WA8LMF Mirror of WB4APR Website - 21 July 2008 APRS RFID



APRS - RFID: is a project to provide all ham radio operators with an RFID name tag that they can wear during any Ham radio or public service event that will identify them passively as being in the area or in a room or building. . Traditionally, most of APRS position and identification depends on GPS, but GPS does not work indoors in most cases. . This project will provide a seamless identification of ham radio volunteeers where needed.

REQUIREMENTS: The design of such a system would need to consider a number of unique requirements that are best for this amateur radio project. Here are some things to consider:

  • Kit Format - This should be a great club project
  • Innexpensive - The name tags should be under $30 (key chain xmtr) and the reader system under $150
  • Detection Range - 100 feet area detector desired, or 5 foot doorway detector
  • CALLSIGN UNIQUE - The devices must map as-is to existing callsigns
  • LOW POWER - Should be passive or able to be powered from a small quarter size battery

    SOLAR POWER? The nametag shown above has enough solar panels to generate about 0.1W in full sun, but more like about 0.01W in ambient room lighting. The device could charge up over several minutes such that when it passed through the sensor-door, it could fire off a 0.1 second data ID burst.

    IDENTIFICATION PROCESS: Notice, that once this CALLSIGN ID has been received, all of the following information can be transmitted in a packet identifying the location of this individual. And in many cases, this is a full set of information for any APRS person on the move...

  • His CALL, DATE and TIME are captured
  • His POSITION (of the doorway) is plotted with a special RFID icon within a vicinity list of that door
  • Possibly his DIRECTION can be included
  • The local FREQUENCY (and tone/shift) identified with that area is included so he can be contacted
  • The FUNCTION in progress at that location would be included in the position text

    This RFID nametag allows every participant at a special event to be located when he passes through various checkpoints or data entry device. See the special event example where we use APRS handhelds for entering the scores of scout troops from dozens of checkpoints at scouting events. Just knowing where all the hams are is important in many venues.

    RFID BACKGROUND: This RFID concept dates back to the mid 1990's when we conceived of an APRS system for tracking APRS users inside the buildings at Dayton. It subsequencly evolved to use DTMF and was called APRStt and was initially introduced at the RAC convention in 2001 and subsequently at Dayton in 2002. By the next year, Voice response had been added. This APRStt system demonstrated the ability to let not just the 5% of ham radio operators with APRS, but now 100% of all mobiles and HT's or traveling operators out of their local area to be identified from anywhere in the world when they are operational. Since Kenwood introduced global APRS text-messaging and email into their APRS HT in 1998, APRStt was developed to include the other 95% of ham radio operators by acting as a gateway between their existing DTMF HT's and the rest of the APRS community. . This RFID project is just an extension of that to every member of a local club or event.

    The rest of this page is from the APRStt web page that describes the value that can be obtained if all we know is a CALLSIGN and where it was detected! This applies equally well to the APRS-RFID project as to the wider range APRStt (DTMF) project. Please see APRStt web page.

    KATRINA INCENTIVE: After Katrina, APRS responded to the ARRL initiative to make sure that every ham radio operator in a disaster area can be located by his frequency. This initiative was called the Automatic Frequency Reporting System AFRS. At that time, the Voice FREQUENCY field was added into the APRS system so that we could find the voice contact frequency for all APRS operators. In addition, not only could APRS users report their operating frequency, but also the wide area Voice repeaters used by travelers could beacon their frequency onto the front panel of all APRS radios. See the LOCALINFO Initiative. In response to that initiative, Kenwood developed the D710 mobile radio that not only automatically includes the operators present voice operating frequency in every position report, but also can tune to any other APRS operators frequecny or travelers repeater with just the push of the TUNE button.

    The combination of the original APRS, the addition of Frequency in AFRS, the use of Repeater Frequency Objects, and APRStt, gives a univeral, global, system for identification and localization of all radio amateurs by only their callsign. Any station in the world can be located (or contacted live) through any of the live RF APRS application programs or on the web by any of the WEB based APRS systesm such as FINDU.COM as shown below:

    APRStt ON THE MAP: On the APRS map above, not only do you see all of the usual APRS operators (about a 32 mile wide map between Washington DC on the left, and Annapolis to the right), but in the lower right, you also see the 147.105 "travelers repeater" along with a simulation of what the DTMF users would look like. All DTMF users (with the -12 SSID) show on the map as a LIST in the vicinity of the repeater where they were last heard.

