Hello and piece.....
I bought an indoor antenna like this:

I wanted to change this antenna from receiver into a transmitter for my robot, and i am using Holtek ICs to send and receive instructions.
So how can i change this kind of antenna into transmitter?
Or its better to use external antenna like this one:

Thank you all..................

 

The problem is i want to amplify the radio waves so i can control my Robot from a large distances.
Tnx.....Bob

 

The size of an antenna is determined by its radio frequency.
But you forgot to tell us your robot's radio frequency.

 

its about 435 Hz

 

435Hz is a fairly low audio frequency, not a radio frequency.
Is it actrually 435MHz?

If you make a directional antenna then its range is better than a single vertical whip antenna. Look in Google for Yagi antenna.

 

Hook it up to a transmitter instead of a receiver. Then impedance match it so that the transmitter power actually gets to the antenna.

 

i will try this, but do i need an amplifier?

 

A "Gain" antenna on the transmitter and the receiver will make a good difference.
As to an amplifier , that all depends on how much range you are trying to get out of the system (you haven't told us that).
The "rabbit-ears" type antenna can be made to work but probably not as well as a antenna (s) actually designed for the frequency in question.
Directional antennas will have more gain but depending on what you are trying to accomplish may present other problems (as in keeping the antenna pointed in the proper direction).