Receiver for multiple signal spectra

1. A radio receiver for receiving first signals of a first frequency spectrum having principal energy in a first frequency band and second signals of a second frequency spectrum having principal energy in second and third frequency bands located on either side of the first frequency band, the receiver comprising:

an input for receiving an incoming signal;

frequency shifting means for frequency shifting the incoming signal to form an intermediate frequency signal; and

a filter for filtering the intermediate frequency signal, the filter having a frequency response that has a first passband and a second passband separated by a central stopband; and

a control unit for controlling the frequency shifting means, the control unit having:

a first mode for reception of the first signals, in which it controls the frequency shifting means so as to frequency shift the incoming signal so that (a) the first frequency band of the incoming signal is shifted onto one of the first and second passbands and (b) one of the second and third frequency bands of the incoming signal is shifted onto the central stopband; and

a second mode for reception of the second signals, in which it controls the frequency shifting means so as to frequency shift the incoming signal so that (a) the second and third frequency bands of the incoming signal are shifted onto the first and second passbands respectively and (b) the first frequency band of the incoming signal is shifted onto the central stopband.

2. A radio receiver as claimed in claim 1 , wherein, in the first mode, the whole of the first frequency band is shifted onto the said one of the first and second passbands.

3. A radio receiver as claimed in claim 2 , wherein, in the first mode, the whole of the said one of the second and third frequency bands is shifted onto the central stopband.

4. A radio receiver as claimed in claim 2 , wherein, in the second mode, the whole of each of the second and third frequency bands is shifted onto, respectively, the first and second passbands.

5. A radio receiver as claimed in claim 1 , wherein, in the first mode, the whole of the said one of the second and third frequency bands is shifted onto the central stopband.

6. A radio receiver as claimed in claim 1 , wherein, in the second mode, the whole of each of the second and third frequency bands is shifted onto, respectively, the first and second passbands.

7. A radio receiver as claimed in claim 6 , wherein, in the second mode, the whole of the first frequency band of the incoming signal is shifted onto the central stopband.

8. A radio receiver as claimed in claim 7 , wherein the second and third frequency bands are coterminous with the principal energy bands of the second signals.

9. A radio receiver as claimed in claim 1 , wherein, in the second mode, the whole of the first frequency band of the incoming signal is shifted onto the central stopband.

10. A radio receiver as claimed in claim 9 , wherein the central frequencies of the first and second passbands are spaced apart by substantially the same spacing as the central frequencies of the second and third frequency bands.

11. A radio receiver as claimed in claim 1 , wherein the central frequencies of the first and second passbands are spaced apart by substantially the same spacing as the central frequencies of the second and third frequency bands.

12. A radio receiver as claimed in claim 1 , wherein the first frequency band is coterminous with the principal energy band of the first signals.

13. A radio receiver as claimed in claim 1 , wherein the second and third frequency bands are coterminous with the principal energy bands of the second signals.

14. A radio receiver as claimed in claim 1 , wherein the first signals have principal energy in a single central peak and the second signals have principal energy in two peaks symmetrically disposed about the central peak of the first signals.

15. A radio receiver as claimed in claim 1 , wherein the first signals are signals of a first protocol and the second signals are signals of a second protocol.

16. A radio receiver as claimed in claim 15 , wherein the first and second protocols are satellite location protocols.

17. A radio receiver as claimed in claim 1 , wherein the stopband is centered on 0 Hz.

18. A method for receiving first signals of a first frequency spectrum having principal energy in a first frequency band and second signals of a second frequency spectrum having principal energy in second and third frequency bands located on either side of the first frequency band by means of a comprising a filter having a frequency response that has a first passband and a second passband separated by a central stopband; the method comprising:

receiving the first signals by frequency shifting an incoming signal so that (a) the first frequency band of the incoming signal is shifted onto one of the first and second passbands and (b) one of the second and third frequency bands of the incoming signal is shifted onto the central stopband; and

receiving the second signals by frequency shifting the incoming signal so that (a) the second and third frequency bands of the incoming signal are shifted onto the first and second passbands respectively and (b) the first frequency band of the incoming signal is shifted onto the central stopband.