MIC-E.txt INTEGRATING APRS ON VOICE CHANNELS APRS and VOICE REPEATERS PROPRIETARY Copyright 1993,4,5,6 WB4APR THE NEW TAPR/PACCOMM MIC-ENCODER REV 0 will be available any day now! ----------------------------------------------------------------------- As mobile GPS/APRS continues to grow, we can eliminate the need for every mobile to have a TNC, digital radio, and second antenna by simply integrating the position report into a very brief tone burst at the end of a voice tramnsmission over any two-way radio. With this scheme, no additional hardware is required in the vehicle, other than a GPS unit. The system not only reports position and vehicle type, but also one of 7 canned messages and 4 analog telemetry values! By transmitting a position report at the end of a voice transmission, not only is this a period of dead time due to the almost universal courtesy beeps found on amateur repeaters, but the tone burst can be easily muted out at the repeater receiver, so that the other mobile users DO NOT HEAR it! If the tone burst is about 0.3 seconds, then it will be virtually transparent to voice repeater operation. The APRS MIC-ENCODER achieves a complete position report, course, speed, and digipeater information in about 30 bytes including header, vice the 90 or more bytes in a normal APRS position report. At the voice repeater receiver, a TNC picks off the position report and digipeats it out onto the dedicated APRS digital frequency for mobile position reporting. By using a special TNC that determines the path based on the bits in the TO-SSID, the packet can be kept very short. In addition, the special APRS NODE TNC appends the repeater frequency onto the end of the position report so that digital users can see where the packet originated. If all voice repeaters digipeated onto the same digital position reporting channel (usually 145.79 if available) then anyone monitoring the APRS frequency will see ALL mobile position reports from ALL GPS mobiles on ALL frequencies! APRS MIC ENCODER: In order to make the APRS LOCATOR SYSTEM practical, the MIC-ENCODER had to meet several design constraints: * Must interface to UNMODIFIED radios via the MIC connector * Must use standard AX.25 for compatibility with existing TNC's * Must compress position report into about 0.3 seconds * Must be low enough in power to be powered from the MIC jack * Must accept the readily available NMEA output from GPS receivers * Optionally has 4 analog channels for telemetry The result is a 1200 baud position report compressed to 32 bytes including beginning and ending FLAGS. This equates to about 320 ms, including CALLSIGN, DIGIPEATER PATHS, and a minimum message capability. Plus, the packets are still receivable on ANY AX.25 TNC. PACKAGING: Although the electronics could be miniaturized into about 1 cubic inch, the requirement for user access to switches and the requirement for withstanding the pulling and tugging on the MIC cord results in a robust dash board box design. The cicruit is powered by the mic connector and the only external input is via a standard 1/8 inch phone jack to receive the NMEA data from the GPS unit. This makes the entire mobile vehicle position reporting system as portable as the microphone! Simply move the MIC from vehicle to vehicle, and as long as the radios are compatible at the MIC connector, then the vehicles are GPS ready! The suggested front panel for the MIC ENCODER is shown below. It connects to the radio with only a single 6 conductor pigtail back to either a back-to-back JACK/PLUG or soldered in parallel to the existing MIC jack. --------------------------------------------------------- | R A T E R C V P A T H M S G A U T O O N | | L V L ----------------- | | /^\ (O) | | | | | / \ | | | O O | | | (O) | (O) | 7 | 7 | (O) (O) | | | \___/ | | | | | P T T | | | O F F O F F | | ----------------- | --------------------------------------------------------- On the APRS MIC ENCODER, there are several configuration switches that give the operator real-time control over other dynamic MIC choices as follows: ON/OFF - Used to enable or disable the Mic Encoder packets AUTO - Auto will transmit when repeater is silent more than N secs. PATH - Used to set digi HOPS or North/South/East or West routes MSG - Used to indicate up to 7 pre-defined messages Normally the MIC encoder will only send a POSIT if the POSIT timer has elapsed AND the user has been talking AND releases his PTT. In the AUTO