So last year this time, I taught a couple of classes on how to make a morse code radio transmitter. I am bring this class back, and plan to teach it about once per month. There are still four seats available for the September class
https://calendar.dallasmakerspace.org/events/view/3488
At that time, I also started working on a design for a matching receiver, but ended up abandoning it because I thought it would be too much to get built in a single class.
Well a year of contemplation later, and a bit of nudging from @zmetzing and I have a new approach. The idea is to break the receiver into individual modules, and take each module as a single class. I believe this will be a more manageable approach. If each module class is offered regularly, then people can come to the classes they can and build their radio as they can.
A direct conversion receiver only has a few needed modules. Basically four (the RF Preamplifier is optional).
So yesterday, I started at the right side of the block diagram (that way you can use what you have built to test the new module) and created an audio amplifier module. Basically a NPN preamplifer and an LM386 amplifier. I am packaging these modules in custom 3D printer holders to allow for swapping them into and out of various radio designs.
Today, I finished building and testing the second module; a product detector built with a dual gate mosfet arrangment of two J310 JFETs. I am using a signal generator to simulate both the RF input and the Local Oscillator. The product detector takes two signal frequencies as input and produces the sum of those frequencies and the difference of those frequencies at the output. The local oscillator is tuned to be within a kilohertz or so of the RF frequency and the difference is in the audio range (that kilohertz or so), which is then presented to the audio amplifier (along with the sum which is too high a frequency for you to hear). Tomorrow I plan to create the band pass filter for the 80M band to match the receiver with the Mighty Mite transmitter.
