Mystery reggen - simple(st) FM receiver?

[doctormcgoveran]

neat going on the reciever, decod31 it is great to see it work, don't let every body who shops at walmart and bought a better one than you built and has to run you in the ground bother you.

[rockangel1967]

bla bla...you uys should see my valve tube FM radio i have built :-)

[dmctactic]

Idiot, can you tune to another station with this smart device that you have there? You can only connect to one station.

[decod31]

@dmctactic Of course I can, you just need to be good at what you do. Tuning knobs are for mortals. ;-D

[dmctactic]

@decod31 You probably want to pretend to be an expert or something which you aren't. Your "genius" FM receiver is nothing but a transistor with a base connected to a capacitor and a wire to the ground. you only get a signal because you live close to the transmitting tower; so there is no way you can tune another station with your genius circuit.

[decod31]

@dmctactic Give me break, where's your sense of humor? This is more or less the standard regenerative receiver circuit known for ages. Tuning it is simply done by deforming the coil and/or adding some capacitance to the tank circuit. I can easily tune to 3 stations where I live. Besides, it wasn't even the point of the circuit to make a fully usable receiver, just to demonstrate something simple. I never claimed to be expert and couldn't care less, although I do hold M.Sc. of relevant field.

[EIectroMania]

@decod31 holy shit you do have a Masters degree? hey that's awesome, it inspires me to study hard !!! :D i wanna get my BS in EE as soon as possible yay! :D

[theemusic92]

@dmctactic Wow dude chill the fuck out.

[ChiIdKiIIer]

@dmctactic i think he changes the resistors everytime he wants to change the radio station hehe until he gets to his favorite station :D

[ChiIdKiIIer]

@dmctactic change the stupid resistance and viola!

[hecanet]

great work...

I see you have about 3 resistors and a capacitor at one end of the breadboard...what are the values and how did you connect them - in series/parallel and why?

are those the 10k you have in the schematic and why 3 of them?

[decod31]

@hecanet Schematically there is only 1 resistor. Nothing more really than the original schematic I drew. In this video I think I just had 2 resistors in series with the voltage supply to make the 10k or maybe 20k. The 3rd one is not doing anything, both of its legs are just connected to ground and used for connecting the external ground wires. The extra capacitor is equally doing nothing.

[hecanet]

@decod31 Thanks for the quick response.

Did you try using electrolytic cap as the output cap? I am just curios. I guess my question would be 'how did you determine the values of the caps you used?'

Lastly, the 2 coils used, which of them is connected to the base and which is connector to the collector and the resistor - the loop/jumper-like wire or the 3-turn wire? It wasn't very obvious from the video nor the schematics

Thanks for all the tips. I really appreciate it all.

[decod31]

@hecanet Didn't try electrolytic, but it should work as AC-block if the polarity is right. The cap isn't critical if it is large enough. The shorter coil is connected to the base, but values are guess work as the environment is not well controlled. In principle the tank coil inductance can be calculated from the frequency and cap. Simulating the circuit as an amplifier will tell you if it's going to work, you just need to adjust the feedback etc. to get a proper gain and bandwidth.

[hecanet]

@decod31 Thanks....I will try this at home....Just ordered GOOIT GY560 portable FREQUENCY COUNTER from ebay for more fun....$24.00 for greater RF fun...ha ha ha ha

Thanks for all the tips...keep in touch...most of my youtube videos are under hecanet.

[hecanet]

@decod31 I made this FM receiver last night. A little modification was introduced though... a small trimmer was added in parallel with the tank coil and the 10pf was flipped around to connect between collector and emitter (I adopted the schematic I used for my fm transmitter) and it works very great. Was able to tune in to a couple of stations - 97.3 etc.

Thanks for the tips...I will make and upload my video later.

[decod31]

@hecanet Mean to say DC-block of course about the electrolytic cap...

[ThePrudhviram]

can you give me the circuit diagram plz

[decod31]

@ThePrudhviram ...in the description.

[sunres7]

whats that yellow wire for?

