Anytone AT-D878UV analog APRS transmissions not working

My analog APRS transmissions with the AT-D878UV was not received by any other stations. The problem was that when the codeplug is created (using New in the CPS), the values for Transmit delay and Prewave Time is set to 0 (zero) for APRS and this will not work (probably to battery saving as this is not a problem with the AT-D578UV for example, which will work with much lower values for Transmit Delay and Prewave Time).

Solution:

In the CPS -> APRS -> set Transmit Delay to 600 ms and Prewave time to 600 ms.

Source: https://www.reddit.com/r/AnyTone/comments/han0y5/aprs_problems_the_solution_anytone_atd878uv/

Ana Aprs Tx should be set to “Narrow” according to IARU region 1 bandplan.

What is Transmit Delay and Prewave Time?

I’ve tried to find an explanation to these values online but haven’t found anything closer than “it controls the time after activating the transmitter until data is being sent”. So I tried setting each value, one at a time to it’s maximum and this is what I think it does:

• Transmit Delay: The radio starts transmitting a packet but it sounds like it waits “Transmit Delay” milliseconds before it starts transmitting any valuebla data. During this time my guess it is filling the packet with zeroes.
• Prewave Time: The radio pulls the PTT but waits “Prewave Time” milliseconds before it starts to send the packet. During this time, the radio just sends carrier.

If I set the Prewave Time too high, my receiver will not receive and decode the packet. I’ve experimented with values for Prewave Time with different values and between 80-600 ms it seems to be working.