Radio Broadcast (Nov. 1925-Apr 1926)

Record Details:

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228 RADIO BROADCAST ADVERTISER J{eHne IJourJleceiVer^ WITH ONE OF THESE 3 DIALS ACCURATUNE MICROMETER CONTROLS ACCURATUNE dials fv not only enhance immeasurably the attractive appearance of your set but they insure clear and precise reception of programs, and with even those stations now so closely grouped on the lower wave lengths easily and readily segregated. This type recommended for Neutrodyne and Radio Frequency sets. Priced at $3.50 A. J. Vernier FOR use on Super-Heterodyne and Regenerative receiving sets, the A. J. offers a degree of tuning efficiency not usually associated with dials that sell at this price. Beautifully constructed of genuine Bakelite, the A. J. possesses a dignity of appearance that lends an air of richness to your receiver. Priced at $2.25 Recording Dial ON this new style recording dial, ample space has been provided to jot down call letters, thus insuring a permanent record of dial settings. The dial itself is beautifully proportioned, made of genuine Bakelite with handsome embellishments on a matted background. Truly a product of master craftsmen who specialize in the manufacture of dials. Priced at $1.75 MYDAR RADIO CO, 3 CAMPBELL ST. NEWARK, ~ N. J. if Tested and approved by Radio Broadcast if Don't borrow your neighbor's antenna by attaching your lead-in to the far end of his wire. You don't know what he is doing and besides, antenna wire is cheap and serves the purpose far better. Don't attach your antenna to a kite. Don't use your telephone line for an antenna. Connection to an electric light socket is not encouraged or recommended; light socket attachments are approved. MEASURING THE RESISTANCE OF COIL UNITS HERE is described a method whereby those having the proper facilities may measure the resistance of coils tuned successively to several prearranged frequencies. With the aid of a radio oscillator, a thermogalvanometer and a resistance box, a curve, plotting resistance against frequency, may be Measuring Circuit FIG. 3 made from the several readings obtained. The circuit diagram for the layout is shown in Fig. 3. To measure the resistance of a coil, the procedure is as follows, assuming that readings are to be taken at 1500 kc. (200 meters) 1200 kc. (250 meters) 1000 kc. (300 meters) and so on, for every 50 meters up the scale to 545 kc. (550 meters.) Put the oscillator into operation setting its frequency control at 1500 kc. (200 meters). Couple the coil to be measured, Li, to the oscillator output coil L2. This will cause a deflection of the needle of the thermo-galvanometer. Now by varying the coupling between Li and L2, the galvanometer reading may be varied to one of the numbered markings of the meter scale such as 20-40-60-70-80, etc. Since the next step requires the addition of resistance to the measured circuit, until the reading of the meter drops to one-quarter of its original value, it is well to vary the coupling to a point where this division will be simple. At an original reading of 60 or 80, it is quite easy to add resistance to the circuit until the reading falls to 15 or 20. Resistance is added to the circuit by means of the controls on the resistance box which, until this time, had been set at zero. When the one quarter reading is obtained, reference is made to the resistance box and the resistance noted. This constitutes the resistance of the coil and the meter at that particular frequency. Usually the resistance of the meter is known and its value may be deducted from the reading obtained. This whole system is repeated for each frequency point to be measured. TUBES AND R.F. COILS: HOW THEY SHOULD BE MATCHED IN A RECEIVER TO OBTAIN maximum efficiency in a receiver using radio frequency amplification, it is necessary to have transformers designed for the type of tube used in the set. This statement has been amply justified as the result of exhaustive tests made by independent engineers who were interested in the problem. If a receiver is using the c-299 or uv-199 type of dry cell tubes, with proper transformers, and is changed over to the c-301-A or uv-201-A