[decod31]

@sunres7 It's the output wire for audio. Coupled through a capacitor to block DC and connected to the input of the powered speakers.

[HACKERS41]

CAN SOME ONE HELP ME PLZ. THE IS TWO GROUND HOW DO I USE THEM PLZ.

[tiputipu0052]

for AM radio receiver, i want to use 2 transistors as darlington, and then i use amplifier to drive speaker....i want to ask that...when i use simple 1 npn transistor, i use 100k ohms resistor to bias with collector-base......what bias resistor should i use if im using 2 transistor as darlington??? , if i use 3 transistors as darlington??? if i use 4 , if i use 5???

[decod31]

@tiputipu0052 You half the resistor. Darlington pair doesn't help

with this circuit much, but you can try. Audio volume is a tradeoff between gain, bandwidth and nonlinearity. With additional stages this could be improved, but to get high gain and good mixing in a single transistor circuit is difficult no matter what the hfe. Simplest improvement would be to tune it to operate just as a bandpass filter and an amplifier (which it does relatively well) and use a biased diode for enhanced mixing.

[tajiknomi]

hay....m the beginner of this field..i have just baise the transistor as a swtich....it works.....but i wanna know about it that when we disconnect the base current in NPN transistor...the LED tend to OFF....it means that a resistance b/w Collector and emitter is higher....my question is that ...." WHY WE USE TRANSITOR AS A SWITCH...?????? WE CAN CONSTRUCT THE SAME CIRCUIT....WITHOUT TRANSITOR..AND ALL I NEED TO OFF THE CIRCUIT ..I WILL CONNECT A KEY IN CIRCUIT....!!!

[hecanet]

@tajiknomi we need transistor as a switch because sometimes we want to turn on/off the switch by other means...for instance, when certain condition is met, a signal line could turn from high to low or low to high and we want the switch turned on/off to start another activity automatically.

For instance, if you use a light/sound detector, when the light/sound is on/off you want the switch to flip accordingly and you want it automatically - that is why we use transistor as switches.

[855h0le]

Usually this is for a.m. but the leads (Coils) are much shorter though in YOUR case. SO it is possible its FM. I know a bit more about the RF thing than most. (I read your description) I used to use drinking straws wrapped with copper etc. Have you ever used the Leads behind the Head of Cassette deck? Its a Broadband Receiver and a very sensitive audio amplifier.

[decod31]

@855h0le I haven't used a cassette deck for this, but mixer mic input work quite well. Gives a nice quality and enough gain. I'm sure about FM. Mainly because I have a signal generator which can input pure FM at 100 MHz and I also have a spectrum analyzer and frequency counter which I can use to check the frequency of oscillation when the circuit is oscillating.

[855h0le]

@decod31 Just Remember one thing- Just cause your in the FM Band, doesnt mean your Transmitting FM. When you looked at the screen- did you seen if its Transmitting FM? (im a idiot) I had a Spectrum Analyzer. I traded it in for a Shotgun when I was 20.. It was worth $6000 at the time!! Grrrr What Make and Model is yours and how much you paid? I paid $150 for mine at Pawn Shop.

[decod31]

@855h0le I have a cheap chinese Atten 1GHz, I got it from ebay. I think I paid $400. Well, the circuit is a receiver and it's not really transmitting FM, just continuous wave, the spectral purity is awful, but the generator which is generating the signal is FM or maybe phase modulation based on sidebands. Sounds ok on a regular FM radio and sounds pretty much the same on my receiver circuit.

[sandraparker100]

i have tried this circuit but..it requires more power for coupling..as the coils are small so need more energy for couple ...please tell what if i want to use a 1.5V battery...can you add more transistors how....

[solidsnake19902342]

where is the second coil???

[decod31]

@solidsnake19902342 There are two open loops in the circuit. They are the coils. The coil with several turns on the right is part of the actual resonant circuit and the single loop coil on the left is the feedback coil. Can't go much simpler than that. 100 MHz is VHF so everything couples to everything really easily and often even too much so.

