What is APRS?

APRS is a system for transmitting GPS messages and geographic coordinates based on PACKET (AX.25 protocol) and AFSK 1200 modulation. APRS is designed to operate in a small area of ​​one region, in the area of ​​operation of one digital repeater (digi) or a group of repeaters connected to a network.

Another application of APRS is automatic weather stations that report temperature, pressure, and wind speed over the air. They can be seen on APRS card. There are fixed and movable beacons. Beacons that change their location together with the radio amateur and transmit coordinates on the air are called “trackers” from the English word “tracking”. The path ("track") will be drawn on the site that collects the APRS data. Or, using the GPS coordinates of other stations broadcast on the APRS frequency 144.800 MHz, you can find other radio amateurs nearby in the APRSdroid program.

Using APRS, you can transmit messages within a certain area without using the Internet. That is, all APRS stations listen and transmit on the same VHF frequency. Traditionally in the Eastern Hemisphere the frequency of 144.800 MHz is used in the two-meter band, but in America the frequency is 144.625 MHz. FM modulation, transmission method - PACKET 1200 bps. In the 70 centimeter band the frequency is 432.500 MHz.

APRS is called a global network - a packet from the air passes through the gateway and ends up on the website https://aprs.fi or [https://aprs2.radiorubka.org]https://aprs2.radiorubka.org/). This way, other radio amateurs can monitor APRS station activity using a web browser. You can configure the APRSDROID or APRSIS32 or UIVIEW32 program to send APRS packets over the TCP-IP Internet, without using the airwaves. To work via TCP-IP you will need to obtain a password (only licensed radio amateurs can use APRS) - to connect to APRSdrroid via TCP-IP you need to obtain a passcode. It is issued by team AT aprsdroid.org within a few days or a couple of weeks after submitting an electronic copy of your amateur radio license.

What is PACKET radio?

Packet radio is the transmission of messages and data in the form of packets using the AX.25 protocol. The history of PACKET dates back to the 70s of the last century. Then, long before the advent of the Internet, packet radio was used to organize Electronic Bulletin Boards (BBS) with radio access. Then weather stations appeared, where packets can consist not only of text, but also of bit fields, for example, temperature values, wind speed. Packet radio is not for radio sports competitions, nor is it the domain of weak signals. Using packet radio, you can make radio calls (QSO) with neighbors in the region. Previously All that is required for this is a computer with a TNC controller on both sides and a VHF radio station of the 2-meter range (144 MHz), with the ability to connect a linear input and audio output to them.

What is AFSK 1200 modulation?

Modulation, along with the radio station, represents the lowest, physical layer for transmitting messages.
AFSK transmission uses two tones 1200Hz and 2200Hz, which change during the transmission of information.

• modulation type - FSK
• speed 1200 baud (bps)
• 2 tones are used 1.2 kHz for "Mark" and 2.2 kHz for "Space"
• frequency shift between tones is 1 kHz.
  *due to rapid manipulation, it appears as a spectrum approximately 1300-1400 kHz wide.
• at the beginning of the transmission there is a preamble of short flags used to synchronize modems, with a period of 6.7 ms.
• the volume level of both tones must be the same (the audio spectrum of the AFSK signal must be flat).
• AFSK 1200 packet modulation is widely used by amateur radio operators on VHF in the 2 meter band (144-146 MHz) for APRS transmission on a frequency of 144.800 MHz in Europe and Asia and 144.390 MHz in America, 145.175 MHz in Australia.

What other modulation types are there for APRS?

• FSK modulation at 300 baud (used on short waves in the 30 and 20 meter bands).
  The two tones Mark and Space are separated by an interval of 200 Hz. The radio operates in SSB mode for data transmission.
• BPSK modulation - used on amateur radio satellites DO-64 (DELFI-C3), AO-73 (FUNcube-1). Speeds 300, 600, 1200, 2400 baud.
• G3RUH FSK is used on VHF when transmitting at 9600 baud. Coding using a polynomial and limiting the spectrum width are used. Application: amateur radio satellites CubeSat.
• 9600 bps GMSK - used on the FalconSat-3 satellite for APRS.

