Radio Broadcast (May 1929-Apr 1930)

16 14 12 §10 value mentioned are employed, the effect is to reduce slightly the amplification obtained at the low-frequency end of the range. This is because the resonance of the primary circuit is farther removed with the result that there is less current flowing in that circuit and less voltage developed in the secondary circuit. Where antenna values less than 200 mmfd. are employed, the voltage step-up will increase until the resonant peak of the primary is reached at 550 kc. Where still smaller values of antenna are employed, so that the resonant point of the input circuit comes well within the operating range of the receiver, the effect, as a whole, is rather detrimental but can be minimized by observing special precautions, as explained later. With the fundamental arrangement as described, the effect of the antenna circuit upon the secondary circuit of the receiver, is exactly the reverse of the arrangement described in paragraph one. Its effect is to decrease the effective inductance of the tuned input circuit. This effect is not very serious and may be compensated by a few added turns on the secondary coil, an increase in inductance of between 1 and 2 per cent, being adequate. There is some difference in the character of the voltage step-up curve, depending upon whether the capacity coupling between the primary and secondary coils is aiding or opposing the magnetic coupling. If it is aiding, the voltage step-up at 1500 kc. will be considerably higher and the final response curve over the frequency range will be almost a straight line. If the capacity coupling is opposing the magnetic coupling, there will be a decrease in the amplification at 1500 kc. with a gradual rise to maximum at 550 kc. When the antenna circuit is allowed to become resonant to some frequency within the broadcast range the detuning effect upon the secondary becomes objectionable on the inductive side of resonance unless the input is properly loaded. One method of obviating this condition is in providing S Copper Shielding Tube -Coupling9.3% Curve 1~50 mmfd. Antenna Curve 2 100 mmfd. Antenna Curve 3 200 mmfd. Antenna Curve 4 300 mmfd. Antenna a small shunting capacity across the primary (See Fig. 4) for use when an especially small antenna is employed so that the resonant point of the input system will always be outside of the lowest frequency in the broadcast range. A preferred arrangement would be to combine the loading means and volume control. This arrangement is obtained by employing a fixed value of resistance permanently connected between antenna and ground with an adjustable arm connecting to the primary coil. (See Fig. 5) When coupling this arrangement it is 1500 unnecessary to provide several switch arrangements to accommodate antennas of various sizes, the one connection being sufficient. A typical series of values that might be employed in designing a circuit of this type, are: TRANSFORMER NO. 1. Lpri = 650 to 700 microhenries Lsec = 260 Coupling = 12 per cent. Shunted capacity for very small antenna — 100 mmfd. Voltage step-up 1400 kc. = 7 600 kc. =11 TRANSFORMER NO. 2. LPri = 650 to 700 microhenries Lsec = 260 microhenries Coupling = 10 per cent. Shunted resistance across primary = 10,000 ohms Voltage step-up about as No. 1 TRANSFORMER NO. 3. Lpri = 400 microhenries Lsec = 200 Coupling = 10 per cent. Shunted resistance across primary = 5000 ohms Amplification values — 1400 kc. =6 600 kc. =8 to 9 1500 . „ , In certain of the experiments the primary coil consisted of a small flat bobbin having a \" diameter core and a TV slot wound with approximately 200 turns of No. 36 d.s.c. wire. The secondary consisted of a If" supporting form, wound with 100 turns of No. 28 enameled wire. The primary was located at the low-potential end of the secondary and in the same plane as the secondary winding. The entire transformer was enclosed within an openended copper can 2\" long and 2\" in diameter. The accompanying curves (Fig. 6) give a series of absolute values of amplification obtained under various conditions and are complete in themselves. remarking, while the testimony of Louis G. Caldwell was being taken, "I think advertising is a fast disappearing part of the radio service." Maybe he was talking about television. The testimony which attracted the greatest attention was that of Col. J. I. McMullen, of the Office of the Judge Advocate General of the Army, who stated that, in his opinion, the Schloemilch and Von Bronck patents anticipate Alexanderson and that the two Federal District Court opinions, favorable to Alexanderson, were based on evidence which did not adequately set forth the Schloemilch and Von Bronck claims. These cases, he said, were "a rather put-up job by the General Electric Company to have the Alexanderson patents validated over the Von Bronck." Lt. Com. Harold Dodd stated that the Navy paid the Alien Property THE MARCH OF RADIO (Continued from page 215) Custodian about §1690 for the Schloemilch and Von Bronck patents. In Canada, these patents constituted a successful defense against Alexanderson by Fada Badio, Ltd., when it was sued by the Canadian General Electric Company there. The Canadian patent law makes all research work done in Europe relevant in fixing dates; in the United States, however, only foreign publication is of weight ; hence it does not follow that American and Canadian judges differed on these cases — they each passed judgment on a different case. Col. Manton Davis, with his usual crystal logic and courtesy, called the attention of the Senate Committee by letter to the decisions of Judges Bodine and Thatcher in the Splitdorf and Atwater Kent cases. It must be said that these decisions are only indirect refutation of Col. McMullen's statements because, if what he says is true, the German patents were not adequately presented before the Judges who rendered these decisions. After all, the argument is quite academic because all the principal radio manufacturers have long ago admitted the validity of the Alexanderson patent and agreed not to contest or to aid anyone in contesting it. Just what the Senate has to do with this matter, which has been and could again be brought to the courts, is not clear. Delving into such matters is, of course, very interesting, but we suspect some of those who have taken frequent opportunities to address the press through the medium of Senate hearings to be mere busybodies. If the charges they make are true, they should hasten to the courts rather than the Senate and the press. 2.-J6 • AUGUST 1929 •