @:PI8HGL.#ZH1.NLD.EU #:18347 [Den Haag] FBB $:HD_2000_261C
From: PA2AGA@PI8HGL.#ZH1.NLD.EU
To : HDDIG@EU
Date: Tue, 26 Sep 00 19:50:26 MET
Message-Id: <hd_2000_261C>
From: pa2aga@pe1mvx.ampr.org
To: hd_broadcast@pa2aga.ampr.org
X-BBS-Msg-Type: B
Date: Sat, 23 Sep 2000 11:38:16 -0700
From: Scott Moore <samiam@cisco.com>
Subject: Compression et all
Sylvan Butler wrote:
>
> 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).
>
> I like digital modes also. But...
>
> One problem which explains why those have had little effect on ham radio.
> Ham radio has not progressed in digital data transfer since about 1985. For
> the most part in the U.S. we are stuck on 1200bits/sec. Yes, 1.2kBIT/sec.
> Sometimes 2.4kbit/second. A few have 9.6kbit, and a very few have 56kbit.
> You have almost no choice in 9.6kbit equipment, and for 56kbit or faster you
> have to build your own, or buy commercial (i.e. not ham band) wireless gear.
>
Is that a legal limit, or a technology limit ?
My understanding is that you can seek specific licences for experimental work
in the ham bands, and that such demonstrated experimental work is what leads
to new modes being put into the rules.
> So that's about it... Until high data rate digital transmission becomes the
> norm, there is just no bandwidth for digital voice, much less digital video.
>
> I'd actually like to work with some higher power 2.4ghz gear (bandwidth
there
> does 1mbit and more), but I'm not up to building my own from scratch (kit if
> no exacting alignment I could do). So I pretty much have to stick with
> commercial stuff, and maybe an amp. But I have nobody within range to
> experiment with, and I can't leave it running unattended, because it has to
> have automatic transmit power control... Oh well, maybe someday.
>
> sdb
>
Well, I am not a ham, as stated before. Most of the guys I have worked with
over
the years were hams because they liked to build their own equipment and
tinker.
I assume someone must be of that mindset, since someone started packet radio.
> --
> More guns means less crime. ISBN:0-226-49363-6
> ***
> Watch out for munged e-mail address.
> User should be sylvan and host is cyberhighway.net.
> Do NOT send me unsolicited commercial e-mail (UCE)!
------------------------------
Date: Sat, 23 Sep 2000 18:42:02 GMT
From: "Hank Oredson" <horedson@att.net>
Subject: Compression et all
"Charles Brabham" <n5pvl@swb.net> wrote in message
news:Df4z5.71$q53.6000@nnrp1.sbc.net...
>
> "Gary Coffman" <ke4zv@bellsouth.net> wrote in message
> news:us7pssgkl7e154a642iu4kscrpuha943hi@4ax.com...
> >
> > snip<
> >
> > 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.
>
> Thousands of Hams cooperated to build the AX25 packet network and HF
> forwarding nets that the tcpip goons showed such intolerance about and
> actively worked to undercut. - So your "theory" does not hold water.
The correct statement is "tens of thousands of hams worldwide."
The growth was pretty fast in the late '85 - '88 time frame.
Peaked at roughly 55,000 hams and over 5,000 servers.
I'm sure we will hear from the anti-ham folks:
"Oh no, it never happened, blah blah ..."
> You are just indulging in some of the very behavior I described...
>
> "The constant insults and accusations directed against the general Ham
> community didn't go over too well, either."
>
> I guess that sort of behavior is so deeply ingrained that it has become a
> "knee jerk" or just plain "jerk" reaction by tcpip buffs such as yourself.
>
> Thank you for the direct verification of my opinion. It's nice to be proved
> right.
There is an awful lot of "anti-ham" opinion out there.
Tends to discourage the newcomers.
Many have told me this.
--
... Hank
http://horedson.home.att.net
------------------------------
Date: Sat, 23 Sep 2000 11:55:33 -0700
From: Scott Moore <samiam@cisco.com>
Subject: Compression et all
Gary Coffman wrote:
> 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.)
>
No, I would not be for HDTV/HAM, or understand the point thereof. I was
thinking more about slow scan and standard TV. HDTV is about what you can
do with the present 6mhz bandwidth, which is too much for most hams, since
that has worked with broadcasters by finding the nearest high mountain,
not a very ham friendly mode.
> 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.
>
I disagree. Mpeg is compressable and expandable by an intel cpu. Now I know
that mpeg is simpler to expand than to compress, but 400 mhz chips can
expand quite well, and we are headed north of 1ghz.
I'll let the 100,000 thing you said stand, but no, I don't personally
beleive that either. Mpeg 1 and mpeg 2 chipsets exist, and are being
interated with handheld cameras now. I think you are talking about
studio equipment.
> 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?
>
I think that the first target is slow scan or similar. Mpeg-1 technology
is considered old now, but that would be adequate for ham use. Further,
the number of frames per second and total resolution could be jiggered
To be continued in digest: hd_2000_261D
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