I think this is a superregenerative circuit which oscillates locked to the input signal. I do not understand it!
The sensitivity is high and was used when a valve (tube) could cost a weeks wages.
Oh yes it is! Look up Wikipedia superregenerative receiver.
The circuit oscillates at two completely different frequencies and detects FM by slope detection.
The output is a form of pulse width modulation. Like I said, I do not understand it.
This must be one of the most complcated circuits made from the fewest components.
I have built that circuit with wires of copper to connect the components using BF255 and DL2032 as power supply, but I can't listen to anything when I connect the headphone output to computer speakers, what could be wrong ?
C is a 2 to 20 pf variable capacitor and L is made up of 4-5 quirks of copper with an internal diameter of 5mm.
They are supposed to tune in the 88-108 Mhz range
In that case, I have nothing more to add. I have no idea how that circuit is supposed to work! I'm not saying that it won't, of course; simply that I personally don't know how it would.
As I said in #6, the BF255 is not as agile as the BF199 by a factor of 2 0r 3.
You could try tuning the circuit to a lower frequency to see if it will work or get super fast transistors.
The antenna loading will be critical. Circuits such as this which need to be set up optimally are not the best for newcomers. Have you read up on superregenerative receivers and understand them?
A two transistor bistable circuit looks to have each transistor in saturated mode but they always work. This circuit is similar but I think it should run with two oscillating frequencies. The first controlled by L and C and the second one controlling squegging using the output capacitor as the time setting.
Thinking about it, the output load may be critical. Apparently simple circuits doing lots of things can be difficult to analyse and optimise. Better to use several stages each doing its own thing.
Super regen receivers can work and are used in car fobs but will be made to a standard layout.