They can find transmittors, but their objective is to find the studio, which needs a live link to the transmitter.
As I understand it, the pirates break out onto the roof of tall buildings, especially public housing towers, and place transmitters. These will be found, so they gotta have a way of linking them back to home.
Sure, they could use mobile data (has its own opsec problems), or hacked residential wifi and a VPN (add real prisong itme of a hacking charge to the sheet when you get court).
Apparently what they often do is use a cantena link - a focussed beam of wifi to some distant place, which can be very difficult to pinpoint accurately. I also saw a doc where they used lasers.
These days though, I think a lot of them just stream on the internet.
Below are some interesting reads on the culture:
https://en.wikipedia.org/wiki/Pirate_radio_in_the_United_Kin...
https://www.transdiffusion.org/2008/08/01/on_the_run_the
http://www.thepiratearchive.net/
https://web.archive.org/web/20090324075718/http://www.freewe...
Plus the overuse of device radios, storage etc. 802.11s does great at keeping power low while acting as a pass through, but storing data on the device requires a lot of availability for the device, and duplication has to be done to make sure you can access your stripes. Good for single use messages, bad for anything large.
which is generally legal.
but then we are back to the original problem, the internet being down...