mode, however, after a specified AUTO time period, AND after the repeater has been silent for the QUIET period, then a position packet will be initiated and transmitted. Most voice repeaters will never even key up on such a brief burst due to built in ker-chunk filters. The TNC on the repeater input, however, will hear it and digipeat it normally. ROUTING PATH: There are actually two routing systems, one that can use standard TNC's at the repeater and the other that takes advantage of a new specialized APRS NODE TNC. We will call the standard mode the DIGI mode and the other, the SSID mode. In the DIGI mode, the path switches just select how many hops along one of two preset digi strings will be transmitted in the packet. The advantage of this method is that it is compatible with ANY TNC and will work with existing systems. The disadvantage is that each digi hop takes 7 bytes, and just a 3 hop path almost doubles the length of the packet. The second mode uses only the 4 SSID bits for all routing information. This keeps the packet short, while also allowing for up to 7 hops in all directions! The high order PATH bit selects between OMNI or DIRECTIONAL routing and the 3 routing bits are used to tell the repeater how to route the packet. The following table shows how the routing is handled in both the DIGI and SSID mode. In DIGI mode the TO-SSID is always 0 and the actual digi path is included in the packet. In SSID mode, there are no digis transmitted and the switch setting are transmitted in the 4 bits of the TO SSID. In the following example, assume the MIC-ENCODER has been loaded with the digi string of RELAY,WIDE,WIDE,DIG4,DIG5,DIG6,DIG7 D/O PATH SSID DIGI MODE SSID MODE AS DIGIPEATED BY THE NODE --- ---- ---- ------------------- ---------------------------------- 0 000 0 none none 0 001 1 RELAY WIDE-1 0 010 2 RELAY,WIDE WIDE-2 0 011 3 RELAY,WIDE,WIDE WIDE-3 0 100 4 DIG4 WIDE-4 0 101 5 DIG4,DIG5 WIDE-5 0 110 6 DIG4,DIG5,DIG6 WIDE-6 0 111 7 DIG4,DIG5,DIG6,DIG7 WIDE-7 1 000 8 none NORTH UNPROTO path 1 001 9 RELAY SOUTH UNPROTO path 1 010 10 RELAY,WIDE EAST UNPROTO path 1 011 11 RELAY,WIDE,WIDE WEST UNPROTO path 1 100 12 DIG4 NORTH UNPROTO path + WIDE 1 101 13 DIG4,DIG5 SOUTH UNPROTO path + WIDE 1 110 14 DIG4,DIG5,DIG6 EAST UNPROTO path + WIDE 1 111 15 DIG4,DIG5,DIG6,DIG7 WEST UNPROTO path + WIDE CONVENTIONAL DIGIPEAT ROUTING: First notice that in the DIGI mode, the paths 0 through 3 simply select the number of digi hops in the original string to use. The paths 4 to 7 start over again at the 4th position. THis can be thought of as a completely independent second DIGI string. Usually you would load RELAY,WIDE,WIDE,WIDE,WIDE,WIDE as the digi string. If you select 4 you get WIDE, if you select 5 you get WIDE,WIDE and so on. THis separation into two distinct strings gives you the chance to have a path beginning with RELAY or beginnning with WIDE. This is important for operating in areas which do not have the dual alias WIDE-RELAY digipeaters yet. Although the longest path is now limited to four hops, anything beyond 2 WIDES is frowned on anyway... APRS NODE ROUTING: The APRS NODE has two routing methods, depending on whether the surrounding APRS packet network is capable of the WIDE-N algorithm or not. If WIDE-N is available, then the APRS REPEATER node simply digipeats the packet to WIDE-N where N is the number of hops indicated in the packet SSID. If N is greater than 7 then it is a directional packet and the North, South, East, or West paths stored at the NODE are used. If WIDE-N is not yet available, then the NODE builds a digipeater string using the same algorithm as the MicEncoder; offering the optional 3 and 4 hop alternatives for 1 through 7 and still uses the directional paths for numbers greater than 7. ALso in the directional path, if the 3rd SSID bit is set, then a WIDE is added to the end of that path. WIDE-N ROUTING: In WIDE-N mode, every APRS digipeater repeats every WIDE-N packet it hears and then subtracts ONE from the SSID. They also keep copies of all such packets for 60 seconds and ignore all DUPES of the same packet. THis is a very effecitve OMNI routing method that permits the packet to go out N hops in all directions without any duplication! IMPLEMENTATION: The key to the success of the MIC-ENCODER is that it is very versatile and can operate in all required modes. This allows for growth and improvment in the APRS systems without obsolesence. There are five