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Method of Aligning a Radio Receiver and Means for Indicating the Alignment of a Radio Receiver

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Method of Aligning a Radio Receiver and Means for Indicating the Alignment of a Radio Receiver Europâisches Patentamt © European Patent Office @ Publication number: 0 003 634 Office européen des brevets Bl © EUROPEAN PATENT SPECIFICATION @ Date of publication of patent spécification: 07.1 0.81 (g) Int. Cl.3: H 04 B 1/26, H 03 J 3/14 @ Application number: 79300029.0 (g) Date offiling: 09.01 .79 (54) Method of aligning a radio receiver and means for indicating the alignment of a radio receiver. © Priority: 09.02.78 US 876386 @ Proprietor: MOTOROLA, INC. 1303 East Algonquin Road Schaumburg Illinois 60196 (US) (43) Date of publication of application: 22.08.79 Bulletin 79/1 7 @ Inventor: Gould, Larrie Alan 5622 Woodhollow @ Publication of the grant of the European patent: Arlington Texas 7601 6 (US) 07.10.81 Bulletin 81/40 Inventor: Reed, Kim Warren 6036 East Belknap FortWorth Texas 761 17 (US) @ Designated Contracting States: CH DE FR GB NL @ Représentative: Newens, Léonard Eric et aJ, F.J. CLEVELAND CO. 40/43 Chancery Lane © Références cited: London WC2A 1 JQ (GB) DE-A-2 624 787 DE-B-1 034 716 GB-A-559 555 US - A - 3 896 386 o 8 O Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been m paid. (Art. 99(1 ) European patent convention). Courier Press, Leamington Spa, England. Background of the Invention Briefly, according to the invention, an FM The present invention pertains to the radio radio frequency receiver having a tuned receiver art and, more particularly, to a means intermediate frequency (IF) stage followed by a for, and a method of aligning a radio receiver. detector stage may be aligned by first The radio receiver art has developed several alternately applying a noise signal and then a techniques for the aligning of radio receivers. predetermined frequency signal to the IF stage. Alignment is a process whereby various stages The receiver is then adjusted such that the of the receiver are properly tuned to the desired output of the detector stage reponsive to the frequency. For example, when a modulated applied noise signal bears a predetermined signal of predetermined frequency is applied to relationship to the detector stage output the radio carrier frequency input stage of a responsive to the applied predetermined receiver, the local oscillator stage, tuned frequency signal. Preferably, the frequency of intermediate frequency stage, and detector the receiver's local oscillator is adjusted until stage must all be adjusted to maximally the voltage at the detector output is the same reproduce the signal at the detector (or whether the noise signal or the predetermined demodulator in FM radio receiver) output. frequency signal is applied. A typical alignment procedure known in the The means for indicating receiver alignment prior art is as follows. A predetermined includes a signal generator for generating a frequency signal is applied at the radio predetermined frequency alignment signal, a frequency input, or antenna connection, of the noise source for generating a random noise receiver being aligned. The local oscillator is signal and a switching means which alternately adjusted such that the output from the mixer is couples the predetermined frequency alignment the input signal converted to the receivers signal and the noise signal to the receiver's intermediate frequency which, in a common FM intermediate frequency stage. A comparator radio is 10.7 MHz. The intermediate frequency compares the output of the detector stage stage is then adjusted such that the alignment responsive to the predetermined frequency signal is directly in the centre of its passband. alignment signal being coupled to the IF stage For receivers employing a fixed tuned IF stage, with the output of the detector responsive to however, the receiver may be misaligned due to the noise signal being applied to the IF stage. the center band of the filter being at other than An error signal is produced indicative of the the derived intermediate frequency. This results tuning of the receiver stage with respect to the in misalignment. Finally, a DC tuning meter is predetermined frequency alignment signal. connected to the output from the detector stage Preferably the comparator comprises a and the detector is adjusted such that the capacitor which has one terminal coupled to the output reading is zero volts DC. Also, due to output of the detector and the other terminal component value drifts caused by aging and coupled through a meter to reference, or ground thermal effects, a reading of zero volts DC may, potential. The switching means further includes in fact, correspond to a misaligned receiver. a means which short circuits the meter during The above described prior art alignment the time that one of the predetermined procedure suffers from numerous