[aprssig] What's " AI SAT ?

Sun Apr 7 21:20:46 EDT 2019

 A new satellite.       http://amsatindia.org/    

There was a discussion, in another group, about why nothing from AISAT is showing up in APRS.FI.

K4KDR provided some samples of the signals so they could be analyzed.

The direwolf "-dp" option was used to produce a hexadecimal dump, of the frame, so we could see what is going on.

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

 K4KDR-6>CQ,AISAT*,::CQ-0     :=3747.66N/07736.67W`de K4KDR scott23192 at gmail.com Virginia  FM17es{847
------
U frame UI: p/f=0, No layer 3 protocol implemented., length = 111
 dest    CQ      0 c/r=0 res=3 last=0
 source  K4KDR   6 c/r=0 res=3 last=0
 digi 1  AISAT*  0   h=0 res=3 last=0           <--  The “h” bit indicates that the
                                                                                digipeater address has been used
                                                                               It should be 1 in this case.  There should NOT be
                                                                               the * character in the address field.

 digi 2          0   h=0 res=3 last=1

I reformatted this so the bytes would be in groups of 7 so it is easier to read.

  000:  86 a2 40 40 40 40 60          “CQ”       
            96 68 96 88 a4 40 6c          “K4KDR”  SSID 6
            82 92 a6 82 a8 54 60          “AISAT*”      <--   WRONG!!!!!

                                                                                                                  The * character is used only for the
                                                                                                                  human readable monitoring format.
                                                                                                                  It should not be a character in the
                                                                                                                  station address.

        40 40 40 40 40 40 61          “      “              WRONG!!!   Field should not
                                                                                     be here if not needed.
        03 f0                                    expected control, protocol
        3a 43                                                                                      :C
  020:  51 2d 30 20 20 20 20 20 3a 3d 33 37 34 37 2e 36  Q-0     :=3747.6
  030:  36 4e 2f 30 37 37 33 36 2e 36 37 57 60 64 65 20  6N/07736.67W`de
  040:  4b 34 4b 44 52 20 73 63 6f 74 74 32 33 31 39 32  K4KDR scott23192
  050:  40 67 6d 61 69 6c 2e 63 6f 6d 20 56 69 72 67 69  @gmail.com Virgi
  060:  6e 69 61 20 20 46 4d 31 37 65 73 7b 38 34 37     nia  FM17es{847

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

This is my analysis:

(1) Digipeating does not work normally.  A digipeater should only change the via path.  The information part should not be changed.  Why is it converted into “message” format?
(2) Only the needed digipeater fields should be present.  If they are not needed leave them out.  Don’t fill them with blanks.
(3) A station address should never contain the * character.  That is only in the human readable standard monitoring format.  The * after a station indicates that the H bit is set.
(4) When a digipeater uses up an address in the via path, it must set the “H” bit to 1.  If it responded to an alias, it should substitute its own callsign.

Here is an example of expected behavior:

K4KDR-6>CQ,ARISS:=3747.66N/07736.67W`de K4KDR scott23192 at gmail.com Virginia  FM17es
K4KDR-6>CQ,RS0ISS*:=3747.66N/07736.67W`de K4KDR scott23192 at gmail.com Virginia  FM17es

ARISS is recognized as an alias by RS0ISS.
RS0ISS substitutes its own call and marks that digipeater field as being used.
The * is not a character in the address.  It is the human readable way to indicate that the “H” bit is set.
Only the via path is changed.
The Information part is not changed at all.

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73,
John WB2OSZ