What is a transmission? What does it do exactly?

A Transmission:
1. shows a speaking portrait of the unit
2. it plays a wav
3. it displays text as long as the wav is or as long as you set it to play
4. it creates a blinking circle around the unit in the location, if it exists
5. it creates a minimap ping on the location where the unit is inside the location, if it exists in that location
6. it acts like a wait (creates wait blocks) - the rest of the actions will run when the transmission is over
7. you can cancel transmissions with the escape button in singleplayer

What annoys me is that you can't have a transmission without a wav.

Answer: A silent .wav.

Yeah, there's some virtual sounds that are completely silent, I often use those, although I usually don't use waits due to their wait blocking problem. I just do everything that they do, minus the wait.

I always use tbafire for silent transmissions

Cheathunter, seriously, try to check other sources before asking for help. If you can test it by yourself, do not ask the question. Staredit's help file has the explaination of what each of the trigger actions and conditions do. Stop making new topics about simple questions like this one because you might get them closed.