I guess I can use an atmega8 microcontroller to build a simple radio transmitter maybe using one extra simple component (such as a transisitor not another complex component like another IC). The radio transnmitter would be used to transmit binary somehow (not audio or speech). I guess it would use the internal oscillator somehow. So my question is is there a circuit that uses only an atmega8 and a simple wire (for the aerial) to build a simple transmitter? If not what the minimal circuit, with an atmega8, to transmit binary information? There are of course various way to encode binary information.
For my undergraduate Electronics Engineering degree Transceivers class we had a lab final on designing and building an FSK transmitter and receiver pair which had to reliably transmit and receive a signal over only 1 meter. It was not easy and let me tell I walked away from that class with great respect for commercial RF products. Motorola says RF design is an Art which I would say is closer to black magic. The reason for this is EVERYTHING comes into play when designing an RF device. The size of the parts, the board layout, trace with, proximity to other components, cross talk, parasitic capacitance or inductance, power supply stability and a host of other items.
If you are doing this for fun then by all means build it. The transmitter side can be as simple as a piece of wire on the pin ( cut to some multiple of the carrier frequency) but you will need a tuned amplifier for the receiver. If you are looking for a low cost transceiver look at the NRF24L01. They can be purchased for less than $1ea on ebay and interface directly with an Atmega8 over SPI.