QRZ! Ham Radio 4/QRZ Ham Radio Callsign Database - Volume 4.iso/digests/digital/940335.txt

Internet Message Format | 1994-11-13 | 18KB

Date: Mon, 10 Oct 94 04:30:19 PDT
From: Ham-Digital Mailing List and Newsgroup <[e-mail]>
Errors-To: [e-mail]
Reply-To: [e-mail]
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Subject: Ham-Digital Digest V94 #335
To: Ham-Digital


Ham-Digital Digest          Mon, 10 Oct 94       Volume 94 : Issue  335

Today's Topics:
              continuous data transfer over +/- 2 miles
                    FAX Software for KAM/KAM Plus?
                 WANT: Computer Aided Dispatch system

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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.
----------------------------------------------------------------------

Date: Sat, 8 Oct 1994 14:05:56 GMT
From: [e-mail] (Gary Coffman)
Subject: continuous data transfer over +/- 2 miles

In article <[e-mail]> [e-mail] (Steve Hochschild) writes:
>I need to send a continuous data stream at about 1200 baud over a distance of
>about 2 miles.
>
>I am trying to instrument an amateur race car and send real time telemetry
>back to the pits.  I am a total novice on this, but someone told me packet
>radio would be a way to go.  After reading the FAQ, I don't think that this is
>so, rather, I think I need some other form of digital transmission...
>Any ideas ???

Packet may not be best for pure telemetry. It will give you an error
free data stream by error detection and retries, but you'd have to run
at least 9600 baud packet to get 1200 bps raw throughput, and really
need a transceiver on each end. If instead you can tolerate the occasional
transmission error, or use FEC, then what you want is a simple half-duplex
modem over radio. The most ancient of these, the Bell 202 Standard type,
will give you a raw 1200 bps throughput. A PSK modem would be more robust,
however. The ones used to decode amateur satellite telemetry would do.

Telco modems generally can't be used because of their internal "smarts"
which insist on attempting to setup a duplex link, and dropping it if
carrier is momentarily lost. Only the ancient dumb modems meant for
leased lines can generally be used.

Gary
--
Gary Coffman KE4ZV          |    You make it,     | gatech!wa4mei!ke4zv!gary
Destructive Testing Systems |    we break it.     | emory!kd4nc!ke4zv!gary
534 Shannon Way             |    Guaranteed!      | [e-mail]
Lawrenceville, GA 30244     |                     |

------------------------------

Date: Sun, 9 Oct 94 14:33:30 -0500
From: Kevin Charles Alewine <[e-mail]>
Subject: FAX Software for KAM/KAM Plus?

Anyone had any luck finding a good FAX send/receive program for
the KAM? Freeware, shareware, or commercial, any suggestions
would be appreciated!

Thanks!
--
-------------------------------------------------
|  K.C. Alewine, South Lake Tahoe, California   | Air Traffic Controller
|  Internet: [e-mail]               | Lake Tahoe ATCT
|  Ham packet radio: WI7C@WA6EWV.#NOCAL.CA.USA  | Ham Call WI7C
-------------------------------------------------

------------------------------

Date: Sun, 09 Oct 94 09:50:32 EDT
From: [e-mail]
Subject: WANT: Computer Aided Dispatch system

I would like to know what info turns up here. Several people who work for me
will be attending a meeting at the Dulles Marriott this week to discuss 911
service for PCS and Celluar users.



 In article <[e-mail]>, <[e-mail]> writes:
> Newsgroups: rec.radio.amateur.digital.misc
> Path:
interramp.com!psinntp!rutgers!netnews.upenn.edu!msuinfo!caen!spool.mu.edu!sol.c
tr.columbia.edu!news.msfc.nasa.gov!news.larc.nasa.gov!lerc.nasa.gov!purdue!yuma
!csn!nowhere!aitsun20!sjames
> From: [e-mail] (Scott James)
> Subject: WANT: Computer Aided Dispatch system
> Message-ID: <[e-mail]>
> Sender: [e-mail] (Internet News Administration)
> Nntp-Posting-Host: aitsun20
> Organization: TeleCommunications, Inc.
> X-Newsreader: TIN [version 1.2 PL2]
> Date: Fri, 7 Oct 1994 21:16:59 GMT
> Lines: 14
>
>
> I'm looking for a Computer Aided Dispatch (CAD) system
> that links radio modem technology with a GIS display.
> These systems are used by Federal Express (I think)
> and 911 agencies.
>
> If you know of any products or companies that can help
> me find such a system, please email me with the info.
>
> thanks in advance!
>
> scott james
> N0LHX
>

