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Machine translation
1. (WO1994016496) DEVICE AND METHOD FOR TUNING A BAND-PASS FILTER
Note: Text based on automatic Optical Character Recognition processes. Please use the PDF version for legal matters

Claims:

1. Method for adjusting an RF bandpass filter, especially a combiner filter, comprising
deriving an RF sample signal proportional to the power of a modulated RF signal passing forward to the bandpass filter, reflected from the input of the bandpass filter, or passed through the bandpass filter;
down-converting the sample signal by another RF signal;
detecting the signal strength of the mixing result;
adjusting the centre frequency of the passband of the bandpass filter on the basis of the detected signal strength,
c h a r a c t e r i z e d in that
the down-conversion of the sample signal comprises mixing the sample signal with an RF signal having a substantially different frequency and being unmodulated or differing in modulation in such a manner that the signal obtained as a mixing result is an AC signal of a lower frequency; and that
the DC component is removed through filtration from the AC signal before detection.
2. Method according to claim 1, c h a r a ct e r i z e d in that the down-conversion of the sample signal comprises mixing the sample signal with an RF signal having a frequency differing from that of the sample signal at least in an amount corresponding to the frequency modulation of the sample signal.
3. Method according to claim 1 or 2, c h a r a c t e r i z e d in that the sample signal is proportional to the reflected RF power, and that the bandpass filter is adjusted so that the level of said mixing result is at its minimum value.

4. Method according to claim 1 or 2, c h a r a c t e r i z e d in that the sample signal is proportional to the forward RF power passing through the bandpass filter, and that the bandpass filter is adjusted so that the level of said mixing result is at its minimum value.
5. Method according to claim 1 or 2, c h a ra c t e r i z e d in that a first sample signal proportional to the reflected RF power and a second sample signal proportional to the forward RF power are derived; each sample signal is mixed with substantially the same RF signal for forming a first and a second AC signal; DC components are separated from the AC signals, the strength of the AC signals is detect-ed; and the bandpass filter is adjusted on the basis of a reflection coefficient calculated from the detection results.
6. Device for adjusting an RF bandpass filter, especially a combiner filter, comprising
means (21, 41) for deriving an RF sample signal proportional to the RF power of a modulated signal passing forward (Pf) to the bandpass filter, reflected (Pr) from the input of the bandpass filter, or passed through (Pf ) the bandpass filter;
mixing means (29, 31, 49) for down-converting the sample signal (Pf, Pr, Pf ) ;
detecting means (28, 34, 48) for detecting the strength of the down-converted sample signal;
a control means (23) for adjusting the centre frequency of the bandpass filter in response to said detection result;
c h a r a c t e r i z e d in that
the mixing means (29, 31, 49) mixes the sample with an RF signal having a substantially different frequency and being unmodulated or differing in modu- lation in a manner such that the signal obtained as a mixing result is an AC signal having a lower frequency, and that the device further comprises
filter means (26, 32, 46) for removing the DC component from the AC signal before the detection means.
7. Device according to claim 6, c h a r a ct e r i z e d in that the frequency of said RF signal differs from that of the sample signal at least in an amount corresponding to the frequency modulation of the sample signal.
8. Device according to claim 6, c h a r a ct e r i z e d by an adjustable oscillator means (24) for generating said signal having a substantially different frequency.
9. Device according to claim 6, 7 or 8, c h a ra c t e r i z e d by a filter means (27, 33, 47) for lowpass filtering the down-converted sample signal before detection, and the filter responses of the lowpass- and highpass-filter means are such that they weight the centre frequencies of the down-converted sample signal.
10. Device according to claim 6, 7, 8 or 9, c h a r a c t e r i z e d in that the device com-prises
means (21) for deriving a first RF sample signal

(Pf) proportional to forward RF power passing to the bandpass filter and a second RF sample signal (Pr) proportional to RF power reflected from the input of the bandpass filter;
a first (29) and a second mixing means (31) for down-converting the first and the second RF sample signal, respectively;
a first (26) and a second (32) highpass filter for filtering the first and the second down-converted sample signal, respectively;
a first (28) and a second (34) detector means for detecting the strength of the first and the second down-converted sample signal; and that
the control means (23) is responsive to the detection results of both the first and the second detector means for controlling the bandpass filter.
11. Device according to claim 10, c h a r a ct e r i z e d in that the device comprises
means ( 41 ) for deriving a third sample signal

( Pf ) proportional to the RF power of the frequency-modulated signal passed through the bandpass filter;
a third mixing means ( 49 ) for down-converting the third RF sample signal, respectively;
a third highpass filter (46) for filtering the third down-converted sample signal;
a third detector means (48) for detecting the strength of the third down-converted sample signal; and that
the control means (23) is responsive to the detection results of the first, the second and the third detector means for adjusting the bandpass filter.