# Why does the APRS specification suggest to use 7-bit ASCII for user-defined data formats?

The APRS specification document says the following:

Although there is no restriction on the nature of user-defined data, it is highly recommended that it is represented in printable 7-bit ASCII character form.

What is the reason for this suggestion? Is it a matter of hardware/software compatibility and if so how relevant is this today?

• Hello and welcome to ham.stackexchange.com! – rclocher3 Jun 9 '20 at 23:12

• I was able to send a message containing solely ~ characters using direwolf. I wasn't able to test if it could be received because I was unable to figure out how to do an audio loopback on Linux. – Noah McIlraith Jul 19 '20 at 15:42
• I also found the following information which seems to imply that ~ gets escaped: "A packet starts and ends with a 0x7E Flag which in binary translates to 01111110. The six '1' bits in a row is a pattern reserved to inform the receiver/decoder about the packet boundaries. In any other case a series of five or more '1' bits is stuffed with an extra '0' bit before the remaining bits follow." – Noah McIlraith Jul 19 '20 at 15:45