------------------------------

Date: Sat, 8 Oct 1994 13:23:18 GMT
From: [e-mail] (Gary Coffman)

References<[e-mail]> <[e-mail]>, <374q1p$[e-mail]>
Reply-To: [e-mail] (Gary Coffman)
Subject: Re: 56k+ Packet System

In article <374q1p$[e-mail]> [e-mail] (Val Kartchner) writes:
>In article <[e-mail]>,
>Gary Coffman <[e-mail]> wrote:
>>Well then you need a GRAPES 56kb RF modem. It's $250, and with the
>>necessary transverter and digital interface, it's still under $600.
>>Most of the voice radios being used for 1200 baud packet cost nearly
>>that much. 46 times the throughput for about the same money is an
>>unbeatable deal.
>
>But what specific components do you need and where do you get them?  I've
>got a catalog from Down East Microwave, and I don't know what transverter
>to put with the GRAPES modem.  I need enough power output to reliably get
>the signal to go 8 miles.

Their no tune 432 transverter may be sufficient by itself for such
a path, assuming LOS and directional antennas. Or you can add the
amplifier they offer. They offer the whole package assembled and
tested, or as separate kits. We typically operate 3-7 watt systems
over 50-100 mile paths. Those paths are mountaintop to mountaintop,
but using omni vertical antennas on at least one end of the path.
For non-LOS use, more power, or a gain antenna, may be required.
We have one user who's running 100mW and a 1/4-wave vertical, but
he can see the switch on the mountain about 10 miles away.

You need about 2 microvolts into the modem to get a low BER, less
than one error in a million bits. So you can do any necessary path
calculations based on that.

Gary
--
Gary Coffman KE4ZV          |    You make it,     | gatech!wa4mei!ke4zv!gary
Destructive Testing Systems |    we break it.     | emory!kd4nc!ke4zv!gary
534 Shannon Way             |    Guaranteed!      | [e-mail]
Lawrenceville, GA 30244     |                     |

------------------------------

Date: Sat, 8 Oct 1994 13:49:31 GMT
From: [e-mail] (Gary Coffman)

References<[e-mail]> <36sg1g$[e-mail]>, <36uta3$[e-mail]>
Reply-To: [e-mail] (Gary Coffman)
Subject: Re: 56k+ Packet System

In article <36uta3$[e-mail]> [e-mail] (Rick Spanbauer) writes:
>Donald Jeff Dionne ([e-mail]) wrote:
>: Erich Muschinske ([e-mail]) wrote:
>: : >Sorry to rain on your parade, but others have been down the path
>: : >you want to take before you, and it doesn't work. Adapting high
>: : >speed telephone modem techniques to multipoint to multipoint radio
>: : >systems is a lost cause. The problems of packet radio are *different*
>: : >from those of the telephone network, and require different solutions.
>: Not really.  Multipath and such are impediments to any modulation scheme that
>: relies on phase information, such as QAM but it can still be workable.
>
>    I wouldn't be too quick to dismiss QAM out of hand.  The HDTV and
>    catv folks are looking hard at VSB, QAM for both wired and broadcast
>    systems.  These system rely on adaptive equalizers to deal with
>    reflections, though we'll need a fairly long one in over the air apps..
>    Any of these systems promise >> 10 mbps.  To the best of my knowledge,
>    both are still untested in broadcast applications, however.

