FM transmission system and method

1. An RF transmission system comprising:

an RF transmitter receiving a base band media signal and generating a broadcast signal on a broadcast frequency, the broadcast frequency being a one of a plurality of transmission frequencies within a frequency band;

a radio data control module:

periodically performing an interference detection measurement to determine whether an interfering signal at the broadcast frequency exceeds a threshold criteria, and

selecting an open frequency if an interfering signal at the broadcast frequency exceeds the threshold criteria, the open frequency being one of the plurality of transmission frequencies wherein RF interference is within predetermined acceptance criteria; and

driving the RF transmitter to transmit an identification of the open frequency on the broadcast frequency by mixing, onto the base band media signal, a digital indication of an alternate frequency command and a digital indication of the open frequency, and, following such transmission, to switch the broadcast frequency to such open frequency.

2. The RF transmission system of claim 1 , wherein the interference detection measurement comprises a measurement of RF signal strength at the broadcast frequency during an increment of time during which the RF transmitter discontinues transmission.

3. The RF transmission system of claim 2 , wherein the increment of time occurs when the media signal meets predetermined null criteria.

4. The RF transmission system of claim 1 , wherein the interference detection measurement comprises receiving an RF signal at the broadcast frequency and the presence of an interfering signal is determined by determining a difference between the received RF signal and the broadcast signal of the RF transmitter.

5. An RF transmission system comprising:

an RF transmitter receiving a base band media signal and generating a broadcast signal on a broadcast frequency, the broadcast frequency being a one of a plurality of transmission frequencies within a frequency band;

a radio data control module:

periodically performing an interference detection measurement to determine whether an interfering signal at the broadcast frequency exceeds a threshold criteria, and

selecting an open frequency if an interfering signal at the broadcast frequency exceeds the threshold criteria, the open frequency being one of the plurality of transmission frequencies wherein RF interference is within predetermined acceptance criteria; and

driving the RF transmitter to transmit an identification of the open frequency on the broadcast frequency and, following such transmission, to switch the broadcast frequency to such open frequency; and

further comprising an RF receiver:

receiving a tuning frequency identification signal from the radio data control module, the tuning frequency identification signal indicates an identified frequency, the identified frequency being a one of the frequencies within the frequency band;

receiving an RF signal on the identified frequency;

providing an indication of the received RF signal to the radio data control module; and

selecting an open frequency comprises determining RF interference at each of a plurality of transmission frequencies within the frequency band by:

providing a sequence of frequency identification signals to the RF receiver;

receiving an indication of the received RF signal at each of the sequence of identified frequencies; and

the acceptance criteria is the frequency with the weakest interfering signal.

6. The RF transmission system of claim 5 , wherein the radio data control module drives the RF transmitter to transmit an identification of the open frequency on the broadcast frequency by mixing, onto the base band media signal, a digital indication of an alternate frequency command and a digital indication of the open frequency.

7. The RF transmission system of claim 6 , wherein the interference detection measurement comprises a measurement of RF signal strength at the broadcast frequency during an increment of time during which the RF transmitter discontinues transmission.

8. The RF transmission system of claim 7 , wherein the increment of time occurs when the media signal meets predetermined null criteria.

9. The RF transmission system of claim 6 , wherein the interference detection measurement comprises receiving an RF signal at the broadcast frequency and the presence of an interfering signal is determined by determining a difference between the received RF signal and the broadcast signal of the RF transmitter.

10. An RF transmission system comprising:

an RF transmitter receiving a base band media signal and generating a broadcast signal on a broadcast frequency, the broadcast frequency being a one of a plurality of transmission frequency within a frequency band;

a radio data control module:

determining RF interference at each of a plurality of transmission frequencies within the frequency band;

selecting an open frequency, the open frequency being one of the plurality of transmission frequencies wherein RF interference is within predetermined acceptance criteria; and

driving the RF transmitter to transmit an identification of the open frequency on the broadcast frequency by mixing, onto the base band media signal, a digital indication of an alternate frequency command and a digital indication of the open frequency, and, following such transmission, to switch the broadcast frequency to such open frequency.

