Simple FM Tuner Transistor Alternative

Thread Starter

rohanroy93

Joined Nov 2, 2023
2
Hi, I am trying to make a simple fm tuner as per the circuit diagram attached. Problem is, BF494 transistors are not readily available in my locality. Hence, I have used 2N3904 transistors as an alternative choice but the tuner doesn't seems to work. Can this transistor be used in this circuit?
 

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Audioguru again

Joined Oct 21, 2019
6,610
The original circuit is a latch with DC positive feedback, not a radio.
If the latch transistors operated like a regen amplifier then the circuit would detect AM pops and clicks interference but will receive an FM station if it is tuned to the side of a station and detect the FM by "slope demodulation".

It would probably pickup a few FM stations at the same time because it has only one tuned LC circuit.
It would sound very muffled like an AM radio because it is missing the pre-emphasis that all FM radios have.

Correctionl It is the FM radio station transmitter that has pre-emphasis (treble boost). Then all FM radios have ds-emphasis Treble reduction. Nit this simple radio does not has a de-emphasis filter so it will sound shrill and harsh.
 

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Thread Starter

rohanroy93

Joined Nov 2, 2023
2
That would be a pretty poor detector.

A 2N3904 is an excellent choice for this circuit, indeed I have used a 2N3904 in a circuit like the one below.

This (below) would be much better. It is a regenerative detector.
View attachment 306556
http://www.vk2zay.net/article/195
Hi Dick, thank you so much for sharing this circuit with me. I will definitely follow your suggestion and build this one. I have one doubt that I'd like to clarify, could you please tell me the turns and uH rating of the 1st inductor?
 

MisterBill2

Joined Jan 23, 2018
17,814
The circuit looks a lot like the one-tube regenerative receiver publishes about 1962. It will be able to receive FM but it will also transmit and this will not be good. Not a good receiver but not everybody can tell the difference.
 
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