APRS TX - portapack-mayhem/mayhem-firmware GitHub Wiki

[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 right AX.25 format.

The App has settings for:

  • "Source:" Address is typically the transmitting Callsign. The field is selected by moving the cursor to the right side of the Label using the arrow buttons, and selecting each alphanumeric character needed then stepping the cursor on to the next position until all 6 fields are completed. Then step on to "SSID:" and select the numeric number 0-15. The most common SSID value for the PortaPack is 0.
  • Destination Address "Dest.:" is typically the receiving Callsign. The field is selected by moving the cursor to the right side of the Label using the arrow buttons, and selecting each alphanumeric character needed then stepping the cursor on to the next position until all 6 fields are completed. Then step on to "SSID:" and select the numeric number 0-15. When testing, 0 is the best choice.
  • The message content can be added in the "Info field:" by selecting the "Set" Button. A maximum of 30 characters can be added, but not the typical maximum of 67 or 256.

At the bottom of the App Screen, you will find:

  • Select the Primary Frequency by cursor for TX from the on-screen keypad. In general, Region 1 (Europe and Africa) is 144.800, Region 2 (Americas) is 144.390, and Eastern Asia is 144.640. Other areas vary.
  • Select the Frequency Step size by cursor, then use rotary selection e.g 12k5
  • Select the Deviation by cursor, then use rotary selection e.g. 5kHz
  • The Gain IF setting is a range of 0-47, and Amp is either 0dB or 14dB (on or off). Note that the color of the gain setting changes color based on the TX total output power setting. It is a combined total of IF and AMP: 0-17 Green, 18-38 Yellow, 39-47 Orange, and 48-61 Red.

The transmission is triggered by the "Start" Button and stops after the end of the message sequence.

A great way to test transmission is by running another local SDR receiver set to your PortaPack frequency and observing the results on the spectrum display. I used an RTL-SDR device with the software SDR++ piped into the software QTMM AFSK1200 Decoder, both of which are free software.

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

• Position Lat/Long: nnnn.nnA/nnnn.nnB/ > Example: New York City, USA could be: 4071.27N/7400.59W/Hello from NYC

• Altitude can be expressed in the message by adding /A=1234 > Example: Example: New York City, USA at 105 ft above sea level could be: 4071.27N/7400.59W/Hello from NYC /A=105

• Local Date and Time (MDHM): @nnnnnnnn/ where the first two numbers are the Month, the next two numbers are the Day, the next two numbers are the Hours, and the last two numbers are the Minutes (in 24-hour format). > Example: April the 18th at 16:54 in the afternoon could be: @04181654/Happy World Ham Day

• Zulu/UTC Date and Time (MDHM): /nnnnnnnnz/ where the first two numbers are the Month, the next two numbers are the Day, the next two numbers are the Hour, and the last two numbers are the Minutes (in 24-hour format). > Example: April the 18th at 16:54 in the afternoon UTC could be: /04181654z/Happy World Ham Day

• Putting it all together: New York City, USA on April 18th at 16:54 local time at 105 feet above sea level and a message could be: > @04181654/4071.27N/7400.59W/Happy World Ham Day /A=105