As in technical requirements on the receiver of border of subranges and their quantity are not set, we count coefficient of overlapping of all range. We choose two section block of condensers of variable capacity Tesla of Cmin=5pf and Cmax=385pf, overall dimensions of the block 25*25*25mm. We define Cd range, having set by scheme Sskh=30pf capacity, on a formula:
Nonlinearity of characteristics of intensifying devices and diodes is the reason of nonlinear distortions. The greatest nonlinear distortions are created on the detector and UNCh. The total value of nonlinear distortions is determined from expression:
If at invariable inductance of a contour overlapping of all range of the receiver with the variable condenser, and also for convenience and the bigger accuracy of installation of frequency and setup of the receiver for stations of range of short and ultra-short waves cannot be provided, the range of the receiver shares on separate subranges. The preliminary choice of number of intensifying cascades and selective contours of the receiver needs to be made on each subrange separately. Therefore predesign of the receiver needs to be begun with a choice of number of necessary subranges and definition of their borders.
As terminal cascades of amplifiers of low frequency it is possible to use both single-cycle, and duple schemes. The scheme of the output cascade is defined by purpose of the amplifier and requirements imposed to it. As at my Rvykh=0,150vt amplifier, I choose the duple cascade in the class AV mode on low-power transistors.
P=2 * (Fm max + fsopr + ∆f, where fsopr-admissible inaccuracy of interface of settings of contours which for kilometer and hectometer range is chosen equal 3÷5; fg-possible deviation of frequency of a heterodyne equal (0,5÷*0,001*fcmax;
The entrance chain of the receiver with the magnetic antenna contains two subranges in this scheme: subrange of kilometer waves ( and subrange of hectometer waves (Page. Communication of a contour of an entrance chain with the frequency converter transistor the transformer. The Frequency Converter (FC) is assembled according to the scheme with a separate heterodyne. As loading 4 links of the Social Insurance Fund of PF1P-2, communication of the Social Insurance Fund with an exit of the mixer and an entrance of UPCh inductive serve in a chain of a collector. The first UPCh cascade the second is brought together according to the aperiodic scheme, broadband, one-planimetric with partial inclusion of a contour in a collector chain. The diode detector is assembled according to the consecutive scheme with the shared burden. For automatic adjustment of strengthening the scheme ARE with a delay included in a chain of the UPCh emitter assembled according to the aperiodic scheme is used. The UNNCh cascade is assembled according to the resistive scheme with direct inclusion of loading, the UNCh cascade is executed according to the beztransformatorny scheme on single pair of complementary transistors.
In receivers with the magnetic antenna where for increase in the effective operating height of the magnetic antenna and selectivity on the mirror channel equivalent quality of contours of an entrance chain can be made rather high (about 100÷20, increase weakening of a path of a radio frequency to 3÷6, respectively reducing easing in a path of UPCh and UNCh.
From the economic point of view the designed radio receiver has the following advantages: all elements used in the receiver domestic that considerably reduces the cost of each element and the receiver in general; as in the receiver domestic radio components that in case of failure of one of them are used, search of new radio of an element will be easier from the point of view of the material and physical parties; in the receiver only the most necessary elements which are necessary for normal operation of the radio receiver are used and in the scheme is not used what excess element, i.e. the receiver is executed in optimum option that reduces its prime cost.
In most cases UNNCh cascades can be executed on low-power transistors. Thus, if the strengthened frequencies do not exceed units of kilohertzes, the choice of transistors is made in low-frequency parameters for the following reasons: