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[Automatic Packet Reporting System] The APRS TX App sends messages on the selected frequency. The App allows the configuration of the APRS stream. The App is marked as Beta, but it does send decodable messages in AFSK in the correct AX.25 format.

Fields

Source: Your own licensed amateur radio callsign (e.g. W1ABC). The field accepts up to 6 alphanumeric characters. Move the cursor to the right side of the label using the arrow buttons and select each character. Then move to "SSID:" and select a number from 0–15. The most common SSID for a PortaPack is 0.

Dest.: This is not the callsign of a receiving station. In APRS, this field must contain a valid APRS destination address. The recommended value for general use is APRS (which falls under the generic AP* wildcard accepted by all APRS decoders). For experimental or custom software, APZNNN (where NNN is a version number) is the correct choice per the APRS Protocol Reference. Entering a random callsign or leaving this field empty will cause APRS decoders (such as OpenWebRX, Direwolf, or aprs.fi) to ignore or incorrectly parse the packet. Set SSID to 0.

Path: The digipeater path tells the network how far to relay your packet.

• WIDE1-1 — single hop, recommended for most mobile and portable use
• WIDE1-1,WIDE2-1 — two hops, wider area coverage
• Leave empty for direct RF only (no digipeating)

Info field: The message content. Select the "Set" button to enter text (maximum 30 characters). Important: The very first character of the Info field must be a valid APRS Data Type Identifier (DTI). Without it, APRS decoders cannot determine the packet type and will not display the content correctly.

Note: The ! DTI is an exception — it may appear anywhere up to the 40th character position. All other DTIs must be the first character.

APRS Data Type Identifiers

The first character of the Info field defines what kind of data follows. Source: APRS Protocol Reference v1.0, Chapter 5.

Character	Type	Messaging	Example Info field
>	Status — simplest, no coordinates needed	No	>Hello from PortaPack
!	Position without timestamp	No	!4071.27N/07400.59W-Hello from NYC
=	Position without timestamp	Yes	=4071.27N/07400.59W-Hello from NYC
/	Position with timestamp	No	/181654z4071.27N/07400.59W-Hello
@	Position with timestamp	Yes	@181654z4071.27N/07400.59W-Hello
:	Message to a specific station	Yes	:W1XYZ :Hello there
;	Object report	No	;OBJECT *181654z4071.27N/07400.59W/
_	Weather report (no position)	No	_10092345c000s000g000t068
T	Telemetry	No	T#001,100,200,300,400,500,00000000

"Messaging" means the packet signals that the station is capable of receiving and acknowledging APRS messages. Use = or @ if you want two-way messaging; use ! or / for position-only beacons.

For beginners, start with > (status). It requires no coordinates, no timestamp, and is decoded by all APRS software.

The ?GPS? placeholder in the Info field is automatically replaced by the current GPS coordinates if a GPS module is active or Manual GPS has been set. Example: !?GPS?-Hello from PortaPack

Timestamp formats

Timestamps appear inside position packets that use the / or @ DTI. The format is always 7 characters.

Format	Example	Meaning
DDHHMMz	181654z	Day 18, 16:54 UTC — recommended
DDHHMM/	181654/	Day 18, 16:54 local time
HHMMSSh	165400h	16:54:00 UTC (hours/minutes/seconds)

The APRS Protocol Reference recommends always using zulu (z) format for on-air transmissions.

Note: The MDHM format (Month/Day/Hours/Minutes) seen in some older examples is only valid for positionless weather station reports and must not be used in position packets.

Position coordinate format

Latitude: DDmm.hhN or DDmm.hhS (8 characters) Longitude: DDDmm.hhE or DDDmm.hhW (9 characters — always 3 digits for degrees, with leading zero if needed)

Example: 4071.27N/07400.59W = New York City area

• 40 degrees 71.27 minutes North
• 074 degrees 00.59 minutes West (note the leading zero)

The character between latitude and longitude is the Symbol Table Identifier (/ = primary table, \ = alternate table). The character immediately after the longitude is the Symbol Code. Common symbol codes: - = house, > = car, [ = jogger, / = dot/waypoint. See the APRS Symbol Tables for the full list.

Frequency

APRS operates on dedicated frequencies per region. Transmitting on the wrong frequency means nobody will receive your packets.

Frequency	Region
144.390 MHz	North America (USA, Canada, Mexico), Colombia, Chile, Indonesia, Thailand
144.800 MHz	Europe, Africa, Russia, Middle East
144.575 MHz	New Zealand
144.640 MHz	Japan, Eastern Asia
145.175 MHz	Australia
145.825 MHz	ISS (International Space Station) — worldwide, only when ISS is in range (~10 min passes)

The default frequency in the app is 144.390 MHz. Change it using the on-screen keypad at the bottom of the screen.