What is AX.25

AX.25 is one of the transmission protocols (such as INET TCP-IP v4, IPv6, IPX, APPLETALK). The difference between AX.25 and others is that it is used primarily by radio amateurs, on nodes operating in PACKET mode. Also, through AX.25 applications can exchange information both on one personal computer and on different ones. The AX.25 protocol operates at the logical and software levels (above the physical). The transfer of information between programs that support AX.25 is organized using sockets (file streams). One-to-many access. Low-level (“raw”) data packets consisting of 0 and 1 are transmitted inside the sockets. To check the integrity of data packets, AX.25 uses frames that are organized according to the HDLC standard. There are two types of stations - end node stations and intermediate nodes (relay) that communicate with each other - one transmitter and one or many receivers. It is possible to route traffic - with intermediate nodes (relays) and limit the number of intermediate nodes for each message. The terminal nodes are called terminal nodes - TNC terminal node controller. Intermediate nodes can be repeaters (digipeater or, abbreviated as digi) or gateways to the Internet - “gates” (from the word gate - gateway). Through gateways, message traffic enters the APRS network (from the air to the computer network) or goes outside (broadcast). Any data can be transmitted through AX.25, even TCP-IP packets. Due to the low speed of radio interfaces (1200 baud), radio amateurs use AX.25 for short messages encoded in 7 bits (only Latin letters and numbers) or bit fields (telemetry, weather). All end nodes transmit data over one channel (on the same frequency). All APRS stations have the same rights to use the transmission channel. To avoid overlapping transmissions from different stations ("collisions"), APRS implements monitoring of radio channel occupancy by the TNC node before the start of transmission.

What is HDLC

HDLC protocol for monitoring the integrity of AX.25 frames and synchronization of the receiver and transmitter. A zero (0) is encoded by a change in the modulation state from negative to positive, and when a unit (1) is transmitted, the modulation state does not change. The beginning and end of the frame are marked with the synchro sequence 01111110 (or 0x7e). Long transmissions of 1 are prohibited (a 0 is inserted before each consecutive 1). A 16-bit checksum is added to the end of the message. A special feature of the protocol is its insensitivity to changes in signal polarity. That is, inverting the amplitude of the modulating signal from + to - and vice versa does not cause transmission problems.

What is KISS

KISS is a special protocol for interaction between a computer and a TNC. Since there is a serial port between the computer and the TNC, data from the computer is packed into HDLC frames and transmitted between two points - the computer and the TNC.
Both of these devices must understand this protocol. Programs for digital amateur radio types fldigi or MixW can act as KISS controllers. However, for KISS, either hardware TNC controllers or software emulators of TNC controllers are usually used. The KISS protocol transmits both data and commands to control the TNC. The KISS protocol was invented so that different programs and controllers could communicate “in the same language.”

TNC models

For example, the popular Kantronics hardware controllers for amateur radio, MFJ-1270B or the KISS software controller, which emulates a hardware controller only in PC memory, is used to connect APRS programs to it.

List of TNC controller models that are implemented in hardware:

• AEA PK-88 Terminal Node Controller
• Kantronics KPC-3
• Kantronics KPC-3 Plus
• Kantronics KPC-9612
• Kantronics KAM-98
• Kantronics KAM-Plus
• Kantronics KAM-XL
• MFJ-1270CX (discontinued model)
• MFJ-1270CTX (discontinued model)
• MFJ-1270B
• MFJ-1270X
• MFJ-1275
• BUX Communications Corp (BUX CommCo™) RASCAL™ (“Radio And Sound Card Adapter Link”™)
• RIGblaster Standard
• RIGblaster Plus (West Mountain Radio)
• RIGblaster Advantage
• RIGblaster Plug and Play
• Tigertronics SignaLink USB
• Tigertronics SignaLink SL-1 Plus
• Timewave HamLink USB
• Timewave PK-96
• Timewave PK-232/DSP
• built-in TNC controller for Kenwood TS-2000 transceiver.
• Kenwood transceivers models TM-D710, TM-D710A, TM-D710E, TM-D710GA.
• controllers built into D-Star standard radios.
• Byonics - TinyTrak4
• KISS TNC based on Arduino (here)
• homemade TNC controller IZ1DNJ

