The File->Configure->Station dialog

This dialog allows you to set your callsign and SSID, station location, symbol, and other basic information about your APRS station. All of this information gets transmitted with your station packets.

• Callsign: Your amateur radio call sign. You may optionally add a "Sub station ID" (SSID) from 1 to 15 separated from the callsign by a hyphen (e.g. "KX4XX-14")
• Latitude and longitude are specified with degrees and decimal minutes. Xastir lets you enter up to three digits past the decimal point for the minutes.
• If you have the coordinates in some format other than degrees and decimal minutes (such as decimal degrees, degrees-minutes-seconds, UTM, MGRS) you must convert to degrees and decimal minutes using the coordinate calculator accessed by clicking the "Calc" button next to the latitude/longitude field. Enter your coordinates there and click the "Calculate" button; whatever you entered will be converted to all the formats Xastir knows about. When you click "OK" in the calculator box, the correct format will be populated in the latitude/longitude fields.
• Station symbol: This is the icon that will be used to represent your station on APRS displays, and the characters in the dialog box are those that are transmitted in your station packet to communicate what icon should be used. Select the icon you want using the "Select" button, which will pop up a dialog box with all the available icons. Choose the one you like and the "Group/Overlay" and "Symbol" text boxes will be filled in.

Icons from the "secondary symbol table" allow you to specify an overlay character. After you select the icon, it will put a "\" into the "Group/Overlay" box. You can replace this backslash with an upper case letter or a single digit. The resulting icon will have the letter or digit drawn on top of it on APRS displays. Only upper case letters and digits are valid for overlay characters

• Power - Height - Gain - Directivity: This "PHG" information is used to communicate how your station is transmitting.
  • Power in watts
  • Height Above Average Terrain (HAAT) in feet. It is important to note that HAAT is NOT the height of the tower on which your antenna is mounted. It is the height of your antenna above the average terrain in the 16km circle surrounding your station. Use an online HAAT calculator to set this, don't just use your mast height.
  • Gain: The gain of your antenna
  • Directivity: If you are using a directional antenna, the bearing of its main lobe.
• Comment: An arbitrary comment you want associated with your station.
• Station ambiguity: Your station's latitude and longitude will be transmitted over APRS. You can select options here to reduce the precision with which your station is located. While marked in fractional miles here in this dialog box, what actually happens is that digits of the latitude and longitude are left out. Selecting ".11 miles" means your latitude and longitude will be transmitted with only one digit past the decimal for minutes instead of two. "69.09 miles" means only the degrees part of your position will be transmitted.
• Send compressed posits check box: Normal APRS packets are in a human readable ASCII format that includes your latitude and longitude accurate to two digits of decimal minute ("DDMM.MM" format). The compressed posit format uses a Base-91 compression technique to pack a little more information into the packet. Compressed posits contain your position to an extra digit of precision. Compressed posits are not compatible with position ambiguity. If you're choosing compressed posits, it's because you want your position more precisely specified.