possible operational situations as follows: NO TNC AT REPEATER: MIC-E path is set to 0 and anyone monitoring the (OR SIMPLEX VOICE) the repeater output with APRS can track users. STANDARD TNC @ REPEATER: MIC-E path is set to 1 thru 7 in DIGI mode. The TNC with the alias of RELAY (or WIDE) repeats packets onto the APRS packet channel. APRS NODE @ REPEATER: NODE routes according to MIC-E SSID bits only. DIGITAL APRS CHANNEL: MIC-E path can be 1 thru 7 in DIGI mode. The BIG difference between the MIC-E DIGI mode and the SSID mode is the length of the packet due to the DIGI fields. THis means for interim compatibility, MIC-E users can operate generally with a path of 1,2, or 3 on all possible channels without specific configuring. Of course, if they select SSID mode while on an APRS NODE repeater channel, their packets will be much shorter because they will be routed by the SSID alone. SETTING DIGI or NODE MODE: To initialize the MIC-E between the DIGI mode and the SSID mode, the Mic-E checks the 4th analog input AD3 on power up. If its analog value is 0 or 1, then the MIC-E will operate in DIGI mode. If the analog value is any other value, then no digipeaters will be transmitted and routing will be done based on the SSID alone. A 10 K pull up resistor permits this input to still be used while in SSID mode. *** IMPORTANT *** TO FORCE THE Mic-E INTO DIGI MODE, (REQUIRED FOR NOW!) JUMPER AD3 TO GROUND. JUMPER PIN X to pin X on the DB-9 CONNECTOR. MIC-ENCODER ALGORITHM: The MIC-E monitors the PTT line and will send a brief POSIT compressed into about 0.3 seconds when the PTT is released and as long as the POS-PERIOD has elapsed. This prevents repetative reports when the PTT is used in rapid sequence. The MIC-E also has an AUTO mode which will key-up the transmitter on its own at least every AUTO-PERIOD if the radio channel has been quiet for a given QUIET period. This permits mobiles not actively talking, to be tracked without interference to other users. In addition, the MIC-E can append 4 channels of analog telemetry and/or a BEACON text onto the end of the POSIT. If the telemetry is added, then it will always be 5 bytes. If the BEACON TEXT is added, then APRS will display that on the LATEST STATUS page and the posit is ignored. The MIC-E is based on the APRS Micro-Interface-Module (MIM) designed by Dr. Carl Wick (N3MIM) and produced by Dr. Will Clement. The MIC-E is configured via its serial port using a PC program called MIC104.exe. This program provides a nominal TNC type command mode for setting the MIC-ENCODER configuration. It provides the standard cmd: prompt. Once the MIC-E is configured, you use the PERM command to cause the MIC-E to save the configuration in EEPROM. The following items can be configured: MYCall Sets the MIC callsign MYSymbol Sets the APRS symbol character VIA digi1,, etc Sets the Unproto digipeater path TXDelay Sets the key up delay PERiod Sets the nominal MIC cycle period POSIT N Sets POSIT period as N * cycle period TELEMETRY N Sets TELEMETRY period as N * POS period BEACON N Sets BEACON period as N * POS period AUTO N Sets AUTO period as N * POS period QUIET N Sets the QUIET period as N * cycle period BText Sets the Beacon Text PTT (1:0) Sets sense of the PTT signal. For the MIC-E, this is 1 since an external PTT transistor is used. MIC-E HARDWARE INTERFACE: As noted, the initial MIC-E prototype is a standard MIM with a few external components to integrate it to the user configuration switches and to the microphone PTT circuit. The 8 digital BIT inputs on the MIM are used as follows: D8, D7, D6, D5 Routing BITS. These are placed in the TO SSID field D4, D3, D2 Three message bits. Active low. D1 PTT INPUT. Active LOW. A5 Multiples the PERIOD by N where N is between 1 and 15. HO The Hold OFF is active LOW PTT PTT output is ACTIVE HIGH since an external PTT transistor is required. NOTE: SInce all bits have internal pull up resistors, then the default values are "1" so we use ACTIVE LOW negative logic. A SWITCH to GROUND is considered to indicate the condition. GPS INPUT STRING: Currently, ONLY the $GPRMC is supported since it has both position, course and speed. $GPRMC,123456.xx,A,3859.11xx,N,07629.12xx,W,123xxx,321.x,..... HARDWARE ITEMS: THere are two subtle hardware items in the circuit. First, there is an LED on the PTT output line that shows when the Mic-E is pulling the PTT low. This shows the user that a POSIT is pending and will be sent when he releases