摘要:

An absorption wavemeter, using a “butterfly” circuit and crystal rectifier, is described. It is calibrated over the range 250–850 Mc/s, with an accuracy of between 1 and 2%.

DOI:10.1049/ji-3a-1.1946.0215

出版商:IEE    

年代:1946

数据来源: IET

摘要:

Low-speed cathode-ray oscillographs are widely used for examining voltage waveforms in all branches of electrical engineering, and they are now familiar and generally accepted instruments. The special oscillographs designed for examining rapid transients were little used before the war, but radar research required reliable instruments for examining very short pulses. This paper outlines the difficulties which must be overcome in designing a high-speed oscillograph, and describes the characteristics required in the time-base generator, the cathode-ray tube and the signal-input circuits. The limitations of present instruments at the very highest writing speeds are enumerated, and possible remedies are suggested.

DOI:10.1049/ji-3a-1.1946.0216

出版商:IEE    

年代:1946

数据来源: IET

摘要:

A method of measuring pulse voltages up to 10 kV at a frequency of 200 Mc/s is described. The voltage to be measured is applied to one end of a three-quarter wavelength line, short circuited at the other end. The sinusoidal distribution of voltage thus set up is used as a potential divider, the voltage at a small, known distance from the voltage node being measured with a valve peak-voltmeter. A method of eliminating the input capacitance of the valve voltmeter is described. Possible sources of error are discussed and their magnitude is estimated.

DOI:10.1049/ji-3a-1.1946.0217

出版商:IEE    

年代:1946

数据来源: IET

摘要:

The application of pulse modulation to signal generators involves difficulties with regard to external modulation and output-level monitoring. Direct anode- or grid-modulation proved unsatisfactory, but a method using a pulsing diode on the oscillator grid is reasonably satisfactory, and details are given of a unit which was widely used.An improved method switches the generator output with a gate valve, the oscillator operating at a constant level throughout. Starting delay and variation of pulse length with carrier frequency are avoided, but the l.f. modulating pulse is also present in the output, and has to be removed by filters. Two practical applications of this system are described. A suggested improvement uses a pair of grounded-grid triodes in a balanced switching arrangement.

DOI:10.1049/ji-3a-1.1946.0218

出版商:IEE    

年代:1946

数据来源: IET

摘要:

The propagation constants of screened twin cables at frequencies of 200 Mc/s and above are usually measured by a resonance method, the resonating element being a screened air-spaced twin line. Such a system can also resonate in unbalanced modes, and unless it is truly symmetrical these modes are detected on the recording instrument, causing errors in the results obtained for the balanced system. This trouble is avoided by(a) arranging that the bridge, which is moved along the line to bring the balanced system into resonance does not tune the unbalanced one,(b) artificially balancing the system to compensate for any lack of symmetry, or(c) choosing the conditions of measurement such that the unbalanced systems are heavily damped and have a negligible effect on the results.Measurements made with the balanced measuring line will usually detect any lack of symmetry in the cable sample, but will give no quantitative measure of its extent. This is therefore obtained directly by treating the cable as three unbalanced systems, which are measured separately on an unbalanced coaxial-line measuring equipment. The conditions of measurement are so chosen that when the system being measured is in resonance the others are in anti-resonance, and thus have the minimum effect on the results. The results give a direct measure of the balance of the cable and the propagation constants of the unbalanced systems. The constants for the balanced system can be derived from them.Measurements are made in this way on a number of twin cables in the preferred list of the Inter-Services R.F. Cables Technical Committee; good agreement is in general obtained between the results derived from three unbalanced measurements, those obtained from the balanced measuring line and those calculated from the standard formulae.

DOI:10.1049/ji-3a-1.1946.0219

出版商:IEE    

年代:1946

数据来源: IET

摘要:

A field-strength measuring set, capable of operation over the frequency range 400 to 4 000 Mc/s, has been designed and constructed. The mixing unit employs a local oscillator of range 400 to 800 Mc/s, and is used with a wide-band i.f. amplifier, 0.5 to 3.5 Mc/s. Harmonic frequencies of the local oscillator are used to receive signals on frequencies higher than 800 Mc/s. It is possible to use the receiver with several types of antenna, and the equipment is normally supplied by batteries.

DOI:10.1049/ji-3a-1.1946.0220

出版商:IEE    

年代:1946

数据来源: IET

摘要:

This note describes a sensitive, wide-range wavemeter, using a capacitance-loaded coaxial line as the resonator. The concentric line has a sliding central conductor, which serves to vary simultaneously the length of the line and the capacitance loading. The electrodes of the capacitor are so shaped as to produce an almost linear relationship between the position of the central conductor and the resonant frequency of the wavemeter. A crystal detector and galvanometer are used to indicate resonance.

DOI:10.1049/ji-3a-1.1946.0221

出版商:IEE    

年代:1946

数据来源: IET

摘要:

A visual-alignment signal generator covering the frequency range 10 to 100 Mc/s, incorporating variable cyclic frequency modulation up to a maximum of ± 20 Mc/s, is described. It is primarily intended for visual observation of the frequency response and sensitivity of amplifiers with band-widths up to about 30 Mc/s.

DOI:10.1049/ji-3a-1.1946.0222

出版商:IEE    

年代:1946

数据来源: IET

DOI:10.1049/ji-3a-1.1946.0223

出版商:IEE    

年代:1946

数据来源: IET

摘要:

The paper describes a diode noise generator designed as a standard source for measuring the noise factor of i.f. amplifiers in common use with centimetre-wave receivers.The output cable is fitted with an adaptor which plugs into the crystal holder of standard mixers and provides a convenient method of signal injection.The method of measurement requires no knowledge of the bandwidth, gain, or detector law of the amplifier under test.

DOI:10.1049/ji-3a-1.1946.0224

出版商:IEE    

年代:1946

数据来源: IET