[Pianoman0488]

Without a schematic, it's hard to tell. Are you sure this isn't AM you're picking up?

[decod31]

@Pianoman0488 You didn't read the description because the schematic is there. It appears that only 50% of people read the description before commenting. I've checked the reception with a signal generator operating in the 100 MHz range with FM modulation and it picks the signal up fine.

[Pianoman0488]

You're right. I'm not familiar with Youtube's new layout and completely missed it.

Although, now that I have read it, cool circuit!

Putting the 'ol trig. product-to-sum identities to work!

[tiputipu0052]

you are biasing the collector with base and i have tried this million times but nothing happens...please do it step by step on bread board....otherwise its for no use because you havent showed the components completely.......

[decod31]

@tiputipu0052 I made quick video about it... Not step by step, but there are links to closeup images about the stuff while operating and all the component values are listed. It helps to have an adjustable voltage source while tuning it. Even if it doesn't work at some voltage you usually get it working with another.

The name of the video is "Another demo of the single transistor FM receiver... "

watch?v=jZ-iUHyKo3g

[tiputipu0051]

this is not a 293906 transistor...you are just makeing people fool...2n3906 doesnot amplify upto that level...thats why you are hiding your video...

[decod31]

@tiputipu0051 What the hell are you talking about... It's 2N3904 as said and it works just fine they way it is shown in the video. Other people have made it work as well. The speakers are active with built in amplifier which should be obvious from the video, but nothing out of the ordinary. And what do you mean by hiding? Nothing is hidden.

[darknidevle89]

hehe this is cool not bad

[gonioelect]

can i use bc548/148

[decod31]

Should be ok. Any small signal transistor with some gain at 100MHz should work. Datasheets will tell. Some parameters might chance the optimal values, but the circuit isn't too hifi anyway.

[wallaaaah]

How did you make the coils? Did you just try to make bigger ones or adjust them until it worked? and is that black thing sticking up an antenna of some sort? just wondering because it says that no antenna is required in the information.

[decod31]

Just trial and error. The black thing is supposed to be an antenna, but after this video I tried without it and it worked just as well.

Sometimes I use a frequency counter to get the oscillations tuned to approximately correct frequency, but it's not that necessary.

[Faztlan]

Now to amplify the signal from an FM transmitter.

[qseru82]

this is very simple!

[cobrachoppergirl]

lol wow. can you listen to the output with like crystal radio type earbuds?

[decod31]

Possibly, I didn't try, the output without an amp is pretty weak, but maybe it's still strong enough to be heard with those crystal earbuds.

[Flapjackbatter]

Neat :) This I must build some day. :)

[gonioelect]

hi i cant open circuit diagram page can U send me circuit diagram please!

[decod31]

There was an unfortunate loss of files when I updated my ISP. However I have updated the links for this video now. They should work.

[decod31]

I changed my ISP, not updated. ;-)

[HIDDENTECH2]

hi nice work... CAN I ADD a bigger coil and a diode and try to make a powered crystal radio ???? im looking for some way to power a crystal radio so I can use it without a ground connection.

[mumish13]

use a preamp to ampliify the af sounds! take a view on google a condenser mike preamp!

[Ajikshan]

is it really FM or AM??

[decod31]

It can detect both. The frequency range is determined by the resonant circuit and can be anything within reason. I have verified with a signal generator that it does detect 100MHz FM signals. However the demodulation is more efficient with AM than FM.

Mostly it's just an RF amplifier which also happens to demodulate the signal to some extent due to transistor nonlinearity.

[decod31]

I've heard that it can also detect SSB when feedback is properly adjusted (so that the device oscillates and creates the missing carrier), but I have not verified this.

The circuit can also be viewed as a negative resistance amplifier where adjusting the feedback will determine the gain and if very high it will just make it an oscillator.

[Abdelkarimist]

wooooooow that's exactly what i 've been lookin' for ..... can i get the circuit diagram of this device..including the components plus their values ?....pleeeeeeease (decod31).

