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 Post subject: Low Noise DC receiver idea
PostPosted: Aug Sun 01, 2021 10:27 pm 

Joined: Mar Thu 01, 2018 1:30 am
Posts: 843
Low noise mixer + low noise AF preamp with parallel 2n4401 transistors.

Add an active AF 300Hz to 2.7KHz filter with a low noise opamp and feed the audio to an AB Pushpull output stage again with a low noise opamp and negative feedback. This should be a very "quiet" receiver with its low intrinsic noise. Notice how the diodes have been replaced with 2n7000 switching mosfets in mixer stage to reduce the noise figure of this balanced mixer. They can be driven with a flip flop like 74F74 and 2F input (LO) frequency.

Use 1% metal film resistors and precision capacitors. Together with CW/DSB transmitter, it would make a very good transceiver with pleasant audio to listen to. It can also be used as a general purpose receiver to monitor 80m to 10m ham bands.

Correction: Remove 68K and 18K resistors in series and use a single 6K instead from base to Vcc+.

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