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ZL3AI > APRDIG 04.03.03 13:07l 176 Lines 6997 Bytes #999 (0) @ WW
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To : APRDIG@WW
TAPR APRS Special Interest Group Digest for Saturday, March 01, 2003.
1. RE: TXD (Final answer?)
2. Re: Handling 100 3-min trackers
3. RE: TXD (Final answer?)
4. PCSAT 3:00P.M. EST Pass
5. Useful Information --- TNC Power Drains
6. Re: Useful Information --- TNC Power Drains
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Subject: RE: TXD (Final answer?)
From: Henk de Groot <henk.de.groot@hetnet.nl>
Date: Sat, 01 Mar 2003 17:15:02 +0100
X-Message-Number: 1
At 21:14 28-2-03 -0500, Wes Johnston wrote:
>But alas, the problem is that even though it is not transmitting, it is not
>listening either. In that 200ms, my rig in the vicinity of the long tx
Yes, that't killing for normal packet but not for APRS! In APRS most of the
time you will not receive the other station anyway so being deaf during for
another 200ms is not a problem. This is exactly ALOHA behaviour, just
transmit when you have something without listening (only in Pure ALOHA
stations did not even attempt to listen, in APRS its still trying to do
that). The 18% efficiency is the result of that kind of channel access. The
"deaf" period is of course bad news for CSMA channel access, so it will
make the efficiency worse.
When the network load is kept below the 18% QRG utilisation the loss of
carrier detection during 200ms before transmission doesn't have any (or
very minor) effect. Reason is that on an 18% loaded channel the risk of
collisions is low anyway, therefore listening before transmission will not
gain much, in more than 82% of the cases you will not hear anything even if
you could receive all other stations (which you can't).
Kind regards,
Henk.
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Subject: Re: Handling 100 3-min trackers
From: "Phil Pacier, AD6NH" <ad6nh@arrl.net>
Date: Sat, 1 Mar 2003 10:45:57
X-Message-Number: 2
On 02/27/03, "Robert Kirk <isobar@cablespeed.com>" wrote:
>At 09:54 PM 2/26/03 -0500, Bob Bruninga wrote:
>>I was asked how I would handle 100 3-min trackers in a 3 digi event:
>[...]
>
>Sounds like an interesting application, Bob. assuming it's not just
>theoretical, who's got these 100 trackers to use in an event?
>
>Bob Kirk
>N3OZB
It's not completely theoretical. The Baker to Vegas Challenge Cup Relay
has for the past couple of years seen APRS trackers used in chase vehicles.
The number of trackers has been around 30, which nears channel capacity
already. With 220 teams this year, and the price of tracking packages
dropping, the likelyhood of this is great. Before, only the KPC3+ TNC
would allow time slotting, which is the only way to avoid collisions in an
ALOHA netowork. Now that the TinyTrak3 allows slotting, the price of a
tracker drops dramatically.
See http://b2v.aprsca.net for the tracking page. 73
Phillip Pacier - AD6NH
www.aprsca.net
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Subject: RE: TXD (Final answer?)
From: Jeff King <jeff@aerodata.net>
Date: Sat, 1 Mar 2003 11:46:19 -0500
X-Message-Number: 3
On Sat, 01 Mar 2003 17:15:02 +0100, Henk de Groot wrote:
>At 21:14 28-2-03 -0500, Wes Johnston wrote:
>>But alas, the problem is that even though it is not transmitting, it is not
>>listening either. In that 200ms, my rig in the vicinity of the long tx
>
>Yes, that't killing for normal packet but not for APRS! In APRS most of the
>time you will not receive the other station anyway so being deaf during for
>another 200ms is not a problem. This is exactly ALOHA behaviour, just
>transmit when you have something without listening
This conversation reminds me of a "problem' we had back in the PBBS days in
the late 80's.
We had a new PBBS pop up, the normal sort of thing, the fellow was going to
set the world on fire and do a much better job then the other 8 or so PBBS's
in the area. Of course, he was single frequency sharing his user channel with
forwarding as well as another PBBS on the channel.
He quickly found that his forwarding was unreliable having to share the
channel with other stations. So he "discovered" that if he set his TXD to 127
(1.27 seconds) he could knock just about every other station off the air and
his forwarding would proceed uninterrupted. He just couldn't understand why
all the other folks that wanted to use the frequency were upset.
Point being, APRS is based on CSMA. The fact that the network is
over-extended is no excuse to ignore this. CSMA does have some value on
APRS and users should not be encouraged to ignore it.
-Jeff
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Subject: PCSAT 3:00P.M. EST Pass
From: "Matthew Stennett" <wa4tkg@iwon.com>
Date: Sat, 1 Mar 2003 14:59:55 -0500 (EST)
X-Message-Number: 4
The 3p.m. Saturday pass for the East coast seemed as though the satellite
was NOT "active" somehow. That is to say, I SAW other stations (myself
included) were getting into PCSAT, and yet my GPS fix on FIND U.com shows
my last stated positon from more then a day ago.
What's the deal with that?, is the FIND U link down, or is something else
wrong? I'll be on PCSAT for the duration of the next two weeks 24/7, since
we won't be able to play with it for a couple of months soon....might as
well while we can. Then, back to local BBS frequency.
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Subject: Useful Information --- TNC Power Drains
From: WA8LMF2@aol.com
Date: Sat, 1 Mar 2003 15:18:34 EST
X-Message-Number: 5
I just inventoried the total power drain that my ham shack makes on a 12 VDC
batttery plant, and measured the current drains of various TNCs -- an issue
if you are leaving trackers running in the car 24/7 or are solar-powering a
remote digipeater.
Here are the results measured on a Simpson 260 VOM with a 13.3 VDC power
input:
AEA PK232 MBX 970mA
MFJ 1270B 325mA
Kantronics Original KAM with enhancement board 250mA
Kantronics KPC3+ 12mA ( ! )
Stephen H. Smith wa8lmf @ aol.com
Home Page: http://wa8lmf.com
Ham Radio/Mobile SSTV page: http://members.aol.com/wa8lmf/ham
APRS Stuff
http://members.aol.com/wa8lmf/aprs
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Subject: Re: Useful Information --- TNC Power Drains
From: "Ev Tupis (W2EV)" <w2ev@arrl.net>
Date: Sat, 01 Mar 2003 15:34:33 -0500
X-Message-Number: 6
>AEA PK232 MBX 970mA
>MFJ 1270B 325mA
>Kantronics Original KAM with enhancement board 250mA
>Kantronics KPC3+ 12mA ( ! )
Stephen,
Is this a "stock" KPC3+ or was it configured for low drain?
Fascinating study, either way, though!
Ev, W2EV
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END OF DIGEST
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