Kenwood CS-1352 Instruction Manual

Frequency M e a s u r e m e n t :1. Connect the sine wave of known frequency tothe C H 2 input jack of the oscilloscope and setthe S W E E P T I M E / D I V control to X - Y .2. Connect vertical input probe (CH1 INPUT) tothe unknown frequency.3. Adjust the C H 1 and C H 2 size control for a con-venient easy-to-read size of display.4. The resulting pattern called a L i s s a j o u spottern, shows the ratio between the twofrequencies (see Fig. 27).U N K N O W N F R E Q U E N C Y T OV E R T I C A L I N P U T S T A N D A R DF R E Q U E N C Y T O H O R I Z O N T A LI N P U TA M P L I F I E R S Q U A R E W A V E T E S TIntroduction:A square wave generator and the oscilloscope,such as this oscilloscope can be used to displayvarious types of distortion present in electronic cir-cuits. A square wave of a given frequency containsa large number of odd harmonics of that frequen-cy. If a 5 0 0 Hz square wave is injected into a cir-cuit, frequency components of 1.5 kHz, 2.5 kHzand 3.5 kHz also are provided. Since vacuumtubes and transistors arenon-linear, it is difficult toamplify and reproduce a square wave which isidentical to the input signal. Interelectrodec a p a c i t a n c e s , j u n c t i o n c a p a c i t a n c e s , s t r a yc a p a c i t a n c e s a s well a s limited device andtransformer response are a few of the factors whichprevent faithful reproduction of a square wavesignal. A well-designed amplifier can minimize thedistortion caused by these limitations. Poorlydesigned or defective amplifiers can introduce dis-tortion to the point where their performance is un-satisfactory. A s stated before, a square w a v e con-tains a large number of odd harmonics. By injec-ting a 5 0 0 Hz sine wave into an amplifier, w e canevaluate amplifier response at 5 0 0 Hz only, but byinjecting a square wave of the same frequency w ecan determine how the amplifier would response toinput signals from 5 0 0 Hz up to the 15th or 2 1 s tharmonic.The need for square w a v e evaluation becomes ap-parent if we realize that some audio amplifiers willbe r e q u i r e d d u r i n g n o r m a l u s e to p a s ssimultaneously a large number of different frequen-cies. With a square w a v e , w e have a controlledsignal with which w e can evaluate the input andoutput quality of a signal of macy frequencies (theharmonics of the square wave) which is what theamplifier sees w h e n amplifying complex waveforms of musical instruments of voices.The square w a v e output of the signal generatormust be extremely flat, so that it does not con-tribute to any distortion that may be observedwhen evaluating amplifier response. The os-cilloscope vertical input should be set to DC as itwill introduce the least distortion, especially at lowfrequencies. When checking amplifier response,the frequency of the square wave input should bevaried from the low end of the amplifier bandpassup toward the upper end of the bandpass;however, because of the harmonic content of thesquare wave, distortion will occur before the upperend of the amplifier bandpass is reached.It should be noted that the actual response checkof an amplifier should be made using a sine wavesignal. This is especially important in an limitedbandwidth amplifier (voice amplifiers).The square w a v e signal provides a quick check ofamplifier performance and will give an estimate ofoverall amplifier quality. The square wave also willreveal some dificiencies not readily apparent whenusing a sine wave signal. Whether a sine wave orsquare wave is used for testing the amplifier, it isimportant that the manufacturer's specifications onthe amplifier be known in order to make a betterjudgement of its performance.Testing Procedure (refer to Fig. 28):1. Connect the output of the square wavegenerator to the input of the amplifier beingtested.2. Connect the C H 2 probe of the oscilloscope tothe output of the amplifier being tested.3. If the DC component of the circuit being testedsufficiently low, to allow both the A C and D Ccomponent to be viewed, use the DC position231 / 2 : 11 : 11 - 1 / 2 : 16 : 1R A T I O O FU N K N O W NT OS T A N D A R DFig. 2 7 L i s s a j o u s ' w a v e f o r m s used forfrequency m e a s u r e m e n t