[rcxdude]

I think the big radio telescope is the main barrier. At this point there's only one in the world with enough transmit power to talk to it, and a handful that can receive the signal.

[perihelions]

https://en.wikipedia.org/wiki/Canberra_Deep_Space_Communicat...

(pdf) https://deepspace.jpl.nasa.gov/files/820-100-H.pdf

70 meter antenna, 80 kW X-band transmit power (122 dBW EIRP)