    APRStt VOICE RESPONSE: In advanced dedicated APRStt nodes (usually with their own frequency), these DTMF users can also "visualize" APRS data or receive APRS messages by hearing voice reports from the APRStt voice synthesizer. In effect, the centralized APRStt engine, lets everyone in the club or at an event participate in the exchange of APRS data, not just those with the APRS D7 or D700's. Even the old codger that shows up with his venerable 20 year old HT can participate!

    Its as simple as getting some repeater controllers, Echolink, and IRLP nodes, and any other ham radio applications that receive DTMF to accept the DTMF callsign burst and generate the APRS data for transmission over to the APRS network. But even if we dont get controller manufacturers to add this to their products, we can probably add a DTMF chip to any of the small APRS PIC devices such as the Micro-Track or Opentrackers and design them to be DTMF ==> APRS gateways. THey can be either stand-alone devices on any frequency or easily added onto older non-programmable repeater controllers:

    The DTMF chip plus a Microtrack could simply connect to the repeater RX audio and to an easy whip antenna as shown above. Done.

    Or for special events, or simplex nets, or any place you want to make it easy for non-APRS voice users to be visible to APRS, a simple Opentracker+ with a DTMF chip could go on a dongle and be attached to any HT making that HT be an APRStt gateway for everyone else at that event as shown below.

    Or for marathons or any large mass movement of ham radio operators, imagine if you placed one of these automomous APRStt Gateways at every checkpoint along the Marathon route. As Hams moved about the event, if ever they changed locations from one area to another, all they had to do was send their DTMF callsign memory, then the APRS event map would know approximately where they were and/or what frequency they were monitoring.. The APRS symbol for a DTMF user is a gray DTMF keypad. But for future expansion, it can have up to 36 overlay characters for special applications. The APRS symbol for an APRStt gateway is a green square with "TT" in the middle of it.

    Field Data Entry: Since these same DTMF radio users can also enter small text messages, they can also be used for entering data from checkpoints or other field applications. See how to use an APRS HT for field-data entry

    Or lets say for an event which has maybe 6 operating frequencies, repeaters, simplex channels or whatever. Simply placing one of these APRStt devices on each of those frequencies connected to an HT on a pole would then be able to localize all ham radio participants on the APRS map, at least showing what channel they were presently on as whown below:

    In the above view, the "location" of each APRStt receiver is given a completely arbitrary position so that it shows up conveniently in an out of way place on the APRS event map. Clustered around it are the DTMF callsigns that have checked in (by DTMF) on that particular frequency.

    For Programmers, here is more detail:

    Click for the callsign-only APRStt spec (for repeaters, Echolink, IRLP and other simple DTMF input systems)
    Click for APRStt Repeater Spec for building an APRStt engine

    Click for the full APRStt spec though it is lagging behind the above two files which are streamlined for quick implementation and simplicity.

    APRStt will revolutionize ham radio because it lets 100% of ham radio users "check-in" to the global APRS system to facilitate end-to-end contact between operators. APRS users have been doing this since 1995 or so, but now the other 95% of ham radio operators can participate. The simplest form of APRStt is each user putting his DTMF callsign into a DTMF memory in his radio. If there is an APRStt engine monitoring his favorite repeater, then all he has to do to appear on APRS is to send his DTMF memory! He will appear on the global APRS system as an object within ambiguity range of that voice repeater and showing that frequency! See how important voice frequency is to APRS. The image to the right is the roll-your-own way to do it if it is not implemented in the controller or the VOIP software.

    APRStt responds! On hearing the DTMF callsign and sending out the position and frequency packet on the APRS channel, the more advanced APRStt implementations will respond by voice with "Welcome W3XYZ!" as confirmation. This is really no different than what mobiles do now "WB4APR LIstening", except that using the DTMF method is machine readable and allows this presence to the global ham radio community via APRS instead of falling on deaf ears.

