Question: Simple FM reciever????

[samy555]

The following is FM radio reciever circuit from:
**broken link removed**

**broken link removed**

I do not intend to implement, but Surprised by the way the two transistors T1&T2 connected.
The tuned recieved FM signal inter the collector of T2 and out of its base to feed to the audio amplifier
It is the first time in my life watching that stage audio feed from the base of the transistor
Can you help me understand the work of those two

transistors?
Thank you very much

 

[audioguru]

The base-emitter of T2 causes the supply voltage for T1 to be only 0.7V and shorts the tuned LC circuit. But the collector of T2 turns off T1.
The "FM radio" is missing most parts that are in a real radio.

 

[unclejed613]

that is NOT an fm detector, but an AM detector (a regenerative detector by the looks of it). it's using slope detection to get FM to act like AM, and will only work when tuned off-center from the carrier. the audio will also be very distorted. a real FM detector will be a discriminator circuit or a PLL, both of which are much more complex than the circuit you posted

 

[aeiou]

The base-emitter of T2 causes the supply voltage for T1 to be only 0.7V and shorts the tuned LC circuit. But the collector of T2 turns off T1.
The "FM radio" is missing most parts that are in a real radio.

Would this mean that T2 is permanently on - its only role is to bias T1 so that it is barely on?
Thus any spike coming from the tuning circuit is amplified by T1, to the point of almost shorting out T1.
This decrease in V across T1 is passed on to C2 and on to the audio amp.

C2 and R1 essentially isolate the the left and right halves of the circuit, ie tuning from the audio amplifier on the right. R1 limits the current through T1 and T2.

I tried to make the circuit, but not having an LM386 have had no luck so far getting a squeak out of the earphones (I tried to use a 2n2222 in place of the LM386.)

 

[audioguru]

The Two transistors actually have positive feedback from the base of T2 to the collector of T1. Then maybe they oscillate at the radio frequency or almost ocillate with high gain like a regen radio.

The LM386 amplifier is missing a capacitor between pin 8 and pin 1 so its voltage gain is only 20.