the PTT. Second, the HOLDoff is connected to the receiver AND to the AUTO switch. If AUTO is set to OFF, then the switch GROUNDS the HOLDoff so that no matter what the receiver is doing, the MIC-E will never initiate an AUTO- posit. If the switch is in the AUTO position, then the receiver audio establishes the value of the HOLDoff, and this permits a long period of silence to eventually (via the QUIET TIMER) allow a POSIT to be transmitted regardless of the state of the PTT. RADIO INTERFACING: THere are three ways to wire the MIC-E to your radio system depending on your preference: A) Wire the MIC-E in parallel to your mic at its connector B) Wire the MIC-E internally to the radio or to an auxiliary input (But the MIC-E must be able to sense the MIC PTT independently) C) Wire the MIC-E to a back-to-back plug jack combination Option A or B is suitable if you only have one radio and mic. I prefer the universal option C where you simply solder back to back connectors and then run a 6 conductor cable of any length to the MIC-E. Conveniently, a standard 8 pin plug and jack will fit very nicely in a standard 1/2 inch to 3/8 inch copper reducing coupling. Just saw it in half so you can place it over the connectors after they are soldered back-to-back. Drill a 1/4 inch hole in the side for the cable to the MIC-E. MIC JACK MIC PLUG >--------* *------> * Note, All lines except >--------|--*--------------|------> the PTT are straight >--------|--|--*-----------|------> through connections >--------|--|--|--*--------|------> >--------|--|--|--|--*-----|------> >--------|--|--|--|--|--*--|------> >--------|--|--|--|--|--|--|------> | | | | | | | | | | | | | *---< PTT out to radio } | | | | | *------< Mic audio } | | | | *---------< Mic gnd } | | | *------------* GROUND } | | *---------------> 5 to 8v DC } to MIC ENCODER | *------------------> Receiver audio } *---------------------> PTT input fm Mic } MIC-ENCODER ASSEMBLY NOTES: The MIC-ENCODER is the original APRS TELEMETRY TNC transmitter on a chip (MIM Module) with different code for the MIC-ENCODER algorithms. The following partial schematic shows how the MIC-ENCODER evolved from the MIM: MICROPHONE RADIO ---------- -------- MIC >-----------------------------------------*----------------> AUDIO 47k | *--/\/\/--* *-------------> MIC gnd | | +8v <----------*--------------------------------------*--------< +8 V | | | \ 1k | D1 | | / PTT >---*---------------------|<----------------------\------*-> PTT | | | MIC audio | / | | |-|----------------------| | * | | D2 | * * | MIC GND | V LED | *-|<-|-* MIM MODULE *-|----------* --- | PTT in | | | D3 | | * * * | PTT OUT *--|<--* |-|---------------|----|-| 5.6K |/c | | *----/\/\/\-----| Q1 NPN | *----*-----* |\e | | | c\| Q2 NPN | | S1 * | |--------*-----||-------------< RCV AUDIO | \ | e/| | .2 uf | | * === | - | | | | 6uF | ^ D4 | | | | | | | GND >----------*----*----*-----*----------*-----------*--------> GROUND CIRCUIT DESCRIPTION: D1 isolates the microphone PTT from the radio PTT input so that the Mic-E can key the PTT line while also sensing the MIC PTT condition. D2 prevents the MIC-E from grounding the PTT lead when the MIC-E is turned off. Q1 is an open collector PTT transistor. The LED shows when the Mic-E is holding a PACKET, waiting for the user to release the MIC PTT. D3 isolates the LED from the mic PTT. The 47K minimizes circuit loading and the isolated MIC ground is connected to the lower end of the MIM audio pot to minimize ground loop noise. Q2, D3 and the lower two caps are an audio rectifier to drive the HOLDOFF input to the MIM when the radio is in use. S1 is the AUTO switch. When OFF, it asserts hold off, so that the MIC-ENCODER will never auto-initiate a posit on its own. Bits D2 to D8 connect the PATH and MESSAGE switches and A5 is the RATE adust pot as follows: D8 D7 D6 D5 D4 D3 D2 A5 +5v * * * * * * * * * | | | | | | | | | ---------------------- | | | | | | / | 7 | 7 | *----->\ 5k | | | / --------------------- \ | | | ----- ----- ----- //// //// //// MESSAGE BITS: The 3 message bits select one of seven pre-defined messages unless custom definitions are provided. In addition, all message numbers above 3 will change your symbol color as shown. MSG COLOR DEFAULT DEFINITION --- ------- ------------------- 0 normal Off duty 1 normal Enroute 2 normal In Service 3 normal Returning 4 dim yel Committed 5 Brt yel Special 6 dim red PRIORITY Trips alarms & centers all maps to unit 7 