Another demo of the single transistor FM receiver...

A little demo of my single transistor FM receiver. Some people didn't believe this could work so here it is again...

Closeup of the breadboard while operating:

http://users.tkk.fi/~plahteen/yep/schem2.jpg

External wiring:

http://users.tkk.fi/~plahteen/yep/wires.jpg

Audio quality sample: (they talk mostly finnish)

http://users.tkk.fi/~plahteen/yep/asample.mp3

The circuit schematic (this works as such, but is slightly simplified from what I have in the video):

http://www.niksula.cs.hut.fi/~plahteen/misc/old_projects/s1.png

Conceptual schematic of the feedback circuitry (oscillation starts in the falstad circuit simulator, I used a coupling value of 0.05 in the transformer):

http://users.tkk.fi/~plahteen/yep/feedback.png

Netlist file for falstad circuit simulator (only low frequency oscillator due to sim limits):

http://users.tkk.fi/~plahteen/yep/recv.txt

If you see the voltage across the capacitor in the simulation it should ring up to about 460mV in 140ms when you reset the simulation.

Paint drawing of the connections:

http://users.tkk.fi/~plahteen/yep/handd.png

Category:

Science & Technology

Tags:

• radio
• receiver
• FM
• single
• transistor
• rig
• simple

[vintagegarage]

Hi,

This sounds very interesting. I would think Super-regenerative Rx is simple, this is even better. However, I am puzzled as to how can you tune into different station, there are no variable caps or varactors??

[decod31]

@vintagegarage I just tune it by mechanically adjusting the inductor or by changing the bias voltage. Although that tends to also change the gain and make it oscillate or not work at all. Never the less I usually manage to find at least couple of channels with relative ease.

[devil2heart]

will transistor bc639 works for this experiment?

[decod31]

@devil2heart BC639 appears to have f_T of only 100MHz where 2N3904 has 300MHz so it might not work so well, but you can try.

[gahasitha]

can I have a circuit schematic of this?

[decod31]

@gahasitha Sure, there is a link in the description if you open it up fully (s1.png). The component values are a bit trial and error (especially the inductors), but I've listed the values I used in schem2.jpg.

Unless you are familiar with the idea I suggest you also check the description from my other video "Mystery reggen - simple(st) FM receiver?" so you have an idea how it works.

[tiputipu0052]

thanks your the best....

[decod31]

@tiputipu0052 I put a link in the description to a pic I made with paint. There are component values, but I try to avoid taking it too seriously because two coils are never the same and breadboards aren't the same either. 100 MHz is very high frequency and unintended parasitic reactances are always present. It's shouldn't be too difficult to get this working if you just follow my schematic. You need some amplification and it helps to have an adjustable voltage source (to tune it a little bit).

[decod31]

@tiputipu0052 It's a java application you can find using google. It allows you to simulate simple (usually low frequency) circuits and look at voltages and currents in time across components. My circuit needs to be assembled in such a way that it starts oscillating at the desired frequency. With the simulator you can check that the loading due to resistances and couplings is ok and oscillation occurs. It has limited resolution so I just run the sim with low frequency, but the principle is sound.

[tiputipu0052]

@decod31 please just help me out of this dilema..i have been trying for about 1.5 years now to make a simple FM radio..but all i have made is a crystal radio so far..please i want you to draw your FM receiver on a paper for me please like i did in my videos....dont draw circuit like in books, it looks very complex..just make it on paper quickly like did in my videos free hand and post it...also dont forget to mention the values of components...ill be waiting thanks a lot...