An Accidental radio?

[audioguru]

Sorry. I see what might be a transformer on your schematic. If its primary is 10k then the output of the amplifier is only 50 micro-watts max.

You should be using an LM386 audio amplifier IC. With a 9V supply it can provide about 500mW into an 8 ohm speaker, and draw very low current when not playing loudly. 10,000 times more power than your amp.
If you want to make a simple 3-transistor amp then this circuit is fairly good:

 

[Hayato]

Yes you are TOTALLY wrong!

An inductor and a capacitor can be connected either in series or in parallel to form a tuned circuit.
Suitably connected to an amplifier with feedback, they can form part of an oscillator.


If a coil and capacitor have an AC signal applied to them, at some frequency, where Xl = Xc, the will resonate. They will not increase the signal power, (signal voltage or signal current will be increased, but NOT power).

JimB

Totally is a very strong word.

Yes, I know that they can be connected in parallel or series.
And I'm sorry, I did type "power", but without the intention to mean power, the word "strengh" did not come to me by the time I was typing.

But you have to agree with me in one thing: when the tuned circuit resonates, it is oscillating.

 

[audioguru]

It does not oscillate. It resonates.

 

[Hero999]

Same thing.

 

[Hayato]

It does not oscillate. It resonates.

That is the point!
To resonate we need both systems oscillating with the same frequency.

https://en.wikipedia.org/wiki/Resonance

 

[JimB]

But you have to agree with me in one thing: when the tuned circuit resonates, it is oscillating.

I think that there is a problem here with the use and meaning of the word "oscillate".

I dont know of any electrical/electronic person who would use the word "oscillates" to describe a tuned circuit which was being stimulated by an AC signal.
A circuit is usually described as "oscillating" when it is generating the AC signal.

While I have been writing these few words, I realise that there are many "ifs and buts" to this description.
However Hayato, how you were using the word "oscillates" was wrong.
I think you had the correct understanding, but using the wrong words.

JimB

 

[Hayato]

I think that there is a problem here with the use and meaning of the word "oscillate".

I dont know of any electrical/electronic person who would use the word "oscillates" to describe a tuned circuit which was being stimulated by an AC signal.
A circuit is usually described as "oscillating" when it is generating the AC signal.

While I have been writing these few words, I realise that there are many "ifs and buts" to this description.
However Hayato, how you were using the word "oscillates" was wrong.
I think you had the correct understanding, but using the wrong words.

JimB

Ok, now we've reached the ideas consensus.

 

[Roff]

I think that there is a problem here with the use and meaning of the word "oscillate".

I dont know of any electrical/electronic person who would use the word "oscillates" to describe a tuned circuit which was being stimulated by an AC signal.
A circuit is usually described as "oscillating" when it is generating the AC signal.

While I have been writing these few words, I realise that there are many "ifs and buts" to this description.
However Hayato, how you were using the word "oscillates" was wrong.
I think you had the correct understanding, but using the wrong words.

JimB

I think this is a language or semantics difference. When a tank is excited, the current does "slosh" back and forth, finally dying out. We generally call it damped oscillation (as many of you know). In the strictest sense of the word, oscillation doesn't have to be sustained, although I agree with Jim that we normally think of oscillation in that sense.

 

[catcat]

Sorry. I see what might be a transformer on your schematic. If its primary is 10k then the output of the amplifier is only 50 micro-watts max.

You should be using an LM386 audio amplifier IC. With a 9V supply it can provide about 500mW into an 8 ohm speaker, and draw very low current when not playing loudly. 10,000 times more power than your amp.
If you want to make a simple 3-transistor amp then this circuit is fairly good:

The speakers I use arent strong and the y would be gone in a puff of smoke without it; I use them instead of resistors since they dont sacrafice volume.

 

[Hero999]

I think this is a language or semantics difference. When a tank is excited, the current does "slosh" back and forth, finally dying out. We generally call it damped oscillation (as many of you know). In the strictest sense of the word, oscillation doesn't have to be sustained, although I agree with Jim that we normally think of oscillation in that sense.

My point exactly - you've beaten me to it.

