40m Direct Conversion Receiver


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.