Bandwidth reduction of an FM broadcast signal using a baseband precompensation technique

1. A method of processing a baseband multiplex signal, the method comprising:

frequency modulating the baseband multiplex signal using a first frequency modulator to produce a first modulated signal;

filtering the first modulated signal to produce a first filtered signal;

detecting the first filtered signal to produce a first detected baseband multiplex signal;

correcting the first detected baseband multiplex signal to reduce or eliminate distortion in a predetermined frequency range of the first detected baseband multiplex signal to produce a first corrected signal;

frequency modulating the first corrected signal using a second frequency modulator to produce a second modulated signal;

detecting the second modulated signal to produce a second detected baseband multiplex signal;

correcting the second detected baseband multiplex signal to reduce or eliminate distortion in a predetermined frequency range of the second detected baseband multiplex signal to produce a second corrected signal; and

frequency modulating the second corrected signal to produce a third modulated signal.

2. The method of claim 1 , wherein the predetermined frequency range of the first detected baseband multiplex signal is about 0 to 53 kHz.

3. The method of claim 1 , further comprising:

filtering the second modulated signal prior to the step of detecting the second modulated signal.

4. The method of claim 3 , further comprising:

filtering the third modulated signal to produce a third filtered signal;

detecting the third filtered signal to produce a third detected baseband multiplex signal;

correcting the third detected baseband multiplex signal to reduce or eliminate distortion in a predetermined frequency range of the third detected baseband multiplex signal to produce a third corrected signal; and

frequency modulating the third corrected signal to produce a fourth modulated signal.

5. A method of processing a baseband multiplex signal, the method comprising:

frequency modulating the baseband multiplex signal using a first frequency modulator to produce a first modulated signal;

filtering the first modulated signal to produce a first filtered signal;

detecting the first filtered signal to produce a first detected baseband multiplex signal;

correcting the first detected baseband multiplex signal to reduce or eliminate distortion in a predetermined frequency range of the first detected baseband multiplex signal to produce a first corrected signal;

frequency modulating the first corrected signal using a second frequency modulator to produce a second modulated signal;

wherein the step of correcting the detected baseband multiplex signal to reduce or eliminate distortion in a predetermined frequency range comprises the steps of:

subtracting the baseband multiplex signal from the first detected baseband multiplex signal to produce a difference signal;

filtering the difference signal to produce a second filtered signal;

adding a delayed version of the difference signal to the second filtered signal to produce a filtered precompensation signal; and

adding a delayed version of the baseband multiplex signal to the filtered precompensation signal to produce the first corrected signal.

6. A method of processing a baseband multiplex signal, the method comprising:

frequency modulating the baseband multiplex signal using a first frequency modulator to produce a first modulated signal;

filtering the first modulated signal to produce a first filtered signal;

detecting the first filtered signal to produce a first detected baseband multiplex signal;

correcting the first detected baseband multiplex signal to reduce or eliminate distortion in a predetermined frequency range of the first detected baseband multiplex signal to produce a first corrected signal;

frequency modulating the first corrected signal using a second frequency modulator to produce a second modulated signal;

wherein the step of correcting the detected baseband multiplex signal to reduce or eliminate distortion in a predetermined frequency range comprises the steps of:

filtering the baseband multiplex signal to produce a second filtered signal;

filtering the first detected baseband multiplex signal to produce a third filtered signal;

multiplying the second filtered signal by a first weighting factor to produce a first weighted signal;

multiplying the third filtered signal by a second weighting factor to produce a second weighted signal;

combining the first and second weighted signals to produce a combined weighted signal; and

combining the combined weighted signal with a delayed version of the first detected baseband multiplex signal to produce the first corrected signal.

7. The method of claim 6 , wherein each of the first and second weighting factors ranges from 0 to 1 and the sum of the first and second weighting factors is 1.

