Increase the sensitivity of the receiver. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / radio reception
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VHF radio "MANBO" has many advantages. However, due to the absence of resonant circuits in the input circuits and the low efficiency of the antenna (headphone wire is used), the receiver has insufficient sensitivity, which limits its use at a great distance from radio stations.
It is not difficult to eliminate this drawback by supplying the receiver with an additional radio frequency amplifier (URCH), assembled according to the diagram shown in the figure. It's best to do it on a breadboard first. In this case, it will be easier, in particular, to select the resistor R2 according to the maximum gain. The consumed current must be within 1,5 ... 2 mA.
An additional URF is mounted in the receiver by surface mounting from the side of the printed conductors. Since the distance between the cover and the board is small, the transistors were carefully sawn to a thickness of 3 mm.
It practically does not require the adjustment of the URF, the sensitivity is comparable to a full-size receiver with a whip antenna. The current consumption increases slightly. If the receiver is excited at high volume, it is necessary to connect a 6800 pF capacitor between the input of the variable resistor of the volume control and the common wire.
Since the additional amplifier is connected to the receiver only through the power circuits and the antenna input, the proposed modification can be carried out in any similar radio receiver.
From the editor. The very delicate and unpleasant job of filing transistors, proposed by the author, can be eliminated if transistors with very thin cases are used. They are available among microwave devices. These are, for example, transistors of the KT371AM, KT372 KT382.KT391A-2 series, etc.
Author: G. Voronin, Nizhnyaya Tura, Sverdlovsk region; Publication: cxem.net
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