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[aprssig] Project-25 for amateur radio

Robert Bruninga bruninga at usna.edu
Sun Aug 17 05:02:29 UTC 2008


> But is there any user-accessible interface 
> for this data, or is it just some reserved 
> bandwidth in the protocol that'd require 
> hacking the radio to get at?

Donno.  Waiting for the P25 expert to be indetified.  Again, I
forgot my QST to bring in the authors email address.

Bob, WB4APR

> 
> Scott
> N1VG
> 
> Robert Bruninga wrote:
> >> 48 bits of data can get you a position...
> >> 36 bits can represent a 6-character, 6-bit callsign. 
> >> Seems like even accounting for some overhead,
> >> a 1.5 or 2 second transmission would be plenty 
> >> to get a basic position out.
> > 
> > Scott, looks like you can have a new project.  Make a dongle
for
> > these P25 radios that takes GPS input and sends out the
right
> > bits for APRS.  Lets define the format... Howabout something
> > like:
> > 
> > CCCCCC-SS>PX:AAAAGGGG,CC,SS,AAA/$,freetext up to 17 bytes
(or
> > more)
> > 
> > PX is some code for your dongle that does this process
> > Where AAAAGGGG are the 8 bytes of lat/long
> > CC and SS are course and speed
> > AAA is the altitude
> > /$ is the symbol and
> > Freetext can go on the end.
> > But free text can also contain FREQ if it is available
> > 
> > But in general, the FREQ will be added when this is received
at
> > the Repeater site and conerted to APRS.  The repeater that
> > receievd this and does the conversion KNOWS what freq it is
on.
> > 
> > THen you also have to make the dongle at the repeater to
convert
> > this to APRS.  I suggest this standard conversion.
> > 
> >
CCCCCC-SS>AP25xxx,WIDE2-2:!DDMM.mmN/DDDMM.mmW$CSE/SPD/FFF.FFFMHz
> > 17-bytes-of-free-text!DAO!
> > 
> > Notice that FFF.FFFMHz is inserted by the digi.
> > !DAO! Is on the end so that it does not mess up text
displayed
> > on all existing radios.  Notice that if there is no GPS data
in
> > the user uplink data, then the repeater dongle inserts its
own
> > position, and a P25 generic SYMBOL with a randomised
LATITUDE to
> > make all users on this repeater appear as a list on all APRS
> > maps.  Seee details on this process on the
> > www.aprs.org/aprstt.html web page.
> > 
> > By doing it this way, evevn if the P25 radio user does not
use
> > GPS, he still appears in APRS with a frequency and
location...
> > If he has  your dongle.
> > 
> > I have no idea how many P25 users there are...  But we need
to
> > get all radios on APRS eventually...
> > 
> > Bob, WB4APR
> > 
> >> John Habbinga wrote:
> >> > Bob, there is a low-speed data mode transmitted along
with
> > digitized
> >> > voice on Project 25.  However, it passes data at 88.9
bit/s.
> > As far
> >> > as I know, there are no applications that has made use of
> > this
> >> > feature.  I doubt that it would be very practical to use
> > "APRS over
> >> > P25," but I could be wrong.
> >> > 
> >> > On Fri, Aug 15, 2008 at 3:38 PM, Robert Bruninga 
> >> <bruninga at usna.edu> wrote:
> >> >> I noticed the QST article on Project 25 using digital
voice
> > on
> >> >> repeaters.
> >> >>
> >> >> I noticed a sentence about simple text transfer. And
> > intended to
> >> >> bring the article to work with me for noon time reading,
> > but
> >> >> forgot it.
> >> >>
> >> >> If the radios are capable of digitally exchanging
> > callsigns,
> >> >> then there is no reason why they cannot appear on APRS
just
> > like
> >> >> DTMF users.  SO if anyone can point me to a point of
> > contact
> >> >> within that project group, I'd like to invite them to
> > consider
> >> >> joining the global APRS system too.
> >> >>
> >> >> See http://www.ew.usna.edu/~bruninga/aprstt.html
> >> >>
> >> >> Bob, WB4APR
> >> > 
> >> > _______________________________________________
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> >> > https://lists.tapr.org/cgi-bin/mailman/listinfo/aprssig
> >> > 
> >> > 
> >> 
> >> 
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> >> 
> > 
> > 
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> 
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