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The low-pass filter with a "Notch" suggested Paul Carr (N4PC). Board made according to scheme I. Podgorny, EW1MM. The low-pass filter has the characteristic close to the characteristic of the quartz filter, which completely eliminates the disadvantages inherent in conventional passive RC-filters. The filter allows you to select Telegraph (CW) and other narrow-band signals and to suppress tonal noise (bearing) and adjacent on the frequency of the CW station. Included CW/NOTCH filter on the LF output path of the transceiver or receiver. Control frequency selection and suppression is a variable resistor. The 12V supply.
KIT: documentation, printed circuit Board (drilled with a mask Board size 120x80 mm), all the electronic components needed for installation.