[cbhl]

You can change the frequency that a thing communicates on by changing the length of the wire in the antenna, and you can change the strength of the signal by changing the shape of the antenna, and the ROM will be none-the-wiser.

An example of the former is "homemade AM radio", where you wrap a lot of wire in a coil, and changing where you complete the the circuit along the coil allows you to "tune into" different frequencies.

An example of the latter is the cantenna, a directional antenna that can be made from a Pringles can.