I recently purchased a Cactus V2 radio flash controller from Gadget Infinity on Ebay. Although they worked decently out of the box, I personally wasn't getting very good consistancy or distance out of them. So following the lead of some other members of the strobist.com group, I decided to add an antenna.
I used the antenna from an old cordless phone I had laying around in the garage, because the size was perfect and all I had to do was take the old phone apart and I had everything I needed.
I simply soldered the blue wire onto the antenna on the Cactus trigger circuit board. It is a hole in the circuit board with a little silver ring around it.
Next I drilled a hole it the top of the cover to fit the antenna cover through. The antenna cover is rubber and has a square base, so it holds itself in place. The blue wire simply slides into the cover.
With this modification the reliability of the trigger improved to nearly 100%, and the distance from which it will function has grown exponentially. Formerly I could only get about 25 feet away with any success. So far I have been able to get about 200 feet and still it works perfectly. I have not tried any further than 200 feet, but my suspicion is that it will work as far as 1000 feet.
Strobist info: I shot this in a light box with modeling lamps, and put my 430ex inside the box to the left and in front of the trigger. I fired the flash remotely with my Canon STE2 in ETTL mode.