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ZL3AI > APRDIG 18.05.04 21:16l 221 Lines 9062 Bytes #999 (0) @ WW
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From: ZL3AI@ZL3VML.#80.NZL.OC
To : APRDIG@WW
Subject: Re: DAMA was mentioned here Now ALE
From: "Bill Vodall WA7NWP" <wa7nwp@jnos.org>
Date: Mon, 3 May 2004 13:20:49 -0700
X-Message-Number: 37
>maybe we can get them to consider ALE on HF at the same time as well...
Check out the HFLINK yahoo group:
---
HFlink
ALE. Automatic Link Establishment
Use of ALE and selective calling. Transceivers, antenna sytems, hardware,
firmware, software, standards, signals, and protocols for communications
using ALE systems. Dependable HF communications networks utilizing ALE with
SSB and/or Data. Coordination of activity, development of ALE operating
methods and protocols, applicable to the Amateur Radio Service. ALE for
organizations, emergency networks, and disaster preparedness. HFlink
maintains records for ALE channel frequency lists, nets, callsigns, and
other information useful for operation of ALE in the amateur bands. ALE
enables SSB operators to automatically set up a frequency and clear
channel, to call other stations. Some military and commercial HF SSB
transceivers are available with ALE options. But for simple operation, ALE
only requires a soundcard interfaced to a ham transceiver and a computer
running ALE software. For a ham multi-band automatic frequency system, ALE
requires a serial port transciever control bus interface, and a
multi-frequency antenna.
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Subject: Re: Attn: Armchair Lawyers
From: Steve Dimse <k4hg@tapr.org>
Date: Mon, 3 May 2004 16:36:42 -0400
X-Message-Number: 38
On 5/3/04 at 3:18 PM Jeff King <jeff@aerodata.net> sent:
>Again, then what mode should 144.39 APRS be operated under then? Pure Aloha or
>CSMA? That is the defining question.
Who said it was pure anything? You've been here long enough to know APRS is
a pyramid of pragmatic kludges built on top of one another. That is has
good and bad consequences, I'd say one of the good ones is it lets one use
common sense to solve questions like what is good amateur practice in APRS,
as Bob has stated, and not resort to an academic discussion as you have
done...
Steve K4HG
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Subject: Re: DAMA was mentioned here !
From: Jeff King <jeff@aerodata.net>
Date: Mon, 03 May 2004 14:42:22 -0500 (CDT)
X-Message-Number: 39
Hi Wes:
Yes, I have pondered DAMA for some time, but the cell handoffs where always
the problem. DAMA works real good, but best I can determine, it is mostly
for home stations (DAMA is basically polling).
Quoting wes@johnston.net:
>Jeff King enlightened me to MACA, and I think it is my preferred method.
>MACA allows for multiple "hosts"... I tx a request for a time slot for XX
>number of bytes, and any digipeater hearing me TX's an ACK for my request to
>send... and
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Subject: Re: On digipeater naming conventions
From: "DG2JW" <DG2JW@privateasylum.com>
Date: Mon, 3 May 2004 23:57:58 +0300
X-Message-Number: 40
Very intelligent comment and well said.
Julian
OH8GEJ/KB9YXM
----- Original Message -----
From: "Robert Bruninga" <bruninga@usna.edu>
----snip----
>Agree completely!. If we want to give a digi a geographical
>name then use the Amateur Radio Standard Maidenhead Grid!
>Its even built into most GPS units. Bob
---snip---
>For some reason... the US hams keep thinking of US unique
>approaches...
----snip---
>If there was a 6x6 maidenhead location that have multiple digis...then
>the callsigns are different... and that still makes it unique... and
>universal...
>
>Let's think BIG PICTURE... more than just N. America / USA...
>
>my 2 cents...
>
>ALOHA
>AH6LS
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Subject: Power control, was yada yada
From: Jeff King <jeff@aerodata.net>
Date: Mon, 03 May 2004 14:41:16 -0500 (CDT)
X-Message-Number: 41
Quoting Bill Vodall WA7NWP <wa7nwp@jnos.org>:
>This shouldn't be a legal issue but rather a fascinating technical
>issue. We should
>be able to find some way to "mine" the databases to see just how well the
>PocketTrackers are working and compare them to the smarter trackers running
>higher power. Might be time to revist the "Rate" field of PHGR.
