DTMF-Paging <=> APRS Gateway Spec 12 Feb 09 ------------------------------------------------------------------- The conversion between APRS and DTMF-Paging formats are discussed in this document. Even in 2007 there are probably as many DTMF text paging radios as there are APRS display radios. Hence the need for a common translation between the two. In the late 1990's there were tens of thousands of FT-51 and TH-78 DTMF paging radios which can send and receive text messages using DTMF. Although text messages were usualy constrained to 6 or 12 byte strings, they can be combined together to the full message memory which is ten such sextets or 60 characters. There are several major categories of applications: 1) Two way text and data exchange between these radios 2) Displaying local APRS data ON these radios 3) Sending APRS type data from these radios 4) Using *ANY* HT to send DTMF data to these radios or Net control Generally these operations take place on a separate simplex channel than the APRS traffic. The radio is set to receive-paging mode, and it will monitor and display any APRS traffic converted to DTMF, or any DTMF data from other radios. THe radio can also send DTMF data that is converted back to APRS and placed on the APRS channel. Operating scenario 4 has the largest potential since it will let ALL amateur radio operators at an event use ANY of their existing HT's with a DTMF pad to send in data to net control. For applications, please see www.aprs.org/messages/DTMF2net.txt This spec defines the DTMF-Paging-to-APRS translation between the APRS side or the gateway and the DTMF side. This system is a subset of the overarching APRStt (touchtone) which can apply to all DTMF radios but uses voice synthesis for the return path to the user. See www.aprs.org/aprstt.html MESSAGE RECEPTION: The special DTMF radio must be in Message Paging Receive mode. The display consists of three parts: XXXXX YYYYY Z Z Z Z Z Z Where XXXX and YYYY are the usual dual band frequency displays and Z Z Z Z Z Z is a larger font 6 character message window. When a page or text message is received, the frequency field say, XXXX, changes to display the SENDING station's 3 digit paging address or group code and memory number and the ZZZZZZ window displays any text. Although multiple incoming messages will fill any available message memory sextets, the sending station ID is lost in the additional memories, so it is best to keep all data to a single 6 byte window where possible. Obviously, Messages are expected to use as many of these memories as needed. But first it is important to understnd how these message memories are handled: If the 10 message sextets are full then there are two options: 1) additional incoming messages are ingored. 2) incoming messages are overwritten into memory #0 (default). ADDRESSING: The paging and messaging system uses 3 digit addresses for both individual messages and group calls. For APRS we will define the individual callsign addresses as simply the numeric equivalent of the amateur call's suffix. APR for example is 277. Then we have defined several group codes 990 to 999 for the several types of APRS traffic. This way, receipients can select or opt-out of certain data types. The header for a page or text message contains the GROUP number, GGG and the Senders Callsign ID, CCC like this: GGG*CCC MESSAGE TYPE: The radios can monitor for up to 6 group codes and so the following assignments have been made for the several data types that everyone might want to receive: 999 can mean STATUS data (or any free text) 998 can mean FIXED position data 997 can mean MOVING vehicles 996 can mean WX data 995 can mean DIGIpeater data 994 can mean MESSAGES 993 can mean satellites-in-view xxx are individual messages from xxx The Radio operator enters all of these GROUP codes into his paging memory so that he can receive these data. Or he can selectively eliminate some types of data by omitting the 3 digit group code. ON-AIR-FORMAT: The on air format for these messages are: GGG*CCC - which opens the Paging squelch. #MMMMMMMMM# - which is the message function up to 6 bytes. #mmmmmmmmm# - or additional message lines up to 10 lines. These messages may be manually stored in ANY DTMF radio and can be used to manually send messages to the FT51/TH78 series radios. This method can be very powerful for remote data entry at amateur radio field events. Please see www.aprs.org/aprsevent.html DTMF PAGING RADIO SETUP: Each FT51/TH78 has to be set up for DTMF paging and messaging. This involves setting the USER's digital ID, which for this appliaction should be the numeric equivalend of his three letter callsign suffix. For example, WB4APR has the suffix of APR which is 277 on a DTMF pad. Next, the user must store the above 3 digit APRS group ID's that he wants to receive. Then he must enable TEXT PAGING which squelches the radio on that channel so that it will only respond to PAGING. APRS-to-DTMF FORMATS: This process is the conversion from normal local APRS traffic into a DTMF equivalent CALLSIGNS: First the callsign is converted to 6 bytes. This provides the DTMF user the ability to see the full callsign of the station and be able to match it to the CCC numeric equivalent ID. CCCCCC is used if no SSID is present CCCCCS is used for 5 byte calls with one digit SSID's CCCCSS is used for 4 byte calls with two digit SSID's CCCCSS is used for all other calls with PREFIX dropped to fit. POSITION: The position data is converted to a BEARING and RANGE from the DTMF/APRS gateway location. The BEARING is converted to angles-of- the-clock which gives 30 degree resolution. This uses the digits 0-9 and then T,E,V for Ten, Eleven and twelVe o'clock directions. The distance is expressed in two digits of MILES or Kilopmeters according to local usage. The resulting 3 digit POSITION field is labled as CMM for "Clock bearing and 2 digits of miles". FREQUENCY: If a FFF.FFFMhz frequency string is present, then it is converted to 6 bytes FFFFFF. HEADING/SPEED: Two bytes are used. HS where Heading is N,S,E,W and speed is in 10's of MPH or KPH. Example, 60 MPH is "6". MESSAGES: Any Messages heard on the APRS channel directed to any station with the suffix of XYZ will be sent as a page on the DTMF paging channel to the paging address of ### which is the DTMF hash of the XYZ callsign suffix. The DTMF Gateway further encodes the APRS sender's call into its comparable 3 digit DTMF number ###. On receipt, the message lines will appear as being from station ###. For now, the DTMF gateway does not store nor prepare a traffic list for future replay. Instead, for now, it simply repeats the message each time the APRS packet is seen. ANYWAY I will work very closely with any volunteer to finalize the details of this spec for optimum compatibility with existing and future APRS. Bob, WB4APR