Forums & Frequently Asked Questions for CWOP

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Frequently Asked Questions (FAQ)

1. How often should I send data and to which server? Any packet rate that you are comfortable with is fine with us as long as it is not faster than one data packet every 5 minutes. The current recommendations on which servers to send packets to and how often to send those packets are linked from the upper right of this and most other pages under "APRS servers to use".

2. How can I change items in the CWOP database? Just send an e-mail. If you're sending latitude/longitude changes, use decimal degrees and if elevation change, use meters above sea level. If your zip code or town has changed, note that. Also, if you'd like to have a personal web page added, send the URL. Note that only you can change the plotted location on findU maps by entering new values of latitude and longitude into your local software.

3. What is the APRS latitude/longitude position format? In an APRS weather data packet, the part between "z" and "_" is the latitude and longitude of the station position. The particular format used is from the LORAN position format and is capable of about 60 feet resolution on the maps. The format is "ddmm.hhN/dddmm.hhW" without the quotation marks, where d is degrees, m is minutes and h is hundredths of minutes. The first eight characters represent latitude (north in this case), and the last nine characters represent longitude (west in this case). The hemispheres are represented by capital letters; N, E, S, W and remove the need for plus or minus signs on the latitude and longitude. Note that LEADING ZEROS ARE REQUIRED. Also note that there must be only two numbers to the right of the decimal point in the latitude or longitude, and that colons are not allowed. Many examples of correct format positions are contained here, and here and there is a web-based DMS, LORAN, decimal conversion tool. Any lat/lon changes for the CWOP database should be in decimal degree format.

4. How can I find my latitude, longitude and elevation? While there are several different ways, one is to go to ACME mapper and enter your nearby town and your state at the bottom and press "find". Then change to a high resolution image and double click on your actual location. Your latitude and longitude is then given in the "Lat/Long" box. Once you have your latitude and longitude in decimal degrees, copy and paste (without the quotes) "" into your browser and then change the first number to your latitude and the second number to your longitude and then press enter. In the resulting text, you'll see your elevation in feet, and in meters (which is what is used in the CWOP database).

5. What is the APRS time format? In an APRS weather data packet, the part between "@" and "z" is the time of the weather station clock when the packet was sent. However, many computer clocks frequently have large errors and to avoid these errors, the data time is taken as the time that the packet arrives at the server. This does introduce an error of the time that it took for the packet to travel from the station to the server, but that is usually not significant for weather uses. Marc, CW0009, operates a CWOP station in Antwerp, Belgium and has a time synced computer clock accurate to within one second. Marc sends six packets per hour on the 10 minute mark. You can see Marc's data here. The last two numbers in the time column are the time in seconds that it took to connect, send the packet through his ISP, across the Atlantic to the APRS-IS server, and to The total time error is usually less than one minute and is not a problem for our uses.

6. Why do I have two IDs for CWOP? Actually, you have three IDs because there are three different databases involved. To reduce confusion, we've tried to make the IDs the same or similar where possible. The first database is the mySQL database of received weather packets. Ham radio stations use the callsign of the station, and CW/DW/EW stations use CWxxxx, DWxxxx, or EWxxxx in the database. The second database is the MADIS set of netCDF files where the ID is called the NWS ID and is a maximum of 5 characters. Ham radio weather stations are identified by APxxx or ARxxx or ASxxx or ATxxx or AUxxx (two upper case letters followed by 3 numbers) and non-ham weather stations are identified by Cxxxx or Dxxxx or Exxxx (upper case C or D or E followed by 4 numbers). The MADIS netCDF files are used to send the data on to users and to store the quality checking information. The third database is the CWOP database. Ham stations have a Provider ID of apxxx or arxxx or asxxx or atxxx or auxxx (two lower case letters followed by 3 numbers) and non-ham weather stations have a Provider ID of CWxxxx or DWxxxx or EWxxxx (2 upper case letters followed by 4 numbers). The key things to remember are that the ham callsign or CWxxxx or DWxxxx or EWxxxx goes in with your data packet and is what you look for on while the quality checking results are identified by the five character NWS ID of APxxx or ARxxx or ASxxx or ATxxx or AUxxx or Cxxxx or Dxxxx or Exxxx. The members list provides the cross reference.