ISS note: Packets sent to 145.825 MHz during an ISS pass are relayed by the onboard APRS digipeater and can be received worldwide. Use ARISS as the path instead of WIDE1-1. Check current ISS pass times for your location before attempting.

⚠️ Transmitting to the ISS requires the same valid amateur radio license as any other APRS operation. Using the ISS digipeater with a fictional callsign is a violation of both national regulations and ITU Radio Regulations Article 25. The ARISS organization monitors activity on 145.825 MHz. See the ARISS website for schedules and guidelines.

Gain settings

At the bottom of the screen:

• Frequency step: select step size with cursor, adjust with rotary encoder (e.g. 12k5)
• Deviation: select with cursor, adjust with rotary encoder (e.g. 5 kHz)
• Gain IF: range 0–47. Color indicates combined output power (IF + AMP): 0–17 green, 18–38 yellow, 39–47 orange, 48–61 red
• Amp: 0 dB or 14 dB (on/off)

Transmission starts with the "Start" button and stops automatically after the packet is sent.

Complete working examples

Some example message formats are as follows. Many more are in the APRS Protocol Reference Manual.

Simplest packet — status message:

• Source: W1ABC, SSID: 0
• Dest.: APRS, SSID: 0
• Path: WIDE1-1
• Info field: >Hello from PortaPack
• Frequency: 144.390 MHz (North America)

Position without timestamp (no messaging):

• Info field: !4071.27N/07400.59W-Hello from NYC
• The - after the longitude is the Symbol Code for a house

Position without timestamp (with messaging enabled):

• Info field: =4071.27N/07400.59W-Hello from NYC

Position with UTC timestamp (no messaging):

• Info field: /181654z4071.27N/07400.59W-Hello from NYC
• Format: /DDHHMMzDDmm.hhN/DDDmm.hhW[symbol][comment]

Position with UTC timestamp (with messaging):

• Info field: @181654z4071.27N/07400.59W-Hello from NYC

Position with GPS placeholder:

• Info field: !?GPS?-Hello from PortaPack
• Requires GPS module active or Manual GPS set

Position with altitude:

• Info field: !4071.27N/07400.59W-Hello from NYC /A=105
• Altitude /A= is always in feet per APRS Protocol Reference

Putting it all together — position, UTC timestamp, altitude and comment:

• Info field: @181654z4071.27N/07400.59W-Hello from NYC /A=105
• April 18th at 16:54 UTC, New York City area, 105 feet altitude

Testing your transmission

A reliable way to verify your packets are correctly decoded is to use a second SDR receiver (e.g. RTL-SDR) with SDR++ and the QTMM AFSK1200 Decoder software, both free. You can also use an online WebSDR or a local OpenWebRX instance. Note that aprs.fi and similar internet-connected receivers will only show your packet if an iGate is within RF range of your transmission.

Legal notice — amateur radio license required

APRS operates on amateur radio frequencies. Transmitting on these frequencies requires a valid amateur radio license in virtually every country.

Country / Region	Governing body	Regulation	License required
USA	FCC	Part 97	Technician class or higher
Europe (ITU Region 1)	National authority (e.g. BNetzA, Ofcom, ANFR)	ITU Radio Regulations Art. 25	National amateur license
Australia	ACMA	Radiocommunications Act 1992	Foundation class or higher
Japan	MIC	Radio Law of Japan	Operator license + equipment type approval
Canada	ISED	RBR-4	Amateur radio operator certificate
Worldwide	ITU	ITU Radio Regulations	National amateur license

The Source callsign must be your own licensed callsign. Using a fictional, unassigned, or third-party callsign is illegal in all jurisdictions and may result in fines, license revocation, or criminal prosecution depending on local law.

The HackRF One is a test and development device, not a certified amateur radio transceiver. In the USA (FCC Part 97), no equipment certification is required for amateur radio — the licensed operator bears full responsibility for the quality and legality of the transmission. In most European countries, the transmitting equipment must additionally meet national technical requirements (spurious emissions, bandwidth). Ensure your transmission complies with the regulations of your country before transmitting on any amateur frequency.

Further reading

• APRS Protocol Reference Manual
• FCC Part 97 — Amateur Radio Service
• ARRL guide to Part 97
• ARISS — Amateur Radio on the International Space Station
• ITU Radio Regulations
• aprs.fi — Live APRS map
• APRS Symbol Tables