    APRStt two-way: Now then, these same more sophisticated APRStt systems can also watch the APRS system for any messages addressed to you. Hearing any, they will SPEAK them back to you on the voice channel! The specialized full two-way APRStt Engine can be as simple as a laptop at any repeater site or located in the valley at a home station as shown below.

    APRStt will revolutionize how you do special events! Everyone with any HT at any event will be able to keep the overall APRS map and communications picture updated with their position, status and other needed data! Now the Kenwood APRS HT's and Mobiles will have someone to talk with! As long as there is an APRStt gateway nearby, DTMF users can send POSITS, MESSAGES, EMAIL and Queries with their TTone pads and hear VOICE responses (on the APRStt channel). APRStt was demonstrated during Dayton in May and the RAC convention in Vernon B.C. in July 2002. If you need to know what APRS is, click here .

    For field events, the APRStt Engine can be as simple as a laptop and two HT's supporting a special event or field activity as shown to the right. Once this suite is activated at an event, it lets EVERYONE listen to APRS information and input APRS information using any two way radio (usually on a dedicated simplex channel).

    APRStt is the gateway for DTMF voice users to report themselves to the global APRS community of users. It enables all non-APRS HT's and Mobile radios to be located and this information is fundamental to facilitating ham radio communications. See some examples:

  • Use DTMF to "check in" as noted above
  • A check-in indicates the date and time of your immediate availablity
  • A check-in puts you on the local/ national or global map
  • A check-in also identifies your voice frequency to everyone
  • Voice response informs the APRStt user of anything he needs to know
  • APRStt can speak incoming messages to APRStt users
  • APRStt allows DTMF origination of messages, emails or anything else in APRS
  • APRStt can speak the position ("LEAD is 3.5 miles NW of FINISH") of special trackers
  • APRStt can speak the bearing and range to any object or even satellites that come into view...
  • Users can QUERY APRStt with DTMF about ANYTHING on the air in APRS...
  • APRS/APRStt can even tie into the global Echooink system for global voice comms knowing only a callsign! See all about AVRS

    Not just DTMF and Voice: Some radios already have paging, and DTMF texting send and receive. These radios can take advantage of APRStt by integrating them into the APRS system.

  • DTMF text receipt and display is possible on some HT's (TH-28/48/78, FT-11/41/51, IC-231) [LATER]
  • APRStt could also do Paging to modified pagers on the HAM bands. [LATER]

    APRStt IS LOCAL: Whether implemented on a repeater, a VOIP node or a simplex frequency, APRStt is simply local, yet transparently integrated with the local and global APRS system. More sophisticated users can take advantage of some of the clever system of abbreviations and short cuts so that positions, messages and many other things can be entered with only a few key strokes. As in the examples above, just sending a callsign is enough to put put you on the global map with a position in the vicinity of the local APRStt repeater or node.

    The remainder of this page is the full APRStt details that would probably only be used for special applicaitons needing more than the basic CALLSIGN identification noted above. But it does show the potential of using our HT keypads like modern teen agers do with their text-messaging from their cell phones!

    For special applications needing better position precision, a fully precise position can be entered with only 6 digits, because the APRStt signal is only on local RF simplex range of the APRStt engine. This establishes the LAT/LONG significant digits and only the lower 6 precise xxxyyy digits are needed to nail down your exact position. For example, xxxyyy is equivalent to DDMy.yyN/DDDMx.xxW because the DDM and DDDM are already known in that area. For fixed events that have known checkpoints or locations, or mile marks, then just a 3 digit position is possible! The DTMF string XYY becomes the YYth position in the X table. For a marathon, simply "013" would put you on the map at mile mark 13. etc. So think outside the box. this is not just using DTMF to enter a LAT/LONG, not at all. This is a system designed from the ground up to serve a specific purpose at the local event or area and to make it SIMPLE for the end user with only DTMF to enter meaningful data.

    There are two proposed methods, either simply using the 3 letter sufix like we do for voice (WB4APR becomes APR) which can be encoded in about 6 digits, or use a HASH function which also takes only 6 digits. THe following describes the HASH approach:

    TT-KEYPAD: We can make this as all inclusive as we want. In addition to the simple examples above we can do ANYTHING in APRS with DTMF with enough patience. Don't let the numbers in the below example fool you. You dont have to remember these. Just type the letters on the DTMF. For example type "WB4APR" on your DTMF pad and the resulting DTMF tones are 924277 which *is* WB4APR in the APRStt hash callsign table. If there is a conflict then fully spell it using the normal TouchTone spelling method WBB4444AP-RR which is 922444427A77 and is a precise match..