11. The RF transmission system of claim 10 , wherein:

the radio data control module:

periodically performs an interference detection measurement to determine whether an interfering signal at the broadcast frequency exceeds a threshold criteria, and

selects a second open frequency upon determining that an interfering signal exceeds the threshold criteria, the second open frequency being one of the plurality of transmission frequencies wherein RF interference is within the predetermined acceptance criteria; and

drives the RF transmitter to transmit an identification of the second open frequency on the broadcast frequency and, following such transmission, to switch the broadcast frequency to such second open frequency.

12. The RF transmission system of claim 11 , wherein the interference detection measurement comprises a measurement of RF signal strength at the broadcast frequency during an increment of time during which the RF transmitter discontinues transmission.

13. The RF transmission system of claim 12 , wherein the increment of time occurs when the media signal meets predetermined null criteria.

14. The RF transmission system of claim 11 , wherein the interference detection measurement comprises receiving an RF signal at the broadcast frequency and the presence of an interfering signal is determined by detecting a difference between the received RF signal and the broadcast signal of the RF transmitter.

15. A portable device comprising:

a media application generating an audio media signal;

an RF transmitter receiving the audio media signal and generating a broadcast signal on a broadcast frequency, the broadcast frequency being a one of a plurality of transmission frequencies within a frequency band;

a radio data control module:

periodically performing an interference detection measurement to determine whether an interfering signal at the broadcast frequency exceeds a threshold criteria,

selecting an open frequency if an interfering signal at the broadcast frequency exceeds the threshold criteria, the open frequency being one of the plurality of transmission frequencies wherein RF interference is within predetermined acceptance criteria; and

driving the RF transmitter to transmit an identification of the open frequency on the broadcast frequency by mixing, onto the base band media signal, a digital indication of an alternate frequency command and a digital indication of the open frequency, and, following such transmission, to switch the broadcast frequency to such open frequency.

16. The portable device of claim 15 , wherein the interference detection measurement comprises a measurement of RF signal strength at the broadcast frequency during an increment of time during which the RF transmitter discontinues transmission.

17. The portable device of claim 16 , wherein the increment of time occurs when the media signal meets predetermined null criteria.

18. The portable device of claim 15 , wherein the interference detection measurement comprises receiving an RF signal at the broadcast frequency and the presence of an interfering signal is determined by determining a difference between the received RF signal and the broadcast signal of the RF transmitter.

19. A portable device comprising:

a media application generating an audio media signal;

an RF transmitter receiving the audio media signal and generating a broadcast signal on a broadcast frequency, the broadcast frequency being a one of a plurality of transmission frequencies within a frequency band;

a radio data control module:

periodically performing an interference detection measurement to determine whether an interfering signal at the broadcast frequency exceeds a threshold criteria,

selecting an open frequency if an interfering signal at the broadcast frequency exceeds the threshold criteria, the open frequency being one of the plurality of transmission frequencies wherein RF interference is within predetermined acceptance criteria; and

driving the RF transmitter to transmit an identification of the open frequency on the broadcast frequency and, following such transmission, to switch the broadcast frequency to such open frequency; and

further comprising an RF receiver:

receiving a tuning frequency identification signal from the radio data control module, the tuning frequency identification signal indicates an identified frequency, the identified frequency being a one of the frequencies within the frequency band;

receiving an RF signal on the identified frequency;

providing an indication of the received RF signal to the radio data control module; and

selecting an open frequency comprises determining RF interference at each of a plurality of transmission frequencies within the frequency band by:

providing a sequence of frequency identification signals to the RF receiver;

receiving an indication of the received RF signal at each of the sequence of identified frequencies; and

the acceptance criteria is the frequency with the weakest interfering signal.

20. The portable device of claim 19 , wherein the radio data control module drives the RF transmitter to transmit an identification of the open frequency on the broadcast frequency by mixing, onto the base band media signal, a digital indication of an alternate frequency command and a digital indication of the open frequency.

21. The portable device of claim 20 , wherein the interference detection measurement comprises a measurement of RF signal strength at the broadcast frequency during an increment of time during which the RF transmitter discontinues transmission.

22. The portable device of claim 21 , wherein the increment of time occurs when the media signal meets predetermined null criteria.

23. The portable device of claim 20 , wherein the interference detection measurement comprises receiving an RF signal at the broadcast frequency and the presence of an interfering signal is determined by determining a difference between the received RF signal and the broadcast signal of the RF transmitter.