[decod31]

Schematic and values are listed in the description along with some explanation although values are only in the general direction of what might work. The output signal should also be amplified as it is quite weak.

[Abdelkarimist]

hi i 'm sorry to say but i accidentally missed the details u sent ..can u resend me the circuit diagram of the simple fm RX plus the component values? i 'll appreciate it so much.

[decod31]

_Youtube description_ has a link to the schematic (push "more info") and read the description, it will also give you a rough idea of how this is supposed to work.

Tuning capacitor is 10pF, transistor is 2N3904, bias resistor is 10k, output capacitor 100nF. Inductors are trial and error so just what you see in the video. None of the values are exact as your breadboard is a major part of the capacitance at these frequencies.

[al93cnc]

this song is so nostalgic, reminds me of the good old 90's

[pablokoruza]

It isn't a mystery, this effect appears in all the amplifiers. Try to plug a long wire in an amplifier input and turn on the volume... touching the wire you'll fill better the effect cause your body will be the antenna. YOU'LL HEAR THE RADIO. Now, he's doing the same, 'cause the transistor is an amplifier and he's also amplifying the transistor output with another amplifier.

The capacitor works with the piece of wire doing a defined resonance helping the radio reception.

[bradmann85]

lol. spice girls on the radio. i was 10 when they were a big hit.

[zezimashock]

why no tuning cap?

and if I where you I would make a little big antenna :)

[decod31]

No particular reason... Just tried something super minimalistic ;-)

Antenna didn't actually appear to be a problem as the signal was quite ok. Tuning was more problematic as expected though.

[zezimashock]

explaime me please :P

i like to learn.

[wow1022]

i hooked the easier one to make up and got some spanish AM station lol i tried adjusting the coil but it didn't change anything

[mrjimbopalmer]

Neat! I got it to work.

[decod31]

Great! Looks like you made a video too.

[mrjimbopalmer]

Yeah. I got it to tune with a variable capacitor as well. Connecting it between the collector and ground will work. It is remarkable to me that this circuit works.

[tutu077]

thank you

[tutu077]

please. i want circuit

[decod31]

See the description. It has links.

[mumish13]

Can i use a 2N2222 for this purpose?

[decod31]

Yes. It should work.

[tchomemade]

Salut! Comment ça fonctionne? Schéma?

[decod31]

It's all in the description (try "More info" or maybe "Plus d'infos" ;-). Good thing we have babelfish...

[tchomemade]

Merci..

[decod31]

Whoops, I think I deleted someones comment accidentally. The question was about what transistor to use and how to determine the measures for the coils.

I used 2N3904 NPN transistor, but it shouldn't matter too much which to use as long as it gives enough amplification at the frequencies in question.

The dimensions for the coils depend so much on the parasitic capacitances that trial and error method probably is the best way to go. Just try size similar to what you see here.

[decod31]

The size of the coil closest to the capacitor is determined by the capacitor value (I used 10p) which together form a tuned circuit that determines the frequency. Although that frequency is also influenced by parasitic capacitances.

The leftmost coil is for feedback an isn't as critical. Notice that its polarity is reversed.

[mountainch]

nice. Can you show me the circuit configuration?thx

[decod31]

I put a link in the description. You can almost see the configuration from the video too. It depends heavily on the parasitic capacitances and inductances so values are trial and error. The first circuit might not oscillate so use the second if you have problems.

[mountainch]

which point of the circuit should i attach the antenna on the circuit?thx

[decod31]

You can attach it at the base of the leftmost transistor however you don't really need one especially considering the difficulty of really tuning this thing.

[mountainch]

where should i attach the antenna?thx

[Kilohercas]

Nice done, but it's really FM band ??? or AM ??

[decod31]

FM band is usually defined as being from 87.5-108 MHz and this was definitely receiving that range (and ignoring the traditional AM signal in the medium wave band) so in that sense it is FM.

However this type of receiver is also sensitive to AM modulation and cannot benefit from the capture effect as typical FM radios without some sort of gain control circuit.

The good thing is that it can be used to listen to airband 108-137 MHz which uses AM.