After the Foundation update of No Mans Sky, Signal Scanners, as we used to know them, are gone (and this makes all answers to this related question outdated). You got the power of building them wherever you want, but something is still wrong.
The option of searching for transmissions is gone. That means, you can no longer search for Transmission Towers (and Observatories as well), so, as it seems, you have to be much more lucky to find crashed ships.
Or am I wrong? Is there a way to find crashed ships much more frequent? Is there a way to scan for Transmission Towers?
Best Answer
It seems that one of the ways of finding a Transmission Tower (and thus possibly a crashed ship) is to perform a scan in your ship while in space. This is what one Reddit user suggested:
Perform the scans while looking at a planet. I can't tell for sure if this matters or not, but I seem to find more locations via this method while looking at the planet I want to scan.
You can also try this method one user posted on a Steam Forum:
You may not be able to reuse the towers as they stated however. Other users in the post found that they could not.
A third method which was posted in the same Steam forum as above states: