The above picture is a block diagram of the receiver section of the 40m direct conversion transceiver i have been building for some time. There is nothing ground breaking in the design, it is fairly typical fair for a direct conversion receiver, taking elements from many different designs and bringing them all together into, hopefully a cohesive whole.
This is all part of the “5 x 7” CW Transceiver project i started to outline here: “5 x 7 Tranceiver”
A few things have changed with this, especially so in the front end where the original circuit as been totally replaced with something a lot more simple.
Band Pass Filter: The band pass filter is a 7th order Chebyshev 50ohm in and out with 0.1db ripple.
Pre Amp / Mixer: The pre amp and mixer both use Mini Circuit devices, MAR-6 MMIC for the pre amp and either TUF-1 or ADE-1 for the diode ring mixer.
Local Oscillator: The LO is an Arduino microprocessor controlled AD9850 DDS VFO.
Buffer Amp: Is a simple common emitter, common collector, gain buffer stage to take the LO amplitude to 10dbm.
Audio Diplexer: This diplexer, out of EMRFD starts to narrow up the bandpass and increase gain of the AF.
Active AF Filter: An active 500hz wide CW filter, 8th order design using a Quad OP Amp.
Audio Amp: Finally, the audio amp using an op amp pre amp and LM386 driver.
The only things left to actually build are the 3 audio stages and then test it all together and see if or how it well it works. Failure is always an option as they say.