Re: TMD710 APRS Problems
Your message format is not correct. This is not a Kenwood radio issue; it is a general APRS issue.
Your use of "@" as the first character indicates a data type of "Position with timestamp (with APRS messaging)". You did not include a timestamp, so any receiver will not understand the formatting of your message, and will misinterpret where your symbol characters are in the message.
You have 4 options to correct this:
1. Replace the "@" in your message with "=", which indicates "Position without timestamp (with APRS messaging) - This is probably not what you want, because your Arduino beacon probably does not support APRS messaging.
2. Add a timestamp before your lat/long. - This is probably not what you want, since you are still advertising messaging capability.
3. Add a timestamp, and replace your "@" with "/". This would indicate the time of the beacon and indicate no messaging capability. This is probably closer to what you want, although you'd have to set up a clock in your Arduino, which can be challenging.
4. Replace the "@" in your message with "!". This is your easiest option. This will indicate no messaging and no timestamp. Everything else is (mostly) correct.
The standard for Altitude with /A= is 6 digits for altitude in feet, so /A=001000 for 1000'.
You may find it enlightening to read the APRS spec, if you're writing your own APRS-generating code.