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[aprssig] Project-25 for amateur radio

Scott Miller scott at opentrac.org
Sun Aug 17 04:56:00 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?

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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>> > 
>> > 
>> 
>> 
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