    EXAMPLE 1. DTMF to Packet Conversions:

    A922444427A77*82D. becomes:WB4APR>APDT,WIDE:/030415z385 . N/0762 . Wv <== A van in the vicinity
    B4927*1531D...............becomes:WB4APR>APDT,WIDE:/030425z3949.27N/08415.31W <== Exact position in the APRS booth!
    C3*20480602803333D becomes:WB4APR>APDT,WIDE::EMAIL :bruninga@maile.earthlink.net Get me at 3.
    C92111278*2775#52D becomes: WB4APR>APDT::WA1APT :Really enjoyed being with you. Looking forward to getting together again.

    In the first case, the CALL, ICON and any comments are included and the position is posted as a 10 mile ambiguous position in the vicinity of the APRStt system. Subsequent TTone entries can refine the position without having to re-enter the call. In the second exmaple, the four digit LAT/LONG places me at an exact location inside the Dayton Arena. The third example is an Email sent to address book #2 (for that user). In the forth case C92111278* indicates a message to WA1APT. The "2775#52" decodes to ARRL#52 which explodes to the text shown. (ARRL RadioGram)...

    EXAMPLE 2. VOICE responses to simple DTMF Queries:
    QND..............................QUERY for the nearest DIGI to me: "AA3JY is NORTHWEST 3.5 MILES"
    QNM.............................Query for the nearest MOBILE to me: "K3FOR is SOUTHEAST 15 MILES"
    QRD*0924277D...........Query for WB4APR relative to downtown: "WB4APR is NORTHWEST 9.3 MILES FROM DOWNTOWN"

    EXAMPLE 3. Automatic Voice tracking of SPECIAL objects. In this case, the main tracker or station or object at an event can be designated as special and then APRStt is placed in SPECIAL TRACKER Mode. It will VOICE report the location of the SPECIAL packets whenever they come in. Positions are reported as direction and distance to known reference points.

    EXAMPLE 4. APRSTT can voice announce satelites in view! Since APRSdata is already putting out an APRS object on 144.39 whenever an active AMSAT is in view, by using the command ACTIVATE AMSATS (AA), APRStt can be told to VOICE report these satellites whenever any are in view...

    NEW: To help very small CUBESAT satellites support an APRS mission, we have added a simple SPACE subset to the APRStt specification to make it easy for HT's to send APRS data via these small satellites using only DTMF tones! See SPACE-APRStt . Thus, ANY radio can send APRS data just like the Kenwoods! (with NOTHING attached)
    The following is the standard Kenwood (or any DTMF) Keypad key definitions:

    To date, the only radio-only APRS signalling method has been the Kenwood D7 and D700 radios with their internal TNC's. But even so, the user interface is still only the HT's ubiquitous TTone keypad. APRStt simply moves the TT-to-APRS conversion from a TNC in the HT, to a PC on the hill so that ANY existing radio can be used instead of requiring a Processor and TNC to be built into every radio! Further, the DTMF users can receive feedback data via the text-to-speech (or CW) process built into APRStt.

    Click here for the APRStt SPEC. and all of my detail implementation notes. or here for a simplified version.

    Click here to DOWNLOAD APRStt01.zip. (Ignore any previous copies such as 04) With this progarm you can begin playing with APRStt on your own and see how it works. Even if you dont build the DTMF hardware interface, this program will let you enter DTMF equivalents on your keyboard to see how the conversions work over on the APRS side. I recommend that you run it on a Laptop with a D7 on low power and then watch what your Base-Station APRS system does with the packets.

    DTMF INTERFACE: APRStt.exe works with a simple $5 DTMF decoder chip on the LPT1 Printer port and runs on any old DOS PC (eventually to be located at your voice repeater site (or other "receive" site (maybe 147.555?))). It performs the TTone to APRS conversion for all DTMF users in the area and sends the packets via its own TNC to the APRS system.