dis- frequency alignment signal and noise signal is advantages. Firstly, it is a complicated and applied to the IF stage. In this manner, the tedious procedure, not generally suited to fluctuation of the meter is indicative of the efficient manufacturing operation. Also, for difference between the magnitudes of the receivers employing fixed intermediate detector stage outputs corresponding to the frequency tuned stages, the above procedure predetermined frequency alignment signal and does not provide optimum alignment. In the noise signal being coupled to the IF stage, addition, it is desirable for purposes such as and, thus, is indicative of the relative alignment field alignment to use a zero centered DC tuning of the radio receiver. meter. For radio designs utilizing a quadrature detector, an output non-zero DC signal appears Brief Description of the Drawings at the detector when the detector is properly Fig. 1 is a block diagram illustrating the basic aligned. This fact precludes the use of zero structure and operation of the preferred centered DC tuning indicators when used in the embodiment of the invention; and prior art aligning procedure. Fig. 2 shows a series of waveforms representative of operation of the preferred Summary of the Invention embodiment shown in Fig. 1. It is an object of this invention, therefore, to provide a simple, efficient and precise method Detailed Description of the Preferred Embodi- for the aligning of a radio receiver. ment of the Invention It is a further object of the invention to Fig. 1 illustrates, in block diagram form, a provide an improved means for indicating the conventional FM radio receiver, indicated relative degree of receiver alignment. generally at 10 in combination with the preferred embodiment of the alignment in- operation of the means for indicating receiver dicator. The receiver is comprised of a alignment, may be understood as follows. A conventional RF input stage 12 adapted for signal source 80 is coupled to the input of the receiving signals from an antenna 11. The RF stage 12. The signal source 80 is adjusted to output from the RF stage 12 feeds to the first generate a predetermined frequency alignment input 14a of a conventional mixer circuit 14. carrier. The alignment carrier signal is con- Applied to the second input 14b of mixer stage verted, via the operation of mixer 14 and local 14 is the output from the local oscillator stage oscillator 16, to the intermediate frequency 16. Local oscillator stage 16 is of conventional whereby the converted signal appears at design, and is tunable over a defined range the mixer output 14c. In its first mode suitable for converting the signal received at the of operation, that is when its contacts mixer first input 14a to the intermediate are shorted together, switch 42 couples the frequency of the receiver. converted alignment signal through the IF stage The converted output appearing at the mixer 20 and detector stage 24 whereby the output output 14c is coupled through switch 22 to the from the detector responsive to the applied input 20a of a conventional tuned intermediate alignment signal appears at the detector output frequency stage (IF) 20. Intermediate frequency 24b. When switch 42 is in its second mode of stage 20 is of standard design employing operation, i.e. its contacts being open circuited, circuits having tuned characteristics about a a random, white noise signal appears at the center frequency f, In a typical _FM radio input 20a of the IF stage 20. It is commonly receiver, fc is selected to be 10.7 MHz. The known to one of ordinary skill in the art that the filtered, amplified and limited signal from IF input 20a of IF stage 20 will contain white noise stage 20 appears at the stages output 20b and when open circuited. An alternate method of passes to the input 24a of a conventional applying white noise to the IF stage would be to detector stage 24. Acting in the known manner, inhibit operation of the local oscillator stage 16 the detector 24 which produces an output or to open circuit the RF stage 12 input. A signal representative of the frequency change of further way to apply white noise to the IF stage signals applied to it, recovers the information; 20 would be to switch the IF stage input 20a e.g. audio signal, contained in the Input RF directly to a white noise source, such sources signal, reproducing this information signal at its being commercially available and shown by output terminal 24b. white noise source 15 in Fig. 1. The alignment indicating circuitry, according During the period that switch 42 is in its to the preferred embodiment of the invention, second mode and white noise is applied through includes switching means, indicated generally the IF stage 20 and detector stage 24, switch at 40, which includes a first switch 42, coupled 44 is closed thereby shorting out the tuning between the mixer output 14c and the IF input meter 60.
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