Radio today (Sept 1935-Dec 1936)

NEW SET TESTERS COMPLETE SET TESTER CI C CA ONLY $10. 9U RELIABILITY AT LOW COST This popular three meter Set Tester checks all parts of radio tube circuits by plugging directly into the receiving set sockets. D.C. Voltmeter Scale 20-60-300-600 D.C. Milliammeter Scale 15-150 A.C. Voltmeter Scale 10-140-700 Panel jacks are provided to make individual range connections. MODEL 710-A Complete in Black Leatherette Covered Case. Dealer Net Price $16.50 MODEL 712-A Same as 710-A but having Triplett moving coil Model 223 2" D.C. Voltmeter (1000 ohms per volt). Dealer Net Price $22.20 Where reliability is desired at low cost, turn to Readrite — all Readrite merchandise is built rugged — it will stand up — it will give dependable performance over a long period of time. OTHER PRODUCTS Readrite manufactures all types of testers used for servicing Radio Sets, including Set Testers, Tube Testers, Resistance, Continuity and Capacity Testers, Point-to-Point Testers and inexpensive Indicating Meters. SEE YOUR JOBBER THIS COUPON BRINGS FACTS 1 READRITE METER WORKS | 1911 College Drive, Bluflton, Ohio ■ Please send me full information on 1 Model 710-A Readrite Complete Set I Tester | Catalogue | Name I Street Address I City State USES OF RECTIFICATION — JOHN RIDER {From page 26) Heterodyne detection A much better representation of detector action is shown in Figs. 5 and 6. What is indicated here is identical to what is accomplished in beat oscillator arrangements for e.w. reception ; this arrangement is a feature in several commercial receivers and is also used as a tuning indicator or "station spotter." Fig. 5 illustrates the wave envelope of two signals of different frequencies fed into the detector tube. These two voltages are alternately in phase and out of phase, thus giving rise to the variation in amplitude. The rate of amplitude variation occurs at the difference frequency. Fig. 6 shows the voltage across the load of the detector tube and you can see that the lower half of the input voltage pattern has been eliminated. In effect the input voltage has been rectified and with proper equipment in the load circuit of the detector, the signal which would be extracted from the rectified wave would be of the frequency representative of the rate of amplitude variation. In order that the picture of Fig. 6 be as clear as that shown in Fig. 4, it would be necessary to filter out all the frequencies represented by the lines running vertically. They appear in this pattern, because this test was made by using comparatively low frequencies, whereas the carrier used in Fig. 3 and not appearing in Fig. 4 was of a high frequency and was filtered out. From what has been said, you can gather that the heterodyning process to produce a difference frequency is also founded upon rectification. As far as basis of operation is concerned, the heterodyne oscillator used for e.w. reception, the signal beacon for spotting stations as used in the receivers, and the operation of the first detector (also known as modulator, translator, mixer, etc.) used in super heterodyne receivers also depend upon rectification. The process of rectification ss applied to detector tube is applicable to the diode circuit, which is substantially identical to the half wave rectifier or the full wave rectifier, depending upon the use of a half wave or full wave diode detector. An example of the half wave and full wave diode circuit detector as used in commercial receivers is shown in Figs. 7 and 8. Ignore the a-f. circuit connections and you will find that this circuit is identical to the half wave and full wave rectifiers of Figs. 1 and 2. In Fig. 7, the 1.0 megohm resistor is the E of Fig. 1 and the two diodes Fig. 7 — The half wave diode detector is similar to the half wave power rectifier. Fig. 8 — Second harmonic distortion in detection is eliminated by using the full wave diode detector. constitute the signal plate. In Fig. 8 the two diodes are used as the two plates of Fig. 2, and the 150,000 ohm resistor is the R of Fig. 2. Demodulation In grid bias detectors of the three or more element variety, rectification takes place in the plate circuit, because only the positive half of the modulated wave envelope is amplified ■ — the negative half being eliminated. In the grid-leak and condenser type detectors, rectification occurs in the grid circuit. When a modulated wave is applied to the grid of the tube, grid current flows through the grid leak. This rectified current varies in amplitude in accordance with the modulation of the carrier and a voltage is developed across the grid leak-condenser combination, which combination is in effect the load upon the rectifier system. This voltage is applied to the grid of the detector tube and is amplified in the plate circuit by ordinary amplifier action and is productive of the detector output. . . . Once more rectification is the basic principle. 28 Radio Today