Bandsweep with the New Homebrew 40 meter Direct Conversion Receiver

It is inhaling nicely but some improvements are still pending. Click on the video above to see and listen to the bandsweep done on 40 this morning. 

-- The front end consists of capacitive divider input impedance matching circuit, followed by one LC circuit and an FET RF amp.  

-- The VFO is a super-simple Colpitts design by Farhan.   The two feedback capacitors do double duty in the LC tan circuit.  

-- I am using an old variable capacitor instead of the PTOs that we have been experimenting with.  

-- The mixer is singly balanced using one trifilar toroid and two diodes.  We have found out that even with these three simple devices, there is significant variation in how people connect them to VFO, RF in and audio out.  I think we have found the best way to do this:  Be sure to put the VFO on the primary of the transformer, and let this signal turn the diodes on and off. 

-- For the AF amplification, I have one FET, followed by two BJTs.  I have a small audio transformer between the speaker and the final AF amp.  There is plenty of audio. 

You may wonder why, after all the SSB superhet transceivers, I am building a simple Direct Conversion receiver.  Well, we hope to help a bunch of high school kids build one, so we need to be really familiar with how it works.  And I find that as simple as it is, there is still a lot to learn in a project like this.