List of TNC software controllers and PACKET/AFSK audio software modems:

• UZ7HO SoundModem - see website UZ7HO packet radio(Windows)
• AGWPE soundmodem -AGW Packet Engine(Windows)
• Thomas Sailer, HB9JNX/AE4WA "soundmodem" (Linux: Ubuntu and Debian, Mint, etc.)
• WB2OSZ DireWolf(Linux and Raspberry Pi)
• MixW http://goryham.qrz.ru/digi/mixw/packet.htm
• fldigi https://github.com/la5nta/fldigiattach

What is Mic-E?

Mic-E is a mode that combines voice and digital communications (E stands for Echolink) - transmitting APRS packets through voice repeaters. An APRS packet is transmitted every time after each press and release of the PTT button or on a timer. This mode is implemented in some radio stations. For more reliable transmission, the packet length is reduced to 0.3 seconds; only data is transmitted in digital compressed form: position, vehicle type, speed, course (direction of movement). The Mic-E message is short, only 30 bytes, while a regular APRS message is 90 bytes.

In order for Mic-E to work, the repeater must recognize Mic-E messages and must be able to process such packets. To prevent other users from hearing noise, the repeaters are protected against short presses of the PTT switch, and packets shorter than 0.3 seconds do not pass through the repeater and do not cause the noise suppressor to open. However, messages on the repeater's Mic-E frequency go to the APRS network. With appropriate repeater settings. ;-)

Mic-E is supported by Kenwood, Anytone and Yaesu radios. Full list of radios with Mic-E support:

• Yaesu FTM-350
• Yaesu VX-8G
• Kenwood D72
• Kenwood TH-D7A, D7E
• Yaesu FTM-400DR
• Yaesu FT1D
• Kenwood TH-D74
  Anytone D878UV
  Anytone D578UV
• Yaesu FT-1D(R)
• Yaesu FT-2D(R)
• Yaesu FT-3D(R)

The first version of MIC-E was implemented as a separate “box” (manufactured by TAPR/PACCOMM) which was connected to the microphone and speaker of the radio station by wires.

Sender's call sign in APRS

The sender and receiver's APRS call sign consists of a maximum of 6 characters. Example: RS0ISS, UB3ZZZ - matches the amateur radio call sign.

Recipient's call sign in APRS

Can be a real amateur radio call sign (6 characters) or a standard recipient provided in the APRS system:

AIR, ALL, AP, BEACONCQ, GPS, DF, DGPS, DRILL, DX, ID, JAVA, MAIL, MICE, QST, QTH, RTCM, SKY, SPACE, SPC, SYM, TEL, TEST, TLM, WX, ZIP.

For example, a GPS receiver is used by trackers that send station coordinates to the Internet, TEL and TLM - for telemetry.

What is SSID

The numeric value in the source (i.e. sender) address field is worth after the call sign suffix separated by a hyphen is called the SSID field.
Example: UA1AA-7,-7 this is the SSID. The SSID field determines the station type and icon on the map (unless otherwise specified in the icon field).
SSIDs are used to separate multiple APRS stations belonging to the same call sign. For example, RV1VV house, RV1VV-2 cottage, RV1VV-5 smartphone, RV1VV-13 weather station.

Examples of standard SSIDs:

Basic APRS symbols

What is the UNPROTO path and WIDE value?

The UNPROTO path contains instructions for repeating packets and only affects digital repeaters.

According to the oldest standard, to transmit packets through a node, the TNC end device had to specify the word RELAY in the PATH field. The word RELAY means that such a packet must be retransmitted on the air by a digi repeater. As the number of repeaters increased, digi repeaters also began to be combined into chains and stars to increase coverage. In this regard, variants of the WIDEn-N path began to be used. This is done to prevent endless retransmission of packets and limit the coverage of one packet to the territory - with each retransmission, the number specified in the SSID (for example, -7) n is reduced by 1 and eventually the packet will no longer be processed by relays.

ЗнаUNPROTO path value for one repeater: WIDE1-1.

!Note the indication UNPROTO WIDEn-n makes sense if there is at least one operating digital repeater (digipeater) in a given area.

