[aprssig] APRS/Winlink puzzles

Mon Aug 24 02:47:49 EDT 2009

Hi Lynn, et al,

Ok, so this is making more sense now, and also maybe a little less...

I looked again at the various bits of the puzzle, and I'm thinking now about the time problem.  It appears that my TH-D7 tried several widely separate times to send the message, as there are position reports that roughly correspond to the messages, at the times reported on aprs-is.  The rig was probably turned off in between, hence the large time gaps.

I'm thinking now that that my home station reacted to the first "ping" message sent out at 15:28z (8:28 local) by trying 4 times to send it to me here in California.  It wasn't seeing 4 separate messages on aprs-is after all, but rather doing several retries on just the first one because it never heard an ack.  (There is supposed to be an ack, isn't there?)  Note the messages are spaced 1 minute, 2 minutes, and then 4 minutes apart.  Sounds like Bob's retry algorithm, no?

So, then the next part of the puzzle....  Why weren't the other messages at 18:52z and 23:39z seen by my home station and copied to RF?  Did Xastir "learn" from the lack of Acks on the first message that I wasn't home?  (I'm running version 1.8.4, if that matters.  Yes, it's ancient, but the system just keeps running, so I leave it alone.)

And, a TH-D7 question...  Is there any way to "cancel" the re-try of a message from the D7?  It seems to have an annoying memory for incomplete things sometimes.

Thanks,

Greg  KO6TH

Date: Mon, 24 Aug 2009 00:33:55 -0400
From: ldeffenb at homeside.to
To: aprssig at tapr.org
Subject: Re: [aprssig] APRS/Winlink puzzles

Greg,

Everything on APRS-IS hears everything on APRS-IS that fits the
configured filter.  Everything on APRS (RF) hears everything within
range of the receiving station.  APRS software determines what it will
show you and how it will show it.

I suspect the reason your D7 didn't hear anything is that there were no
bi-directional IGATES that considered your station "local".  The answer
was placed back on APRS-IS which is why your home xastir saw it, but if
there wasn't a bi-directional IGate to put it back onto RF, your D7
never knew it got answered.

Dave referred to the stations as digis, but digis only work with the RF
side of APRS by retransmitting what they received.  IGates are the
necessary bridge to (receive from RF) and from (transmit to RF) the
APRS-IS.

Lynn (D) - KJ4ERJ

Greg D. wrote:

  Hi Dave,

Ah, thanks for the explanation.  I didn't realize that Xastir (and
probably the others) "look for" things to send.  I guess that makes
sense.

So, does this mean that by having my home station configured without an
SSID, that it prevents others from picking it up also?  I've never been
able to get a response except when I'm within RF range of home.  Or is
it that bi-directional operation is really rare?  My station is just an
iGate, not a digi, if that matters.

Greg  KO6TH

  Date: Sun, 23 Aug 2009 20:41:56 -0700

From: davidf4 at mindspring.com

To: aprssig at tapr.org

Subject: Re: [aprssig] APRS/Winlink puzzles

  This part is easy.  If you have Xastir configured for just
your call (without any dash number) then it displays all messages that
it sees destined for your dash number stations.

So Winlink did send back a response via aprs-is and your home station
saw it.  But apparently the digi's that were near your -7 station
either didn't recognize that you were in that area or aren't set for
bi-directional digi'ing.

Dave

KD7MYC

  -----Original
Message-----

From: "Greg D." 

Sent: Aug 23, 2009 5:51 PM

Then when I got home, the following was waiting for me on my Xastir
screen:

08/13 08:28 WLNK-1   >(Sent to:KO6TH-7) APRSLink v2.8.8.0
www.winlink.org/aprslink fo

08/13 08:29 WLNK-1   >(Sent to:KO6TH-7) APRSLink v2.8.8.0
www.winlink.org/aprslink fo

08/13 08:31 WLNK-1   >(Sent to:KO6TH-7) APRSLink v2.8.8.0
www.winlink.org/aprslink fo

08/13 08:35 WLNK-1   >(Sent to:KO6TH-7) APRSLink v2.8.8.0
www.winlink.org/aprslink fo

Puzzle #1:  Why did the messages go out through my system at home in
California, when I was somewhere in Oregon at the time?

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