QAM is fine, but not over typical voice grade amateur radios. The
GRAPES RF modem uses MSK, but it would generate QAM by a relatively
simple EPROM change. The detector would have to be redesigned however.
That's certainly doable, and may be an upgrade path for the modem. What
the RF modem offers that voice grade radios don't offer, however, is a
consistent RF section with known phase, frequency, and amplitude responses.
You'll never get that from a random collection of amateur voice grade radios,
and DSP can't compensate for *all* of them on the same channel at the same
time. There's no way to *train* to multiple signals from multiple *different*
kinds of radios coming along multiple paths in a random packet by packet
sequence.

>: I think what needs to happen is for us to adopt a standard for high speed
>: packet over standard bandwidth channels.  With *very* little effort, 19.2 is
>: more than possible, and probabily 38.4 without too much trouble at all.  Of
>: course multipath and fading will kill it :-) who cares?  for local stuff,
>: I'll live with that, and the high speed backbone links can stay ugly low
>: tech FSK (that went out with the 1970, IMHO).
>
>    At this point in time, we should aim much, much higher than
>    19200.  I've read at least a couple of papers over the past year
>    describing 80-128 kbps modems implemented in fairly slow DSP.  IMO,
>    any interesting, modern application, say talking head teleconferencing,
>    wants 100 kbit/sec or more BW delivered to the user.  We should be
>    aiming for a few mbit/sec per channel, and at least 256 kbit/sec
>    delivered to the user.

We have 128 kb *now* with modified GRAPES RF modems, and 256 kb is within
conception without major modifications. Switching to multi-level QAM
could double or triple even that, though paths would require higher SNR
to give acceptable BER. Of course these are all *raw* rates, use of
compression will allow even higher effective throughputs with any of these
systems. To go above 1 Mbit/s raw will require rather fundamental redesign
of equipment. But crude FSK equipment with that throughput is now available
in the microwave range.

>: Another thing we need to realize is that $600 is just plain silly, and far
>: out ot reach of the end user.  It's got to be $150 and use you hand held.

This is the fundamental fallacy of amateur packet. Anyone seriously doing
packet will dedicate a radio to that use. Take the typical FT-530 at around
$500 and the typical 9600 TNC such as the Kantronics 9612 at $220, and
you've *already* spent more than needed for a 56 kb system, and your system
is much less capable and reliable than the 56 kb unit.

>: All very do-able, but there are lots of issues to consider for the hardware.

It's *not* doable at amateur volumes. The market is too small to allow
hitting a $150 price point with a DSP modem. And even if you could retail
it for $300, you still have all the limitations of varying models of voice
radios I've outlined in other messages.

>    Perhaps the most important aspect of developing new modems is to have
>    the stuff available off the shelf.  In these days of surface mounted
>    components, it is simply impractical to have people stuff a board
>    with fine pitch 208 pin PQFP's using their Radio Shack 40 watt iron....

That's right, they have to spend $50 for a static hot air torch like
the Weller Pyropen. Works fine for SMD assembly. SMD is definitely the
wave of the future for all homebrew construction. Amateurs are going
to have to get used to it. (The existing GRAPES modem doesn't use SMD
however, though future versions might.)

Gary

--
Gary Coffman KE4ZV          |    You make it,     | gatech!wa4mei!ke4zv!gary
Destructive Testing Systems |    we break it.     | emory!kd4nc!ke4zv!gary
534 Shannon Way             |    Guaranteed!      | [e-mail]
Lawrenceville, GA 30244     |                     |

------------------------------

Date: Sat, 8 Oct 1994 13:11:16 GMT
From: [e-mail] (Gary Coffman)

References<[e-mail]> <36u4fd$[e-mail]>, <[e-mail]>
Reply-To: [e-mail] (Gary Coffman)
Subject: Re: 56k+ Packet System

