DOI:10.1049/ree.1978.0060

出版商:IERE    

年代:1978

数据来源: IET

摘要:

The paper forms a continuation of earlier work which established the need and feasibility of introducing a dedicated traffic information service, using a single medium frequency in time division multiplex, to serve the United Kingdom. A study of the effectiveness of a muting system in the receiver relying entirely on signal strength for restricting the coverage of each transmitter to local areas, revealed that variations of signal with vehicle movement gave spasmodic mute operation. This deficiency would have been particularly prevalent in fringe areas, causing only parts of messages to be heard, leading to possible confusion and ambiguity when interpreting the information. A field trial was therefore set up to pursue the development of a system still based on the original concept, but which would overcome the problem of message fragmentation when motoring in an urban environment or leaving a service area. A description is given of the various listening modes offered by a prototype receiver, designed to respond to tone codes in transmission. An analysis of results, based on the probability of communicating with a moving vehicle, shows that the problem of message interruption due to local field-strength variations has been overcome.This work represents an improvement stage in the development of the system and, although alternative muting arrangements have been developed since the work described was completed, the use of ‘open’ and ‘close’ codes has been retained as a valuable part of the system

DOI:10.1049/ree.1978.0061

出版商:IERE    

年代:1978

数据来源: IET

摘要:

A new method is proposed with which it is possible to find a delta-modulated signal of the half sum of two analogue signals through a direct operation on their delta-modulated form. With a direct operation it is also possible to form a delta-modulated signal of the product of an analogue signal by a constant. The resulting modulated signal includes an error which is generally considered negligible. The hardware implementation of the method is both, simple and modular employing only conventional full adders and D-flip-flops. This leads to the possibility of realization of digital filters with straight delta-modulated input and output signals which are not intermediately transformed. Multiplexing for changing coefficients is also possible.

DOI:10.1049/ree.1978.0062

出版商:IERE    

年代:1978

数据来源: IET

摘要:

A broadband high-gain dielectric-coated horn antenna operating in two orthogonal TE10+TE/TM12and TE01+ TE/TM21mode sets to generate circularly polarized elliptical shaped beam is described. The aperture E-field distribution can be tapered by virtue of the higher order TE/TM modes to cause the E-plane far-field beamwidth approximately equal to H-plane beamwidth of the other orthogonal set of modes, resulting in low off-axis polarization axial ratio. Because of the tapered aperture field distribution, the radiation patterns will also have low sidelobe levels. The radiation characteristics together with the on-axis gain of the antenna are derived from an electric vector potential on the basis of the vector diffraction formula. Analytical results are established in good agreement with experimental results on radiation pattern and gain measurements. This antenna which can be used as a communication satellite antenna to illuminate efficiently an elliptical zone on the earth surface will offer better directivity, high on-axis gain, low sidelobe levels and low cost.

DOI:10.1049/ree.1978.0063

出版商:IERE    

年代:1978

数据来源: IET

DOI:10.1049/ree.1978.0065

出版商:IERE    

年代:1978

数据来源: IET