There are various upgrades to both the control and video antennas that can be done (bird & pilot side), prices range from just a few bucks up to 100's of bucks (or even more).
There are also threads on this forum, that show you how to improve signal by just moving the existing bird side antennas to new locations, cost free.
I personally, have upgraded to a
full stage 3 kit with extra antenna on the bird and pilot sides, range is increased (not sure what the max is yet - but I have flown around 2 miles without loss of control or video - I think the available battery power will set the limits rather than the new antennas capabilities).
More importantly, the signal is solid and strong, without any loss or drop.
Google is your friend, there are a number of options, some suppliers even offer a fitting service.
I would always advise using some sort of tracking system when flying beyond sight. I cannot recommend
Flytrex Live enough.... It works!
On one occasion it helped me find my bird over 2 miles away after a bad flight when everything went wrong (my own fault - I inadvertently installed a new but
faulty 4mm GPS antenna). But that's another story.
Kev