DOI:10.1049/ji-3-2.1948.0002

出版商:IEE    

年代:1948

数据来源: IET

摘要:

Automatic equipment is described for measuring the virtual height of the reflecting regions of the ionosphere. The system comprises a transmitter, which scans a wide frequency range some twenty-five times per second, and a receiver which is tuned slowly through the same range. Each time the frequency of the transmitter passes through the pass-band of the receiver, a pulse is produced which is displayed on an oscillograph, together with other pulses produced by waves reflected from the ionosphere. The advantages of this technique are enumerated.The equipment enables a record, covering the range 2–16 Mc/s, to be obtained in a few seconds. The apparatus is fully automatic and produces records as required without manual operation. The equipment has been designed with a view to duplication, is robust and easy to service, and is semi-portable.

DOI:10.1049/ji-3-2.1948.0003

出版商:IEE    

年代:1948

数据来源: IET

摘要:

The space charge in the screen-anode space of a beam tetrode is examined, taking into account the effect of electrons returned from the virtual cathode into the region between the grid and cathode. As with previous investigations which do not take into account the effect of the returned electrons in the cathode-grid space, it is found that over a range of anode voltages just below the knee, three solutions of the problem satisfy Newton's laws of motion for the electrons and also Poisson's equation for the charge distributions. Two of these solutions give rise to discontinuities in the characteristic. The third, however, is continuous for all anode voltages from zero up to the knee, and corresponds closely to experiments on actual valves. In it, a virtual cathode which remains at a fixed point between the screen and the anode is set up. The question arises, What property of this solution determines its correspondence with experiment? It is found that Maupertuis's principle of least action, as an integral of momentum with respect to distance, can be applied. The principle of least action as it stands cannot, however, be applied to a single arbitrarily chosen electron, but by calculating the action per unit of time, it can be applied to all three solutions, whether electrons are reflected or not. This leads to the conclusion that the action per unit of time is least for the third solution. Since this corresponds to the conditions observed experimentally, it is asserted that, in problems concerned with the motion of charged particles in which more than one consistent solution can be found, the actual state set up will be that for which the action per second is least.A simple theory of the effect of perturbations of the space-charge density, due, for example, to the random fluctuations of the cathode emission, is developed. The rate of growth of a perturbation depends on its size, and if it is small, it is unlikely to grow to such an extent, before being swept to the anode, as to cause instability of a particular charge distribution. It is concluded that such perturbations do not form an alternative explanation of the fact that the state containing the virtual cathode is always that set up.The growth of the perturbations is shown to depend on whether the anode potential remains constant or can vary during the passage of a perturbation. It is concluded that the theory of the fluctuations of a space-charge-limited current cannot be dealt with accurately on the assumption that the fluctuation current is independent of the anode load.Finally, the fluctuations of the space-charge-limited current in diodes and triodes is described on the basis of the given theory of perturbations. For identical space-charge conditions near the cathode, the diode has a planar electric field which exercises no electron-optical action, while the triode has a strong focusing action in the space between grid and cathode. The conclusion, that the perturbations can grow to a greater extent in diodes than in triodes, agrees with the experimental results on the noise of diode and triode valves.

DOI:10.1049/ji-3-2.1948.0006

出版商:IEE    

年代:1948

数据来源: IET

摘要:

If the probe current of a coaxial-line standing-wave detector is passed through a pair of rectifiers, a simple relation may be obtained between the mean current through either of the rectifiers, the capacitance of the probe to the inner conductor, and the frequency and peak amplitude of the voltage on the line.At a frequency of 600 Mc/s, errors are introduced into voltage measurements made with this circuit, owing mainly to the shunting of the rectifiers by stray capacitance. These errors may be reduced to 5–10% by using low-resistance silicon crystal rectifiers at their maximum current rating, and the magnitude of the errors can be deduced from a simple test made at low frequency. The shunting effects of stray capacitance across the rectifiers may be compensated, for to a large extent by a variable inductive stub, tuned to resonate with the stray capacitance at the operating frequency. The compensation is not perfect, however, and the use of a stub is a disadvantage with large rectifier currents.Measurements of 600-Mc/s pulsed voltages made with this probe circuit were found to agree, within the limits of experimental error (±3%), with the corresponding values deduced from measurements of the power dissipated in a calorimeter which terminated the coaxial line.

DOI:10.1049/ji-3-2.1948.0007

出版商:IEE    

年代:1948

数据来源: IET

摘要:

An expression is derived from which, by substitution of appropriate numerical values, an equation can be obtained for any of the intermodulation products which can be generated by the simultaneous transmission of any number of sinusoidal waves through a device with an output/input characteristic likeV=a1v+a2v2+a3v3…. This expression is used as a basis for classification of products, and a table of representative products is drawn up. Information is given about the numbers and relative importance of products of different kinds.

DOI:10.1049/ji-3-2.1948.0008

出版商:IEE    

年代:1948

数据来源: IET

摘要:

The matrix algebra has a natural application to electric circuit theory, especially to the method of solution by means of substituted variables, such as symmetrical components.The solution of circuit equations by the method of diagonalizing the impedance matrix is developed in the paper, and applied to the solution of the difference equations of ladder networks. An extension to systems of difference equations follows.Diagonalizing is equivalent to the use of substituted currents, voltages and impedances such that there is no mutual coupling between the substituted networks. The substituted currents are then calculated without difficulty and the original circuit currents obtained by a simple transformation.The method has the additional advantage that, since the transformation is independent of the circuit constants, it may be applied to all circuits possessing the same degree of symmetry.Ladder networks may also be solved by regarding them as a series of four-terminal passive networks.The elements of matrix algebra are included for completeness.

DOI:10.1049/ji-3-2.1948.0010

出版商:IEE    

年代:1948

数据来源: IET