Equivalent attenuation of contours of the preselector for receivers of a short-wave wave band of der = 0 gets out. Have to be 0,0 For ensuring the demanded selectivity of a contour of the preselector and UVCh high-sound therefore dep = 0,00 is defined Further the generalized rasstroyka of the mirror channel
As the relation of the maximum frequency of the set range to minimum more than 3 – it is necessary to break all range into 2 subranges, and with uvelicheny the maximum frequency to 30,5 MHz for achievement of the demanded pass-band in 9,5 kHz.
The entrance chain has to possess resonant coefficient of transfer not less than 0,5 and possess rather sharp selectivity. The entrance chain with a capacitive coupling with antenna and inductive communication with the first UVCh cascade meets these requirements.
The program of work is constructed as follows: the first three sections consider the set characteristics of the radio receiver, structure of the reception path providing the set parameters. Further on their basis the main requirements to creation of a reception path are output.
KHz 12 / 70 dB). Its parameters are most approached to the specification. As sensitivity quite low – can be neglected that fact that a quantity of hindrances will be present nevertheless, but their level will be quite small. Suppression
In superheterodyne receivers frequency selectivity is determined by easing by mirror, neighboring and through canals of reception. In receivers with unary transformation of frequency weakening of the mirror channel provides the preselector and resonant UVCh. Resonant characteristics of the preselector and UVCh have to be such that the linear highway had a pass-band not less set (2,5 kHz.). Procedure of definition of means of ensuring of selectivity consists in the following:
There are standard schemes and calculations of a filtration of intermediate frequency. In our case it is expedient to use the ceramic filter as the simplest and convenient form. From the list provided below the most suitable is the CFK465E10 filter (kHz 0 / 3 dB,
Selectivity shows in how many time resonant coefficient of strengthening at a frequency of setup of the receiver strengthening more than a coefficient at other frequencies. For radio receivers of short-wave range selectivity is normalized on mirror, neighboring and through canals.