Brt red EMERGENCY! "ditto " SERIAL PORT FOR GPS AND CONFIGURATION: All users should consider using the APRS standard 1/8 inch stereo phone plug/jack for their serial data port on the MIC ENCODER and other small stand-alone-trackers. The phone plug is small, readily available, and is compatible with the nominal mono 1/8 inch phone plug found on many GPS units: GPS UNIT or PC LAPTOP MIC-E or embedded TNC --------------------- ---------------------- mono or stereo PLUG 1/8th inch stereo JACK TXD (data out) --------------------> TIP RXD (data in ) <-------------------- RING GND *-------------------* SLEVE To help remember, just think of the DATA comming out of the male plug tip. This applies to the GPS by itself or to the laptop used to CONFIGURE the stand-alone tracker. By using a "closed-circuit" jack, an internal GPS can be normally connected to the internal MIC-E or TNC, but plugging in the LAPTOP opens that circuit and connects the laptop to the TNC... 9 PIN CONNECTOR OPTION: Although the Mic-Encoder uses a standard DB-9 for its external connections, only pins 2,3, and 5 are the serial port for the GPS and for configuration with a laptop. Most of the other pins are defined as follows: Pin 1 Analog input #1 Pin 2 RXD Data from the PC or GPS to the Mic-E Pin 3 TXD Data to the PC Pin 4 n/c May be used for speaker audio if not avail on mic Pin 5 Ground Pin 6 Analog input #2 Pin 7 n/c Pin 8 Analog input #3 Pin 9 Analog input #4 BE SURE TO NEVER put more than 5 volts on any of the analog inputs, nor make them negative with respect to ground. You may add your own 5.1 volt zeners for protection. USE OF MIC-ENCODER BEACON TEXT: The Mic-E's BText is included on the end of a posit report. But due to APRS processing on receive, only the BText will get through and the posit will be ignored. This is why you should always set your BText rate at a lower rate than your POSIT rate. For NON-GPS equipped MIC-Encoders, a null posit 000000/000000 will normally be transmitted. For fixed station use, however, you can put your full LAT/LONG in the BText, and APRS will get the posit from that. Use the format of BT 3859.11N/07629.11W$000/000 Where $ is the usual symbol character. If you choose to do this, then you can put no other text in the BText, or the MESSAGE bits will end up not being properly parsed. A good example for this, is as a burgler alarm at a fixed location. Put the location in the BText as above, and connect the MESSAGE bits and RATE bit to contact closures in your alarm system. Have AUTO ON. When the bits get tripped, the message rate increases by a factor of 16 and the message changes to EMERGENCY or PRIORITY... DETAIL INSTALLATION INSTRUCTIONS: 1) First you must determine how to power the MIC-E. Measure the voltage at your MIC jack with a 330 Ohm load. If it is between 5 and 7 volts connect directly to the MIM 5 volt input which will use only a Zener to regulate to 5 volts. BE CAUTIOUS, HOWEVER, because this input has the regulator bypassed. If 7.5 or more, connect to the Vin pin on the MIC-E. Check all your radios with compatible connectors and plan to work with all of them... 2) Interfacing ANYTHING to your microphone circuit is not trivial. Any ground loop will add noise to the MIC audio (remember the alternator noise problems...) Drawing 15 ma from the MIC circuit adds to this problem too. Separately powering the GPS from the 12 volt system and then connecting that data ground to the MIC encoder is also a potential noise source. Be sure to use the isolated MIC ground as shown in the circuit. Do not just connect this wire to just any-ole ground! If you do, circulating ground currents will degrade the packet audio. If your packets do not sound clean, you may have to power your MIC-E with a 9v battery to get clean power and audio... NOTES ON THE NEW TAPR/PACCOMM MIC-ENCODER: 1) The MIC-E was only designed to work with radios with separate PTT circuits. Many HT's with combined PTT/MIC audio lines will not work. 2) The Mic-E is not a true RS-232 voltage levels. The data only swings between 0 and 5 volts on output and may be incompatible with some RS-232 serial ports. JUMPERS JP1 REGULATOR BYPASS - With this jumper ON, you can bypass the regulator chip when available MIC power is less than 7.2 volts. External power must be fed to wire-point X. In this case, you will be using the 10 ohm R4 and Zener diode D10 for regulation. WARNING: Do NOT use this option for supply voltages greater than 