This reflex radio project was inspired by Robert Bazian 's design. His reflex radio is the `darndest` thing I have seen and his spectacular results inspired me to come up with my own version! These designs are similar to two-transistor circuits used in some ancient Japanese `Boys Radios` except that the inter-stage transformer directly drives the speaker. The antenna coil is just 20 turns wrapped around four insulated posts as seen in the photos and shown in the diagram below. I used nylon posts but ordinary bolts covered with tubing would work fine. The dimensions are not particularly critical; those shown happen to fit inside the case I chose.
The signal is coupled to the receiver by two turns wrapped right on top of the 20 turns. This winding technique is simple but it has the drawback of having more than desirable capacitance and that limits the tuning range with a standard 365 pF variable ca