[aprssig] Airborne Digis

[Keith VE7GDH]

Greg NV6G wrote...

> My thoughts were perhaps to set WIDE1-1,WIDE2-1,SAR1-1 and turning on
> preempting on our airborne digi setting it to only digi on SAR1-1.  My
> question here is, if the airborne digi preempts, hitting on SAR1-1
> what happens on the RF network with the WIDE1-1,WIDE2-1, will they be
> skipped or will they be processed?

I just gave it a try. In a T2-301 (5W radio with OT2m built into it) I
enabled SARn-N with pre-emptive digipeating turned on for that alias. On
a T2-135, I entered a path of TEST1-1,TEST-2-1,SAR3-3 and forced it to
beacon. Watching the return coming back from the T2-301, all of the digi
path ahead of the SARn-N were marked as used...

<Digi Echo>
VE7GDH-2>APOT21,TEST1-1*,TEST2-1*,VE7GMI-3*,SAR3-2
:!4848.96N\12327.30WkT2-135 P1

A suggestion... if you used a path something like...

WIDE1-1,WIDE2-1,SARn-N,WIDE2-1

and the airborne digi with pre-emptive digipeating (e.g. from Argent
Data a Tracker 2... i.e. OT2m, T2-135 or T2-301) responded to the 
SARn-N, it would leave the remainder of the path intact. If the SARn-N 
was SAR1-1, then any regular WIDEn-N digis that heard it would respond. 
If the SARn-N was e.g. SAR2-2, the remainder of the SARn-N would have to 
be acted upon before any WIDEn-N digis would respond to remaining path. 
Of course, if you had an airborne SARn-N digi and several mountain-top 
SARn-N digis, you probably wouldn't need any additional path. If any of 
your teams happened to make it to a WIDEn-N digi or fill-in digi, the 
SARn-N would still be available if the airborne digi heard it.

The advantage of being on your own frequency is no "QRM" from regular
APRS users and the advantage of being on 144.390 (in North America) is
that they could take advantage of the regular APRS infrastructure.

I followed up my test with a beacon using a path of
WIDE1-1,WIDE2-1,SAR3-3 and watched it coming back from my own SSI digi
and from the T2-301 which had pre-emptive digipeating turned on for
SARn-N...

<Digi Echo>
VE7GDH-2>APOT21,SSI*,WIDE1*,WIDE2-1,SAR3-3
!4848.96N\12327.30WkT2-135 P1

<Digi Echo>
VE7GDH-2>APOT21,WIDE1-1*,WIDE2-1*,VE7GMI-3*,SAR3-2
:!4848.96N\12327.30WkT2-135 P1

Another time made a bit more noise...

<Digi Echo>
VE7GDH-2>APOT21,SSI*,WIDE1*,WIDE2-1,SAR3-3
!4848.96N\12327.30WkT2-135 P1

<Digi Echo>
VE7GDH-2>APOT21,VE7DID-1*,WIDE2-1,SAR3-3
!4848.96N\12327.30WkT2-135 P1

<Digi Echo>
VE7GDH-2>APOT21,VE7DID-1*,SSI*,WIDE2*,SAR3-3
:!4848.96N\12327.30WkT2-135 P1

<Digi Echo>
VE7GDH-2>APOT21,VE7DID-1*,SSI*,WIDE2*,VE7GMI-3*,SAR3-2
!4848.96N\12327.30WkT2-135 P1

<Digi Echo>
VE7GDH-2>APOT21,WIDE1-1*,WIDE2-1,SAR3-3
:!4848.96N\12327.30WkT2-135 P1

<Digi Echo>
VE7GDH-2>APOT21,WIDE1-1*,VE7RNA-10*,WIDE2*,SAR3-3
:!4848.96N\12327.30WkT2-135 P1

Perhaps WIDE2-1,SARn-N would have been better from my QTH. My test was
right beside my own SSI digi and of course within earshot of other
WIDEn-N digis in at least a couple of directions.

The "Tracker 2" series which is capable of pre-emptive digipeating is
available from Argent Data at www.argentdata.com.

73 es cul - Keith VE7GDH
--
"I may be lost, but I know exactly where I am!"