where HDA - the operating antenna height. For usually used HDA ferrite antennas in SV range-. 15 mm. The operating height of the shtyrevy antenna is approximately equal to a half of its geometrical length.
In the UNCh cascade I took a chip of IMS K174UN4B which represents the amplifier of power of low frequency with a nominal output power of 1,5 W on loading 4 Ohms. Just such power is set to me for the receiver. The chip consists of the entrance cascade, the coordinating cascade, the cascade of strengthening of tension and the output cascade.
URCh cascades carry out, as a rule, on discrete transistors. In URCh find application both bipolar (BT), and field (PT) transistors. Bipolar transistors possess bigger conductivity of direct transfer (y2 and work at the small consumed current (. 2 m.
Number of electoral systems of the preselector in each range define proceeding from the set weakening of the mirror channel (σ) which has to be provided at the maximum frequency of range (f0 = to fMAKC), i.e. in "the worst point".
Having made the decision on number of oscillatory contours of the preselector and value of their good quality, we check implementation of the requirement of TZ for weakening of a hindrance with a frequency, equal intermediate (PCh), at a range frequency (f, the next to FPCh:
Each UPCh block is equipped with strip filters. Thanks to sharp distinction of resonant frequencies of filters each of them resounds only on that intermediate frequency on which it is adjusted, thus other filter does not influence operation of cascades.
The number of transformations of frequency in the receiver and value of intermediate frequency of FPCh gets out, first of all, of conditions of providing requirements for easing mirror (σ) and next (σ) channels, and also taking into account other factors. In the designed receivers these requirements usually can be provided when using one transformation of frequency and standard value of FPCh. In the household equipment the following values of FPCh are accepted:
At MPRES = 2 in the preselector it is expedient to use the one-planimetric input device and resonant URCh which besides additional weakening of hindrances provides decrease in coefficient of noise of the receiver.
One of features of modern transistor receivers is broad application in them the pyezokeramichesky filters of the concentrated selection (FCS). They provide sharp selectivity on the neighboring canal, have the small sizes, small weight and constancy of frequency of control. For normal work of the Social Insurance Fund it is necessary to coordinate with an exit of PCh and an entrance of UPCh.
The output unregulated cascade has an asymmetrical exit 8 to which resonant loading is connected. At connection of loading it is necessary to watch, that a conclusion 8 (the collector of the transistor V on a direct current was connected to the case.
The dynamic head of the designed receiver gets out of a condition of ensuring rated output power and the set range of the reproduced frequencies. For UZCh IMS of a domestic production should choose: K174UN7, K174UN8, K174UN9, K174UN15, KF174UN17, etc. or similar schemes of production of foreign firms. The chosen IMS has to provide rated output power not below provided in TZ at minimum possible current of rest. IMS which are not demanding a large number of additional elements are preferable.
Antenna systems of mediumwave range can be carried out rather compactly for placement within the city which does not have high-rise ferroconcrete building. But nevertheless it is desirable to take out the radio centers of this range out of limits of city line. In the mediumwave range it is not required uses of so high capacities of radio transmitters, as in long-wave. At competently designed and constructed antenna systems there is enough power of 5 - 15 kilowatts for ensuring profitable high-quality broadcasting on the big industrial region or on some nearby cities, more than one million inhabitants numbering in total. At smaller number of the population in a zone of a broadcasting of mediumwave radio station it is difficult to speak about its profitability. After all charges of the radio centers of this range are rather high.