WSPR Message Format

This page contains details of the WB8ELK WSPR message encoding. It can easily be understood by Jr High Students. Another popular encoding scheme is the qrplabs method documented here.

Second Message 

The second message is typically called the Telemetry Message.  This uses the same format as the Standard Message, but letters and numbers are used to designate other information.  The discussion below uses the WB8ELK scheme.  

2 Character Power (Fine Altitude)

This value is used in conjunction with the previous value for power to get a refined altitude.  The previous message gave the altitude rounded to the lowest 1000 meters.  This value provides how much higher the balloon is.  The value indicates the number of 60 m increments to add to the rounded measurement.  So if this power is the 10th allowed value, the balloon would be 600 m above the rounded value.

4 Character Grid Square 

This is the same as the standard message.  It is useful to help identify which telemetry message goes with which balloon.

Callsign

For example, the first one or two letters of a callsign designate the country.  Stations in the United States can start with A, K, W or N.  The wb8elk format for the second message uses prefixes that are not used by any nation.   No nation has a call sign that starts with 0 or Q.  In order to tell the transmission of one balloon from another the third value of the callsign can be any number.  When you launch you need to select a number that is not being used.  To further separate one balloon from another, there are 5 specific time slots every 10 minutes. These techniques are used by all of the encoding schemes not only wb8elk.  

The remainder of the coding is specific to the encoding scheme.  So the WB8ELK coding goes like this.  If Q and 9 are chosen to designate the balloon, there are 4 other positions that can be used to encode data (Qa9bcd).  The letter "b" designates the solar panel voltage in tenths of a volt above 3.2v. The letter "c" and "d" designate the last two characters of a 6-character grid square.  These letters in combination with the 4 character grid square forms a 6-character grid square which provides an accurate position to within 15 miles. Position "a" is a combination of temperature and number of gps satellites.  The coding is a little complex.  First consider temperature.  If the value is X, Y or Z the temperature is 25 deg C.  If the value is U, V or W the temperature is 20 deg C and so on through the alphabet.  Now consider the number of satellites found by the gps.  If there are 4 or 5, the value will be the first letter in the triple e.g. X or U.  If there are 6 to 9 satellites found by the gps, the value will be the second letter i the triple e.g. Y or V.  If there are more than 9 the value is the third letter.

Note: In addition to Q and 0 used as initial characters 1 is used.  However, 1S (Spratly Islands) and 1A (SMO of Malta) are assigned to entities with small population and should not be used.

Custom Telemetry Messages

There is nothing to prevent the use of custom telemetry messages that carry additional data from sensors.  There are other callsign prefixes that are not used by any country.  Here they are: Pick one of the following B1,B2,B3,B4,B5,B6,B7,B8,B9, C1, D1, E1,E2,E4,E5,E6,E7,E8,E9, H1, J1,O1,O2,O3,O4,O5,O6,O7,O8,O9,P1,S1,T1,Y1,X1,Z1. These will be able to cary slightly less data because they are the beginning two characters of the callsign e.g. T1abc. However, they wil be of the correct format to be received and forwarded through the wspr network.  You can download your data from wsprnet.org.  They provide a large daily file of all the messages they have received in the month.  Alternatively, data can be downloaded from WSPR.live