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Sound to LED

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Hi Ms,
Thanks for re-posting the original author's VHF Tracking Receiver project.
1) On your modified super-regen tuner, you want to short your emitter tank circuit. Then its positive feedback cap (C to E) won't work. The original circuit also has a 680 ohm emitter resistor that you shorted in yours.
2) You are talking about changing the bias of your tuner's transistor. Have you added the original sensitivity control? The author admits that reception of strong local stations is garbled unless the sensitivity control is turned down all the way and the antenna is shortened, even with a proper audio amplifier capacitively coupled to it.
Changing the bias of a transistor without an emitter resistor providing it with DC negative feedback is very difficult.

Aren't you still trying to light an LED to the beat of the noise and distortion of your 1-transistor tuner and 3-transistor amp? I am interested to see how your LED passed 150mA without smoking. :D
 
I found something else interesting.

When I tried shorting the tank circuit at the emitter, I got absolutely nothing from the speaker.

I changed the capacitor in the tank circuit to 12 pf instead of 35pf. What I noticed is that any frequency under 100Mhz is literally cut-off. the audio contained in the frequency between 100 and 103Mhz is chopped. anything above that is ok, but still, the volume is low.

When I replaced 12pf with a 47pf, I get more distortion.

I assume that the regen component of my circuit contains either a frequency divider or frequency multiplier.

I have used controls, but in my finished product, I want to omit them. The only control I want to see in my finished product is the tuning control. I find that the resistor between base and emitter determines maximum sensitivity to a point. At this point, I want to maximize the resistance, because I want to pick up long distance radio stations (more than 90km away) that some radios pick up. I am still unsure as to which value resistor I should use between the base and the end of the 27K resistor. I'm afraid if it is too low, remote stations will be cut out, and possibly local ones. If it is too high, I might not get enough power to the antenna or I might not get enough volume.
 
You appear to be wanting a high performance FM radio receiver?, yet you are basing it on a very crude low performance model, the super-regen receiver.

While a super-regen can give good sensitivity, the rest of it's performance is pretty poor - particularly it's selectivity and audio quality.

There's no frequency divider or multiplier in a super-regen, just a critical oscillator tuned to the required frequency, nor is there any FM demodulator, FM reception is by slope detection - one reason for their poor audio quality.

If you want a high performance FM radio, you should be looking at super-het designs.
 
mstechca said:
When I tried shorting the tank circuit at the emitter, I got absolutely nothing from the speaker.
That's right. Its positive feedback from collector to emitter also got shorted.

I changed the capacitor in the tank circuit to 12 pf instead of 35pf. What I noticed is that any frequency under 100Mhz is literally cut-off. the audio contained in the frequency between 100 and 103Mhz is chopped. anything above that is ok, but still, the volume is low.
That's right. The collector tank tunes the "stations". The volume is low because it is a super-regen, not a real radio. The original circuit boosted the volume by using a real audio amp with a gain of 200.

When I replaced 12pf with a 47pf, I get more distortion.
I am not sure which cap you changed.

I assume that the regen component of my circuit contains either a frequency divider or frequency multiplier.
It certainly doesn't have a f-div. nor f-mult. It just operates at the hairy edje of oscillation due to its positive feedback.

I have used controls, but in my finished product, I want to omit them. The only control I want to see in my finished product is the tuning control. I find that the resistor between base and emitter determines maximum sensitivity to a point. At this point, I want to maximize the resistance, because I want to pick up long distance radio stations (more than 90km away) that some radios pick up. I am still unsure as to which value resistor I should use between the base and the end of the 27K resistor. I'm afraid if it is too low, remote stations will be cut out, and possibly local ones. If it is too high, I might not get enough power to the antenna or I might not get enough volume.
It needs a sensitivity control like the original. It doesn't have auto gain control for its RF parts like a good real radio. You should also bias the audio amp properly and cap-couple its input. Then you can adjust the bias of the RF transistor with a sensitivity control without upsetting the bias of the audio amp.

BTW, the transistors in your 3-transistor audio amp need more current, which would reduce the gain, so it needs another transistor. Then it will have enough current and gain (like a real amp) to apply negative feedback to reduce distortion (like a real amp).

If you like distortion, you should make Philips' "FM Mono radio in a single IC". I got a radio with that IC for free by signing-up for a credit card. It sounds awful and fades all the time. My $15.00US FM stereo Sony Walkman works perfectly (super-heterodyne) and even came with pretty-good headphones.
 
I changed the capacitor in the tank circuit to 12 pf instead of 35pf. What I noticed is that any frequency under 100Mhz is literally cut-off. the audio contained in the frequency between 100 and 103Mhz is chopped. anything above that is ok, but still, the volume is low.

When I replaced 12pf with a 47pf, I get more distortion.
I'm not talking about the capacitor connected to the collector. I'm talking about the capacitor in my circuit between emitter and ground. The 0.1uH inductor remained the same during the tests. Look at my circuit and you will see it.
 
I think it is time for a reality check.

mstechca,
you are using a technology (super-regenerative radio) of which you appear to have very little understanding, to do a task for which it is totally unsuited.

I am sorry that I cant be any more constructive other than to suggest that you completely re-think this project.

JimB
 
Thanks Jim,
I wanted Ms to see why his "tracker" project is unsuited to be a radio, but now he appears to be changing parts at random without rhyme nor reason.
 
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