7.5 volts or you may cook everything. DEFAULT is OFF. See JP6. JP2 AD0 INPUT - With jumper on pins 1 and 2, AD0 will read supply voltage in tenths of a volt. Meaning 126 = 12.6 volts. With jumper on 2 and 3, AD0 reads external voltage on pin 1 of the extternal connector. JP3 MIC MODE - This jumper initializes the MIC into DIGI mode. DIGI mode means the PATH switch will select the number of DIGI hops from the configuration VIA path string. Later when MIC-NODES are installed at voice repeaters, you will operate in SSID mode to keep the packets shorter. DEFAULT is ON. JP4 GPS INPUT - With the jumper in place, the GPS can be programmed externally from the DB-9 JP5 TBD - Default on pins 1 and 2. JP6 5 VOLT POWER - This jumper bypasses the 10 ohm series resistor in the Zener regulator circuit and relies on the source impedance of the MIC circuit power for current limiting. WARNING: Be sure to never use this jumper when supply voltages are above 5.8 volts. DEFAULT is OFF. JP7 TTL INPUT - With jumper on 1 and 2, you may input TTL data at wire point 12. On position 2 and 3, data input is quasi RS-232 on pin 2 of the DB-9 connector. DEFAULT is 1 and 2. JP8 GPS INPUT - With Jumper on, the internal GPS-20 is connected to the MIC Serial input port. With jumper off, you may use the DB-9 for external serial connection to your PC for configuring the MIC-E. J3 Mic-E LOADING - This jumper allows you to minimize the impedance loading of the Mic-E on your existing Mic Circuit. Use the highest value resistance that still gives suitable packet audio level without loading down the voice audio. DEFAULT is on pins 3 and 4 for 10K. ----------------------------------------------------------------------- APRS REPEATER NODE: This special TNC NODE is designed to be intgrated into typical amateur voice repeaters. The TNC performs a number of special functions to fully implement the APRS LOCATOR SYSTEM: * It has true DCD to destinguish between voice and data * It uses this DCD signal to mute the repeater audio during packets * It digipeats all position reports from the repeater receiver to the dedicated APRS digital channel * It implements the APRS Directional Digipeating algorithm * It implements the APRS FLOOD-N digipeater algorithm for OMNI packets * It appends ADDText (usually the rptr freq) to the end of all packets ("Via 146.940") * It uses the external carrier detect for the APRS packet channel for true CSMA effeciency, but this need only be an audio COR detector. Notice that although the APRS REPEATER NODE function only listens on the voice repeater input and only transmits on the digital APRS packet frequency, it must also have a secondary carrier detect on the APRS packet channel to avoid collisions. This special APRS node function is NOT involved in any further routing on the APRS digital channel (I mean that it does NOT serve as a general purpose APRS digipeater on the digital channel). All it does is to insert the appropriate directional or OMNI digipeater path and digipeat the packet. This distinction, of course, is only a functional distinction, since APRS digipeater functions can be co-located, or even built into the same NODE box as long as dual digital receiver channels are maintained. PERFECT DCD OR MUTE CONSIDERATIONS: Since the ultimate acceptance of the POSIT-PACKET on voice repeaters will be determined by the minimization of the BRAAAAAAP sound on the repeater output, the DCD and subsequent muting of the repeater transmitter are very important. The APRS NODE must therefore provide a separate MUTE signal that is 99.99% percent accurate. Since most voice repeaters have simple analog delay lines of up to 50 ms to eliminate the squelch tail, the actual MUTE decision can be made as late as 50 ms after the initial DCD, and still be able to mute the packet from the repeater output. NOTES: Notice that the APRS REPEATER NODE will also work on the digital channel! In other words, the APRS REPEATER NODE algorithms can also be running simiultaneously in all of the APRS DIGI's so that the APRS compressed format will be picked up directly on the digital channel. These original packets are distinguishable because they DO NOT have an original DIGI field. Once a NODE processes them and adds the DIRECTIONAL or WIDE routing, they will be forwarded as usual. Notice that the NODE hardware can actually do both functions as long as dual digital receive channels are provided. APRS PROPRIETARY APRS PROPRIETARY