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[aprssig] DAO quantified.

Andrew Rich vk4tec at people.net.au
Sun May 11 13:02:15 UTC 2008


Playing with a tracker on the bench here

The first line is APRS

The second line...well you get the picture

VK4TEC-12>APRS,WIDE: <<UI>>:=2734.45S/15306.22E'SATS 07
RAW,27344572,S,153062245,E

VK4TEC-12>APRS,WIDE: <<UI>>:=2734.45S/15306.22E'SATS 07
RAW,27344572,S,153062245,E

VK4TEC-12>APRS,WIDE: <<UI>>:=2734.45S/15306.22E'SATS 07
RAW,27344572,S,153062245,E

VK4TEC-12>APRS,WIDE: <<UI>>:=2734.45S/15306.22E'SATS 07
RAW,27344572,S,153062245,E

VK4TEC-12>APRS,WIDE: <<UI>>:=2734.45S/15306.22E'SATS 07
RAW,27344573,S,153062245,E
  ----- Original Message ----- 
  From: Wes Johnston, AI4PX 
  To: TAPR APRS Mailing List 
  Sent: Sunday, May 11, 2008 1:31 PM
  Subject: [aprssig] DAO quantified.


  I'm hoping this attachment goes through the list.

  The pic on the left is a screen shot from aprs.fi , the right is findu.com .  I am setting up a tracker for a club and am running it in the back of my car for a few days to see if I've got it setup the way I want.  Actually another local ham and I have been getting a kick out of the fact that my speed can vary from when one tracker transmits and the other transmits.  We get a kick out of how the rear of my car can be going faster or slower than the front and in a different direction.

  The call of the tracker is k4scg-15 and it's running DAO on Scott Miller's OpenTrak.
  My mobile call is ai4px-9 and i'm running a d700.

  The D700 transmits with a 60' (18meters) ambiguity, DAO adds digits of precision down to 2' (60cm).  

  In the pic on the left, you can see the difference in location from the DAO tracker vs my d700.  k4scg-15 is exactly in the correct spot on the north side of the street near the mailbox.  ai4px-9 incorrectly appears in the neighbor's driveway.

  Findu does not display the added precision, so k4scg-15 appears in the same qth as my d700.

  What's great about this is that any aprs station can decode the position to 18meters.  Clients like aprs.fi and xastir can decode the 60cm positions.

  By the way, this is not meant to make one web site appear better than the other.  It was a very convenient way to show the difference between mic-e packets and DAO enabled packets.  APRS.fi and findu just provided an easy way to contrast the improved precision on the same photo.

  -- 
  Wes
  ---
  Where there's silence, there is no Hope. 


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