So, you have a TNC and a radio but no GPS receiver. An APRS station can still be constructed without a GPS receiver. After setting up your TNC and connecting it to your radio, it is time to setup a basic APRS beacon station. Please consult your TNC's manual for specific connection requirements and configuration commands though a GPS receiver is not required a computer or terminal to communicate with the TNC is required. There are a few basic setting that need to be set on your TNC to have it beacon your station's position. The commands that need to be set are MYCALL, BTEXT, BEACON, and UNPROTO.
MYCALL should be self explanatory. This setting is your callsign issued to you by the FCC. A SSID or Secondary Station IDentifcation can be added as a "-1", "-2", "-3" ... up to "-15" to your callsign. An SSID has a special meaning in APRS; each one represents a symbol to describe the APRS station. To learn more about what each SSID means in APRS, please consult the APRS Protocol Specification; the link is below. For now do not worry about this, just use your callsign without an SSID.
BEACON is a setting that specifies the time interval that the APRS message should be broadcast. A setting of 180 should be a good starting point for a stationary station with no GPS receiver to constantly update its position. Most TNCs should equate 180 to 1800 seconds which is equal to 30 minutes.
UNPROTO is a setting that you specify the amount of ... want (sic-pl) your APRS message a practical setting is to use "APRS VIA RELAY" or "APRS VIA WIDE" Use one of these settings (without the quotes) until you become more familiar with the protocol and how the APRS network is setup and functions.
BTEXT is a little more complex to setup not because of setting the parameter, but because you need to assemble some information about your APRS station to create the string of information to place in the BTEXT setting. Lets look at a sample BTEXT of "!4030.00N/10420.10W-Hello from WZ0ZZZ". The "!" specify that the APRS message does not have any time information associated with it. The "4030.00N" and "10420.10W" portions are the station's current latitude and longitude positions, respectfully, separated by a "/". The "/" means that we are using the primary symbol table, but you will need to find your station's position. One way is to borrow a GPS receiver. Another way is to go to Microsoft's TerraServer website at http://terraserver.microsoft.com. Then click on advance find on the left-hand side of the page. Now click on address. Enter your address information and click on the GO button. Once the query completes select one of the available images. Now, once the image load click on the Info button at the top of the image, this will display coordinates on the image. Most coordinates will be in the form of 104.3350, lets use this number as an example. To turn this in to the format that is used by APRS, first take the whole out of the decimal that leaves number of 0.3350 Now take 0.3350 and multiply it by 60 which will equals 20.10. Now to piece it back together, 104.3350 will be convert to 10420.10 for APRS. Be sure to add an N, W, E, or S as appropriate, all coordinates in the US will be N for the latitude and W for the longitude. The "-" specify that the APRS station is a house. There are many different symbols available to describe the APRS station. To find other symbols that you can use consult the APRS protocol specification document below. The brief text afterwards is a short message that you can attach to the APRS message. Be careful, the message needs to be short, so nothing longer that 43 characters.
I hope this helps.
For more information please read the following source documents: