[aprssig] TEMPn-N and callsign digipeating

Sun May 28 21:33:44 EDT 2006

I've been 1/2 heartedly reading this... and the thing I can't grasp is _why_ 
change the alias to TEMPn-n?  During an emergency, the last thing I want to 
be doing is reconfiguring a bunch of trackers.  Much easier to just leave 
the 144.99 alt input digis with WIDE1-1 ONLY out of the gate, and make the 
only configuration change to the trackers to change the offset from simplex 
to +600.

As you say, the thing that is paramount here is to make sure that only 
trackers TX on 144.99... all routed/digipeated traffic must stay on 144.39 
so the trackers have nothing but other trackers to compete with.  Before the 
new WIDEn-n system, it used to frustrate the heck out of me to see my 
tracker loose against some packet from some station 200 miles away.  Alt 
input allows my tracker to only compete with other LOCAL trackers to get to 
the local digi.

My suggestion for high digi's that want to be alt input is that they go 
ahead and invest in a set of 2m cavities tuned 144.39/99.  That way the digi 
won't go deaf on 99 when it transmits on 39.

Also, holdoff sensing on 144.39 is very desireable.  I've had much better 
luck with hold off than I have just digipeating blindly onto 144.39.  I made 
my home station an alt input digi, to relay packets to the real digi here in 
town 6 or 8 miles away.  I really thought that 50 or 65watts 6 miles from my 
local digi would "blast" me into the local digi over the top of the more 
distant stations the local digi was hearing.  Didn't work that way... 20 to 
50% of the time, the local digi wouldn't decode the alt input packet.  I 
know this b/c I could hear my home station relay it out on 144.39, but the 
local digi never digipeated it.  In a nutshell, carrier sensing on 144.39 is 
more important that I originally thought WRT alt input digipeater.

XCD pins and PTT lines can be "dioded" together to keep two TNCs from both 
trying to key the same radio at the same time, BTW.  A proper alt input site 
should really have two TNCs, and two 2m radios... one as RX only, and the 
other Y'ed to the TX side of both TNCs.

Wes
----- Original Message ----- 
From: "Robert Bruninga" <bruninga at usna.edu>
To: <wa7nwp at jnos.org>; <aprssig at lists.tapr.org>
Sent: Sunday, May 28, 2006 7:15 PM
Subject: Re: [aprssig] TEMPn-N and callsign digipeating

At the expense of confusing everyone for Field Day which
plans to use TEMPn-N digipeating on 145.01, I am really
excited about how we can permanently use TEMPn-N
for special situations on 144.99 along with the low-power
devices.  This is the ultimate arrangement AFTER field day:

1)  We begin building digis for low-power users with simple
144.99 ==> 144.39 digis using the alias of WIDE1-1 only.
ANY TNC can do this.  This is the alternate input channel
for low power APRS that has been previously published.

Very high digis on mountains that hear too much are ideal
for conversion to 144.99 alt-input digis, since they can
hear the low-power trackers over a very large area with
no QRM.

2) We ADD TEMPn-N support to these digis.

3) Remember that D700 mobiles should always be configured
to act as TEMPn-N digis too for emergency operations.

With #2, and #3 above, then we can instantly provide
an alternate channel for reali-time APRS support by simply
asking D700's in key areas to park on a hill and set their
radios to 144.99.  They then act as hop-by-hop links
into an out of affected areas, but the permanent
ALT-INPUT-CROSS-CHANNEL digis provide the cross link
back to 144.39.

THis way, there is no digi-to-digi traffic on 144.99 and
even the big alt-input digis do not contribute a single
bit of QRM to that "input" channel, but the D700
TEMPn-N digis can serve as range extenders into that
system!  Wow.

We can use this FD as a TEST of this concept!  It will
be on 145.01 this year since we have already published
that frequency, but it can then become permanent
on 144.99.

Imagine a single mountain top digi in California that can
hear tens of thousands of square miles, listening on
144.99 and the ONLY thing there are low power trackers.
The QRM level would be 0.01 what it is now on 144.39.
Remember this digi does not digipeat on 144.99, but
does cross digipeat to 144.39.  Thus it does NOT add
to any QRM that would reduce the reliability of the
trackers.  Yet, everyone on 144.39 could hear them.

And if this digi also supported TEMPn-N, then a mobile
parked on a hill even a hundred miles away, could
easily serve as an emergency link back to 144.39
by a simple twist of the frequency knob...

Hummh...   I'll write up a plan.
think about any really big digis that hear too much.
Maybe they are ideal for this application...

Bob, WB4APR

>>> bruninga at usna.edu 05/28/06 6:32 PM >>>
Yes, to transition to and from TEMPn-N, then
actual calls would be needed or other generics.

But if a TEMPn-N packet arrives at your location
as DIGI1,DIGI2,TEMP3-1, then it went through
two TEMPn-N diigs to get to you, so any TEMPn-N
response would get back to him.  But if the sender
sent the packet via  RELAY,TEMP3-3, AND there
was a RELAY digi on that frequency then
it would arrive as DIGI1,DIGI2,TEMP3-2
and you would have to have a quick eye to notice
that DIGI1 cannot be a TEMPn-N digi, because
only 1 n-N hop was used (3-2).

BUT!!! Under this emergency operations scenario,
a REPLYING staiton could always use the return
path with explicit calls and it would have to always
work.  Maybe we have to come up with procedures
to eliminate these kinds of problems:  Rules:

1)  TO be CERTAIN of successful reply to an incomming
TEMPn-N messsage, try listing each digi explicitly.

2) Hum,m,h... we cannot tell senders to avoid
creative mixing of TEMPn-N and explicit digis, becuause
that is what this is all about.  Creating paths as needed
in special circumstances.  Therefore, I guess the
rule of thumb is to always reply with explicit list of
digis unless one is smart enough to actually figure out
how the packet got to you in the first place.  ANd
some arriving paths will simply be ambiguous to be
sure...

So only rule is #1?

Bob

>>> wa7nwp at jnos.org 05/28/06 6:13 PM >>>
>>>> wa7nwp at jnos.org 05/28/06 12:54 PM >>>
>>... getting some TEMPn-N activity here for Field Day.
>>...   Does a TEMPn-N D700 mobile digi automatically
>>digipeat on the stations callsign or will it be necessary
>>to add it to the UIDIGI settings?
>
> Im not sure I follow, but TEMPn-N packets should work
> just exactly like WIDEn-N packets, but of course will
> only go through other TEMPn-N digis.

Once we learn (thanks to callsign substitution) the digi's to use to get
to a desired alternate station, we want to switch from using the generic
Tn-N to specific calls.  For example, once I learn that the path to the
WB4APR-13 airmail station is via the WA7NWP-7 TEMPn-N digi, I would switch
to using WA7NWP-7 to Connect to WB4APR-13.  The question is, does WA7NWP-7
have to be added to one of the four UIDIGI settings on the D700 or will
the D700 automatically digipeat on mycall.  (Yes I know - it'll take about
2 minutes to test it here.  Which I will do after the shortly upcoming
afternoon adventure..)

Bill

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