Telegraph filter to the receiver. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Telegraph filter to the receiver. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Knots of amateur radio equipment. Filters and matching devices

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To narrow the bandwidth of the IF path when receiving telegraph signals, the radio amateur W. Doty (WA4DID) suggests using a filter, the schematic diagram of which is shown in the figure. This filter can be made in the form of an attachment connected to the receiver with short (up to 50 cm) shielded wires, or mounted directly on the receiver's chassis.

Terminals The input is connected to the receiver mixer anode through a 1000 pF capacitor; the signal from the Output must be fed to the grid of the first IF amplifier. The supply voltage can be obtained from a separate battery or from the power source of the receiver (through a resistor divider).

telegraph filter to receiver

The frequency of the L1C1 circuit and quartz resonators Kv1, Kv2 must be equal to the intermediate frequency of the receiver. With an exact match of the frequencies of quartz, due to their high quality factor, self-excitation of the filter is possible, therefore it is more expedient to choose frequencies with a spacing of about 100 Hz.

In the transparency band, the filter has much lower attenuation compared to the EMF.

Setting up the filter comes down to setting up the L1C5 circuit and selecting the capacitance of the neutralizing capacitors C3C4.

Instead of 2N706 transistors, KT315 transistors can be used in this design.

Author: W. Doty (WA4DID); Publication: N. Bolshakov, rf.atnn.ru

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