'Solar Gravity Lens Transmitter/Receiver

Rather than just passive observation, the gravity lens effect of a star
can instead be used for interstellar communication, by using the sun's
gravitational field to focus radio transmissions at other star systems
in the local stellar neighborhood. Transmissions that need to travel
lightyears can easily become grabled and broken up by the vast expanses
of interstellar gasses. Transmissions focused by the gravity lens
effects can help overcome this with less power than would otherwise be
needed to punch through the interference.

These transmitter/receivers would still by necessity have to be fairly
large and powerful in their own right. The focal length would vary
depending on the distance to the target star, but would still be
between 550 and 800 or so AUs. Like with the observatories, a
civilization may build a huge halo of Gravity Lens communicator arrays
around their home star, one for each neighboring star with someone to
talk to.'

It doesn't take long to realise having such an array at a safe distance
from a black hole could increase the power output beyond anyone's
imagination. The transmission would be aimed to cause a slingshot
effect using it's massive gravity to maybe even manipulate time itself,
so a future civilisation could send us information.

This makes more sense than a civilisation just sending out a weak
transmission from their own planet.