Here is my viper remote. It's old and the original antenna was damaged and replaced by a simple wire. The range with the wire is limited to about 80ft line of sight.

I wanted to replace this wire with an antenna suitable for the 433mhz frequency the remote uses.

Step 1: Opening the Remote.

Getting open this old 2 way remote was easy. Now I have access to the circuitry.

Step 2: The Rf Board.

This rf board slots into the bigger board that contains the lcd display. You can see the antenna connection.

Step 3: The Replacement Antenna.

Here it is. Nothing fancy but a spring of correct length for the frequency band. Using my Tools I bent the end out to allow soldering onto the circuit board.

Step 4: Connection of the New Antenna.

Quick easy solder and the antenna is now on the board.

Step 5: Reassembly!

Using a plastic cable Tie, my old remote is reassembled. Now my range is around 800ft line of sight and I'm very happy.
Not bad for a 10 minutes job eh?

Update:

I made the antenna pretty afterwards in this instructable;

https://www.instructables.com/id/Covering-a-Spring-Antenna/