Although it is possible to enter into UNPROTO the call sign of the correspondent with an asterisk at the end (like RA1AAA*), practice shows that this does not make sense, because the path in the message received in APRSdroid is hidden, all packets from any stations in line of sight are displayed on the ecoan, and not just those “directed” using the UNPROTO path.

See article on APRS.FI "How APRS paths work"

Using an empty UNPROTO path in APRS

A packet that does not have a WIDE path specified will not be relayed by any relay, but can still be listened to directly. Его может перехватить iGate и передать в APRS-IS через Интернет.
A packet without a path is like an undirected, general call (without indicating the destination call sign). For example, transmission RX1XX:

RX1XX>APRS:!60.56ND31.501E&

It can be seen that when the UNPROTO path is empty, the transmission does not contain the call sign of the second correspondent or instructions to relay the packet. But the operator of any APRS radio station can respond to such a message manually.

Using the "CQ" and "ALL" paths in UNPROTO

Just like with an empty path, such a packet is ignored by relays, but it can be listened to directly.

RX1XX>APRS:CQ:!60.56ND31.501E&

With CQ and ALL, the call is an "all" broadcast.

Using a special UNPROTO path for satellites

The general call path should be specified as the path for APRS communications via satellite repeaters:

APRS path options for the International Space Station (ISS):

From Earth to Earth, through the ISS relay, the two simplest options for the UNPROTO route are:

• ARISS
  *ARISS,CQ

(The second option is a general call).

Source - site fars.k6ya.org

More complex options for the UNPOROTO path, from the topic "APRS via ISS" on the website cqham.ru:

• ARISS,RS0ISS,WIDE1-1,WIDE2-2
  ARISS,RS0ISS*,WIDE1-1

(The call sign of the space station rs0iss-3 or rs0iss-4 may be indicated in the response relayed message - it does not matter, therefore the option RS0ISS* is selected; WIDE1-1 and WIDE2-2 for relays of packets to the Internet via i-Gates).

If relaying packets to the Internet via i-Gate is not needed:

ARISS,RS0ISS

(Then you need to receive your own signals relayed through the digital repeater of the space station)

ISS Beacon from Space to Earth (only used on the Space Station):

• CQ,SGATE

(Does the relay add SGATE to distinguish "downstream" from "upstream" packets?)

What is the relationship between WIDE and SSID?

• • Northern, Southern, Eastern and Western paths are not used in the new N-N paradigm.
    The original scheme no longer works. The idea was that the SSID would participate in subtraction from the maximum number of hops, so that houses -0, -1, -2 would be relayed the least (since they have a large coverage area), and SSID -6, -7 - satellites and aircraft, SSID -12...-15 - small devices would be relayed further than others.
    In practice, this generated "avalanches" of packet repetitions if the number of relays was more than one. Instead, a new N-N scheme is invented.

Source - http://wa8lmf.net/DigiPaths/,.

UNPROTO path schemes above WIDE2-2 are not used due to the low probability of successful packet delivery through 3, 4, 5, etc. nodes Amateur packet radio uses PACKET modulation without error correction - not very tolerant of low-quality radio channels.

The choice between WIDE1-1 and WIDE2-2 schemes depends on the repeater settings and the TNC (Terminal Node Controller) firmware version on the repeater node. I recommend finding out from the owner of Digi, or through friends, which scheme is used in a given area. Or use trial and error. With a single repeater - the WIDE1-1 path.

It is possible to build your own packet node using DireWolf, configuring it appropriately for APRS relay. Before this, you need to register the radio station with Roskomnadzor.

How to send a broadcast message - a bulletin - via APRS?

Bulletin, as follows from the meaning of the English word, is a message attached to a button (bullet) on a bulletin board.
You can call it a pinned message.

To send a newsletter, indicate in the “to” field:BLN#, in the message text - the message itself.
Example: To: BLN#

Xastir will begin sending this message periodically. From other radio amateurs and on the website https://aprs.fi the bulletin will be visible in a separate column “View” - “Bulletings”.

What are newsgroups?