Charge a capacitor up and connect it to an inductor and it'll oscillate for a period of time than die away, this is damped oscillation. Undamped (continious) oscillation is only possible by using an amplifier to cancel out the losses in the system or a continious source of external energy to excite it.

 

[audioguru]

The speakers I use arent strong and they would be gone in a puff of smoke without it.

Your speaker is tiny but only 1/2W won't hurt it. 1/2W is the max power from the amplifier that occurs only briefly in music and speech, unless the volume control is turned too high so the amplifier is clipping all the time.

 

[RadioRon]

Some prevous posts implied that you can only receive AM with a crystal set, which I would like to refute. It is certainly possible to build a crystal set for receiving FM clearly. Some of them use well designed slope tuners, while I have seen at least one that implements a Foster-Seeley detector. I had a book around here that had a few circuits, but I couldn't find it just now.

 

[catcat]

How to make a slope tuner?

And audioguru about the transformer is just to be better safe than sorry without sacrificing volume.

 

[catcat]

My point exactly - you've beaten me to it.

Charge a capacitor up and connect it to an inductor and it'll oscillate for a period of time than die away, this is damped oscillation. Undamped (continious) oscillation is only possible by using an amplifier to cancel out the losses in the system or a continious source of external energy to excite it.

will this detect fm(1fmd.jpg)? (If not please explain better)

And about amps I REALLY cant find radio and amp explenations on the net. At least we could compare the amps in the atacched pic (1amps.jpg)

 

[audioguru]

How to make a slope tuner?

You tune an AM radio to the side of a station. The slope of the radio's tuned circuit causes an increase in amplitude when the FM swings closer to the tuned frequency and decreases when the FM swings away from the tuned frequency. The change in amplitude is AM. The curve in the slope causes distortion. AM detects static.

And audioguru about the transformer is just to be better safe than sorry without sacrificing volume.

No. An audio transformer severely reduces volume to a speaker when compared to an amplifier that delivers adequate current to the speaker.
My simple 3-transistor amplifier has a power output that is low but is 10,000 times more than yours.

will this detect fm(1fmd.jpg)? (If not please explain better)

No. It is just an oscillator. Look at FM detectors in Google.

And about amps I REALLY cant find radio and amp explenations on the net. At least we could compare the amps in the atacched pic (1amps.jpg)

Some of those circuits invert, some don't. Some of those circuits have voltage gain, some don't. Some of those circuits have a low output impedance and others have a high output impedance. Learn about transistors and you will understand.

 

[JimB]

And about amps I REALLY cant find radio and amp explenations on the net.

Try googling "rf amplifier" I got over 7 million hits.

JimB

 

[catcat]

I thought a lc tuner ignores all but one freqency without being less sensitive to the sides.

 

[audioguru]

I thought a lc tuner ignores all but one freqency without being less sensitive to the sides.

An LC tuner tries to pass one frequency and reject the others.
A radio has many LC tuned circuits because just one does not reject the untuned frequencies good enough. Also, for FM reception you want a wide bandpass but with very sharp edges which is impossible with just a single LC tuned circuit. The wide bandpass is for low distortion and the ability to pass stereo signals. The sharp edges avoid adjacent station interference.

When a capacitor is in parallel with a coil then at resonance they are a very high impedance. An amplifier connected to them must also have a high impedance. Your oscillator circuit had a high output impedance at the transistor's collector, but a low impedance at the transistor's base.
If you used the parallel LC to replace the transistor's collector resistor then it would be a tuned amplifier.

 

[AllVol]

When using an LM386 as an audio amplifier, if I touch pin 2 with a bare wire held in my fingers, I can pick up a radio station (AM) whose transmitter is located ~2 miles (~3 kilometers) away. The bare wire alone will not work, however.

 

[Hero999]

I've explained this before.

The transistor is non-linear and when an AM signal is applied to it causes detection, this is the same principle as an crystal radio. I bet you can't recieve and FM stations on it!

The LM386 has lots of transistors in it right?
They are non-linear, so they cause detection and amplification of AM signals. You only hear the strongest signal when you touch the pin beause you're acting as an aerial.