8. The method of claim 6 , wherein each of the first and second weighting factors are frequency dependent.

9. The method of claim 6 , wherein each of the first and second weighting factors is adjustable.

10. An apparatus for processing a baseband multiplex signal, the apparatus comprising:

a first frequency modulator for frequency modulating the baseband multiplex signal to produce a first modulated signal;

a first filter for filtering the first modulated signal to produce a first filtered signal;

a detector for detecting the first filtered signal to produce a first detected baseband multiplex signal;

a correction circuit for correcting the first detected baseband multiplex signal to reduce or eliminate distortion in a predetermined frequency range of the first detected baseband multiplex signal to produce a first corrected signal;

a second frequency modulator for frequency modulating the first corrected signal to produce a second modulated signal;

wherein the correction circuit comprises:

a first combiner for subtracting the baseband multiplex signal from the first detected baseband multiplex signal to produce a difference signal;

a second filter for filtering the difference signal to produce a second filtered signal;

a second combiner for adding a delayed version of the difference signal to the second filtered signal to produce a filtered precompensation signal; and

a third combiner for adding a delayed version of the baseband multiplex signal to the filtered precompensation signal to produce the first corrected signal.

11. The apparatus of claim 10 , wherein the predetermined frequency range is about 0 to 53 kHz.

12. The apparatus of claim 10 , wherein the first frequency modulator, the first filter, the detector, the correction circuit, and the second frequency modulator are implemented in one or more processors.

13. An apparatus for processing a baseband multiplex signal, the apparatus comprising:

a first frequency modulator for frequency modulating the baseband multiplex signal to produce a first modulated signal;

a first filter for filtering the first modulated signal to produce a first filtered signal;

a detector for detecting the first filtered signal to produce a first detected baseband multiplex signal;

a correction circuit for correcting the first detected baseband multiplex signal to reduce or eliminate distortion in a predetermined frequency range of the first detected baseband multiplex signal to produce a first corrected signal;

a second frequency modulator for frequency modulating the first corrected signal to produce a second modulated signal;

wherein the correction circuit comprises:

a second filter for filtering the baseband multiplex signal to produce a second filtered signal;

a third filter for filtering the first detected baseband multiplex signal to produce a third filtered signal;

a first multiplier for multiplying the second filtered signal by a first weighting factor to produce a first weighted signal;

a second multiplier for multiplying the third filtered signal by a second weighting factor to produce a second weighted signal;

a first combiner for combining the first and second weighted signals to produce a combined weighted signal; and

a second combiner for combining the combined weighted signal with a delayed version of the first detected baseband multiplex signal to produce the first corrected signal.

14. The apparatus of claim 13 , wherein each of the first and second weighting factors ranges from 0 to 1 and the sum of the first and second weighting factors is 1.

15. The apparatus of claim 13 , wherein each of the first and second weighting factors are frequency dependent.

16. The apparatus of claim 13 , wherein each of the first and second weighting factors are adjustable.

17. An apparatus for processing a baseband multiplex signal, the apparatus comprising:

means for frequency modulating the baseband multiplex signal to produce a first modulated signal;

means for filtering the first modulated signal to produce a first filtered signal;

means for detecting the filtered signal to produce a detected baseband multiplex signal;

means for correcting the detected baseband multiplex signal to reduce or eliminate distortion in a predetermined frequency range of the detected baseband multiplex signal to produce a corrected signal;

means for frequency modulating the corrected signal to produce a second modulated signal;

wherein the means for correcting the detected baseband multiplex signal comprises:

means for filtering the baseband multiplex signal to produce a second filtered signal;

means for filtering the detected baseband multiplex signal to produce a third filtered signal;

means for multiplying the second filtered signal by a first weighting factor to produce a first weighted signal;

means for multiplying the third filtered signal by a second weighting factor to produce a second weighted signal;

means for combining the first and second weighted signals to produce a combined weighted signal; and

means for combining the combined weighted signal with a delayed version of the detected baseband multiplex signal to produce the corrected signal.

