. Practical wireless telegraphy; a complete text book for students of radio communication . e tones are obtained from arc trans-mitters, the beat current does nothave anywhere near the musical pitchthat can be obtained from the radio-frequency alternator. The arc gener-ator of Fig. 291 might be replaced bya radio-frequency alternator of smalloutput or by a buzzer excitation sys-tem, but a generator giving genuinelyundamped oscillations is preferred. The precise actions taking place inthe heterodyne receiver of Fig. 291 canbe explained by the series of curves inFig. 292. The oscillations 0-1, i
. Practical wireless telegraphy; a complete text book for students of radio communication . e tones are obtained from arc trans-mitters, the beat current does nothave anywhere near the musical pitchthat can be obtained from the radio-frequency alternator. The arc gener-ator of Fig. 291 might be replaced bya radio-frequency alternator of smalloutput or by a buzzer excitation sys-tem, but a generator giving genuinelyundamped oscillations is preferred. The precise actions taking place inthe heterodyne receiver of Fig. 291 canbe explained by the series of curves inFig. 292. The oscillations 0-1, indi-cated on the upper line, are those in-coming at a given station (without thelocal arc generator in operation) whilethose on the second line 0-2 corres-pond to the frequency of the arc gen-erator and are of a lower order offrequency than the incoming oscilla-tions. The third curve 0-3 indicates theresultant beat current due to the in-teraction of the local frequency andthat of the incoming signal. This cur-rent has zero value when the two Fig. 291—Early Form of Heterodyne RECTlflEDBEAT CURRENT Aa^a/ PERIODICTELEPHONE CURRENT Fig. 292—^Turves Showing the Functioning of the HeterodyneReceiver. groups of oscillations oppose and max- 280 PRACTICAL WIRELESS TELEGRAPHY. imum value when they assist or are in phase, and the frequency of the beat current is thenumerical difference of the frequency of the incoming oscillations and that of the. localgenerator. When rectified by the crystal, the successive cycles of the beat current take the form ofthe curve 0-4, where the negative halves have been cut off and the positive halves remain,for operation of the telephone, as shown by the curves of line 0-9. 224. The Vacuum Valve as a Source of Radio*-Frequency Oscillations. —If a three element vacuum valve is connected up as in Fig. 293 with the correct values ofinductance for the coils L-4, L-S, L-6 and L-7, and for the condensers, C-3, C-4 and C-5,oscillations of radio-fr
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Keywords: ., bookcentury1900, bookdecade1910, booksubjecttelegra, bookyear1917