Newsgroups are the same as subscriptions. Examples of groups: ALL, SPB, BALOON
To receive messages from them, you need to subscribe.
Subscriptions are carried out by the ANSRVR advertisement server, the functions of which can be performed by the APRSISCE/32 program.

How to subscribe to a newsgroup?

An ANSRVR advertisement server must be located within the station's APRS coverage area.

Subscribe with the command TO:ANSRVR with the following text.

1) to subscribe:

Example:
TO:ANSRVR
J list of groups separated by spaces

or (the preferred option is to subscribe and simultaneously send CQ to group members):

TO:ANSRVR
CQ group_name J

another option is to subscribe in monitoring mode
K list of groups or call signs separated by spaces

Example:
TO:ANSRVR
K RUSSIA

2) to unsubscribe

Example:
TO:ANSRVR
U list of groups separated by spaces

3) list of available world groups

TO:ANSRVR
?

There are also local groups, for example, SPB.

3) list of world groups with owners:

TO:ANSRVR
D

4) отправка сообщения в группу:

TO:ANSRVR
message: CQ group_name message

Example #1 of sending a CQ all-call to a CQ group:

TO:ANSRVR
CQ CQ your_callsign

Example No. 2 sending the message “Hello wsem!” to the SPB group.
TO:ANSRVR
CQ SPB Hello wsem!

(If you do not send a CQ, you will automatically be kicked out of the group within 24 hours).

5) see what group I am in

TO:ANSRVR
L

6) request a group description

TO:ANSRVR
D group name

How to send a message "some text" to the SPB newsgroup?

To: ANSRVR
ALL SPB some text

or

To: ANSRVR
CQ SPB some text

The same goes for other groups.

What types of APRS messages are there?

• GPS position (station coordinates, speed, course and altitude)
• Azimuth (for "fox hunting" - time, coordinates, azimuth)
• Objects and entities (examples like “Lighthouse”, “Apartment Museum”, “Gathering Place for Participants” are objects. “Time”, “Center of the Storm” are entities)
• Weather (temperature, wind, pressure, humidity)
• Telemetry (voltage, current)
• Messages (from someone to someone), similar to SMS
• Broadcast messages (bulletins, news, announcements)
• Requests (to stations, directly) - end with a question mark (?). Ignored by gateways (receiving gates) and repeaters.
• Responses (stations to requests and any messages)
• Statuses (for example, Mic-E is on)
  *other.

What programs are available for APRS?

*UI-View32*(Windows) - tracker, node, gateway or digi
APRS-IS/32(Windows) - tracker, node, gateway or digi
UISS(Windows) - for radio communications through the International Space Station
Xastir(Linux) - for tnc, node, gateway or digi
Direwolf(Windows, Linux) - can work as an APRS tracker, receiving gateway or digital repeater. In Russia, operation is allowed only under the control of an operator or rx-only gateway.
aprsdigi- for organizing a digi repeater
APRSdroid(Android) - to send your coordinates to the APRS network
U2APRS(does not work on latest versions of Android)
aprs· Python language module for connecting to APRS using TCP-IP (installation via PyPi).
APRSISCE/32**(WinCE)

What are APRS objects?

Using the APRS object principle, a radio amateur can mark non-living entities on the map, that is, objects - such as a camp, lighthouse, headquarters, museum, etc. In the USA, they sometimes refer to the center of a natural disaster - a hurricane. You can calculate the distance to an object in the same way as to another radio station.

Sources:

http://www.aprs.org/doc/APRS101.PDF

http://www.aprs.org/aprs11/SSIDs.txt

http://aprs.gids.nl/uidigi/protocol.txt

http://www.aprs.org/ansrvr.html

https://www.dxzone.com/catalog/Software/APRS/

https://base.garant.ru/70263118/- Order No. 184 of July 26, 2012

https://digital.gov.ru/ru/documents/4725/- Order No. 156 of 05/07/2015

https://www.consultant.ru/document/cons_doc_LAW_208732/- Order No. 156 of 05/07/2015

http://www.ax25.net/kiss.aspx

https://destevez.net/2016/06/kiss-hdlc-ax-25-and-friends/

http://www.aprs.net/vm/DOS/MICE.HTM

Date of last change: 06/07/2025

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