18. The apparatus of claim 17 , wherein the predetermined frequency range is about 0 to 53 kHz.

19. The apparatus of claim 17 , wherein the means for frequency modulating the baseband multiplex signal to produce a first modulated signal, the means for filtering the first modulated signal to produce a first filtered signal, the means for detecting the filtered signal to produce a detected baseband multiplex signal, the means for correcting the detected baseband multiplex signal to reduce or eliminate distortion in a predetermined frequency range of the detected baseband multiplex signal to produce a corrected signal, and the means for frequency modulating the corrected signal to produce a second modulated signal, are implemented in one or more processors.

20. The apparatus of claim 17 , wherein each of the first and second weighting factors ranges from 0 to 1 and the sum of the first and second weighting factors is 1.

21. The apparatus of claim 17 , wherein each of the first and second weighting factors are frequency dependent.

22. The apparatus of claim 17 , wherein each of the first and second weighting factors are adjustable.

23. An apparatus for processing a baseband multiplex signal, the apparatus comprising:

means for frequency modulating the baseband multiplex signal to produce a first modulated signal;

means for filtering the first modulated signal to produce a first filtered signal;

means for detecting the filtered signal to produce a detected baseband multiplex signal;

means for correcting the detected baseband multiplex signal to reduce or eliminate distortion in a predetermined frequency range of the detected baseband multiplex signal to produce a corrected signal;

means for frequency modulating the corrected signal to produce a second modulated signal;

wherein the correction circuit comprises:

means for subtracting the baseband multiplex signal from the detected baseband multiplex signal to produce a difference signal;

means for filtering the difference signal to produce a second filtered signal;

means for adding to a delayed version of the difference signal to the second filtered signal to produce a filtered precompensation signal; and

means for adding a delayed version of the baseband multiplex signal to the filtered precompensation signal to produce the corrected signal.

24. A method of processing a baseband multiplex signal, the method comprising:

frequency modulating the baseband multiplex signal using a first frequency modulator to produce a first modulated signal;

filtering the first modulated signal to produce a first filtered signal;

detecting the first filtered signal to produce a first detected baseband multiplex signal;

correcting the first detected baseband multiplex signal to reduce or eliminate distortion in a predetermined frequency range of the first detected baseband multiplex signal to produce a first corrected signal;

wherein the step of correcting the first detected baseband multiplex signal includes lowpass filtering the baseband multiplex signal to produce a second filtered signal, lowpass filtering the first detected baseband multiplex signal to produce a third filtered signal, weighting the second and third filtered signals and combining the weighted second filtered signal and weighted third filtered signal to produce a combined weighted signal, delaying the first detected baseband multiplex signal and combining the delayed first detected baseband multiplex signal with the combined weighted signal to produce the first corrected signal; and

frequency modulating the first corrected signal using a second frequency modulator to produce a second modulated signal.

25. A method of processing a baseband multiplex signal, the method comprising:

frequency modulating the baseband multiplex signal using a first frequency modulator to produce a first modulated signal;

filtering the first modulated signal to produce a first filtered signal;

detecting the first filtered signal to produce a first detected baseband multiplex signal;

correcting the first detected baseband multiplex signal to reduce or eliminate distortion in a predetermined frequency range of the first detected baseband multiplex signal to produce a first corrected signal;

wherein the step of correcting the first detected baseband multiplex signal includes subtracting the baseband multiplex signal from the first detected baseband multiplex signal to produce a precompensation signal, lowpass filtering the precompensation signal to produce a second filtered signal, delaying the precompensation signal and combining the delayed precompensation signal with the second filtered signal to produce a filtered precompensation signal, delaying the baseband multiplex signal and combining the delayed baseband multiplex signal with the filtered precompensation signal to produce the first corrected signal; and

frequency modulating the first corrected signal using a second frequency modulator to produce a second modulated signal.

26. The method of claim 25 wherein:

the predetermined frequency range is about 0 to about 53 kHz; and

the precompensation signal includes a portion in the frequency range of about 53 kHz to about 100 kHz.