7. How is the weather data coded into the data packet? When you look at examples of APRS position weather packets here, or here, the part after the longitude "E" or "W" carries the weather data as symbols followed by numbers. The underscore "_" followed by 3 numbers represents wind direction in degrees from true north. This is the direction that the wind is blowing from. The slash "/" followed by 3 numbers represents the average wind speed in miles per hour. The letter "g" followed by 3 numbers represents the peak instaneous value of wind in miles per hour. The letter "t" followed by 3 characters (numbers and minus sign) represents the temperature in degrees F. The letter "r" followed by 3 numbers represents the amount of rain in hundredths of inches that fell the past hour. The letter "p" followed by 3 numbers represents the amount of rain in hundredths of inches that fell in the past 24 hours. Only these two precipitation values are accepted by MADIS. The letter "P" followed by 3 numbers represents the amount of rain in hundredths of inches that fell since local midnight. The letter "b" followed by 5 numbers represents the barometric pressure in tenths of a millibar. The letter "h" followed by 2 numbers represents the relative humidity in percent, where "h00" implies 100% RH. The first four fields (wind direction, wind speed, temperature and gust) are required, in that order, and if a particular measurement is not present, the three numbers should be replaced by "..." to indicate no data available. Solar radiation data can also be coded into the data packet.

8. Why isn't my rain data being displayed on MADIS and MesoWest? The APRS weather format allows for three types of precipitation measurements to be coded into the data packet as discussed above. However, MADIS only accepts two of these, the rate (rxxx in hundredths of inches per hour) and the 24 hour precipitation (pxxx in hundredths of inches). So, if your data packet does not contain rxxx or pxxx, there are no rain data that can be forwarded to MADIS or MesoWest.

9. How can I check my data flow through APRSWXNET/CWOP? The CWOP search tool shows data at various points. Your local app sends your packets to the APRS-IS (Internet Service) and, for each of the past ten days, your last packet seen on APRS-IS is shown along with the number of packets in the last hour of that day, total number of packets in that day, the number of duplicates, and the number of bytes. Your data packets flow from the APRS-IS to the findU server and you can check your weather data on findU by clicking on "WxGraph". Note that you can view your data over the past 12 hours out to 10 days. Every 5 minutes the findU server sends your data to MADIS if your station has been registered. While it is not easy to check the output of MADIS, you can check your data at three places that get data from MADIS. The first, "NOAA Meso Map" will return a map (after a delay) that should have your location in the center and by double clicking there, your data will be listed. The second, "Town/City/Meta" will show the location and other information used in CWOP Quality Checking along with your data for the past day. The third, "MesoWest" will show your data that were sent from MADIS to MesoWest if your station is located in North America. If these three links are not there, then your station has not been registered in CWOP.

10. How do I initially calibrate my barometer? Evan Bookbinder, a senior meteorologist with the NWS Weather Forecast office for Kansas City/Pleasant Hill, MO has given an excellent answer to this frequently asked question.

11. What is the basic process for connecting to a server and uploading data? Assuming that you have followed the directions in the "APRS Servers to use" link above, each TCP connection to port 14580 will begin with receiving at least one text line from the APRS server (terminated with cr/lf). This line identifies the server software you just connected to which you can safely ignore. A line is sent from the server upon connection and upon receiving that line, your client will send a login line. Suppose your CWOP identifier is EW9876. Your login line would be:

user EW9876 pass -1 vers YourSoftwareName 1.0

The CWOP identifier is the user name, the passcode is -1 (minus one), and the software identifier is your software name (no spaces) followed by the version number (containing no spaces). There is a single space between each keyword and each value. Once that is entered (terminate with cr/lf), you will receive an acknowledgement line from the server and it can be safely ignored. After receiving the login acknowledgement, the server is ready to take the single APRS "packet" with the weather data. After the packet is sent, your client can safely disconnect from the server. There will be no acknowledgement of the packet being received at the server (the acknowledgement is handled by the TCP underlying protocol). The APRS "packet" is also terminated by cr/lf. The APRS "packet" is a weather position packet with a very specific header:

EW9876>APRS,TCPIP*:rest of packet

The first "callsign" is the CWOP station identifier for that station as shown. The next item is TCPIP followed by an asterisk. All capital letters must be used for the packet header. The rest of the packet follows the format specified in item#7 above. For example,


Your weather station software will hide all of this underlying activity when a packet is sent.

Forums of Interest to CWOP Members

Discussion of CWOP weather data quality checking with sign-up here.

WXforum covering home weather stations, web pages and code, software, and weather here.

Discussion of the weather and the WxSolution software here.

Discussion of the weather and CWOP/APRSWXNET here.

Page generated on Feb 09, 2014. Site maintained by Russ Chadwick, KB0TVJ. Send any comments to russ at wxqa dot com