In article <[e-mail]> [e-mail] (Daniel T Senie) writes:
>In article <36u4fd$[e-mail]>,
>Victor Voronkov <[e-mail]> wrote:
>>Erich Muschinske ([e-mail]) wrote:
>>> Don't be too fast to dismiss this idea.  One of the things packet networking
>>> desperately needs is a cheap high speed data link.  This is necessary for
>>> operating a cellular packet concept.  It would only have to work with the
>>> radio on the other end, so adapting would not be out of the question.  If
>>> the price of a link could come down to about $600, I would be very interested.
>>IMHO any attempt to get speed more than 9600 on HandHeld or other 'voice'
>>Radio is problem. Even if we find new modulation. With half-duplex
>
>Can I ask a question here? How is it possible to get the necessary S/N ratio
>and other such to get a V.32bis modem to operate correctly over a Cell Phone?
>It seems to me that it IS possible for cell phones to provide a clean enough
>signal to do data over them, so why do hams have so much trouble getting
>the needed S/N ratio to run at 9600? I must really be dense and missing
>something. I understand that the example of V.32bis (14.4kbps) over cellphone
>is point-to-point. So are most amateur 56K links. Why can't we do a high
>speed link over inexpensive gear and limited bandwidth? It seems to work
>for cell...

You *are* missing something Dan. It's not SNR that's the problem. While
it's true that most ham HTs are sorely lacking in adequate SNR over many
paths for *any* type of modulation, including voice, hence the term handi-
scratchie, that's *not* the main problem. Cellular phones are like the
rest of the telephone system in that the phone network handles the addressing
and routing *out of band*. This means that when the phone rings, the modem
*knows* the signal is for it, and can initiate a *training* sequence with
the modem on the other end to equalize and utilize the one transmission
path then in use. It is an *exclusive* circuit with no other modem signals
present.

The only difference that a cellular modem faces versus wireline modems
is occasional signal dropouts due to handoffs, and the usual multipath
concerns. Therefore special modem parameters have to be used such as slow
disconnect so that the modem won't drop the connection during a brief handoff
outage, and robust error detection to handle the multipath induced symbol
errors.  We already have all that in packet.

What we *don't* have on packet is out of band routing and addressing,
and what we *don't* have on packet is *exclusive* use of a frequency
for a pair of stations. A packet modem has to successfully decode the
header of *every* packet on the channel to assure that the packet either
is or is not addressed to it. It *cannot* initiate a training sequence
every time it hears a packet it can't decode. *That's* why packet modems
can't use training, and training is the key to high speed data over a
voice grade circuit. Every telco modem over 2400 baud uses some form
of training at call setup. In packet, setup must be on a packet by
packet basis, and that won't work because not all packets on the
channel are addressed to the same modem.

With the typical Kenmore, Yahoo, Icky, and Motrash radios used by
amateurs, no two of them will have the same bandpass characteristics.
Training is *essential* to compensate for that, and for off channel
stations. Amateur equipment doesn't have the frequency stability of
commercial equipment, so it isn't unusual to have one or more radios
a kilohertz or more off channel. Nor is it unusual to see wide differences
in deviation from one radio to the next, even among those of the same
make and model. Any modulation used has to be tolerant of all those
errors *without* compensation on a packet by packet basis. That's why
systems as slow as 9600 baud are difficult to setup with more than
two stations. 2400 baud is about as fast as an uncompensated system
can work with multiple players.

The limitation is *not* with the modems, it's with the *radios*.
To successfully use high speed packet, we *must* have radios with
identical response characteristics, and that means dedicated data
radios, all optimized for the *same* response. Now it may be possible
to compensate *all* radios the same way in a system by use of DSP,
but it's not likely. There are two many variables outside the control
of the DSP, such as whether the radio is on channel center or not,
and the differing multipath from one radio path to the next. We
need identical radios, *and* a modulation that is tolerant of certain
types of errors. Such systems exist, I keep pointing to the GRAPES
56kb RF modem as an example, but insistance on using voice grade
amateur equipment for high speed packet is futile. Amateur packet
networks are *not* like the telco network, and telco techniques
won't work.

Gary
--
Gary Coffman KE4ZV          |    You make it,     | gatech!wa4mei!ke4zv!gary
Destructive Testing Systems |    we break it.     | emory!kd4nc!ke4zv!gary
534 Shannon Way             |    Guaranteed!      | [e-mail]
Lawrenceville, GA 30244     |                     |

------------------------------

End of Ham-Digital Digest V94 #335
******************************