Thanks for reminding me of this. I had been comtiplating how best to do
airplane tracking to best serve both collision avoidence as well as long
distance location. More of a academic exercise, but interesting none-the-less
The "1 minute updates" just don't cut it when you have a 300+ mph closure rate,
and on the other hand 1 or 2 second update rates, at full power, really hose
the frequency.
Now, I only care about the 1 second updates when I have a plane within a few
miles of me. The FSO's and planes 100's of miles from me, they don't need to
see second by second where I am.
So, the thought I had was a tiered slotting system. One the minute do a 1
watt posit, on the 30 second mark, a 250 mw posit, on the 15 and 45, a 62mw
posit, on the 7, 22, 37 and 52 a 15 mw posit, and then every other second
inbetween, a 2 mw posit.
That way, you could overlay quite a few stations on top of each other, yes,
they would transmit on top of each other, but due to the capture effect,
nearby data would make it through.
And with slotting, you can predetermine lockup time, offset TXD's, and very
likely get 2 posits a second. This would require the 1 pps signal from the
GPS, but it is certainly doable and would even work with existing 1200 baud
technolgy.
Not that relevent to APRS per say, but might be of some interest to those
in General Aviation.
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Subject: Slotted ALOHA
From: "Sadowski, Allan" <allan.sadowski@ncshp.org>
Date: Mon, 3 May 2004 16:44:55 -0400
X-Message-Number: 42
It was interesting to see Jeff's post on ALOHA vs CSMA... in particular
since its been a while since I read Andrew Tannenbaums book that talks
at length on ALOHA protocol.
Of note in the wiki link... is that SLOTTED ALOHA is twice as efficient
as pure ALOHA - claims of 36% channel efficiency.. and multiple posts
here on the sig in the (relatively) distant past - relate that APRS acts
like pure ALOHA (at 18% best case utilization). Interesting because
APRS is supposed to be CSMA/CA and the increasingly widespread use of
transmit only trackers means it really should be categorized as (nearly)
plain ALOHA... Note... that the original ALOHA (as described) was a TWO
CHANNEL system... as was Slotted ALOHA. This probably explains why 18%
is the figure of note for APRS as CSMA - because it (obviously) doesn't
use two channels (and we won't go into the long start-up sequences)...
SO, it's kind of cool that we are now seeing the concept of time
slotting gaining interest. As notionally, it would appear to increase
the bandwidth utilization of a single channel. As someone who worked on
getting time slotting into the TNC2 (which did not see common use... and
that's seven years ago now - my how time flies), it's a simple thing to
implement - and has the advantage of GPS's providing the clock (ALOHA
had the master station sending out clock sync).
All this kind of moot... until time slotting in common use.
As a side note, the newest issue of "IMAGING NOTES" is a focus issue on
Geospational Technology in a Anti-Terrorism role.. and they are pushing
AVL for all the vehicles at Airports... along with permitted and denied
zones for the vehicles. Given the number of vehicles at an airport
(they inferred figures along the lines of 500+ carts, trailers, trucks,
etc) at many airports... and the need for high temporal resolution (less
than a minute per temporal update).... it would seem that lots of low
cost trackers are going to be needed at Airports... and their area of
interest/coverage is going to be a couple of miles at best... that a
slotted scheme on multiple channels would meet those needs amply... and
a reasonable enough cost that every vehicle could have an AVL tracker...
Just thinking as I was typing about how one problem could be solved at a
lower price than Boeing, General Dynamics, or other typical vendor of
this stuff... would bring to the table...
Oh well... there I go again... thinking as I type...
ALOHA
AH6LS
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Subject: Re: DAMA was mentioned here Flexnet?
From: "Brian Webster" <bwebster@wirelessmapping.com>
Date: Mon, 3 May 2004 16:54:43 -0400
X-Message-Number: 43
Just a thought off the top of my head now that we have mentioned DAMA. Is it
possible for us to use FLexnet with UI packets and/or build our devices to
be clients with that system? Flexnet will coexist with regular ax25 and
adapt it's parameters based on channel traffic. I know that if you use
flexnet on both the digi site and the client end it works in some sort of
DAMA mode and the efficiency picks up. Just a thought.
Brian, N2KGC
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