    VOICE INTERFACE: APRStt.exe does NOT need a sound card. It speaks through 8 resistors on the LPT1 port so ANY old PC or laptop can be used... You can even record your own voice for the responses..

    HT DTMF MEMORIES: The APRStt format definitions combined with the TTone memories built-in to most radios allows for nominal APRS operations with only a few key strokes. In fact, the number of key strokes can actually be less than for entering the same message via the keyboard on a Kenwood APRS radio! This is because APRStt uses a heuristic approach to abbreviate most commands...

    The following APRSdos map of Dayton shows me in the vicinity of the AMSAT Dinner using only the DTMF entry of B47*09. Notice my call within a 1 mile ambiguity circle down where the Amber Rose restaurant is located (and near those APRS mobiles parked in its parking lot!).

    The next Dayton map shows me (W4APR-11) located inside the HARA arena at the location of the APRS booth in the North Hall. This position is exact because I used the APRStt exact format of B4927*1531D.

    HOW did I know my LAT/LONG? Easy!. Before Dayton, I copied the MAPS out of the Hamvention Program and added some simple LAT/LONG tick marks along the edges of the map. With one of these in my pocket, I could use DTMF and the 2x2 format to put myself anywhere on the map within 30 miles of the center location of the APRStt recevier. Or using the HAMVENTION map and the 4x4 APRStt format, I could put myself anywhere exactly. Here is the overall Dayton paper map from the brochure with the one-mile grid tick-marks.

    Every event has a MAP. Simply put the LAT/LONG minutes on the edges!

    LINUX IMPLEMENTATION: When it comes to writing the final APRStt software, it would be great if a version was written under LINUX and could then be run as an auxilliary application at your local IRLP node! Rick, KB8DNR suggested that since the Linux box is already up there, already listening for DTMF, and with my other AVRS ideas will also already be linked to 144.39 via its own TNC, then its a perfect software only upgrade!

    APRStt-PL is an addon option [not even started yet] that adds "PL" decoding capability to APRStt. It not only listens for APRS messages formatted via Touch Tones and converts them to APRS packets on 144.39, but it also listens for PL tones on the input of the repeater. Thus, users can enable different PL tones on their HT's to signal any of 38 different states, commands, or pre-arranged controls. APRStt converts these also to packets of the form:

  • W3VPR>APLXXX:> Heard PL 103

    This packet shows that a PL tone of 103 was heard on the W3VPR repeater APRStt program. The applications for this kind of signalling are only bound by the imagniation of the users. Since APRS knows where W3VPR repeater is located, it can use Vicinity Plotting to let you see where this is occuring. Or I can write a program that rings a bell when PL 147 is heard. My kids can then enter a PL of 147 on their $88 Alinco HT when they want to alert me to QSY to the W3VPR repeater to talk them. ETC... See the details on this PL addition.


    Before the entry of the Kenwood D7 into the market, several manufacturers had experimented with using Touch Tone Dual Tone Signalling transmission and display in their handhelds. Several models of Handhelds can send AND receive short TEXT fields via Touch Tones:

  • Kenwood: TH-28A/48A/78A
  • Yeasu: FT-11R,41R,51R
  • ICOM: W31A

    These radios can not only send TTones like any other HT, but they can also display text sent via TTones from other radios. The displays are quite limited to 6 or 8 characters on the screen at a time, but up to 10 such words can be sent. For APRStt then, we can then define how APRStt can take APRS messages sent to one of these users, convert it to DTSS tones and send them the message over the repeater! CLick here for details.

    APRStt.exe is written for any old 25 MHz or so DOS PC. It was demonstrated at Dayton 2002 using only CW responses. See Details, but I have since added VOICE response via 8 simple resistors on the parallel LPT1 port. For Dayton, I released APRStt00.exe so that even without the DTMF chip, experimenters could enter DTMF simulations from its PC keyboard and see the effect of the packets it generates on the APRS channel...

    Click here for a copy of how I added the DTMF chip to the LPT1 parallel port on my PC.

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    The Naval Academy is a registered user of APRS and WinAPRS. The purpose of this web page is to show several applications currently in use at this site and should not be considered as an advertisement or an endorsement of any commercial product. WA8LMF Mirror of WB4APR Website - 21 July 2008