Research And Implementation Of Short-Wave Transmitter Front-End Circuitry

Shortwave communication plays a very important role in both the field of people's everyday mobile communications and the field of military's radar or satellites. Nowadays, with the rapid development of shortwave's communication technology, to some extent, shortwave communication is changing every aspect of the human life. A transmitter is essential to the short-wave communication system, meanwhile, the shortwave transmit front-end circuit which is one of the shortwave transmitter, is very important. Especially in the shortwave broadband area, the transmitter has high requirements on flatness, spectral purity and stability to the shortwave transmit front-end circuit. Therefore, a high flatness, high spectral purity and high stability shortwave transmit front-end circuit can fundamentally improve the performance of shortwave communications hardware system.The paper, at first, provides an overview of shortwave communication, shortwave radio and RF power amplifier's research background, research significance, development situation and development trend. Through the above description, we leads the design of shortwave transmit front-end circuit; secondly, the paper discusses the theoretical basis of shortwave transmit front-end circuit, and it focus on the RF power amplifier and sub-octave band-pass filter to do a more in-depth theoretical analysis and discussion. Third, in the design part of the paper, the shortwave transmit front-end circuit is divided into the following sections to specific circuit design and related simulation: Power amplifier tube circuit, impedance matching circuit, segmented filter circuit and control systems etc. Finally, the paper do some physical testing and analysis of results on the power amplifier circuit, sub-octave segment band-pass filter circuit and the entire shortwave transmit front-end circuit.Due to the wide frequency domain of the design(1.6MHz~ 30MHz), the shortwave transmit circuit has high requirements on flatness, spectral purity and stability. For its requirements on high flatness, we specially introduces the amplifier linearization technique in power amplifier tube to stabilize the output of amplifier tube, then we can obtain high flatness. For the high spectral purity requirements, we design the 7-segment sub-octave band-pass filter circuit to filter the higher harmonic components and the inter-modulation components, then we can obtain better spectral purity,. At last, we ensure high stability of the entire shortwave transmit circuit by the control system which is consisted by current monitoring and over-current protection circuit, VSWR detection circuit and power detection circuit.