Linear Technology Research On Preselected Components Of Short-wave Receiver

Short-wave communication still occupies an irreplaceable position in the field of radio communication, and is widely used in military field, diplomatic, aviation, maritime, meteorology, government departments and so on. That’s due to its strong anti-destroying ability, good flexibility, short construction period, strong recovery capability after being damaged.Increasingly tense spectrum resources, increasingly complex electromagnetic environment, wireless radio’s increasing, multiplied increasing channel transmission power,all these make the mutual interference between channel increasingly serious.Due to these factors, linear of shortwave receiver has to be higher.Improving the performance of the receiver to improve utilization of the shortwave spectrum resource and to avoid false signal response is an effective way. Preselected components is located in the forefront of shortwave receiver, realizing the function of selecting frequency band and inhibiting the interference of out-of-band signal. Preselected components must has small noise coefficient,and it needs certain gain to distinguish weakly useful signals.Besides,the module also needs to have high linear and selectivity to effectively filter useless signals like harmonic and intermodulation interference to minimize the effects of nonlinear distortion signal to the receiver. In a word, the high linearity and low noise of preselected components play an important role on the linearity, sensitivity and resolution of the receiver.This article mainly studied on how to improved the linearity of preselected components from two aspects, one is the linearity of RF filters, second is the linearity of the low noise amplifier. RF filter has two Implementation scheme, LC filters based on elliptic function and short-wave electrically tuned filter. There are two kinds of electrically tuned filter, the first kind is based on varactor 1W407 of TWPEC company, the second is based on the PIN switch tube SMP1371-087 LF of SKYWORKS company. This paper also studied two kinds of Circuit structure about high linear low noise amplifier, one is using NPN transistors MRF555 which is based on negative feedback circuit structure, the other is using amplifier LT5514 and HMC478MP86 based on feed-forward circuit structure.This paper finally developed such a preselected components with both high linearity and low noise figure: the physical size is 120 × 75 × 14 mm3, the gain is between 6.7-8.7 dB and the noise figure is between 5.9-7.9 dB at low noise figure mode; the loss is between 2.9- 4.8 dB and the noise figure is between 3.2-5.4 dB at normal mode, the OIP2 is around about 76 dBm, OIP3 is about 41 dBm.